System adapted to provide an operator increased visibility and associated method

The present invention relates to a system adapted to provide an operator increased visibility, used in particular for using to the aircraft pilotage and an associated method.

The invention is in the field of augmented or EVS vision systems (from English "Enhanced Vision Systems"), which are imaging systems aimed to provide an operator an improved environmental image compared to human perception, the image can be presented with a "head-up" display (or HUD to "head up display" in English) or on a display screen (display says "low head").

These EVS systems find application in particular in the field of assistance to aircraft piloting, particularly during approach and landing, as well as taxiing and take-off in low visibility due to environmental conditions and / or weather deteriorated.

Indeed, in aviation, it is customary to mark the runways / landing at airports with markings such bright markings, such as the approach lights, the bright edge markers and track center .

To ensure safety in air transport, there are regulations requiring a runway visual range given to engage a landing approach, for example. The runway visual range, in English "Runaway Visual Range" (RVR) is defined as the distance to which an aircraft pilot, placed in the axis of the track, can be seen by its natural vision brands or fires which define the track or that guide the axis thereof. RVR is generally evaluated by an automatic calculation incorporating instrumental measures for the transmission coefficient of the atmosphere and the background luminance and information about the intensity of the lighting. For example, an approach known as CAT 1 to Category 1 regulations require a minimum of 550 meters RVR for engaging an approach, other requirements being to satisfy also the regulation and leads down to a decision height (so-called DH) of at least 200ft (200 feet), height at which the pilot must discern visual references to descend below the decision height DH. Such visual range is difficult to achieve in some adverse weather conditions that can make the lighting not discernible by the pilot at DH DH. height at which the pilot must discern visual references to descend below the decision height DH. Such visual range is difficult to achieve in some adverse weather conditions that can make the lighting not discernible by the pilot at DH DH. height at which the pilot must discern visual references to descend below the decision height DH. Such visual range is difficult to achieve in some adverse weather conditions that can make the lighting not discernible by the pilot at DH DH.

EVS systems were designed, in particular to address this problem and improve natural vision piloting crews and extend landing capabilities degraded visibility conditions. The regulation provides inter alia, in the example cited above, descending to 10Oft if the required visual references could be discerned by the pilot to 200ft using EVS and even if it does have not discernible by the human eye.

Are known at present EVS systems having image sensors in the infrared spectral band using the spectral bands from 3 to 5μηι or 8 to 14 μηι and in the spectral band for SWIR "Short Wave Infra Red" signals electromagnetic wavelength which is from 1 to μηι 2.5μηι. The use of sensors in the SWIR spectral band aims to optimize the lamps detection capabilities incandescent commonly used to mark trails.

However, recent light beacons using new lighting techniques emitting diode (LED), which do not transmit beyond a wavelength of 1 μηι.

Patent application WO 2009/128065 A1 discloses an EVS system comprising a plurality of sensors adapted to operate in various spectral bands, comprising the NIR spectral range for "Near Infra-Red" of electromagnetic signals of wavelength extending from 0,7μηι .0μηι 1, and the spectral band of visible light that extends from 0,4μηι to 0.7μηι. This system achieves a fusion of image data acquired by the various sensors. The spectral bands to be merged are selected based on the previously identified weather conditions and the nature of bright markings to be detected.

However, in addition to computational complexity and high manufacturing cost, such a system has limited performance to the performance of the best spectral bands in the equipment. Moreover, it is not possible to predict the performance of the system, that is to say the gain in visibility compared to the human eye because the gain varies depending on weather and atmospheric conditions, the luminance base and the intensity of the light markings. Therefore, it is not easy with such a system to predict whether a value of RVR data, the system will achieve the performance required to engage and drive the landing run.

Is defined in the following the angular resolution as the elementary field of view of a pixel of an image sensor detector. It is generally considered that the angular resolution of the human eye is about 0.8 arcminutes, or 0.0135 ° (or 0.00029 radians). Similarly in the following, high spatial resolution appoint a fine angular resolution, thus an angle of resolution / small elementary field of view.

The invention aims to overcome the disadvantages of the state of the above technique.

To this end, the invention provides, in a first aspect, a system adapted to provide an operator increased visibility for assistance aircraft steering, comprising at least one sensor capable of acquiring image data in a given spectral band and a central processing unit adapted to process the acquired image data and transmitting the processed image data to display a digital image on a display unit.

