1. A photographing system comprising: a photographing section photographing a subject to acquire a frame image including a subject image; and a matching section changing size of one or both of the subject image and a beforehand prepared template image to change a size ratio of the template image to the subject image  and performing pattern matching between the subject image and the template image  size of one or both of the subject image and the template image being changed  for each of size ratios  wherein the matching section repeats image search through pattern matching while sequentially changing the size ratio  and obtains one or more size ratios at which patterns match each other  in a certain order of image search  and holds  as a first size ratio  a size ratio having a largest value among such obtained size ratios  and thereafter performs image search in a manner that pattern matching is performed at a first frequency in a range of a size ratio equal to or larger than the first size ratio  and is performed at a frequency lower than the first frequency in a range of a size ratio smaller than the first size ratio.

2. The photographing system according to claim 1  wherein the matching section holds  as a second size ratio  a size ratio having a smallest value among the obtained size ratios in the certain order of image search  and thereafter performs image search in a manner that pattern matching is performed at a second frequency lower than the first frequency in a range of a size ratio smaller than the first size ratio and equal to or larger than the second size ratio  and is performed at a third frequency lower than the second frequency in a range of a size ratio smaller than the second size ratio.

3. The photographing system according to claim 1  wherein the matching section changes the size ratio to be gradually reduced in each piece of image search.

4. The photographing system according to claim 1  wherein if the patterns do not match each other in the range of the size ratio equal to or larger than the first size ratio in any image search after the image search in which the first size ratio is obtained  the matching section performs pattern matching across all size ratios in subsequent image search.

5. The photographing system according to claim 1  wherein the matching section performs pattern matching through scanning the entire area of the frame image while shifting a region as a matching object.

6. The photographing system according to claim 2  wherein the frame image is divided into a plurality of regions  and the matching section sets the first size ratio and the second size ratio for each of the divided regions to set frequency of pattern matching for image search.

7. The photographing system according to claim 6  wherein the matching section performs pattern matching through scanning the entire area of the frame image while shifting a region as a matching object in a range of a size ratio equal to or larger than a largest value among values of first size ratios in the regions of the frame image.

8. The photographing system according to claim 6  further comprising a motion detection section performing motion detection based on frame difference between the plurality of frame images acquired at time points different from one another  wherein the matching section corrects each of the first and second size ratios for each of the regions of the frame image based on a result of the motion detection.

9. The photographing system according to claim 2  wherein the matching section acquires information on a relevant subject  based on the subject image  and corrects each of the first and second size ratios based on the information.

10. The photographing system according to claim 2  wherein the first size ratio corresponds to a distance between the photographing section and a subject nearest the photographing section  and the second size ratio corresponds to a distance between the photographing section and a subject most distant from the photographing section.

11. The photographing system according to claim 1  wherein the matching section changes the size ratio by changing size of the frame image.

12. The photographing system according to claim 1  wherein the matching section changes the size ratio by changing size of the template image.

13. The photographing system according to claim 1  wherein the subject is a face.

14. A pattern detection system  comprising a matching section changing size of one or both of a frame image including a subject image and a beforehand prepared template image to change a size ratio of the template image to the subject image  and performing pattern matching between the subject image and the template image  size of one or both of the subject image and the template image being changed  for each of size ratios  wherein the matching section repeats image search through pattern matching while sequentially changing the size ratio  and obtains one or more size ratios at which patterns match each other  in a certain order of image search  and holds  as a first size ratio  a size ratio having a largest value among such obtained size ratios  and thereafter performs image search in a manner that pattern matching is performed at a first frequency in a range of a size ratio equal to or larger than the first size ratio  and is performed at a frequency lower than the first frequency in a range of a size ratio smaller than the first size ratio.

15. An electronic unit including a photographing system and a control section performing operation control using the photographing system  the photographing system comprising: a photographing section photographing a subject to acquire a frame image including a subject image; and a matching section changing size of one or both of the subject image and a beforehand prepared template image to change a size ratio of the template image to the subject image  and performing pattern matching between the subject image and the template image  size of one or both of the subject image and the template image being changed  for each of size ratios  wherein the matching section repeats image search through pattern matching while sequentially changing the size ratio  and obtains one or more size ratios at which patterns match each other  in a certain order of image search  and holds  as a first size ratio  a size ratio having a largest value among such obtained size ratios  and thereafter performs image search in a manner that pattern matching is performed at a first frequency in a range of a size ratio equal to or larger than the first size ratio  and performed at a frequency lower than the first frequency in a range of a size ratio smaller than the first size ratio.

FIELD OF THE INVENTION
[0001] The present disclosure relates to a photographing system having a pattern detection function  a pattern detection system used for the photographing system  and an electronic unit including the photographing system.

BACKGROUND
[0002] Recently  a photographing system such as a camera has been mounted in various electronic units. An image pickup device configuring the photographing system has been progressively reduced in size as typified by a CMOS image sensor. Such a photographing system is used not only for a stationary electronic unit  but also for a portable electronic unit.
[0003] In the electronic units  the photographing system photographs an image that is used not only as a photograph but also for various applications. Examples of the applications include a system that recognizes a user face based on an image photographed by the photographing system. For example  Japanese Unexamined Patent Application Publication No. 2006-208558 discloses a camera that uses a result of face detection to reduce a photographing interval for continuous photographing.

STATEMENT OF THE INVENTION
[0004] Accordingly  an embodiment of the present invention provides a photographing system comprising a photographing section photographing a subject to acquire a frame image including a subject image  and a matching section changing size of one or both of the subject image and a beforehand prepared template image to change a size ratio of the template image to the subject image  and performing pattern matching between the subject image and the template image  size of one or both of the subject image and the template image being changed  for each of size ratios  wherein the matching section repeats image search through pattern matching while sequentially changing the size ratio  and obtains one or more size ratios at which patterns match each other  in a certain order of image search  and holds  as a first size ratio  a size ratio having a largest value among such obtained size ratios  and thereafter performs image search in a manner that pattern matching is performed at a first frequency in a range of a size ratio equal to or larger than the first size ratio  and is performed at a frequency lower than the first frequency in a range of a size ratio smaller than the first size ratio.

OBJECTS OF THE INVENTION
[0005] An object according to an embodiment of the present invention is to provide a photographing system  a pattern detection system and an electronic unit  each of which allows process time to be reduced.

SUMMARY
[0006] The face detection process detects a face from an image photographed by the photographing system through  for example  pattern detection. This may result in an increase in process time.
[0007] It is desirable to provide a photographing system  a pattern detection system  and an electronic unit  each of which allows process time to be reduced.
[0008] According to an embodiment of the present disclosure  there is provided a photographing system including: a photographing section photographing a subject to acquire a frame image including a subject image; and a matching section changing size of one or both of the subject image and a beforehand prepared template image to change a size ratio of the template image to the subject image  and performing pattern matching between the subject image and the template image  size of one or both of the subject image and the template image being changed  for each of size ratios. The matching section repeats image search through pattern matching while sequentially changing the size ratio  and obtains one or more size ratios at which patterns match each other  in a certain order of image search  and holds  as a first size ratio  a size ratio having a largest value among such obtained size ratios  and thereafter performs image search in a manner that pattern matching is performed at a first frequency in a range of a size ratio equal to or larger than the first size ratio  and is performed at a frequency lower than the first frequency in a range of a size ratio smaller than the first size ratio.
[0009] According to an embodiment of the present disclosure  there is provided a pattern detection system including a matching section changing size of one or both of a frame image including a subject image and a beforehand prepared template image to change a size ratio of the template image to the subject image  and performing pattern matching between the subject image and the template image  size of one or both of the subject image and the template image being changed  for each of size ratios. The matching section repeats image search through pattern matching while sequentially changing the size ratio  and obtains one or more size ratios at which patterns match each other  in a certain order of image search  and holds  as a first size ratio  a size ratio having a largest value among such obtained size ratios  and thereafter performs image search in a manner that pattern matching is performed at a first frequency in a range of a size ratio equal to or larger than the first size ratio  and is performed at a frequency lower than the first frequency in a range of a size ratio smaller than the first size ratio.
[0010] According to an embodiment of the present disclosure  there is provided an electronic unit including a photographing system and a control section performing operation control using the photographing system. The photographing system includes: a photographing section photographing a subject to acquire a frame image including a subject image; and a matching section changing size of one or both of the subject image and a beforehand prepared template image to change a size ratio of the template image to the subject image  and performing pattern matching between the subject image and the template image  size of one or both of the subject image and the template image being changed  for each of size ratios. The matching section repeats image search through pattern matching while sequentially changing the size ratio  and obtains one or more size ratios at which patterns match each other  in a certain order of image search  and holds  as a first size ratio  a size ratio having a largest value among such obtained size ratios  and thereafter performs image search in a manner that pattern matching is performed at a first frequency in a range of a size ratio equal to or larger than the first size ratio  and performed at a frequency lower than the first frequency in a range of a size ratio smaller than the first size ratio. Examples of the electronic unit include a television apparatus  a digital camera  and a video camcorder.
[0011] In the photographing system  the pattern detection system  and the electronic unit according to the embodiments of the disclosure  image search is performed through pattern matching while a size ratio is sequentially changed. In that operation  a size ratio at which patterns match each other is obtained in a certain order of image search  and a size ratio having a largest value among such obtained size ratios is held as a first size ratio. Thereafter  the image search is performed such that pattern matching is performed at a first frequency in a range of a size ratio equal to or larger than the first size ratio  and performed at a frequency lower than the first frequency in a range of a size ratio smaller than the first size ratio.
[0012] According to the photographing system  the pattern detection system  and the electronic unit according to the embodiments of the disclosure  a first size ratio is obtained  and thereafter pattern matching is performed at a first frequency in a range of a size ratio equal to or larger than the first size ratio  and performed at a frequency lower than the first frequency in a range of a size ratio smaller than the first size ratio  thus achieving a reduction in process time.
[0013] It is to be understood that both the foregoing general description and the following detailed description are exemplary  and are intended to provide further explanation of the technology as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The accompanying drawings are included to provide a further understanding of the disclosure  and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments and  together with the specification  serve to explain the principles of the technology.
[0015] FIG. 1 is a block diagram illustrating an exemplary configuration of a display according to a first embodiment of the disclosure.
[0016] FIG. 2 is a block diagram illustrating an exemplary configuration of a display drive section illustrated in FIG. 1.
[0017] FIG. 3 is a circuit diagram illustrating an exemplary configuration of a liquid crystal display section illustrated in FIG. 1.
[0018] FIGs. 4A and 4B are explanatory diagrams illustrating an operation example of a photographing section illustrated in FIG. 1.
[0019] FIG. 5 is an explanatory diagram illustrating an operation example of an image resizing section illustrated in FIG. 1.
[0020] FIGs. 6A and 6B are explanatory diagrams illustrating an operation example of a pattern comparison section illustrated in FIG. 1.
[0021] FIG. 7 is an explanatory diagram illustrating an operation example of a face detection section illustrated in FIG. 1.
[0022] FIG. 8 is an explanatory diagram illustrating an operation example of the face detection section illustrated in FIG. 1  in the case of one viewer.
[0023] FIG. 9 is an explanatory diagram illustrating an operation example of the face detection section illustrated in FIG. 1  in the case of three viewers.
[0024] FIG. 10 is a characteristic diagram illustrating search time of the face detection section illustrated in FIG. 1.
[0025] FIG. 11 is an explanatory diagram illustrating an operation example of the face detection section illustrated in FIG. 1  in the case of no viewer.
[0026] FIG. 12 is a flowchart illustrating an operation example of the face detection section illustrated in FIG. 1.
[0027] FIG. 13 is an explanatory diagram illustrating another operation example of the face detection section illustrated in FIG. 1.
[0028] FIG. 14 is an explanatory diagram illustrating another operation example of the face detection section illustrated in FIG. 1.
[0029] FIG. 15 is an explanatory diagram illustrating another operation example of the face detection section illustrated in FIG. 1.
[0030] FIG. 16 is an explanatory diagram illustrating another operation example of the face detection section illustrated in FIG. 1.
[0031] FIG. 17 is a block diagram illustrating an exemplary configuration of a display according to a modification of the first embodiment.
[0032] FIG. 18 is a block diagram illustrating an exemplary configuration of a display according to another modification of the first embodiment.
[0033] FIG. 19 is a block diagram illustrating an exemplary configuration of a display according to another modification of the first embodiment.
[0034] FIGs. 20A and 20B are explanatory diagrams illustrating another operation example of a face detection section illustrated in FIG. 19.
[0035] FIG. 21 is a block diagram illustrating an exemplary configuration of a display according to a second embodiment.
[0036] FIGs. 22A and 22B are explanatory diagrams illustrating an operation example of a face detection section illustrated in FIG. 21.
[0037] FIG. 23 is another explanatory diagram illustrating the operation example of the face detection section illustrated in FIG. 21.
[0038] FIGs. 24A and 24B are each another explanatory diagram illustrating the operation example of the face detection section illustrated in FIG. 21.
[0039] FIG. 25 is another explanatory diagram illustrating the operation example of the face detection section illustrated in FIG. 21.
[0040] FIG. 26 is a block diagram illustrating an exemplary configuration of a display according to a modification of the second embodiment.

