CLIAMS:
We Claim:

1. A method for shape/geometry correction of an X-ray baggage scan images, the method comprising:
acquiring, a current x-ray exposure of an examination subject with an x-ray apparatus using an x-ray detector, to obtain an image of the subject having a physical length using a plurality of detector cards consisting of an array of photo detectors.;
computing distance factor for each detector cards, wherein the distance factor is a ratio of pixels captured by the detector card to the physical length captured by the detector card, wherein the distance factor varies with the object distance and the detector distance;
normalizing the computed distance factors for all the detector cards with respect to one detector card;
generating a lookup table by mapping the line of distorted image to the line of corrected image data, wherein the line of corrected image data is the image data which has undergone remapping and also suitable interpolation through lookup table technique; and
downscaling the image to the original size to retrieve the corrected image.

2. The method of claim 1, wherein the step of mapping including:
initializing all indices i, j =0;
contemplatingjth column of the distorted image I of size m x n;
computing the new pixel index inew corresponding to each detector card position using the current pixel index iand normalized distance factor;
creating a new image Nnew by mapping the pixels from index i to new index position inew;
interpolating for filling the non-existent pixel and other pixels are unchanged;
incrementing the column counter j = j+1; and
comparing the column counter to the width of the image, if the column counter has reached the width of the image, downscale the image to original size to get the corrected image for display.

3. The method of claim 2, further comprising:
checking, if the column counter has not reached the width of the image, contemplating the column of the distorted image I.

4. The method of claim 1, wherein the detectors are arranged in “L” shape.

5. The method of claim 1, wherein more physical lengths represents more number of pixels and low physical length represents less number of pixels.

6. The method of claim 1, wherein the distorted image is remapped by means of normalized distance factors.

7. The method of claim 1 where the x-ray baggage scan image is corrected in real-time by applying correction by lookup table to the line scan data of high energy and low energy image data.

8. The method of claim 1 where the high energy and low energy image strip is subjected to downscaling by suitable means (for example: bilinear, nearest neighbour, averaging etc) to get the corrected high energy and low energy image strip.

9. The method of claim 1 can be applied to x-ray scanner of different tunnel sizes by means of respective distance factors and normalized distance factors.

10. The method of claim 1 can be applied to any source and any detector configuration namely anyone other than “L” shape combinations by calculating the distance factors.
,TagSPECI:FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)

“A method of geometry/shape correction of x-ray baggage scan images”

By
Bharat Electronics Ltd
Govt of India Enterprise, Jalahalli,
Bengaluru, Karnataka 560013.

The following specification particularly describes the invention and the manner in which it is to be performed.
Field of the Invention
The invention generally to x-ray imaging, and more particularly the invention relates to a method of geometry/shape correction of x-ray baggage scan images.

Background of the Invention
A typical digital x-ray system includes an x-ray source, an x-ray focusing grid and an x-ray or light detector consisting of an array of photo detectors. The x-ray source emits x-rays, or photons, of a specific energy level in a narrow spray pattern through a body and toward the detectors. After passing through the object or subject or body, the spray pattern includes primary and scattered photons. The x-ray focusing grid, placed between the subject and the detector, absorbs most scattered photons and passes most primary photons onto the array of detector pixels.

In response, each detector pixel in the array provides an electrical output signal representative of the intensity of light or x-rays striking it. Each output signal is then converted to a number known as a digital pixel value, which is in turn output as a particular color on an electronic display or printing device, enabling viewing of the x-ray image.

Before display, it is common to correct the x-ray image for irregularities in the array of detectors. These irregularities, stemming from the uniqueness of each detector plane with reference to the x-ray source in the array of detectors, lead the detector to output different signals in response to the same incident light or x-rays. Correcting the image typically entails adjusting the digital representation of each detector output signal by an experimentally determined number for that detector. The numbers for all the detector pixels, known collectively as a correction map, are usually stored in a digital memory of the x-ray system.

An x-ray system typically has x-ray source detector configuration which causes severe distortions in the reconstructed images, and developing an effective correction method is still a major challenge. Many methods have been proposed in the literature and provide significant improvement in image quality, although drawbacks still exist.

One category of approach using software-based methods estimates and corrects the image based on the system geometry and imaged object, and it has been shown for some applications that
effective correction can be achieved. To combine the strengths of different types of correction methods, hybrid approaches are also often used which could provide well balanced trade-offs among correction effectiveness, calculation time, exposure loss, dose increase, and the like.

