Angular redistribution of inspection data

Abstract

An apparatus for inspecting cargo comprises independent detector arrays 3-99, 3-100,3-101, each comprising a plurality of detectors 30-1 – 30-48, each detector configured to sense and output detector

Description

Field of Invention The invention relates but is not limited to apparatus for inspecting cargo, the apparatus comprising one or more independent detector arrays, each independent detector array comprising a plurality of detectors, each detector being configured to sense and output detector data indicative of a level of transmission of inspection radiation through the cargo under inspection. The invention also relates to a corresponding method of processing a signal for inspecting cargo, and a corresponding computer program or a computerprogram product. Background of Invention The performances of x-ray cargo inspection systems comprising arrays of detectors are a trade-off between capabilities whose requirements are contradictory. Contrast and penetration both require larger detectors, in order to collect more x-ray signal to provide a better signal-to-noise ratio. On the contrary, resolution requires detectors with a smaller pitch, in order to separate objects close to each other. On some x-ray cargo inspection systems, the arrays of detectors are mounted to create an arc of a circle surrounding the cargo under inspection. On some such systems, the arrays of detectors are angularly mounted independently from one another, each array detector being mounted to face a focal point of a source of inspection radiation. Such a mounting of the arrays of detectors has mounting clearances between the arrays of detectors. The mounting clearances provoke artefacts in the corresponding inspection image, such as steps on the images of slanted objects. Summary of Invention Aspects and embodiments of the invention are set out in the appended claims. These and other aspects, and aspects and embodiments which are useful in understanding the invention set out in the claims, are also described in the present disclosure. Any feature in one aspect of the invention may be applied to other aspects of the invention, in any appropriate combination. Brief Description of Drawings Embodiments of the present disclosure will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 schematically represents apparatus for inspecting cargo according to the disclosure, in which a plurality of arrays of detectors are angularly mounted independently from each other, each array detector being mounted to face a focal point of a source of inspection radiation, viewed in a (YOZ) plane; Figure 2 schematically represents a plurality of arrays of detectors, as viewed enlarged with respect to the view of Figure 1; Figure 3 schematically represents an array of detectors, as viewed in a (XOZ) plane; Figure 4 schematically represents a flowchart of steps of a method according to the disclosure; Figure 5 schematically shows an angular deviation between successive detector arrays, in an angular referential where the centre is the focal point of the source of the inspection radiation, before (caption on the left in Figure 5) and after (caption on the right in Figure 5) the repartition of the detector data according to the disclosure is performed; Figure 6A schematically represents an example of a conventional inspection image, comprising artefacts; Figure 6B schematically represents an example of an inspection image obtained after applying to the image of Figure 6A a method according to Figure 3. In the figures, similar elements bear identical numerical references. Description of Example Embodiments Overview The disclosure discloses apparatus for inspecting cargo. The apparatus comprises at least one independent detector array comprising a plurality of detectors. In the apparatus, each detector array is mounted to face a focal point of a source of inspection radiation. The apparatus comprises a controller configured to process detector data. A maximum angular extension of each detector array is defined as an angle of inspection of the cargo under inspection. The controller is configured to space apart the detector data of the detector array, so that the detector data covers the whole angle of inspection. The apparatus of the disclosure enables to cover any detector data clearances due to mounting clearances between a plurality of detector arrays within the apparatus. The disclosure also discloses a corresponding method of processing a signal for inspecting cargo. When the detector array comprises a plurality of sub-arrays separated by a border, the controller may be further configured to process the detector data from the plurality of detectors to angularly redistribute the detector data within the angle of inspection by angularly spacing apart the detector data, to angularly cover any detector data clearances due to clearances at borders between the plurality of sub-arrays within the detector array. The apparatus of the disclosure enables to reduce artefacts created in the corresponding inspection image, due to the mounting of the detectors within a detector array or the mounting of a plurality of detector arrays. The apparatus of the disclosure enables to increase the contrast on objects such as wires. Detailed Description of Example Embodiments Figure 1 schematically represents apparatus 1 for inspecting cargo 2 according to the disclosure. In Figure 1, the apparatus 1 comprises one or more independent detector arrays 3. As illustrated in Figure 2, each independent detector array 3 comprises a plurality of detectors 30. Referring to Figure 1 again, each detector 30 is configured to sense and output detector data indicative of a level of transmission of inspection radiation 4 through the cargo 2 under inspection. Each independent detector array 3 is configured to be angularly mounted independently from another detector array 3 within the apparatus 1. In the apparatus 1, each detector array 3 is mounted to face a source 5 of the inspection radiation 4. In other words, each detector array 3 is mounted in the apparatus such that, in operation, the inspection radiation arrives substantially perpendicularly to each detector array 3. As can be seen in Figure 1, each detector array 3 is positioned in the apparatus 1 with an angle of inclination with respect to another detector array 3 in the apparatus 1. A mounting clearance 7 (or space) between successive detector arrays 3 is necessary to enable mounting