DETAILED DESCRIPTION OF EMBODIMENT
[0041] Hereinafter  embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. It is to be noted that description is made in the following order.
1. First Embodiment
2. Second Embodiment
[1. First Embodiment]
[Configuration Example]
(Overall Configuration Example)
[0042] FIG. 1 illustrates an exemplary configuration of a display 1 according to a first embodiment. The display 1 detects a viewer viewing a screen  and controls a backlight based on the detection result. It is to be noted that a photographing system  a pattern detection system  and an electronic unit according to embodiments of the disclosure are embodied by the first embodiment  and therefore they are described together.
[0043] The display 1 includes a control section 11  a display drive section 20  a liquid crystal display section 13  a photographing section 14  a face detection section 30  a backlight drive section 16  and a backlight 17.
[0044] The control section 11 is configured of a circuit that controls the display drive section 20 and the backlight drive section 16 based on an image signal Sdisp. In detail  as described later  the control section 11 supplies an image signal Sdisp2 to the display drive section 20 to control the display drive section 20  and supplies a control signal to the backlight drive section 16 to control the backlight drive section 16.
[0045] The display drive section 20 drives the liquid crystal display section 13 based on the image signal Sdisp2 supplied from the control section 11. The liquid crystal display section 13 is configured of a liquid crystal display device  and displays an image through modulating light emitted from the backlight 17.
[0046] FIG. 2 illustrates an example of a block diagram including the display drive section 20 and the liquid crystal display section 13. The display drive section 20 includes a timing control section 21  a gate driver 22  and a data driver 23. The timing control section 21 controls drive timing of each of the gate driver 22 and the data driver 23  and generates an image signal Sdisp3 based on the image signal Sdisp2 supplied from the control section 11  and supplies the image signal Sdisp3 to the data driver 23. The gate driver 22 sequentially selects pixels Pix in the liquid crystal display section 13 according to timing control by the timing control section 21 for line sequential scan. The data driver 23 supplies a pixel signal based on the image signal Sdisp3 to each of the pixels Pix in the liquid crystal display section 13.
[0047] The liquid crystal display section 13 includes a liquid crystal material enclosed between two transparent substrates formed of  for example  glass. A transparent electrode formed of  for example  indium tin oxide (ITO) is provided on a surface of each of the transparent substrates  the surface facing the liquid crystal material  and configures the pixels Pix together with the liquid crystal material. The liquid crystal display section 13 includes the pixels Pix arranged in a matrix as illustrated in FIG. 2.
[0048] FIG. 3 illustrates an example of a circuit diagram of each pixel Pix. The pixel Pix includes a thin film transistor (TFT) device Tr  a liquid crystal device LC  and a holding capacitor Cs. The TFT device Tr is configured of  for example  a metal oxide semiconductor-field effect transistor (MOS-TFT)  of which the gate is connected to a gate line GCL  the source is connected to a data line SGL  and the drain is connected to one end of the liquid crystal device LC and to one end of the holding capacitor Cs. One end of the liquid crystal device LC is connected to the drain of the TFT device Tr  and the other end thereof is grounded. One end of the holding capacitor Cs is connected to the drain of the TFT device Tr  and the other end thereof is connected to a holding capacitance line CSL. The gate line GCL is connected to the gate driver 22  and the data line SGL is connected to the data driver 23.
[0049] The photographing section 14 photographs a viewer viewing the screen of the display 1  and supplies a photographed image Pic to the face detection section 30. The photographing section 14 performs photographing  for example  ten times per second  and supplies such photographed images Pic to the face detection section 30. The face detection section 30 detects the face of the viewer based on the photographed images Pic. Specifically  the face detection section 30 checks whether or not a viewer viewing the screen of the display 1 exists. Then  the face detection section 30 supplies a face detection signal Sdet indicating information on whether or not such a viewer exists to the backlight drive section 16.
[0050] The backlight drive section 16 drives the backlight 17 based on the control signal supplied from the control section 11 and the face detection signal Sdet supplied from the face detection section 30. In that operation  the backlight drive section 16 drives the backlight 17 based on the face detection signal Sdet such that if a viewer viewing the screen of the display 1 exists  the backlight 17 is turned on  and if such a viewer does not exist  the backlight 17 is turned off. In this way  the display 1 achieves a reduction in power consumption through controlling light emission of the backlight 17 depending on presence or absence of the viewer.
[0051] The backlight 17 emits light based on the drive signal supplied from the backlight drive section 16  and applies the light to the liquid crystal display section 13. For example  the backlight 17 is configured of a light emitting diode (LED). It is to be noted that the backlight 17 may be configured of  for example  a cold cathode fluorescent lamp (CCFL) without limitation.
(Photographing Section 14 and Face Detection Section 30)
[0052] The photographing section 14 and the face detection section 30 are now described in detail.
[0053] FIGs. 4A and 4B illustrate operation of the photographing section 14  where FIG. 4A illustrates an example of a position of each viewer viewing the display 1  and FIG. 4B illustrates an example of a photographed image Pic.
[0054] The example illustrated in FIG. 4A illustrates a case where three viewers UA  UB  and UC view the display 1. In detail  the viewer UA is at a position near the screen on the left side as viewed from the display 1  the viewer UB is at a position slightly distant from the screen slightly on the right side as viewed therefrom  and the viewer UC is at a position distant from the screen on the right side as viewed therefrom  each viewer viewing the screen of the display 1. A distance d from the display 1 is set in correspondence to a layer number LN (described later)  as described later. The photographing section 14 photographs these viewers to acquire a photographed image Pic as illustrated in FIG. 4B. In the photographed image Pic  a viewer at a position nearer the display 1 is imaged larger. Specifically  in the photographed image Pic  the viewer UA viewing at a position nearest the display 1 is imaged largest  the viewer UB viewing at a position second-nearest the display 1 is imaged second-largest  and the viewer UC viewing at a position most distant from the display 1 is imaged smallest.
[0055] The face detection section 30 checks whether or not a viewer exists based on the photographed image Pic. In that operation  if the face detection section 30 detects the face of a viewer  the face detection section 30 obtains a distance d between the viewer and the display 1. As illustrated in FIG. 1  the face detection section 30 includes an image resizing section 31  a template image supply section 32  a pattern comparison section 33  a processing section 34  and a pattern comparison control section 35.
[0056] The image resizing section 31 reduces the size of the photographed image Pic supplied from the photographing section 14 based on an instruction from the pattern comparison control section 35  and thus resizes the photographed image Pic to form a photographed image Pic2. The template image supply section 32 supplies a template image Ptemp indicating a human face to the pattern comparison section 33. The pattern comparison section 33 detects a human face within the photographed image Pic2 through pattern comparison between the photographed image Pic2 supplied from the image resizing section 31 and the template image Ptemp supplied from the template image supply section 32.
[0057] FIG. 5 illustrates a size reduction process of the photographed image Pic by the image resizing section 31. As illustrated in FIG. 5  the image resizing section 31 sequentially forms a plurality of (in this exemplary case  ten) photographed images Pic2 through size reduction of the photographed image Pic supplied from the photographing section 14. Each photographed image Pic2 is assigned a layer number LN (0 to 9) depending on corresponding rate R of size reduction. The rate R indicates a ratio of size of a photographed image Pic2 to size of a photographed image Pic. Specifically  in this exemplary case  the layer number LN of 0 corresponds to a rate R of 100%  and as the layer number LN increases  corresponding rate R decreases.
[0058] The image resizing section 31 reduces size of a photographed image Pic2 at a corresponding rate R based on information of the layer number LN supplied from the pattern comparison control section 35  as described later. In detail  if the image resizing section 31 receives an instruction to form an image corresponding to the layer number LN of 0  the image resizing section 31 outputs the photographed image Pic as the photographed image Pic2 without size reduction. If the image resizing section 31 receives an instruction to form images corresponding to layer numbers LN of 1 to 9  the image resizing section 31 reduces the size of a photographed image Pic at a rate R corresponding to each of the layer numbers LN  and outputs such size-reduced photographed images Pic as the photographed images Pic2.
[0059] In this exemplary case  the image resizing section 31 allows the rate R to vary in ten stages through setting the layer number LN in ten stages  0 to 9. This  however  is not limitative. Alternatively  for example  the image resizing section 31 may set the layer number LN in nine stages or less or in eleven stages or more to allow the rate R to vary correspondingly.
[0060] FIGs. 6A and 6B each illustrate an operation example of pattern comparison by the pattern comparison section 33  where FIG. 6A illustrates an operation example in the case of using a photographed image Pic2 formed through size reduction at a rate R corresponding to the layer number LN of 7  and FIG. 6B illustrates an operation example in the case of using a photographed image Pic2 formed through size reduction at a rate R corresponding to the layer number LN of 5.
[0061] The pattern comparison section 33 performs pattern comparison between a photographed image Pic2 and a template image Ptemp. In that operation  the pattern comparison section 33 checks whether or not a pattern similar to the template image Ptemp exists within the photographed image Pic2. In detail  as illustrated in FIGs. 6A and 6B  while the pattern comparison section 33 gradually shifts a region to be compared Rcomp having the same size as that of the template image Ptemp in horizontal and vertical directions within the photographed image Pic2 to scan the photographed image Pic2  the pattern comparison section 33 performs pattern comparison between a portion of the photographed image Pic2 in the region to be compared Rcomp and the template image Ptemp. In the case where the template image Ptemp is configured of  for example  20 by 20 pixels  a shifting distance of the region to be compared Rcomp is set to a distance corresponding to two pixels  for example.
[0062] The image resizing section 31 forms the photographed images Pic2 through size reduction of the photographed image Pic at a rate R corresponding to each of the various layer numbers LN  and supplies the photographed images Pic2 to the pattern comparison section 33. The pattern comparison section 33 performs pattern comparison for a photographed image Pic2 corresponding to each layer number LN. For example  in this exemplary case  in the case where a photographed image Pic2 corresponding to a layer number LN of 7 is supplied  the pattern comparison section 33 detects the face of the viewer UA viewing the screen of the display 1 at a position near the display 1 through scanning the photographed image Pic2 as illustrated in FIG. 6A. In the case where a photographed image Pic2 corresponding to a layer number LN of 5 is supplied  the pattern comparison section 33 detects the face of the viewer UB viewing the screen of the display 1 at a position slightly distant from the display 1 through scanning the photographed image Pic2 as illustrated in FIG. 6B. In other words  the face detection section 30 detects viewers at various distances d from the display 1 through pattern comparison using the photographed images Pic2 corresponding to a plurality of layer numbers LN.
[0063] In this way  the face detection section 30 obtains a distance d from the display 1 to a viewer based on the layer number LN associated with the photographed image Pic2 in which the face of the viewer is detected. Specifically  the face detection section 30 detects the viewer UA at a distance d corresponding to the layer number LN of 7 from the display 1 and the viewer UB at a distance d corresponding to the layer number LN of 5 from the display 1. As illustrated in FIG. 4A  the layer number LN and the distance d are in a relationship where the distance d from the display 1 is smaller/larger with a larger/smaller layer number LN.
[0064] The pattern comparison section 33 supplies a result of face detection performed in this way to the processing section 34. In detail  the pattern comparison section 33 supplies information of the layer number LN corresponding to a photographed image Pic2 in which the face of a viewer is detected  the coordinates of the face  the number of detected faces  and the like to the processing section 34.
[0065] In FIG. 1  the processing section 34 determines whether or not a viewer viewing the display 1 exists  based on the result of face detection by the pattern comparison section 33  and informs presence or absence of the viewer of the backlight drive section 16. In addition  as described later  the processing section 34 has a function of obtaining a distance d from the display 1 to each detected viewer  and informing the layer number LN corresponding to a viewer at a smallest distance d from the display 1 as a layer threshold TH1 of the pattern comparison control section 35  and informing the layer number LN corresponding to a viewer at a largest distance d from the display 1 as a layer threshold TH2 of the pattern comparison control section 35.
[0066] The pattern comparison control section 35 controls each operation of the image resizing section 31 and the pattern comparison section 33. The pattern comparison control section 35 includes a memory 36. The memory 36 stores information of each of the layer thresholds TH1 and TH2 therein.
[0067] The pattern comparison control section 35 controls the image resizing section 31 and the pattern comparison section 33 to perform sequential face detection from a region near the display 1 to a region distant from that. In detail  the pattern comparison control section 35 instructs the image resizing section 31 to decrease the layer number LN in order from 9. The image resizing section 31 forms the photographed images Pic2 while sequentially increasing the rate R for size reduction of the photographed image Pic according to that instruction. Then  the pattern comparison control section 35 instructs the pattern comparison section 33 to perform pattern comparison for each of the photographed images Pic2 supplied from the image resizing section 31.