For example, in US 4817121 titled “Apparatus for checking baggage with X-rays” relates to a device wherein a distortion correction means for processing digitally converted data in accordance with a predetermined expression so as to delete distortion is provided between an A/D converting circuit of the image processing device and a main storage circuit for the temporal storage. The distortion correction device is constituted by a transformation means for transforming the measured data received from the x-ray detector means through an analog to digital conversion circuit into data as if the data relate to projection on storage elements which correspond in number to the detecting elements, an operation means for performing correction operation on the transformed data, a temporary storage means for temporarily storing the correction operated data and for applying the stored data to a main storage circuit as picture data, and a control circuit for controlling the transformation means, the operation means and the temporary storage means.

In the correction operation, a number of a selected one of the storage elements is given and operation data of a plurality of detecting elements in the vicinity of the selected storage element to be subject to linear interpolation operation. The thus obtained operation data are temporarily stored in a temporary storage means in the midway of the above mentioned operation and during the outputting operation to the next stage. Those series of operations are performed corresponding to the take-in operation of the instantaneous data of the respective detecting elements and the take-in operation of the data relating to the movement of the baggage.

Further, US 5671297 titled “Method for distortion correction of x-ray images, and device for carrying out the method” relates to an x-ray system for generating an input image by way of an x-ray exposure and an image converter for converting the input image into a series of digital image values and a storage device for storing input image values and output image values and a means for determining the position of corner points of one image in the other image as well as the surface area of the polygons defined by the corner points in the other image and a means for assigning the image values of a pixel to the associated polygon in the other image. This invention is based on the fact that the inaccuracies in the change of the shape and the surface area of the pixel due to the transformation are avoided by the determination of the position of the transformed image not merely based on a single point but on all corner points of the relevant pixel.

Further, US 7162006 titled “Method for de-skewing an x-ray picture of an item of luggage” relates to a method, which makes possible a better recognisability of the items contained in a luggage. A rectification of the previously strongly skewed pictures of the item of the luggage is achieved by means of geometric rescaling. According to this method for geometric rescaling picture of the item of luggage and the mapping geometry of the x-ray radioscopy device are required. The full dynamic range of the intensity values of the picture is used and a so called histogram adaptation is carried out, wherein the height of the luggage item is determined by a light barrier and the x-ray image is subjected to an optical calibration before geometric rescaling.

Furthermore, US 7860214 B1 titled “Correction of x-ray images” relates to a method to make use of attenuators to correct certain deficiencies that arise in x-ray images of spherical and cylindrical objects as a consequence of the varying thickness of sample material traversed by the x-ray beam. Another object is the identification of shapes for appropriate attenuators and their applications for normal x-ray imaging of stationary objects and for line scan imaging of moving objects. An application of attenuators improves image quality, especially along the edges, and aids in the detection of unwanted defects or contaminants that might otherwise be missed.

All of the above mentioned prior art have their own limitations. In view of the above, there is a need in the art for an improved method of geometry/shape correction of x-ray baggage scan images.

Summary of the Invention

An aspect of the present invention is to address at least the above-mentioned problems and/or disadvantages and to provide at least the advantages described below.

Accordingly, in one aspect of the present invention is to develop a method for shape/geometry correction of the x-ray baggage scan images. In the x-ray baggage scanner the item/baggage is conveyed through the conveyor and x-ray source fires x-ray and these rays penetrate through the object and reach the detectors which are arranged in “L” shaped housing. Each single line of image data is captured by all of the detectors arranged in the “L” shape housing and out of the single line of image data each 64 pixel is captured by the corresponding detector card. In an x-ray baggage scanner the x-ray source and the detector plane are not perpendicular to each other and the x-ray source is positioned at the corner and it fires at a specific angle and the x-ray fan beam is spread over the entire tunnel area. The x-ray penetrates the object, gets attenuated and reaches the detectors which are placed in "L" shape. Hence the object is divided non-uniformly by the x-rays and these non-uniform regions are detected by detector cards and are represented as 64 pixels of image data. So from the object a region of small physical length, medium physical length or large physical length gets converted to 64 pixels of image data and this phenomena cause geometry/shape distortion of the x-ray baggage scan images.