This system includes:

- at least one high resolution sensor capable of acquiring image data forming a digital image in a spectral band including at least all or part of the spectral band corresponding to the electromagnetic signals visible to the human eye, first spatial resolution, and angular resolution strictly finer capture the angular resolution of the human eye, and

- a nonlinear processing module adapted to perform a change of spatial resolution while maintaining bright points of said captured digital image to obtain a digital image to be displayed second spatial resolution lower than the first spatial resolution.

Advantageously, the system of the invention is an EVS system using at least one sensor (adjustable or fixed) very fine angular resolution and significantly better than that of the eye in the visible spectral range, which allows:

• to have detection range performance light beacons significantly improved compared to the eye,

• be adapted to LED type light beacons,

• to quantify its performance relative to the visual range of the human eye, regardless of any variation in weather and atmospheric conditions.

In addition, the proposed system is less costly in material and requires less computational resources than a sensor-based system adapted to operate in several different spectral bands.

The system according to the invention may have one or more of the following characteristics, taken separately or in any technically acceptable combination.

Each digital image is defined by a matrix of pixels, each pixel having an associated value, said value being all the higher that pixel is bright, and the nonlinear processing module is adapted to apply a non-linear filtering to a block of pixels of the captured digital image to determine a pixel value corresponding to the digital image to be displayed, said non-linear filtering taking into account, for a block of pixels of the digital image acquired, at least maximum value of said pixel block.

The non-linear filter consists of associating with a pixel of the digital image for displaying a value computed from values ​​higher than a predetermined threshold of the corresponding pixel block of the digital image acquired.

Alternatively, the nonlinear filter is associated with a pixel of the digital image to display a value calculated from a given number of the highest values ​​of the pixel block.

The system comprises a plurality of juxtaposed high-resolution sensors.

The system includes a high definition sensor, adapted to be positioned in an image data acquisition position in a line of sight, and movement of said sensor bodies to move the angle of view of the sensor.

The high-resolution sensor capable of acquiring digital image data is a first sensor in a first spectral band corresponding to visible signals by the human eye, the system further comprising a second sensor capable of acquiring second digital image data in a second spectral band different from the first spectral band.

The second spectral band is in the field of infrared electromagnetic waves of wavelength between 3 and 14 micrometers.

The system further includes an image processing module adapted to effect fusion between said digital image and to display the second digital image data acquired by the second sensor.

The angular resolution of capture is strictly finer than the angular resolution of the human eye, a factor greater than or equal to 3.

According to a second aspect, the invention provides a method adapted to provide an operator increased visibility, for assistance to the aircraft pilotage, implemented by a system comprising at least one sensor capable of acquiring data of image in a given spectral band and a central processing unit adapted to process the acquired image data and transmitting the processed image data to display a digital image on a display unit. The method comprises the following steps:

- acquisition of the image data forming a digital image in a spectral band including at least all or part of the spectral band corresponding to the electromagnetic signals visible to the human eye, the first spatial resolution and angular resolution strictly finer capture the angular resolution of the human eye,

- applying a non-linear processing adapted to perform a change of spatial resolution while maintaining bright points of said captured digital image to obtain a digital image to be displayed second spatial resolution lower than the first spatial resolution.

The advantages of the process are similar to the benefits of the system briefly described above, they are not repeated here.

The method according to the invention may have one or more of the following characteristics, taken separately or in any technically acceptable combination.

Each digital image is defined by a matrix of pixels, each pixel having an associated value, said value being all the higher that pixel is bright, and the non-linear processing comprises applying a non-linear filtering to a block of pixels of the captured digital image to determine a pixel value corresponding to the digital image to be displayed, said non-linear filtering taking into account at least the maximum value of said pixel block.

The non-linear filter consists of associating with a pixel of the digital image for displaying a value computed from values ​​higher than a predetermined threshold of the corresponding pixel block of the digital image acquired.

Alternatively, the value associated with the pixel of the digital image to be displayed is calculated from a given number of the highest values ​​of the pixel block.

The method comprises a further step of acquiring the second digital image data in a second spectral band different from the first spectral band.

The method comprises a step of fusion of the digital image of the second resolution obtained by non-linear processing and the second digital image data.