[0068] In that operation  the pattern comparison control section 35 controls the image resizing section 31 and the pattern comparison section 33 to perform face detection at a relatively high frequency across the blocks from the display 1 to a position of the viewer nearest the display 1  and at a relatively low frequency across the blocks behind the position. In detail  as described later  the pattern comparison control section 35 controls the image resizing section 31 and the pattern comparison section 33 to perform face detection at a high frequency (high-frequency detection M1) in the case of a layer number LN equal to or larger than the layer threshold TH1  at a middle frequency (middle-frequency detection M2) in the case of a layer number LN smaller than the layer threshold TH1 and equal to or larger than the layer threshold TH2  and at a low frequency (low-frequency detection M3) in the case of a layer number LN smaller than the layer threshold TH2.
[0069] According to such a configuration  the face detection section 30 searches a viewer viewing the display 1 through sequential face detection from a region near the display 1 to a region distant from that. In that operation  the face detection section 30 checks whether one or more viewers view the screen of the display 1 in a short process time through face detection at a frequency that varies depending on the distance d from the display 1.
[0070] The photographed image Pic corresponds to a specific example of "frame image" of the disclosure. The face detection section 30 corresponds to a specific example of "matching section" of the disclosure. The layer threshold TH1 corresponds to a specific example of "first size ratio" of the disclosure. The layer threshold TH2 corresponds to a specific example of "second size ratio" of the disclosure.
[Operation and Function]
[0071] The operation and the function of the display 1 according to the first embodiment are now described.
(Outline of Overall Operation)
[0072] First  an outline of overall operation of the display 1 is described with reference to FIG. 1. The control section 11 controls the display drive section 20 and the backlight drive section 16. The display drive section 20 drives the liquid crystal display section 13 based on the image signal Sdisp2 supplied from the control section 11. The liquid crystal display section 13 performs display through modulating light emitted from the backlight 17. The photographing section 14 photographs a viewer viewing the screen of the display 1. The face detection section 30 detects the face of the viewer based on a photographed image Pic photographed by the photographing section 14  and outputs presence or absence of a detected face as a face detection signal Sdet. In that operation  the face detection section 30 operates to perform face detection at a relatively high frequency across the blocks from the display 1 to a position of a viewer nearest the display 1  and at a relatively low frequency across the blocks behind the position. The backlight drive section 16 drives the backlight 17 based on the control signal supplied from the control section 11 and the face detection signal Sdet supplied from the face detection section 30. In that operation  the backlight drive section 16 drives the backlight 17 based on the face detection signal Sdet such that if a viewer viewing the screen of the display 1 exists  the backlight 17 is turned on  and if such a viewer does not exist  the backlight 17 is turned off. The backlight 17 emits light based on the drive signal supplied from the backlight drive section 16  and applies the light to the liquid crystal display section 13.
(Detailed Operation of Face Detection Section 30)
[0073] Operation of the face detection section 30 is now described. The face detection section 30 performs face detection at a relatively high frequency across the blocks from the display 1 to a position of a viewer nearest the display 1  and at a relatively low frequency across the blocks behind the position. Specifically  the face detection section 30 sequentially performs face detection from a region near the display 1 to a region distant from that while sequentially decreasing the layer number LN. In that operation  the face detection section 30 performs face detection at a high frequency (high-frequency detection M1) in the case of a layer number LN equal to or larger than the layer threshold TH1  at a middle frequency (middle-frequency detection M2) in the case of a layer number LN smaller than the layer threshold TH1 and equal to or larger than the layer threshold TH2  and at a low frequency (low-frequency detection M3) in the case of a layer number LN smaller than the layer threshold TH2. Such operation of the face detection section 30 is described in detail below with a specific example.
[0074] FIG. 7 illustrates the face detection operation by the face detection section 30  where (A) and (B) each illustrate a case of one viewer (cases C1 and C2)  (C) illustrates a case of two viewers (case C3)  and (D) illustrates a case of three viewers (case C4). (A) of FIG. 7 illustrates a case where one viewer is at a position near the display 1 (case C1)  and (B) thereof illustrates a case where one viewer is at a position distant from the display 1 (case C2). In FIG. 7  the horizontal axis indicates a distance d from the display 1. In other words  the display 1 is located at the right end of FIG. 7  and the distance d is larger at a position closer to the left end thereof.
[0075] In the case of one viewer (cases C1 and C2)  as illustrated in (A) and (B) of FIG. 7  the face detection section 30 performs face detection through the high-frequency detection M1 across the blocks from the display 1 to the viewer  and performs face detection through the low-frequency detection M3 across the blocks more distant from the display than the viewer. In detail  as illustrated in (A) of FIG. 7  if a viewer is at a position corresponding to the layer number LN of 7 (case C1)  the face detection section 30 performs face detection through the high-frequency detection M1 across the blocks corresponding to the layer numbers LN of 9 to 7  and performs face detection through the low-frequency detection M3 across the blocks corresponding to the layer numbers LN of 6 to 0. In other words  in the case C1  since the viewer is at the position corresponding to the layer number LN of 7  both the layer threshold TH1 and the layer threshold TH2 are set to "7". Consequently  the face detection section 30 performs face detection through the high-frequency detection M1 across the blocks corresponding to the layer numbers LN of 9 to 7 which are each equal to or larger than the layer threshold TH1 (= 7). In addition  the face detection section 30 performs face detection through the low-frequency detection M3 across the blocks corresponding to the layer numbers LN of 6 to 0 which are each smaller than the layer threshold TH2 (= 7). It is to be noted that the middle-frequency detection M2 is not performed in this exemplary case since the layer thresholds TH1 and TH2 are equal to each other.
[0076] Similarly  if a viewer is at a position corresponding to the layer number LN of 2 (case C2)  as illustrated in (B) of FIG. 7  the face detection section 30 performs face detection through the high-frequency detection M1 across the blocks corresponding to the layer numbers LN of 9 to 2  and performs face detection through the low-frequency detection M3 across the blocks corresponding to the layer numbers LN of 1 and 0. In other words  in the case C2  since the viewer is at the position corresponding to the layer number LN of 2  both the layer threshold TH1 and the layer threshold TH2 are set to "2". Consequently  the face detection section 30 performs face detection through the high-frequency detection M1 across the blocks corresponding to the layer numbers LN of 9 to 2 which are each equal to or larger than the layer threshold TH1 (= 2). In addition  the face detection section 30 performs face detection through the low-frequency detection M3 across the blocks corresponding to the layer numbers LN of 1 and 0 which are each smaller than the layer threshold TH2 (= 2). It is to be noted that the middle-frequency detection M2 is not performed in this exemplary case since the layer thresholds TH1 and TH2 are equal to each other.
[0077] In the case of two viewers (case C3)  as illustrated in (C) of FIG. 7  the face detection section 30 performs face detection through the high-frequency detection M1 across the blocks from the display 1 to a first viewer near the display 1  performs face detection through the middle-frequency detection M2 across the blocks from the first viewer to a second viewer distant from the display 1  and performs face detection through the low-frequency detection M3 across the blocks more distant from the display 1 than the second viewer. In detail  as illustrated in (C) of FIG. 7  if a viewer UA is at a position corresponding to the layer number LN of 7  and if a viewer UC is at a position corresponding to the layer number LN of 2  the face detection section 30 performs face detection through the high-frequency detection M1 across the blocks corresponding to the layer numbers LN of 9 to 7  performs face detection through the middle-frequency detection M2 across the blocks corresponding to the layer numbers LN of 6 to 2  and performs face detection through the low-frequency detection M3 across the blocks corresponding to the layer numbers LN of 1 and 0. In other words  in the case C3  since the viewer UA is at the position corresponding to the layer number LN of 7  and the viewer UC is at the position corresponding to the layer number LN of 2  the layer threshold TH1 is set to "7"  and the layer threshold TH2 is set to "2". Consequently  the face detection section 30 performs face detection through the high-frequency detection M1 across the blocks corresponding to the layer numbers LN of 9 to 7 which are each equal to or larger than the layer threshold TH1 (= 7). In addition  the face detection section 30 performs face detection through the middle-frequency detection M2 across the blocks corresponding to the layer numbers LN of 6 to 2 which are each smaller than the layer threshold TH1 (= 7) and equal to or larger than the layer threshold TH2 (= 2). In addition  the face detection section 30 performs face detection through the low-frequency detection M3 across the blocks corresponding to the layer numbers LN of 1 and 0 which are each smaller than the layer threshold TH2 (= 2).
[0078] In the case of three viewers (case C4)  as illustrated in (D) of FIG. 7  the face detection section 30 performs face detection through the high-frequency detection M1 across the blocks from the display 1 to a first viewer nearest the display 1  performs face detection through the middle-frequency detection M2 across the blocks from the first viewer to a third viewer most distant from the display  and performs face detection through the low-frequency detection M3 across the blocks more distant from the display than the third viewer. In other words  the detection frequency varies only between the front and the back of a viewer nearest the display 1 and between the front and the back of a viewer most distant from the display 1  as in the case of two viewers (case C3).
[0079] In the case of four or more viewers  the face detection section 30 operates in the same way as in the case of three viewers (case C4). Specifically  the face detection section 30 performs face detection through the high-frequency detection M1 across the blocks from the display 1 to a first viewer nearest the display 1  performs face detection through the middle-frequency detection M2 across the blocks from the first viewer to a last viewer most distant from the display  and performs face detection through the low-frequency detection M3 across the blocks more distant from the display than the last viewer.
[0080] Next  detailed description is made on search operation of a viewer through sequential face detection from a region near the display 1 to a region distant from that in some of the above cases. In the following exemplary case  the middle-frequency detection M2 is performed at a frequency that is one fifth of the frequency of the high-frequency detection M1  and the low-frequency detection M3 is performed at a frequency that is one tenth of the frequency of the high-frequency detection M1. This  however  is not limitative. The detection frequency in each mode may be determined in consideration of capability of hardware and other factors.
[0081] FIG. 8 illustrates search operation in the case of one viewer. FIG. 8 exemplarily illustrates detailed operation in the case C1 illustrated in (A) of FIG. 7. Specifically  the face detection section 30 performs face detection through the high-frequency detection M1 across the blocks corresponding to the layer numbers LN of 9 to 7  and performs face detection through the low-frequency detection M3 across the blocks corresponding to the layer numbers LN of 6 to 0. In detail  as illustrated in FIG. 8  first  the face detection section 30 performs search D0 across all the blocks corresponding to the layer numbers LN of 9 to 0. Then  the face detection section 30 performs search D1 to D9 only across the blocks corresponding to the layer numbers LN of 9 to 7. The face detection section 30 repeats these ten pieces of search D0 to D9 in total. Consequently  the face detection (low-frequency detection M3) is performed across the blocks corresponding to the layer numbers LN of 6 to 0 at a frequency that is one tenth of the frequency of the face detection (high-frequency detection M1) across the blocks corresponding to the layer numbers LN of 9 to 7.
[0082] FIG. 9 illustrates search operation in the case of three viewers. FIG. 9 exemplarily illustrates detailed operation in the case C4 illustrated in (D) of FIG. 7. Specifically  the face detection section 30 performs face detection through the high-frequency detection M1 across the blocks corresponding to the layer numbers LN of 9 to 7  performs face detection through the middle-frequency detection M2 across the blocks corresponding to the layer numbers LN of 6 to 2  and performs face detection through the low-frequency detection M3 across the blocks corresponding to the layer numbers LN of 1 and 0. In detail  as illustrated in FIG. 9  first  the face detection section 30 performs search D10 across all the blocks corresponding to the layer numbers LN of 9 to 0. Then  the face detection section 30 performs search D11 to D14 only across the blocks corresponding to the layer numbers LN of 9 to 7. In addition  the face detection section 30 performs search D15 only across the blocks corresponding to the layer numbers LN of 9 to 2. Then  the face detection section 30 performs search D16 to D19 only across the blocks corresponding to the layer numbers LN of 9 to 7. The face detection section 30 repeats these ten pieces of search D10 to D19 in total. Consequently  the face detection (middle-frequency detection M2) is performed across the blocks corresponding to the layer numbers LN of 6 to 2 at a frequency that is one fifth of the frequency of the face detection (high-frequency detection M1) across the blocks corresponding to the layer numbers LN of 9 to 7  and the face detection (low-frequency detection M3) is performed across the blocks corresponding to the layer numbers LN of 1 and 0 at a frequency that is one tenth of the frequency of the face detection (high-frequency detection M1) in the blocks corresponding to the layer numbers LN of 9 to 7.
[0083] FIG. 11 illustrates search operation in the case of no viewer. In this case  the face detection section 30 operates to repeat search operation across all the blocks corresponding to the layer numbers LN of 9 to 0.
[0084] In this way  the face detection section 30 performs face detection at a high frequency (high-frequency detection M1) in the case of a layer number LN equal to or larger than the layer threshold TH1  at a middle frequency (middle-frequency detection M2) in the case of a layer number LN smaller than the layer threshold TH1 and equal to or larger than the layer threshold TH2  and at a low frequency (low-frequency detection M3) in the case of a layer number LN smaller than the layer threshold TH2. In other words  the face detection section 30 performs face detection at a relatively high frequency (high-frequency detection M1) for a viewer nearest the display 1  and performs face detection at a relatively low frequency (middle-frequency detection M2) for other viewers. Consequently  the face detection section 30 checks whether one or more viewers view the screen of the display 1 in a short process time. The process time is now described with an exemplary case of three viewers (case C4).