of the detector arrays 3 within the apparatus 1. In Figure 3, each of the detector arrays 3 comprises a 2D matrix of detectors. However, the disclosure also applies to independent detectors arrays comprising 1D lines of detectors only. In Figure 1, the apparatus 1 also comprises a controller 6 configured to process the detector data from the plurality of detectors 30. As can be seen in Figure 2, the detector array 3 (for example the detector array referenced 3-100) comprises 48 detectors 30. The detector data initially covers an initial angle 6 between lines 100-1 and 100-48, passing through the centre of detectors 30-1 and 30-48, respectively. Other numbers of detectors in the detector array 3 are also envisaged. The controller 6 is configured to process the detector data to, for each independent detector array 3 (such as detector arrays referenced 3-99, 3-100 and 3-101), define a maximum angular extension of the independent detector array as an independent angle a of inspection of the cargo 2 under inspection. Therefore, the angle a of inspection of the cargo 2, corresponding to the maximum angular extension (between mixed lines 70-1 and 70-48 in Figure 2) of the independent detector array 3, is defined as the smallest period of the detector data of the apparatus. In other words, in the disclosure, the smallest period of the detector data is no longer the initial angle 5 between the first detector (line 100-1 passing through the middle of detector 30-1 in Figure 2) and the last detector (line 100-48 passing through the middle of detector 30-48 in Figure 2) of the detector array (referred to as 3-100 in Figure 2). As shown in Figure 2, the controller 6 is configured to process the detector data to, for each independent detector array 3 (such as detector arrays referenced 3-99, 3-100 and 3-101), define a maximum angular extension of the independent detector array as an independent angle a of inspection of the cargo 2 under inspection. Therefore, the angle a of inspection of the cargo 2, corresponding to the maximum angular extension of the independent detector array 3, is defined as the smallest period of the detector data of the apparatus. In other words, in the disclosure, the smallest period of the detector data is no longer the initial angle 5 between the first detector (line 100-1 passing through the middle of detector 30-1 in Figure 2) and the last detector (line 100-48 passing through the middle of detector 30-48 in Figure 2) of the detector array (referred to as 3-100 in Figure 2). It should be understood that the controllers is also configured to process the detector data to angularly redistribute the detector data of detector 3-99 within the independent angle a of inspection by angularly spacing apart the detector data. In other words, the distribution of the detector data is not carried out on the initial angle 5 (see line 99-48), but on the angle a (see line 70-1), which, as can be seen in Figure 2, is larger than the initial angle 6, e.g., to cover the mounting clearances 7. Similarly, the controllers is also configured to process the detector data to angularly redistribute the detector data of detector 3-101 within the independent angle a of inspection by angularly spacing apart the detector data. In other words, the distribution of the detector data is not carried out on the initial angle 6 (see line 101-1), but on the angle a (see line 70-48), which, as can be seen in Figure 2, is larger than the initial angle 5, e.g., to cover the mounting clearances 7. The controller 6 may be configured to process the detector data from the plurality of detectors to regularly space apart the detector data within each independent detector array. Additionally or alternatively, the controller 6 may be configured to process the detector data from the plurality of detectors 30 to regularly space apart the detector data between the independent detector arrays 3. In Figure 2, each independent detector array 3 comprises a plurality of sub-arrays 8 (four (4) sub-arrays in Figure 2, but other numbers of sub-arrays are envisaged). In Figure 2, each sub-array 8 comprises a plurality of detectors 30. In Figure 2, each one of the four (4) sub-arrays 8 comprises 12 detectors 30, as a non-limiting example. Each sub-array 8 is mounted, along at least one border 9, adjacent and in angular alignment with at least one other sub-array 8 within the detector array 3. Each border defines a clearance between successive sub-arrays 8. The controller may be further configured to process the detector data from the plurality of detectors to, for each independent detector array 3, angularly redistribute the detector data within the independent angle a of inspection by angularly spacing apart the detector data to angularly cover any detector data clearances due to clearances at borders 9 between the plurality of sub-arrays 8 within the detector array 3. In an example of the disclosure, the controllers is configured to process the detector data from the plurality of detectors 30 to, for each independent detector array 3: calculate a distance Dist, between each detector 30-i and a geometrical centre 10 of the independent detector array 3, calculate an angular position ThAnglet of each detector 30-i, based on the calculated distance Distit calculate a maximum average value MaxAngle of the angles of a first detector (such as detector 30-1 in Figure 2) of the independent detector array (such as the array 3-100 in Figure 2) with a last detector (such as the detector corresponding to line 99-48 in Figure 2) of a previous independent detector array (such as detector array 3-99 in Figure 2) in the plurality of detector arrays, based on the calculated angular position ThAngleit calculate a minimum average value MinAngle of the angles of a last detector (such as detector 30-48 in Figure 2) of the independent detector array (such as the array 3-100 in Figure 2) with a first detector (such as the detector corresponding to line 101-1 in Figure 2) of a next independent detector array (such as detector array 3-100 in Figure 2) in the plurality of detector arrays, based on the calculated angular position ThAnglei. For the first independent detector array of the apparatus: the maximum average value MaxAngle is calculated by increasing the angle of the first detector by the difference between the angle of the last detector of the first independent detector array and the minimum average value MinAngle. For the last independent detector array of the