Other features and advantages of the invention emerge from the description which is given below, with illustrative and non limitative, with reference to the appended figures, in which:

FIG 1 schematically shows an aircraft approaching a runway marked by light beacons;

2 schematically illustrates an enhanced vision system according to a first embodiment;

FIG 3 schematically illustrates two images of different spatial resolutions;

- Figure 4 schematically illustrates an enhanced vision system according to a second embodiment.

The invention will be described in its application to aid aircraft piloting, understanding that it is not limited to this application.

Indeed, the invention is of more general application in any context in which an enhanced vision in relation to human vision of an operator is useful, for example for controlling other types of devices.

1 schematically illustrates an environment of application of the invention, which is the landing of an aircraft.

In the example of Figure 1, an aircraft 2 is on landing approach to a landing field 4 having a runway 6.

The runway is marked by different markers 8, 10, 12, 16, 18. For example, the tags 8 are track center of markers, the markers 10, 12 are beacons runway edge disposed regularly over its entire length, the markers 16 are runway threshold markers and markers 18 are approach ramp tags.

Markers 8, 10, 12, 16, 18 emit at least in the spectral range visible to the eye by the operator and some may be implemented by light-emitting diodes (LED) and other by incandescent lamps .

Advantageously, the aircraft 2 is provided with a system 14 adapted to provide the steering operator with enhanced vision.

It should be noted that the system 14 is shown schematically in Figure 1, and is in practice made up of several elements which are positioned at different locations or grouped, as explained in more detail below.

According to a first embodiment illustrated schematically in Figure 2, a system 14 according to the invention comprises an image sensor 20 in the spectral band of radiation or electromagnetic signals visible to the human eye, of wavelength comprised between 0,4μηι to 0.7μηι but can alternatively be up to 1 μηι.

Alternatively, the image sensor 20 operates in a spectral band having only a portion of the spectral band of electromagnetic signals visible to the human eye.

The sensor 20 is a high resolution sensor, for obtaining a finer level of resolution angular shooting the human eye.

The digital image acquired by the sensor 20 has an associated spatial resolution, the spatial resolution being defined as the number of image data or pixels per unit length. Each pixel has a value associated radiometry, also called intensity value.

Preferably, the sensor 20 is such that the ratio K between the angular resolution of the human eye and the angular resolution image acquisition is greater than or equal to 3. The digital image acquired by such a sensor is known on -résolue because it has a finer angular resolution than the angular resolution attainable by the human eye.

The sensor 20 captures, as a sighting axis, a maximum angle of field of view Θ preferably of the order of 35 ° to 40 °.

Preferably, the sensor 20 is a CMOS sensor ( "Complementarity Metal-Oxide-Semiconductor"), consisting of photodiodes, whose manufacturing cost is moderate.

Alternatively, the sensor 20 is a CCD (standing for "Charge Coupled Device" or charge coupled device) or using any other sensor technology.

In an alternative embodiment, in order to acquire image data corresponding to the angle of field of view Θ, the sensor 20 is replaced by a plurality of angle field sensors less than Θ juxtaposed and adapted capturing image data corresponding to adjacent fields of view or having an overlap portion.

In another alternative embodiment, the high resolution sensor 20 has a field of vision smaller angle than the desired angle, so a smaller field of view, but this sensor 20 is made movable by displacement members, to rotate so as to cover a wide field of view of about Θ. For example, such drive members are formed by a hinged connection or fixed associated with a motor. In this embodiment, the sensor 20 is steerable.

In practice, in the case of use for aiding the piloting of aircraft 2, the sensor 20 is placed for example at the front of the fuselage of the aircraft.

Advantageously, as explained in detail below, capturing a picture surrésolue improves the visibility of luminous markings with a quantifiable performance, even in low visibility conditions.

For example, a weather condition fog type reducing visibility is illustrated schematically by a cloud 21 in Figure 2.

Output of the sensor 20, a digital image on the solved- 0 of the first spatial resolution R 0 is obtained, the image being composed of K * L pixels, for example 5120 * 4096. The digital image is defined by a matrix pixel values.

The data of the digital image on the solved- 0 , first spatial resolution R 0 , are transmitted to a nonlinear processing unit 22, for example via a data bus connected to the output of the sensor 20. The module nonlinear processing 22 is implemented by an unillustrated programmable device, such as a board computer, comprising one or more processors capable of performing calculations and computer program code instructions when they are energized.