[0085] In the case of three viewers (case C4)  as illustrated in FIG. 9  each piece of search D11 to D14 involves search of blocks of three layers corresponding to the layer numbers LN of 9 to 7. In other words  the pattern comparison section 33 detects the viewer UA through face detection within each of three photographed images Pic2 corresponding to the layer numbers LN of 9 to 7. In addition  for example  search D15 involves search of blocks of eight layers corresponding to the layer numbers LN of 9 to 2. Specifically  the pattern comparison section 33 detects the viewers UA  UB  and UC through face detection within each of eight photographed images Pic2 corresponding to the layer numbers LN of 9 to 2. In this operation  the number of layers to be searched is smaller in each piece of search D11 to D14 than in search D15  and therefore time for search operation (search time) is short in each piece of search D11 to D14 compared with in search D15.
[0086] FIG. 10 illustrates search time. In FIG. 10  the horizontal axis indicates the number of layers to be searched. As illustrated in FIG. 10  search time abruptly increases with an increase in the number of layers to be searched.
[0087] The reason for this is as follows. The face detection section 30 performs face detection while sequentially decreasing the layer number LN in search operation. In the face detection  as illustrated in FIGs. 6A and 6B  the pattern comparison section 33 compares a portion of a photographed image Pic2 in a region to be compared Rcomp to a template image Ptemp while gradually shifting the region to be compared Rcomp in horizontal and vertical directions within the photographed image Pic2 to scan the photographed image Pic2. Since the number of times of pattern comparison within a photographed image Pic2 is in proportion to the screen resolution of the photographed image Pic2 (total pixel number)  a photographed image Pic2 corresponding to a smaller layer number LN (larger rate R) involves a larger number of times of pattern comparison. Accordingly  if the number of layers to be searched increases  pattern comparison is added within a photographed image Pic2 corresponding to a smaller layer number LN  resulting in an abrupt increase in search time rather than an increase in search time in proportion to an increase in the number of layers to be searched.
[0088] As illustrated in FIG. 10  search time in each piece of search D11 to D14 illustrated in FIG. 9 is about one thirtieth of search time in search D10 performed across ten layers. Consequently  the face detection section 30 reduces search time compared with  for example  a case of constant search across all the blocks corresponding to the layer numbers LN of 9 to 0 without change of detection frequency.
[0089] A typical display does not necessarily incorporate hardware having high performance. In such a display  therefore  the search D10 across all the blocks corresponding to the layer numbers LN of 9 to 0 may need search time in seconds  for example. Even in such a case  search time is extremely reduced by decreasing the number of layers to be searched  for example  as in each piece of search D11 to D14. In the case of long search time  much time is taken for search operation for photographed images Pic that are photographed by the photographing section 14 and sequentially supplied. Hence  such sequential photographed images Pic may be only partially searched. Even in such a case  a relatively large number of photographed images Pic are allowed to be searched through reducing search time as above.
[0090] In this way  the face detection section 30 performs face detection at a high frequency (high-frequency detection M1) across the blocks from the display 1 to a position of a viewer nearest the display 1. As a result  the face detection section 30 checks whether one or more viewers view the screen of the display 1 in a short process time. Consequently  the display 1 checks presence or absence of a viewer at a high frequency. As a result  for example  if a viewer looks down to start reading a magazine  the display 1 immediately turns off the backlight 17. If the viewer restarts viewing the screen of the display 1  the display 1 immediately detects a face of the viewer and turn on the backlight 17.
[0091] In addition  in the case of a plurality of viewers  the face detection section 30 performs face detection at a slightly low frequency (middle-frequency detection M2) across the blocks from the viewer nearest the display 1 to the viewer most distant from the display 1. As a result  the face detection section 30 detects all viewers in a reduced process time. Consequently  the face detection section 30 may be used not only for an application where a process is carried out based on the position of the viewer nearest the display 1  but also for an application where a process is carried out based on positions of all viewers as described later.
[0092] Furthermore  the face detection section 30 performs face detection at a low frequency (low-frequency detection M3) across the blocks behind the viewer most distant from the display. As a result  for example  even if a new viewer is added in the blocks  the viewer is detected.
[0093] Moreover  when a viewer is at a position a predetermined distance away from the display 1  face detection of the viewer may by useless depending on a placed site of the display 1. In detail  for example  in the case where the display 1 is placed in a small room  even if face detection is performed over a distance from the display 1 to a wall in front of the display 1  no face is detected. Even in such a case  the display 1 reduces frequency of face detection across the blocks behind the viewer most distant from the display 1  leading to a reduction in ratio of process time for such detection operation to the total process time.
[0094] Operation of the face detection section 30 is now described with a flowchart.
[0095] FIG. 12 illustrates a flowchart of search operation by the face detection section 30. In FIG. 12  the minimum detection distance Dmin is a variable for storing a distance d from the display 1 to a viewer nearest the display 1  and the maximum detection distance Dmax is a variable for storing a distance d from the display 1 to a viewer most distant from the display 1.
[0096] The face detection section 30 sequentially performs face detection from a region near the display 1 to a region distant from that  and then acquires a layer number LN at which a face is detected  and sets the frequency of face detection based on the layer number LN. This is described in detail below.
[0097] First  the face detection section 30 sequentially performs face detection from a region near the display 1 to a region distant from that (step S2). In detail  the pattern comparison control section 35 instructs the image resizing section 31 to decrease the layer number LN in order from 9. The image resizing section 31 forms photographed images Pic2 while increasing the rate R for size reduction of a photographed image Pic in order according to that instruction. Then  the pattern comparison section 33 performs face detection through pattern comparison using the photographed images Pic2 supplied from the image resizing section 31 and a template image Ptemp. In that operation  the pattern comparison control section 35 controls the image resizing section 31 and the pattern comparison section 33 to perform face detection at a frequency based on the layer thresholds TH1 and TH2 stored in the memory 36. Then  the face detection section 30 determines whether a face is detected in the face detection process (step S3). If the face detection section 30 determines detection of a face  the process advances to step S4. If the face detection section 30 does not determine detection of a face  the process returns to step S2 for a next face detection process.
[0098] If the face detection section 30 determines detection of a face in the face detection process of step S2  the processing section 34 of the face detection section 30 acquires information of a layer number LN associated with a photographed image Pic2 in which a face of a viewer is detected  the number of detected faces (detection number)  and the like from the detection result in the face detection process (step S4).
[0099] Then  the processing section 34 of the face detection section 30 acquires a distance d (detection distance) from the display 1 to each viewer  based on the layer number LN corresponding to the viewer acquired in step S4 (step S5).
[0100] Then  the processing section 34 of the face detection section 30 updates the minimum detection distance Dmin and the maximum detection distance Dmax (step S6). In detail  the processing section 34 sets a distance d associated with the viewer nearest the display 1  among the viewers  as the minimum detection distance Dmin  and sets a distance d associated with the viewer most distant from the display 1 as the maximum detection distance Dmax.
[0101] Then  the face detection section 30 updates each of the layer thresholds TH1 and TH2 (step S7). In detail  first  the processing section 34 obtains a layer number LN corresponding to the minimum detection distance Dmin acquired in step S6  and supplies the layer number LN as the layer threshold TH1 to the pattern comparison control section 35. In addition  the processing section 34 obtains a layer number LN corresponding to the maximum detection distance Dmax acquired in step S6  and supplies the layer number LN as the layer threshold TH2 to the pattern comparison control section 35. Then  the memory 36 in the pattern comparison control section 35 stores the updated layer thresholds TH1 and TH2 therein.
[0102] This is the end of flow of the search operation.
[0103] Thereafter  the face detection section 30 executes this flow in subsequent search operation. In that operation  the face detection process (step S2) is performed at a frequency based on the layer thresholds TH1 and TH2 updated in step S7 of the previous search operation. In this way  the face detection section 30 updates each of the layer thresholds TH1 and TH2 at every search operation  and sets the frequency of face detection based on the updated layer thresholds TH1 and TH2.
[0104] It is to be noted that the face detection section 30 is desirably configured to maintain the layer thresholds TH1 and TH2 even if the display 1 is in a standby mode  for example. According to such a configuration  when the display 1 is returned from the standby mode to an operation mode  the face detection section 30 checks whether one or more viewers view a screen in a short process time.
[0105] Next  description is made on operation of the face detection section 30 in the case where a viewer viewing the screen of the display 1 moves.
[0106] FIGs. 13 and 14 illustrate search operation in the case of one viewer  where FIG. 13 illustrates a case where the viewer moves closer to the display 1  and FIG. 14 illustrates a case where the viewer moves away from the display 1. In this exemplary case  it is assumed that the viewer is initially at a position corresponding to the layer number LN of 7 as in the case C1 ((A) of FIG. 7 and FIG. 8).
[0107] As illustrated in FIGs. 13 and 14  in the case where the viewer is initially at the position corresponding to the layer number LN of 7  the face detection section 30 performs search D0 to D6 as in the case illustrated in FIG. 8.
[0108] As illustrated in FIG. 13  if the viewer moves closer to the display 1 at timing t1  the face detection section 30 then searches blocks corresponding to the layer numbers LN of 9 to 7 in subsequent search D37  as in the search D1 to D6. In the search D37  the face detection section 30 detects shift of the viewer from the position corresponding to the layer number LN of 7 to a position corresponding to the layer number LN of 8. Thus  the face detection section 30 searches only blocks corresponding to the layer numbers LN of 9 and 8 in subsequent search D38 or later. In other words  the face detection section 30 operates to minimize the number of layers to be searched. Consequently  the face detection section 30 checks whether one or more viewers view the screen of the display 1 in a short process time.
[0109] As illustrated in FIG. 14  if the viewer moves away from the display 1 at timing t2  the face detection section 30 then searches blocks corresponding to the layer numbers LN of 9 to 7 in subsequent search D47  as in the search D1 to D6. In the search D47  the face detection section 30 detects absence of the viewer from the blocks corresponding to the layer numbers LN 9 to 7. Thus  the face detection section 30 searches all the blocks corresponding to the layer numbers LN of 9 to 0 in subsequent search D50. In the search D50  the face detection section 30 detects the viewer at a position corresponding to the layer number LN of 6. Thus  the face detection section 30 searches blocks corresponding to the layer numbers LN of 9 to 6 in subsequent search D51 or later. In this way  even if a viewer moves away from the display 1  the face detection section 30 immediately detects the viewer and changes blocks to be searched depending on the position of the moved viewer.
[0110] FIGs. 15 and 16 each illustrate search operation in the case of three viewers  where FIG. 15 illustrates a case where a viewer nearest the display 1 among the three viewers moves closer to the display 1  and FIG. 16 illustrates a case where the viewer nearest the display 1 moves away from the display 1. In this exemplary case  it is assumed that the respective three viewers are initially at positions corresponding to the layer numbers LN of 7  5  and 2 as in the case C4 ((D) of FIG. 7 and FIG. 9).
[0111] As illustrated in FIGs. 15 and 16  in the case where the viewer UA nearest the display 1 is initially at a position corresponding to the layer number LN of 7  the face detection section 30 performs search D10 to D16 as in the case illustrated in FIG. 9.
[0112] As illustrated in FIG. 15  if the viewer UA moves closer to the display 1 at timing t3  the face detection section 30 then searches blocks corresponding to the layer numbers LN of 9 to 7 in subsequent search D67  as in the search D11 to D14 and D16. In the search D67  the face detection section 30 detects shift of the viewer from the position corresponding to the layer number LN of 7 to a position corresponding to the layer number LN of 8. Thus  the face detection section 30 searches only blocks corresponding to the layer numbers LN of 9 and 8 in subsequent search D68 or later. In other words  the face detection section 30 operates to minimize the number of layers to be searched. Consequently  the face detection section 30 checks whether one or more viewers view the screen of the display 1 in a short process time.
[0113] As illustrated in FIG. 16  if the viewer UA moves away from the display 1 at timing t4  the face detection section 30 then searches blocks corresponding to the layer numbers LN of 9 to 7 in subsequent search D77  as in the search D11 to D14 and D16. In the search D77  the face detection section 30 detects absence of the viewer UA from the blocks corresponding to the layer numbers LN 9 to 7. Thus  the face detection section 30 searches all the blocks corresponding to the layer numbers LN of 9 to 0 in subsequent search D80. In the search D80  the face detection section 30 detects the viewer UA at a position corresponding to the layer number LN of 6. Thus  the face detection section 30 searches blocks corresponding to the layer numbers LN of 9 to 6 in subsequent search D81 or later. In this way  even if a viewer moves away from the display 1  the face detection section 30 immediately detects the viewer and changes blocks to be searched depending on the position of the moved viewer.