apparatus: the minimum average value MinAngle is calculated by decreasing the angle of the last detector by the difference between the angle of the first detector of the last independent detector array and the maximum average value MaxAngle. In such an example, the controllers is further configured to process the detector data from the plurality of detectors 30 to calculate an angle DistrlbutedAnglei for a regular distribution of each detector 30, based on the calculated maximum average values MaxAngle and the calculated minimum average values MinAngle. In such an example, the controllers is further configured to process the detector data from the plurality of detectors 30 to: calculate interpolation coefficients q , based on the calculated angle for the regular distribution, and calculate interpolated detector data V-, based on the interpolation coefficients q . A more detail example according to the disclosure is disclosed below. The controller 6 is configured to process the detector data from the plurality of detectors 30 to calculate the distance Disti between each detector 30 and the geometrical centre 10 of the independent detector array 3 such that: Disti = DACPosition[i] + DACPixelsCount — 1 -----------PDACt 1 L * DACDetectorsCenterToCenter with: DACPixelsCount is the count of detectors inside along the height of each sub-array 8, DAC, DACDetectorsCenterToCenter is the distance, in mm, from the centre of one detector 30 to another detector 30 within the same sub-array 8, DAC, For each detector i: DASi is the index of the independent detector array 3, DAS, containing the detector / DAC, is the same sub-array 8, DAC, number inside the detector array 3, DAS, e.g., between 1 and 4 in Figure 2, pdac, is the detector 30 number in the DAC, For each DACj DACPosition[j] is the distance between the centre 10 of the DAS and the centre of the DACj. The controller 6 is further configured to process the detector data from the plurality of detectors to calculate the angular position ThAnglet of each detector i, based on the calculated distance Disti, such that: ThAnglei = AngleDAS + tan 1 Disti DistDASl with: AngleDAS. being the angle of the detector array 3, DAS, numbered i, the angle being counted in polar coordinates in a referential having a centre being the focal point of the source of inspection radiation and a horizontal direction (corresponding to a spirit level) being counted as having an angle equal to 0; and DistDAS. being the distance of the detector array 3, DAS, numbered i, the distance being counted in polar coordinates in the referential having the centre being the focal point of the source of inspection radiation and the horizontal direction (corresponding to a spirit level) being counted as having an angle equal to 0. The controller 6 is further configured to process the detector data from the plurality of detectors 30 to calculate the angle DistributedAnglei for a regular distribution of each detector, such that: DistributedAnglei = MaxAngleDASj - (PDACi + 0.5) * (MaxAngleDAS. - MinAngleDASi) with MaxAngie is the maximum average value as already disclosed above, and MinAngie is the minimum average value as already disclosed above. The controller 6 is further configured to process the detector data from the plurality of detectors to calculate the interpolation coefficients c?, cf1 and cf1, such that: if DistributedAnglei >ThAnglei then if DistributedAnglei ThAnglei then < cf1 = 1-cf 0 DistributedAnglei — ThAnglei_1 Cl ThAnglei — ThAnglei_1 ci = 0 ( Q1 = 0 I 0 DistributedAnglei — ThAnglei+1 । Cl ThAnglei — ThAnglei+1 ( cl = 1- cf The controller 6 is further configured to process the detector data from the plurality of detectors 30 to calculate the interpolated detector data such that, for all pixels i, the value V, is replaced by the linear combination: W =cf1.Vi_1 + C°.Vi + cfVi+1. A non-limiting example of interpolation coefficients cf, cf1 and cf1 as calculated above, is given in Table 1 below, e.g., fora 15,h independent detector array 3 of twelve detectors 30 (e.g., for i being numbered 180 to 191 in Table 1), in a plurality of detectors 30 of a plurality of detector arrays 3. Detector i C'1 C° C+1 180 0.48515615 0.13388197 0.86611803 181 0.48456954 0.15480283 0.84519717 182 0.48398294 0.11485826 0.88514174 183 0.48339633 0.07490335 0.92509665 184 0.48280972 0.03493739 0.96506261 185 0.48222312 0.00000000 0.99495962 186 0.48163651 0.00000000 0.95496894 187 0.48104990 0.00000000 0.91496502 188 0.48046329 0.00000000 0.87494715 189 0.47987669 0.00000000 0.83491461 190 0.47929008 0.00000000 0.79486670 191 0.47870347 0.00000000 0.83978963 Table 1 As illustrated, in Figure 4, an example method 400 of processing a signal for inspecting cargo, comprises: obtaining, at S1, detector data indicative of a level of transmission of inspection radiation through cargo under inspection, the detector data being sensed and output by a plurality of detectors of one or more independent detector arrays, each independent detector array being configured to be angularly mounted independently from another detector array within an apparatus; and processing, at S2, the detector data to, for each independent detector array: define a maximum angular extension of the independent detector array as an independent angle of inspection of the cargo under inspection, and angularly redistributing the detector data within the independent angle of inspection by angularly spacing apart the detector data, so that the detector data covers the independent angle of inspection. The method 400 of Figure 4 may be performed by the apparatus 1 of any aspects of the disclosure. The disclosure also concerns a computer program or a computer-program product comprising instructions which, when executed by a computer, cause the computer to perform the method 400 Figure 4, or which, when executed by a controller, cause the 5 controller to control the apparatus of any aspects of the disclosure. Figure 5 schematically shows that, after the repartition of the detector data is performed, an angular deviation between successive detector arrays decreases (by approximately 35%), in an angular referential where the centre is a focal point of the accelerator. 0 Figure 6A schematically represents an example of a conventional inspection image, with artefacts indicated by the arrows. Figure 6B schematically represents an example of an inspection image obtained using a method according to Figure 4, the artefacts having disappeared from the inspection image.