Alternatively, the programmable device implementing the non-linear processing module 22, and any other computing unit, is implemented by an FPGA integrated circuit or an integrated circuit of the ASIC type dedicated.

The processing performed by the nonlinear processing unit 22 to switch from the first image I 0 of the first spatial resolution R 0 in a digital image of second spatial resolution R 1; lower than the first spatial resolution R 0 , while preserving points of image contrast, particularly bright points (or points of positive contrast) of the image.

Called points of contrast points or pixels whose associated value is significantly higher or significantly lower than the average value of pixels of the neighborhood, for example greater than 3 times the standard deviation of the pixels of this neighborhood.

The points whose associated value is much higher than the surrounding values ​​are bright spots, the contrast is said to be positive.

The points whose associated value is significantly lower than the surrounding values ​​are dark spots, the contrast is said to be negative.

Note that with a conventional resolution sensor, not on-resolved, it is possible to miss points of high contrast (positive or negative) due to the resolution of the sensor.

The processing performed by the nonlinear processing module 22 keeps points of positive contrast in the digital image to the second spatial resolution lower than the first resolution.

Figure 3 illustrates two such images the 0 and \ with a resolution factor of 3 between the first resolution R 0 and the second resolution Thus, a B block of 3x3 pixels of the digital image I 0 corresponds to a pixel P the image . Correspondence is a spatial correspondence in the respective plates as shown in Figure 3.

More generally, a block of MxN pixels of the image I 0 , corresponds to an image pixel.

In the preferred embodiment, the non-linear processing applied by the module 22 to move from one block B, containing pixels (Bi j ) {= 3x 1 + k, j = 3x j l + k, k € {0,1,2}} of the image I 0 to the pixel P i j of the image consists in associating the pixel Pn ^ the maximum value of M x N block of pixels of the image I 0 :

P Yes = max (fl (J )

Thus, advantageously, the gain provided by the on-resolution image I 0 acquired by the sensor 20 is preserved. The maximum intensity emitted by the light beacons, captured by the image acquisition on-resolved, is stored in the digital image of the second resolution

Advantageously, the nonlinear processing module is adapted to store the detected light points, in other words to maintain the brightest block points because in fact more a point is brighter, the associated value in the image digital high.

The nonlinear processing applied preserves the bright spots but does not preserve dark spots, because only the brightest points of interest in flying aid intended application.

En variante, le module de traitement non-linéaire 22 applique d'autres traitements non-linéaires de type filtrage conservant les valeurs maximales ou traitant les pixels en fonction de leur rang. Un filtrage sur des fenêtres recouvrantes peut également être envisagé.

For example, for a given block, is stored the values ​​of the block of pixels greater than a threshold S. The threshold S may be fixed or dynamically calculated, as for example, increased from 2 to 3 times the standard deviation of block of pixel values. All retained values, which are the values ​​of the brightest pixels of the block according to the selected criteria are then used to obtain the final value of the pixel of the digital image of the second resolution, for example, an average of the figures, so above the threshold S, the considered block is calculated and assigned as final value of the corresponding pixel in the digital image of the second resolution

In another example, orders the pixel values ​​of a block considered in decreasing order of values ​​and 2 is stored (or 3) highest values. The selected values, which are the values ​​of the brightest pixels of the block according to the selected criteria are then used to obtain the final value of the pixel of the digital image of the second resolution, for example, an average of the figures

of the considered block is calculated and assigned as final value of the corresponding pixel in the digital image of the second resolution.

The output of the nonlinear processing module 22, the digital image of the second spatial resolution less than the resolution R R 0 is transmitted to a module 24 for image processing, capable of applying conventional treatments, for example correction radiometry, geometrical alignment for the displayed image on a display unit 26, for example a screen.

In one embodiment, the 22 and 24 processing modules are charged by a single board computer.

In one embodiment, the display is performed by keying on a display screen 26, located at eye of a steering operator, called HUD.

The second resolution is preferably selected depending on the display resolution of the display screen 26, for example a "head-up" display. Alternatively, a display screen "head-down" for example on the dashboard, is used.

Advantageously, such a head-up display can present the operator with enhanced vision of reality that can perceive naturally, and thus help to control operations.

Thus, a display method adapted to provide an operator with a enhanced vision according to the invention comprises a first step of acquiring a first digital image of the first spatial resolution by a high-resolution sensor capable of acquiring image data in a spectral band corresponding to visible signals by the human eye, with a degree of angular resolution strictly greater capture at angular resolution of the human eye.