[0114] In this way  even if a viewer moves  the display 1 immediately detects the viewer and changes blocks to be searched depending on the position of the moved viewer.
[Effects]
[0115] As described above  in the first embodiment  since face detection is performed at a high frequency across the blocks from the display to the position of the viewer nearest the display  whether one or more viewers view the screen of the display is checked in a short process time.
[0116] In addition  in the first embodiment  since face detection is performed at a slightly low frequency across the blocks from the viewer nearest the display to the viewer most distant from the display  all viewers are detected with a reduced process time.
[0117] Furthermore  in the first embodiment  face detection is performed at a low frequency across the blocks behind the viewer most distant from the display. As a result  even if a new viewer is added in the blocks  the viewer is detected  while the ratio of process time for face detection operation across the blocks to the total process time is reduced.
[Modification 1-1]
[0118] Although the backlight 17 is controlled to be turned on or off based on a detection result by the face detection section 30 in the first embodiment  this is not limitative. This is described in detail below.
[0119] FIG. 17 illustrates an exemplary configuration of a display 1B according to modification 1-1. The display 1B changes an image or the like displayed on the liquid crystal display section 13  based on a detection result by the face detection section 30. In this exemplary case  the display 1B has a function of notifying a viewer to move away from the screen of the display 1B if the viewer is extremely close to the screen.
[0120] The display 1B includes a face detection section 30B  a control section 11B  and a backlight drive section 16B. The face detection section 30B includes a processing section 34B. The processing section 34B supplies a distance d from the display 1B to a viewer nearest the display 1B as a face detection signal Sdet2  based on a face detection result by the pattern comparison section 33. The control section 11B processes an image signal such that  if a distance between the display 1B and the viewer is shorter than a predetermined distance  "get away from a screen!" is shown in a form of  for example  on-screen display (OSD)  based on the face detection signal Sdet2 supplied from the processing section 34B of the face detection section 30. The backlight drive section 16B drives the backlight 17 based on a control signal supplied from the control section 11B.
[0121] According to such a configuration of the display 1B  if a viewer is extremely close to the screen of the display 1B  a message is displayed to prompt the viewer to get away from the screen. In that operation  since the face detection section 30B performs face detection at a high frequency (high-frequency detection M1) across the blocks from the display 1B to a position of a viewer nearest the display 1B  the face detection section 30B detects the viewer in a short process time  as in the face detection section 30 according to the first embodiment. Consequently  for example  even if a child suddenly gets close to the screen  the display 1B immediately prompts the child to get away from the screen. It is to be noted that  although a message is displayed to notify a viewer of an event in the exemplary case  this is not limitative. For example  sound may be used to notify a viewer of the event instead of or in addition to that.
[Modification 1-2]
[0122] Although the liquid crystal display section 13 performs display operation in the first embodiment  this is not limitative. Alternatively  for example  an electro-luminescence (EL) display section 13C may perform display operation  as illustrated in FIG. 18. In this case  for example  the face detection section 30 may control the EL display section 13C to perform black display in the case of no viewer.
[Modification 1-3]
[0123] Although the face detection section 30 performs size reduction of the photographed image Pic to form the photographed image Pic2  and performs face detection through pattern comparison between the photographed image Pic2 and the template image Ptemp  this is not limitative. This is described in detail below with an exemplary case.
[0124] FIG. 19 illustrates an exemplary configuration of a display 1D according to modification 1-3. The display 1D includes a face detection section 30D. The face detection section 30D includes an image resizing section 37. The image resizing section 37 forms a template image Ptemp2 through scaling of the template image Ptemp supplied from the template image supply section 32  and supplies the template image Ptemp2 to the pattern comparison section 33.
[0125] According to this configuration  the face detection section 30D generates the template image Ptemp2 through scaling of the template image Ptemp  and performs face detection through pattern comparison between a photographed image Pic and the template image Ptemp2.
[0126] FIGs. 20A and 20B each illustrate an operation example of pattern comparison according to the modification 1-3  where FIG. 20A illustrates an operation example in the case of using a template image Ptemp2 formed through scaling at a first rate RD  and FIG. 20B illustrates an operation example in the case of using another template image Ptemp2 formed through scaling at a second rate RD.
[0127] The image resizing section 37 forms template images Ptemp2 through scaling of the template image Ptemp at various rates RD according to an instruction from the pattern comparison control section 35  and supplies the template images Ptemp2 to the pattern comparison section 33. The pattern comparison section 33 gradually shifts a region to be compared Rcomp having the same size as that of each template image Ptemp2 in horizontal and vertical directions to scan the photographed image Pic  and concurrently performs pattern comparison between a portion of the photographed image Pic in the region to be compared Rcomp and the template image Ptemp2. Consequently  in the operation example illustrated in FIG. 20A  the face detection section 30D detects a face of a viewer UA viewing a screen at a position near the display 1D. In the operation example illustrated in FIG. 20B  the face detection section 30D detects a face of a viewer UB viewing the screen at a position slightly distant from the display 1D. In this way  the face detection section 30D detects viewers at various distances d from the display 1D.
[Modification 1-4]
[0128] In the first embodiment  as illustrated in steps S4 and S5 of FIG. 12  a distance d from a display to a viewer is obtained based on a layer number LN at which the face of the viewer is detected. In that operation  the viewer may be determined to be a child or an adult based on  for example  a photographed image Pic so that the distance d is corrected based on that determination result. Specifically  even if an adult face and a child face are detected together in a photographed image Pic2 associated with the same layer number LN  the child viewer is likely to be actually at a position distant from the display compared with the adult viewer in consideration that a child face is usually smaller than an adult face. Accordingly  the distance d from the display to a viewer is obtained while being corrected in consideration of a difference in size between a child face and an adult face  so that information of a distance associated with each viewer is more accurately obtained.
[Modification 1-5]
[0129] In the first embodiment  as illustrated in FIG. 12  a distance d from a display to a viewer is obtained based on a layer number LN at which the face of the viewer is detected  and the layer thresholds TH1 and TH2 are obtained based on the distance d. This  however  is not limitative. Alternatively  for example  the layer thresholds TH1 and TH2 may be directly obtained from that layer number LN. In this case  for example  among the layer numbers LN at which faces of viewers are detected  a largest layer number LN may be set to the layer threshold TH1  and a smallest layer number LN may be set to the layer threshold TH2.
[Modification 1-6]
[0130] Although the middle-frequency detection M2 is performed at a frequency that is one fifth of the frequency of the high-frequency detection M1  and the low-frequency detection M3 is performed at a frequency that is one tenth of the frequency of the high-frequency detection M1 in the first embodiment  this is not limitative. Alternatively  such frequencies may be designed to be dynamically changed. For example  modification 1-6 is effective in the case where another application is executed based on a detection result by the face detection section 30. Specifically  during execution of the application  if whether one or more viewers view a screen is desired to be exclusively checked  the middle-frequency detection M2 may be performed at a lower frequency. On the other hand  if the number of viewers is desired to be determined  the middle-frequency detection M2 may be performed at a higher frequency.
[2. Second embodiment]
[0131] A display 2 according to a second embodiment is now described. The second embodiment is configured such that a photographed image Pic is divided into a plurality of regions  and frequency of face detection may be changed for each of the divided regions. Here  description is made on an exemplary case where a photographed image Pic is divided into two  or right and left regions. It is to be noted that substantially the same components as those of the display 1 according to the first embodiment are designated by the same numerals  and description of them is appropriately omitted.
[0132] FIG. 21 illustrates an exemplary configuration of a display 2 according to the second embodiment. The display 2 includes a face detection section 40. The face detection section 40 includes a pattern comparison control section 45. The pattern comparison control section 45 includes a memory 46 that stores four layer thresholds THL1  THL2  THR1  and THR2 therein. The pattern comparison control section 45 controls the image resizing section 31 and the pattern comparison section 33 to perform sequential face detection from a region near the display 2 to a region distant from that  as in the pattern comparison control section 35 according to the first embodiment. In that operation  the pattern comparison control section 45 controls the image resizing section 31 and the pattern comparison section 33 to perform face detection at a frequency based on the layer thresholds THL1 and THL2 for an image at a left half of the photographed image Pic  and perform face detection at a frequency based on the layer thresholds THR1 and THR2 for an image at a right half thereof.
[0133] FIGs. 22A and 22B illustrate an example of operation of the face detection section 40  where FIG. 22A illustrates an example of positions of viewers viewing the display 2  and FIG. 22B illustrates an example of the photographed image Pic.
[0134] The photographing section 14 photographs viewers UA  UB  and UC viewing the display 2 as illustrated in FIG. 22A to acquire a photographed image Pic as illustrated in FIG. 22B  as in the case of the first embodiment. The face detection section 40 performs face detection while setting different frequencies for an image in a region PL at the left half of the photographed image Pic and for an image in a region PR at the right half thereof.
[0135] In detail  at the left side as viewed from the display 2  as illustrated in FIG. 22A  the face detection section 40 performs face detection through the high-frequency detection M1 across blocks corresponding to the layer number LN of 9 to 7  and performs face detection through the low-frequency detection M3 across blocks corresponding to the layer number LN of 6 to 0. In other words  since the viewer UA is at a position corresponding to the layer number LN of 7 at the left side as viewed from the display 2  both the layer threshold THL1 and the layer threshold THL2 are set to "7". Thus  the face detection section 40 performs face detection through the high-frequency detection M1 across the blocks corresponding to the layer numbers LN of 9 to 7 which are each equal to or larger than the layer threshold THL1 (= 7). In addition  the face detection section 40 performs face detection through the low-frequency detection M3 across the blocks corresponding to the layer numbers LN of 6 to 0 which are each smaller than the layer threshold THL2 (= 2). It is to be noted that the middle-frequency detection M2 is not performed in this exemplary case since the layer thresholds THL1 and THL2 are equal to each other.
[0136] At the right side as viewed from the display 2  as illustrated in FIG. 22A  the face detection section 40 performs face detection through the high-frequency detection M1 across blocks corresponding to the layer number LN of 9 to 5  performs face detection through the middle-frequency detection M2 across blocks corresponding to the layer number LN of 4 to 2  and performs face detection through the low-frequency detection M3 across blocks corresponding to the layer number LN of 1 and 0. In other words  at the right side as viewed from the display 2  since the viewer UB is at a position corresponding to the layer number LN of 5  and the viewer UC is at a position corresponding to the layer number LN of 2  the layer threshold THR1 is set to "5"  and the layer threshold THR2 is set to "2". Thus  the face detection section 40 performs face detection through the high-frequency detection M1 across the blocks corresponding to the layer numbers LN of 9 to 5 which are each equal to or larger than the layer threshold THR1 (= 5). In addition  the face detection section 40 performs face detection through the middle-frequency detection M2 across the blocks corresponding to the layer numbers LN of 4 to 2 which are each smaller than the layer threshold THR1 (= 5) and equal to or larger than the layer threshold THR2 (= 2). In addition  the face detection section 40 performs face detection through the low-frequency detection M3 across blocks corresponding to the layer numbers LN of 1 and 0 which are each smaller than the layer threshold THR2 (= 2).
[0137] (A) of FIG. 23 illustrates search operation at the left side as viewed from the display 2  and (B) of FIG. 23 illustrates search operation at the right side as viewed from the display 2.
[0138] At the left side as viewed from the display 2  as illustrated in (A) of FIG. 23  first  the face detection section 40 performs search DL0 across all the blocks corresponding to the layer numbers LN of 9 to 0. Then  the face detection section 40 performs search DL1 to DL9 only across the blocks corresponding to the layer numbers LN of 9 to 7. The face detection section 40 repeats the ten pieces of search DL0 to DL9. Consequently  the face detection (low-frequency detection M3) is performed across the blocks corresponding to the layer numbers LN of 6 to 0 at a frequency that is one tenth of the frequency of the face detection (high-frequency detection M1) across the blocks corresponding to the layer numbers LN of 9 to 7.
[0139] At the right side as viewed from the display 2  as illustrated in (B) of FIG. 23  first  the face detection section 40 performs search DR0 across all the blocks corresponding to the layer numbers LN of 9 to 0. Then  the face detection section 40 performs search DR1 to DR4 only across the blocks corresponding to the layer numbers LN of 9 to 5. In addition  the face detection section 40 performs search DR5 only across the blocks corresponding to the layer numbers LN of 9 to 2. Then  the face detection section 40 performs search DR6 to DR9 only across the blocks corresponding to the layer numbers LN of 9 to 5. The face detection section 40 repeats these ten pieces of search DR0 to DR9. Consequently  face detection (middle-frequency detection M2) is performed across the blocks corresponding to the layer numbers LN of 4 to 2 at a frequency that is one fifth of the frequency of the face detection (high-frequency detection M1) across the blocks corresponding to the layer numbers LN of 9 to 5  and face detection (low-frequency detection M3) is performed across the blocks corresponding to the layer numbers LN of 1 and 0 at a frequency that is one tenth of the frequency of the face detection (high-frequency detection M1) across the blocks corresponding to the layer numbers LN of 9 to 5.