In the present method, rectifying the shape/geometry distortion of the baggage scan image by remapping the image, so that the image pixel data changes into actual representation of the non-uniform object lengths as it is divided by the x-ray fan beam. The more object length is represented by more pixels and less object length is represented by less number of pixels. This invention also claims to apply this distortion correction in real-time to the x-ray baggage scan data, while the object is being conveyed through the tunnel. This correction is applied on line scan data by a lookup table technique. This invention also claims that this technique can be extended to x-ray baggage machines of varying tunnel sizes.

Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

Brief description of the drawings

The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which:

Figure 1 illustrates the flow chart describing a method of geometry correction of x-ray baggage scan images, in accordance with one embodiment of the present invention.

Figure 2 illustrates the flow chart describing the steps involved in the conversion of the geometry correction process into a lookup table, in accordance with one embodiment of the present invention.

Figure 3 illustrates the flow chart describing the real-time implementation of geometry correction when the items/baggages are scanned, in accordance with one embodiment of the present invention.

Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.

Detailed description of the invention

The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a component surface” includes reference to one or more of such surfaces.

By the term “substantially” it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.

Figs. 1 through 3, discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way that would limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged communications system. The terms used to describe various embodiments are exemplary. It should be understood that these are provided to merely aid the understanding of the description, and that their use and definitions, in no way limit the scope of the invention. Terms first, second, and the like are used to differentiate between objects having the same terminology and are in no way intended to represent a chronological order, unless where explicitly stated otherwise. A set is defined as a non-empty set including at least one element.

The geometry/shape correction for x-ray baggage scan images is done by computing the normalized distance factors for a particular machine, followed by computation of new indices, followed by interpolation and finally downscaling to the original size. This input image line data to corrected image line data mapping is captured as a lookup table and this lookup table is used for the real-time implementation of this scheme.

Figure 1 show the first example embodiment of the present invention where the correction is done by normalizing the lengths captured by the detectors. This embodiment works as an offline means of geometric correction applicable to x-ray baggage scan images after grabbing.

At step 1, the physical length covered by each detector card is computed from the x-ray firing data 1. At step 2, the method compute the distance factor for all detector cards. The distance factor is defined by the ratio of the pixels captured by the detector card to the physical length captured by the detector card. This parameter changes depending on the object distance and detector distance. At step 3, the method computes the normalized distance factors for all detector cards with respect to one of the detector cards. At step 4, the method initialize all the indices i.e. i, j = 0. Further, in step 5, the method contemplates the column of the distorted image of size. At step 6, the method compute the corresponding new pixel index, using the current pixel index corresponding to each detector card position. At step 7, the method maps the pixel to new index position from which column of the new image is formed. For filling the pixels which doesn’t exist due to absence of image data, the method uses suitable interpolation means. At step 8, the method compare the column counter to the width of the image. The method checks at step 10 by incrementing the column counter j=j+1 at step 9, if the column counter has not reached the width of the image goto step 5, if the column counter crossed the width then gotonext step step 11. At step 11, the method downscale the image to the original size by suitable means to get the geometry/shape corrected image and further display the same at step 12.

Figure 2 illustrates the second example embodiment of the invention which describes a scheme which converts the geometry/shape correction method described in the first embodiment into a lookup table.

Step 1: Compute normalized distance factor of all the detector cards 21.
Step 2: Consider one line of the image data 22.
Step3: Apply correction to the one line of image data usingnormalized distance factors 23.
Step4: Apply suitable interpolation means to the above data 24.
Step 5: Map the input data indices to the corrected output data indices 25.
Step 6: Generate the lookup table 26.

Figure 3 illustrates the third example embodiment of the invention which describes real-time implementation of the geometry/shape correction scheme for x-ray baggage scan images where the image data is captured through line scanning as strips of data and not as the full image.

Step1: Normalize the x-ray baggage scanner 31.
Step2: Place the item/baggage on the conveyor and turn on the conveyor and move the item/baggage through the tunnel for scanning the item 32.
Step3: Get the image strip data 33 which consists of high energy and low energy data from the respective detector cards.
Step4: Apply geometry correction by lookup table 34. Correction is applied to high energy and low energy images separately.
Step 5: Downscale the image strip to original size 35 of the strip which is determined by tunnel size of the x-ray baggage scanner.
Step 6: Display the image strip on the display screen 36. In the line scan mode the item/baggage is displayed right away on the display screen when the baggage is conveyed through the conveyor belt. The lines/strip of the image data is acquired and displayed on the screen.
Step 7: Increment the strip counter 37. Depending on the size of the object we have to increment the strip counter to acquire the entire image and to display on the display screen.
Step 8: Compare image strip count and the total strip count 38. If present strip count is less than total strip count then goto step 3, otherwise goto step 2 and wait for the next item/baggage to be placed on the conveyor belt for scanning.