This first step is followed by a non-linear processing step for obtaining a second image of the second spatial resolution R 2 , less than the first spatial resolution and second angular resolution suited to the resolution of the display device.

Preferably, the factor between the angular resolution and capture the angular resolution of the human eye is greater than or equal to 3, that is to say, the angular resolution of capture is at least 3 times finer than the resolution angle of the human eye.

Advantageously, performance of the proposed system is computable, regardless of weather conditions.

Indeed, a weather condition is characterized by a σ absorption coefficient in a given spectral band.

According to the Beer-Lambert-Bouguer, intensity changes according to the distance X and σ absorption coefficient of the following way:

l (X) l = 0 ; b x p (-s (X -
Where X 0 is a reference distance that is associated with the intensity I 0 of a light beacon.

Taking into account a variation of the angular resolution, where a is the angular resolution of pixels for a vision equipment using the method of the invention and ocher f is the angular resolution of pixels for a reference vision equipment using an equivalent angular resolution the display resolution, we get:

l (X) l = 0 ; e x p (-s (X -

In weather conditions leading to an extinction coefficient of 0.01 m "1 , one obtains for example:

• the same signal to noise ratio for light beacons 500 m with an angle oc resolution reference sensor ref and 1000 meters, with an angular resolution sensor refined by a factor of 25 (a = oc ref / 25), c ' ie a higher resolution level by a factor of 25 results in a gain range of a factor of 2,

• the same signal to noise ratio for light beacons 800 m with an angle oc resolution reference sensor ref and 1000 meters, with an angular resolution sensor refined by a factor between 3 and 4 (a = a ref / 3 , 5), that is to say a higher resolution level by a factor of 3.5 results in a gain range of 25%.

Therefore, it is shown that angular resolution of an upper level makes it possible to quantifiably reduce the detection range brings a vision equipment.

In a variant of this first embodiment, the system of the invention is an EVS system using at least one sensor (adjustable or fixed) very fine angular resolution in a different spectral band from that of the eye, allowing to have detection range performance light beacons significantly improved compared with an EVS system with a resolution of the class of that of the eye in the same spectral band.

A second embodiment of a system 30 adapted to provide enhanced vision according to the invention is shown in Figure 4.

The system 30 includes, in addition to the first sensor 20 adapted to acquire images of very high spatial resolution in the visible spectral band, and the processing unit 22 described above, constituting an initial imaging, a second sensor 32 adapted to acquire the images 2 in a different spectral band than the visible spectral range, preferably in the infrared spectral range.

Preferably, the spatial resolution images the 2 acquired by the sensor 32 is substantially equal to the second spatial resolution R 2 of the images obtained at the output of non-linear processing module 22.

The acquisition by the second sensor 32 forms a second channel imaging.

The system 30 also includes a processing module 34 adapted to perform the image fusion and 2 , corresponding to the same field of view, applying in particular, with techniques known in the field of image processing, a control radiometry on each channel, a geometric alignment to make the images and the two superimposable and a pixel by pixel addition.

The processing module 34 is also adapted to perform any image correction for the display.

In practice, the processing module 34 is implemented by an unillustrated programmable device, such as a board computer, comprising one or more processors capable of performing calculations and computer program code instructions when placed under voltage.

The processing module 34 implements a step of fusion of the digital image of the second resolution obtained by non-linear processing performed in the nonlinear processing step by the module 22, and the second data of the digital image 2 acquired by the sensor 32.

The resultant fused image is then transmitted to a display unit 26, similar to the display unit 26 described above with reference to Figure 2, for example a screen to overlay and display.

Advantageously, the proposed system allows an image acquisition first spatial resolution that is over-determined, which captures the positive points of contrast, that is to say brilliant point from their neighborhood, and preserve these points of positive contrast in the digital image to the second spatial resolution lower than the first resolution. In the end, a digital image of the second resolution

space for display and operation is achieved, but this image has brightness information that would not have been captured with an image acquisition to said second spatial resolution.