[0140] As illustrated in FIG. 23  each piece of search DL0 to DL9 at the left side as viewed from the display 2 is performed at timing corresponding to timing of each piece of search DR0 to DR9 at the right side as viewed from the display 2. This is described below with a specific example.
[0141] FIGs. 24A and 24B illustrate an operation example of face detection using a photographed image Pic2 associated with the layer number LN of 5  where FIG. 24A illustrates face detection in the search DL0 and DR0  and FIG. 24B illustrates face detection in the search DR1.
[0142] As illustrated in FIG. 23  both the search DL0 and the search DR0 involve face detection for the photographed image Pic2 associated with the layer number LN of 5. Accordingly  in this case  as illustrated in FIG. 24A  the face detection section 40 performs face detection through scanning the entire photographed image Pic2.
[0143] On the other hand  for example  as illustrated in FIG. 23  only the search DR1 between the search DL1 and the search DR1 involves face detection for the photographed image Pic2 associated with the layer number LN of 5. Accordingly  in this case  as illustrated in FIG. 24B  the face detection section 40 performs face detection through scanning only the right-half region PR of the photographed image Pic2.
[0144] FIG. 25 illustrates an operation example of face detection using a photographed image Pic2 associated with the layer number LN of 7. This operation example shows face detection involved in the search DL1 and DR1. As illustrated in FIG. 23  both the search DL1 and the search DR1 involve face detection for the photographed image Pic2 associated with the layer number LN of 7. Accordingly  in this case  as illustrated in FIG. 25  the face detection section 40 performs face detection through scanning the entire photographed image Pic2. Specifically  in this example  the layer threshold THL1 is 7  and the layer threshold THR1 is 5. Hence  face detection is performed in both the left side and the right side across the blocks corresponding to the layer numbers LN of 7 to 9 which are each equal to or larger than the largest value (7) of the layer thresholds THL1 and THR1. Accordingly  the face detection section 40 performs face detection through scanning the entire photographed image Pic2 across the blocks corresponding to the layer numbers LN of 7 to 9.
[0145] In this way  in the case where both left search and corresponding right search involve face detection at a position corresponding to a certain layer number LN  the face detection section 40 performs face detection through scanning the entire photographed image Pic2. In addition  in the case where one of left search and right search involves face detection at a position corresponding to a certain layer number LN  the face detection section 40 performs face detection through scanning only a corresponding region in the photographed image Pic2.
[0146] As described above  in the second embodiment  a photographed image is divided into a plurality of regions  and frequency of face detection is set for each of the divided regions. Hence  frequency of face detection is reduced for a region in which no face is expected to be detected  thus achieving a short search time. Other effects are similar to those in the first embodiment.
[Modification 2-1]
[0147] For example  the second embodiment may be modified such that a region for face detection is limited by using motion detection. This is described in detail below with an exemplary case.
[0148] FIG. 26 illustrates an exemplary configuration of a display 2B according to modification 2-1. The display 2B includes a face detection section 40B. The face detection section 40B includes a motion detection section 47 and a pattern comparison control section 45B. The motion detection section 47 performs motion detection using frame difference  based on a series of photographed images Pic. Then  the motion detection section 47 supplies information on a portion in which motion is detected  in each photographed image Pic to the pattern comparison control section 45B. The pattern comparison control section 45B sets the frequency of face detection for individual regions with reference to the information supplied from the motion detection section 47. In detail  for example  a person may not face the display 2B since he/she has just moved to the front of the display 2B  and therefore the pattern comparison section 33 and the like have not recognized his/her face. The motion detection section 47 detects such a person  and supplies information of the person to the pattern comparison control section 45B. In other words  the person may be a viewer of the display 2B soon. For example  the pattern comparison control section 45B sets the layer thresholds THL1  THL2  THR1  and THR2 based on the supplied information such that  when the person faces the display 2B  the face of the person is detected at a high frequency. Consequently  even if a new viewer is added  the display 2B immediately performs face detection for the viewer.
[Modification 2-2]
[0149] Although a photographed image Pic is divided into  for example  two  or right and left (horizontal) regions in the second embodiment  this is not limitative. Alternatively  for example  the photographed image Pic may be divided into three or more horizontal regions  or may be divided into two or more vertical (perpendicular) regions. Alternatively  these may be combined so that the photographed image Pic is divided into a matrix.
[Modification 2-3]
[0150] For example  the modifications of the first embodiment may be applied to the second embodiment.
[0151] While the present technology has been described with the embodiments and the modifications hereinbefore  the technology may be used for various applications. For example  the technology may be used for gamma correction based on a position of a viewer nearest a display. Specifically  for example  different types of gamma correction may be performed between a case of the viewer at the front of the screen of the display and a case of the viewer at a position slightly displaced from the front. Alternatively  sound balance between right and left may be adjusted based on a position of a viewer nearest a display. Alternatively  for example  in the case where a display is a stereoscopic display  parallax between a left-eye image and a right-eye image may be adjusted based on a distance between the display and a viewer. Alternatively  the technology may be used to control the directivity of a microphone to be in a direction toward a speaker in a videoconference system. Specifically  beam forming  which is one of microphone characteristics  is dynamically changed to be in a direction toward a speaker  so that voice of only a desired speaker is captured while surrounding noise is reduced. In addition  the technology may be applied to digital signage. In addition  for example  the various processes in the applications may be performed not only based on the position of a viewer nearest a display  but also based on a position of another viewer.
[0152] Although the embodiments and the modifications have been exemplarily described with a display  the present technology is not limited thereto  and the technology may be used for an application where a position of a face is detected  and operation is performed following the position. For example  the technology may be used for applications of an air conditioner  a humidifier  various types of face care products  and the like  where a position of a user face is followed  and air or mist is fed to the position. In addition  although the technology is used for the applications where operation is performed following a position of a user face in the above exemplary case  the technology is not limited thereto  and the technology may be used for an application where operation is performed while a position of a user face is constantly avoided.
[0153] In addition  although the face of a viewer has been detected in the embodiments and the modifications  the technology is not limited thereto. For example  a detection section having a configuration similar to that of the face detection section 30 may be mounted in a motor vehicle to detect another vehicle approaching. Consequently  for example  an approaching vehicle is detected in a short process time.
[0154] It is to be noted that the technology may be configured as follows.
(1) A photographing system including:
a photographing section photographing a subject to acquire a frame image including a subject image; and
a matching section changing size of one or both of the subject image and a beforehand prepared template image to change a size ratio of the template image to the subject image  and performing pattern matching between the subject image and the template image  size of one or both of the subject image and the template image being changed  for each of size ratios 
wherein the matching section repeats image search through pattern matching while sequentially changing the size ratio  and obtains one or more size ratios at which patterns match each other  in a certain order of image search  and holds  as a first size ratio  a size ratio having a largest value among such obtained size ratios  and thereafter performs image search in a manner that pattern matching is performed at a first frequency in a range of a size ratio equal to or larger than the first size ratio  and is performed at a frequency lower than the first frequency in a range of a size ratio smaller than the first size ratio.
(2) The photographing system according to (1) 
wherein the matching section holds  as a second size ratio  a size ratio having a smallest value among the obtained size ratios in the certain order of image search  and thereafter performs image search in a manner that pattern matching is performed at a second frequency lower than the first frequency in a range of a size ratio smaller than the first size ratio and equal to or larger than the second size ratio  and is performed at a third frequency lower than the second frequency in a range of a size ratio smaller than the second size ratio.
(3) The photographing system according to (1) or (2)  wherein the matching section changes the size ratio to be gradually reduced in each piece of image search.
(4) The photographing system according to any one of (1) to (3)  wherein if the patterns do not match each other in the range of the size ratio equal to or larger than the first size ratio in any image search after the image search in which the first size ratio is obtained  the matching section performs pattern matching across all size ratios in subsequent image search.
(5) The photographing system according to any one of (1) to (4)  wherein the matching section performs pattern matching through scanning the entire area of the frame image while shifting a region as a matching object.
(6) The photographing system according to (2)  wherein the frame image is divided into a plurality of regions  and the matching section sets the first size ratio and the second size ratio for each of the divided regions to set frequency of pattern matching for image search.
(7) The photographing system according to (6)  wherein the matching section performs pattern matching through scanning the entire area of the frame image while shifting a region as a matching object in a range of a size ratio equal to or larger than a largest value among values of first size ratios in the regions of the frame image.
(8) The photographing system according to (6)  further including a motion detection section performing motion detection based on frame difference between the plurality of frame images acquired at time points different from one another  wherein the matching section corrects each of the first and second size ratios for each of the regions of the frame image based on a result of the motion detection.
(9) The photographing system according to (2)  wherein the matching section acquires information on a relevant subject  based on the subject image  and corrects each of the first and second size ratios based on the information.
(10) The photographing system according to (2)  wherein the first size ratio corresponds to a distance between the photographing section and a subject nearest the photographing section  and the second size ratio corresponds to a distance between the photographing section and a subject most distant from the photographing section.
(11) The photographing system according to any one of (1) to (10)  wherein the matching section changes the size ratio by changing size of the frame image.
(12) The photographing system according to any one of (1) to (10)  wherein the matching section changes the size ratio by changing size of the template image.
(13) The photographing system according to any one of (1) to (12)  wherein the subject is a face.
(14) A pattern detection system including
a matching section changing size of one or both of a frame image including a subject image and a beforehand prepared template image to change a size ratio of the template image to the subject image  and performing pattern matching between the subject image and the template image  size of one or both of the subject image and the template image being changed  for each of size ratios 
wherein the matching section repeats image search through pattern matching while sequentially changing the size ratio  and obtains one or more size ratios at which patterns match each other  in a certain order of image search  and holds  as a first size ratio  a size ratio having a largest value among such obtained size ratios  and thereafter performs image search in a manner that pattern matching is performed at a first frequency in a range of a size ratio equal to or larger than the first size ratio  and is performed at a frequency lower than the first frequency in a range of a size ratio smaller than the first size ratio.
(15) An electronic unit including a photographing system and a control section performing operation control using the photographing system  the photographing system including:
a photographing section photographing a subject to acquire a frame image including a subject image; and
a matching section changing size of one or both of the subject image and a beforehand prepared template image to change a size ratio of the template image to the subject image  and performing pattern matching between the subject image and the template image  size of one or both of the subject image and the template image being changed  for each of size ratios 
wherein the matching section repeats image search through pattern matching while sequentially changing the size ratio  and obtains one or more size ratios at which patterns match each other  in a certain order of image search  and holds  as a first size ratio  a size ratio having a largest value among such obtained size ratios  and thereafter performs image search in a manner that pattern matching is performed at a first frequency in a range of a size ratio equal to or larger than the first size ratio  and performed at a frequency lower than the first frequency in a range of a size ratio smaller than the first size ratio.
[0155] The present disclosure contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2011-191036 filed in the Japan Patent Office on September 1  2011  the entire content of which is hereby incorporated by reference.
[0156] It should be understood by those skilled in the art that various modifications  combinations  sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.