In an embodiment of the present invention, the x-ray baggage scan image is corrected in real-time by applying correction by lookup table to the line scan data of high energy and low energy image data.

In another embodiment of the present invention, the high energy and low energy image strip is subjected to downscaling by suitable means (for example: bilinear, nearest neighbour, averaging etc) to get the corrected high energy and low energy image strip.

In yet another embodiment of the present invention, the above mentioned method can be applied to x-ray scanner of different tunnel sizes by means of respective distance factors and normalized distance factors.

In yet another embodiment of the present invention, the above mentioned method can be applied to any source and any detector configuration namely anyone other than “L” shape combinations by calculating the distance factors.

Those skilled in this technology can make various alterations and modifications without departing from the scope and spirit of the invention. Therefore, the scope of the invention shall be defined and protected by the following claims and their equivalents.

Figs. 1-3 are merely representational and are not drawn to scale. Certain portions thereof may be exaggerated, while others may be minimized. Figs. 1-3 illustrate various embodiments of the invention that can be understood and appropriately carried out by those of ordinary skill in the art.

In the foregoing detailed description of embodiments of the invention, various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments of the invention require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus, the following claims are hereby incorporated into the detailed description of embodiments of the invention, with each claim standing on its own as a separate embodiment.

It is understood that the above description is intended to be illustrative, and not restrictive. It is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined in the appended claims. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein,” respectively.

We Claim:

1. A method for shape/geometry correction of an X-ray baggage scan images, the method comprising:
acquiring, a current x-ray exposure of an examination subject with an x-ray apparatus using an x-ray detector, to obtain an image of the subject having a physical length using a plurality of detector cards consisting of an array of photo detectors.;
computing distance factor for each detector cards, wherein the distance factor is a ratio of pixels captured by the detector card to the physical length captured by the detector card, wherein the distance factor varies with the object distance and the detector distance;
normalizing the computed distance factors for all the detector cards with respect to one detector card;
generating a lookup table by mapping the line of distorted image to the line of corrected image data, wherein the line of corrected image data is the image data which has undergone remapping and also suitable interpolation through lookup table technique; and
downscaling the image to the original size to retrieve the corrected image.

2. The method of claim 1, wherein the step of mapping including:
initializing all indices i, j =0;
contemplatingjth column of the distorted image I of size m x n;
computing the new pixel index inew corresponding to each detector card position using the current pixel index iand normalized distance factor;
creating a new image Nnew by mapping the pixels from index i to new index position inew;
interpolating for filling the non-existent pixel and other pixels are unchanged;
incrementing the column counter j = j+1; and
comparing the column counter to the width of the image, if the column counter has reached the width of the image, downscale the image to original size to get the corrected image for display.

3. The method of claim 2, further comprising:
checking, if the column counter has not reached the width of the image, contemplating the column of the distorted image I.

4. The method of claim 1, wherein the detectors are arranged in “L” shape.

5. The method of claim 1, wherein more physical lengths represents more number of pixels and low physical length represents less number of pixels.

6. The method of claim 1, wherein the distorted image is remapped by means of normalized distance factors.

7. The method of claim 1 where the x-ray baggage scan image is corrected in real-time by applying correction by lookup table to the line scan data of high energy and low energy image data.

8. The method of claim 1 where the high energy and low energy image strip is subjected to downscaling by suitable means (for example: bilinear, nearest neighbour, averaging etc) to get the corrected high energy and low energy image strip.

9. The method of claim 1 can be applied to x-ray scanner of different tunnel sizes by means of respective distance factors and normalized distance factors.

10. The method of claim 1 can be applied to any source and any detector configuration namely anyone other than “L” shape combinations by calculating the distance factors.

Abstract

The present invention relates to a method for shape/geometry correction of an X-ray baggage scan images. In an example embodiment this can be accomplished by acquiring, a current x-ray exposure of an examination subject with an x-ray apparatus using an x-ray detector, to obtain an image of the subject having a physical length using a plurality of detector cards consisting of an array of pixels, computing distance factor for each detector cards, normalizing the computed distance factors for all the detector cards with respect to one detector card, generating a lookup table by mapping the line of distorted image to the line of corrected image data, and downscaling the image to the original size to retrieve the corrected image.