CLAIMS

1. - A system adapted to provide an operator increased visibility for assistance aircraft steering, comprising at least one sensor capable of acquiring image data in a given spectral band and a central processing unit adapted to process the acquired image data and transmit the processed image data to display a digital image on a display unit,

characterized in that it comprises:

- at least one sensor (20) high resolution capable of acquiring image data forming a digital image (I 0 ) in a spectral band including at least all or part of the spectral band corresponding to the electromagnetic signals visible to the human eye , first spatial resolution and level of angular resolution strictly finer capture the angular resolution of the human eye, and

- a module (22) of non-linear processing adapted to perform a change of spatial resolution while maintaining bright points of said captured digital image (s 0 ) to obtain a digital image (h) to display second spatial resolution less than the first spatial resolution.

2. - A system according to claim 1, wherein each digital image is defined by a matrix of pixels, each pixel having an associated value, said value being all the higher that pixel is bright, characterized in that the module (22) non-linear processing is adapted to apply a non-linear filter to a digital image acquired pixel block to determine a pixel value corresponding to the digital image to be displayed, said non-linear filtering preserving bright points and taking into account, for a block of pixels of the digital image acquired, at least the maximum value of said pixel block.

3. - A system according to claim 2, characterized in that said non-linear filtering preserving bright spots consists in associating a pixel of the digital image to display a value calculated from values ​​above a predetermined threshold the block corresponding pixels of the digital image acquired.

4. - A system according to claim 2, characterized in that said non-linear filtering preserving bright spots consists in associating a pixel of the digital image to display a value calculated from a given number of highest values of the corresponding pixel block of the digital image acquired.

5. - System according to one of claims 1 to 4, characterized in that it comprises a plurality of high-resolution sensors juxtaposed.

6. - System according to one of claims 1 to 4, characterized in that it comprises a high resolution sensor, adapted to be positioned in an image data acquisition position in a line of sight, and organs moving said sensor to move the angle of view of the sensor.

7. - A system according to any one of claims 1 to 6, wherein said sensor (20) high resolution capable of acquiring digital image data is a first sensor in a first spectral band corresponding to visible signals by the eye human, characterized in that it further comprises a second sensor (32) suitable for acquiring the second digital image data in a second spectral band different from the first spectral band.

8. - The system of claim 7, characterized in that said second spectral band belongs to the field of infrared electromagnetic waves of wavelength between 3 and 14 micrometers.

9. - A system according to any one of claims 7 or 8, characterized in that it further comprises a module (34) An image processing adapted to effect fusion between said digital image and to display the second data digital image acquired by the second sensor.

10. - A system according to any one of claims 1 to 9, characterized in that the angular resolution of capture is strictly finer than the angular resolution of the human eye, by a factor greater or equal to 3.

January 1. - A method adapted to provide an operator increased visibility, for assistance to the aircraft pilotage, implemented by a system comprising at least one sensor capable of acquiring image data in a given spectral band and a unit central computer adapted to process the acquired image data and transmitting the processed image data to display a digital image on a display unit,

characterized in that it comprises the steps of:

- acquisition of the image data forming a digital image in a spectral band including at least all or part of the spectral band corresponding to the electromagnetic signals visible to the human eye, the first spatial resolution and angular resolution strictly finer capture the angular resolution of the human eye,

- applying a non-linear processing adapted to perform a change of spatial resolution while maintaining bright points of said captured digital image to obtain a digital image to be displayed second spatial resolution lower than the first spatial resolution.

12. - Method according to claim 1 1, wherein each digital image is defined by a matrix of pixels, each pixel having an associated value, said value being all the higher that pixel is bright, characterized in that the non-linear processing comprises applying a non-linear filter to a block of pixels of the captured digital image to determine a pixel value corresponding to the digital image to be displayed, said non-linear filtering taking into account the least the maximum value of said pixel block.

13. - Method according to claim 12, characterized in that said non-linear filtering is to associate to a pixel of the digital image for displaying a value computed from values ​​higher than a predetermined threshold of the corresponding pixel block of digital image acquired.

14. - Method according to claim 12, characterized in that said non-linear filtering consists in associating a pixel of the digital image to display a value calculated from a given number of the highest values ​​of the pixel block corresponding digital image acquired.

15. - Method according to any one of claims 1 1 to 14, characterized in that it comprises a further step of acquiring the second digital image data in a second spectral band different from the first spectral band.

16. - Method according to claim 15, characterized in that it comprises a step of fusion of the digital image of the second resolution obtained by non-linear processing and the second digital image data.