We Claim:
1. A photographing system comprising:
a photographing section photographing a subject to acquire a frame image including a subject image; and
a matching section changing size of one or both of the subject image and a beforehand prepared template image to change a size ratio of the template image to the subject image  and performing pattern matching between the subject image and the template image  size of one or both of the subject image and the template image being changed  for each of size ratios 
wherein the matching section repeats image search through pattern matching while sequentially changing the size ratio  and obtains one or more size ratios at which patterns match each other  in a certain order of image search  and holds  as a first size ratio  a size ratio having a largest value among such obtained size ratios  and thereafter performs image search in a manner that pattern matching is performed at a first frequency in a range of a size ratio equal to or larger than the first size ratio  and is performed at a frequency lower than the first frequency in a range of a size ratio smaller than the first size ratio.

2. The photographing system according to claim 1 
wherein the matching section holds  as a second size ratio  a size ratio having a smallest value among the obtained size ratios in the certain order of image search  and thereafter performs image search in a manner that pattern matching is performed at a second frequency lower than the first frequency in a range of a size ratio smaller than the first size ratio and equal to or larger than the second size ratio  and is performed at a third frequency lower than the second frequency in a range of a size ratio smaller than the second size ratio.

3. The photographing system according to claim 1  wherein the matching section changes the size ratio to be gradually reduced in each piece of image search.