Claims

1. Apparatus for inspecting cargo, the apparatus comprising:one or more independent detector arrays, each independent detector array comprising a plurality of detectors, each detector being configured to sense and output detector data indicative of a level of transmission of inspection radiation through the cargo under inspection,wherein each independent detector array is configured to be angularly mounted independently from another detector array within the apparatus; anda controller configured to process the detector data from the plurality of detectors to, for each independent detector array:define a maximum angular extension of the independent detector array as an independent angle of inspection of the cargo under inspection, andangularly redistribute the detector data within the independent angle of inspection by angularly spacing apart the detector data, so that the detector data covers the independent angle of inspection.

2. The apparatus of claim 1, wherein:each independent detector array comprises a plurality of sub-arrays, each subarray comprising a plurality of detectors, each sub-array being mounted, along at least one border, adjacent and in angular alignment with at least one other sub-array within the detector array, andthe controller is further configured to process the detector data from the plurality of detectors to, for each independent detector array:angularly redistribute the detector data within the independent angle of inspection by angularly spacing apart the detector data to angularly cover any detector data clearances due to mounting clearances at borders between the plurality of sub-arrays within the detector array.

3. The apparatus of claim 1 or claim 2, wherein the controller is further configured to process the detector data from the plurality of detectors to:regularly space apart the detector data within each independent detector array, and / orregularly spacing apart the detector data between the independent detector arrays.

4. The apparatus of any one of claims 1 to 3, wherein the controller is further configured to process the detector data from the plurality of detectors to, for each independent detector array:calculate a distance between each detector and a geometrical centre of the independent detector array,calculate an angular position of each detector, based on the calculated distance,calculate a maximum average value of the angles of a first detector of the independent detector array with a last detector of a previous independent detector array in the plurality of detector arrays, based on the calculated angular position,calculate a minimum average value of the angles of a last detector of the independent detector array with a first detector of a next independent detector array in the plurality of detector arrays, based on the calculated angular position,wherein, for the first independent detector array: the maximum average value is calculated by increasing the angle of the first detector by the difference between the angle of the last detector of the first independent detector array and the minimum average value, andwherein, for the last independent detector array: the minimum average value is calculated by decreasing the angle of the last detector by the difference between the angle of the first detector of the last independent detector array and the maximum average value.