4. The photographing system according to claim 1  wherein if the patterns do not match each other in the range of the size ratio equal to or larger than the first size ratio in any image search after the image search in which the first size ratio is obtained  the matching section performs pattern matching across all size ratios in subsequent image search.

5. The photographing system according to claim 1  wherein the matching section performs pattern matching through scanning the entire area of the frame image while shifting a region as a matching object.

6. The photographing system according to claim 2  wherein the frame image is divided into a plurality of regions  and the matching section sets the first size ratio and the second size ratio for each of the divided regions to set frequency of pattern matching for image search.

7. The photographing system according to claim 6  wherein the matching section performs pattern matching through scanning the entire area of the frame image while shifting a region as a matching object in a range of a size ratio equal to or larger than a largest value among values of first size ratios in the regions of the frame image.

8. The photographing system according to claim 6  further comprising a motion detection section performing motion detection based on frame difference between the plurality of frame images acquired at time points different from one another  wherein the matching section corrects each of the first and second size ratios for each of the regions of the frame image based on a result of the motion detection.

9. The photographing system according to claim 2  wherein the matching section acquires information on a relevant subject  based on the subject image  and corrects each of the first and second size ratios based on the information.

10. The photographing system according to claim 2  wherein the first size ratio corresponds to a distance between the photographing section and a subject nearest the photographing section  and the second size ratio corresponds to a distance between the photographing section and a subject most distant from the photographing section.

11. The photographing system according to claim 1  wherein the matching section changes the size ratio by changing size of the frame image.

12. The photographing system according to claim 1  wherein the matching section changes the size ratio by changing size of the template image.

13. The photographing system according to claim 1  wherein the subject is a face.

14. A pattern detection system  comprising
a matching section changing size of one or both of a frame image including a subject image and a beforehand prepared template image to change a size ratio of the template image to the subject image  and performing pattern matching between the subject image and the template image  size of one or both of the subject image and the template image being changed  for each of size ratios 
wherein the matching section repeats image search through pattern matching while sequentially changing the size ratio  and obtains one or more size ratios at which patterns match each other  in a certain order of image search  and holds  as a first size ratio  a size ratio having a largest value among such obtained size ratios  and thereafter performs image search in a manner that pattern matching is performed at a first frequency in a range of a size ratio equal to or larger than the first size ratio  and is performed at a frequency lower than the first frequency in a range of a size ratio smaller than the first size ratio.

15. An electronic unit including a photographing system and a control section performing operation control using the photographing system  the photographing system comprising:
a photographing section photographing a subject to acquire a frame image including a subject image; and
a matching section changing size of one or both of the subject image and a beforehand prepared template image to change a size ratio of the template image to the subject image  and performing pattern matching between the subject image and the template image  size of one or both of the subject image and the template image being changed  for each of size ratios 
wherein the matching section repeats image search through pattern matching while sequentially changing the size ratio  and obtains one or more size ratios at which patterns match each other  in a certain order of image search  and holds  as a first size ratio  a size ratio having a largest value among such obtained size ratios  and thereafter performs image search in a manner that pattern matching is performed at a first frequency in a range of a size ratio equal to or larger than the first size ratio  and performed at a frequency lower than the first frequency in a range of a size ratio smaller than the first size ratio.