5. The apparatus of claim 4, wherein the controller is further configured to process the detector data from the plurality of detectors to calculate an angle for a regular distribution of each detector, based on the calculated maximum average values and the calculated minimum average values.

6. The apparatus of claim 5, wherein the controller is further configured to process the detector data from the plurality of detectors to:calculate interpolation coefficients, based on the calculated angle for the regulardistribution, andcalculate interpolated detector data, based on the interpolation coefficients.

7. The apparatus of any one of claims 4 to 6 when dependent on claim 2, wherein the controller is further configured to process the detector data from the plurality of detectors to calculate the distance between each detector and the geometrical centre of the independent detector array such that:rDACPixelsCount — 1 \Disti = DACPosition[i] + I------------PDACij * DACDetectorsCenterToCenterwith:DACPixelsCount is the count of detectors inside along the height of each sub-array, DAC,DACDetectorsCenterToCenter is the distance, in mm, from the centre of one detector to another detector within the same DAC,For each detector i:DAS, is the index of the independent detector array, DAS, containing the detector / DAC, is the DAC number inside the DAS, e.g., between 1 and 4, PDACi is the detector number in the DAC,.For each DACjDACPosition[j] is the distance between the centre of the DAS and the centre of the DACj.

8. The apparatus of claim 7, wherein the controller is further configured to process the detector data from the plurality of detectors to calculate the angular position of each detector i, based on the calculated distance, such that:ThAnglet = AngleDAS+ tan 1Disti DistDAS.with:AngleDAS. being the angle of the detector array 3, DAS, numbered i, the angle being counted in polar coordinates in a referential having a centre being the focal point of the source of inspection radiation and a horizontal direction, corresponding to a spirit level, being counted as having an angle equal to 0; andDistDAS. being the distance of the detector array 3, DAS, numbered i, the distance being counted in polar coordinates in the referential having the centre being the focal point of the source of inspection radiation and the horizontal direction, corresponding to a spirit level, being counted as having an angle equal to 0.

9. The apparatus of claim 8 when dependent on claim 5, wherein the controller is further configured to process the detector data from the plurality of detectors to calculate the angle for a regular distribution of each detector, such that:DistributedAnglei = MaxAngleDAS - (PDACt + 0.5) * (MaxAngleDAS. - MinAngleDAS.)with MaxAngie is the maximum average value, andMinAngie is the minimum average value.

10. The apparatus of claim 9 when dependent on claim 6, wherein the controller is further configured to process the detector data from the plurality of detectors to calculate the interpolation coefficients such that:if DistributedAnglei >ThAnglei then( Iif DistributedAnglei <ThAnglei then c? =A 1 = 1 - c°DistributedAnglei — ThAngle^ ThAnglei — ThAnglei_r cl = 0 cf1 = 0DistributedAnglei — ThAnglet+1ThAngle( — ThAnglei+14 = l~c°11. The apparatus of claim 10, wherein the controller is further configured to process the detector data from the plurality of detectors to calculate the interpolated detector data such that, for all pixels i, the value V, is replaced by the linear combination:V! = q1. + c?. Vt + cl. Vi+1.

12. A method of processing a signal for inspecting cargo, comprising:obtaining detector data indicative of a level of transmission of inspection radiation through cargo under inspection, the detector data being sensed and output by a plurality of detectors of one or more independent detector arrays, each independent detector array being configured to be angularly mounted independently from another detector array within an apparatus; andprocessing the detector data to, for each independent detector array:define a maximum angular extension of the independent detector array as an independent angle of inspection of the cargo under inspection, andangularly redistributing the detector data within the independent angle of inspection by angularly spacing apart the detector data, so that the detector data covers the independent angle of inspection.

13. The method of claim 12, performed by the apparatus of any of claims 2 to 11.

14. A computer program or a computer-program product comprising instructions which, when executed by a computer, cause the computer to perform the method of claim 12.

15. A computer program or a computer-program product comprising instructions which, when executed by a controller, cause the controller to control the apparatus of any of the claims 1 to 11.16

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