X-ray inspection equipment
The X-ray inspection apparatus addresses the challenge of inappropriate luminance function setup by using a control unit to evaluate and adjust the function based on distribution metrics, enabling accurate inspections regardless of operator expertise.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- ISHIDA CO LTD
- Filing Date
- 2024-12-25
- Publication Date
- 2026-07-07
Smart Images
Figure 2026113251000001_ABST
Abstract
Description
Technical Field
[0001] It relates to an X-ray inspection apparatus.
Background Art
[0002] For example, as described in Patent Document 1 (Japanese Patent Application Laid-Open No. 2012-73056), X-rays are irradiated onto an object to be inspected that is being conveyed, and X-rays in a first energy band and a second energy band that have passed through the object to be inspected are detected. A first transmission image based on the detection result of the X-rays in the first energy band and a second transmission image based on the detection result of the X-rays in the second energy band are acquired. At least one of the first transmission image and the second transmission image is corrected based on a luminance conversion function (luminance conversion table in Patent Document 1). After correction, an X-ray inspection apparatus that inspects the object to be inspected based on a difference image obtained by performing subtraction processing using the first transmission image and the second transmission image is known.
[0003] In order to perform accurate X-ray inspection with such an X-ray inspection apparatus, it is required to use an appropriate luminance conversion function.
Summary of the Invention
Problems to be Solved by the Invention
[0004] However, it is difficult for an operator with little knowledge and experience to determine whether the luminance conversion function is appropriate, and it may take an unnecessarily long time to set the X-ray inspection apparatus (set the luminance conversion function), or a luminance conversion function that cannot be said to be appropriate may be used in the X-ray inspection apparatus.
Means for Solving the Problems
[0005] An X-ray inspection apparatus according to a first aspect of the present invention comprises a transport unit, an X-ray source, a detection unit, and a control unit. The transport unit transports the object to be inspected. The X-ray source irradiates the object to be inspected with X-rays transported by the transport unit. The detection unit detects X-rays of a first energy band and X-rays of a second energy band irradiated onto the object to be inspected. The control unit acquires a first transmission image based on the detection result of the X-rays of the first energy band and a second transmission image based on the detection result of the X-rays of the second energy band. The control unit corrects at least one of the first transmission image and the second transmission image based on a brightness conversion function, and after correction, inspects the object to be inspected based on a difference image obtained by performing subtraction processing using the first transmission image and the second transmission image. The control unit evaluates the brightness conversion function based on the difference image and the brightness value of the background of the difference image.
[0006] In the X-ray inspection device relating to the first aspect, even operators with little knowledge or experience in X-ray inspection can perform accurate X-ray inspections using an appropriate brightness conversion function.
[0007] An X-ray inspection apparatus according to a second aspect of the present invention is an X-ray inspection apparatus according to a first aspect, wherein the control unit evaluates a luminance conversion function based on the distribution information of luminance values in the difference image and the luminance value of the background of the difference image.
[0008] An X-ray inspection apparatus according to a third aspect of the present invention is an X-ray inspection apparatus according to a second aspect, wherein the distribution information includes at least one of the mode, standard deviation, maximum value, minimum value, median, mean value, and number of extreme value points of the luminance value in the difference image.
[0009] In the X-ray inspection apparatus relating to the second and third perspectives, the brightness conversion function can be evaluated with high accuracy based on the distribution information of brightness values in the difference image.
[0010] An X-ray inspection apparatus according to the fourth aspect of the present invention is an X-ray inspection apparatus according to any of the first or third aspects, further comprising a display unit for displaying the evaluation result of the brightness conversion function.
[0011] In the X-ray inspection device relating to the fourth aspect, the operator can easily understand the evaluation of the brightness conversion function.
[0012] An X-ray inspection apparatus according to the fifth aspect of the present invention is an X-ray inspection apparatus according to any of the first or fourth aspects, wherein the control unit determines the suitability of the brightness conversion function based on the evaluation result of the brightness conversion function.
[0013] In the X-ray inspection device relating to the fifth aspect, accurate X-ray inspection can be performed using an appropriate brightness conversion function, regardless of the operator's level of knowledge or experience.
[0014] An X-ray inspection apparatus according to the sixth aspect of the present invention is an X-ray inspection apparatus according to the fifth aspect, further comprising a notification unit that notifies the result of the determination of whether the brightness conversion function of the control unit is appropriate or not.
[0015] In the X-ray inspection device relating to the sixth aspect, the operator can easily determine whether the brightness conversion function is appropriate.
[0016] An X-ray inspection apparatus according to the seventh aspect of the present invention is an X-ray inspection apparatus according to the fifth or sixth aspect, further comprising a storage unit that stores information relating to a first transmission image and a second transmission image. When the control unit determines that the brightness conversion function is unsuitable, it performs a process multiple times to acquire additional first and second transmission images based on the detection result of the X-ray detection unit that irradiates the object to be inspected from the X-ray source to the object being transported by the transport unit. The control unit corrects the brightness conversion function that was determined to be unsuitable based on the information relating to a plurality of first and second transmission images already stored in the storage unit and the plurality of newly acquired first and second transmission images.
[0017] In the X-ray inspection device relating to the seventh aspect, the brightness conversion function can be modified in a relatively short period of time by utilizing data that has already been obtained.
[0018] The X-ray inspection apparatus according to the eighth aspect of the present invention is any one of the X-ray inspection apparatuses according to the fifth to seventh aspects, and when the control unit determines that the luminance conversion function is inappropriate, the control unit performs, a plurality of times, a process of newly acquiring a first transmission image and a second transmission image based on a detection result by a detection unit of X-rays irradiated from an X-ray source onto an object to be inspected conveyed by a conveyance unit. The control unit newly creates a luminance conversion function based on the plurality of newly acquired first transmission images and second transmission images.
[0019] In the X-ray inspection apparatus according to the eighth aspect, for example, when the evaluation of the luminance conversion function is extremely low, data that is not suitable for creating the luminance conversion function can be excluded, and an appropriate luminance conversion function can be created.
[0020] The X-ray inspection apparatus according to the ninth aspect of the present invention is any one of the X-ray inspection apparatuses according to the first to eighth aspects, and the control unit has a plurality of evaluation criteria for the luminance conversion function.
[0021] In the X-ray inspection apparatus according to the ninth aspect, the luminance conversion function can be appropriately evaluated according to the type of the object to be inspected.
Advantages of the Invention
[0022] In the X-ray inspection apparatus of the present invention, even an operator with little knowledge and experience regarding X-ray inspection can perform accurate X-ray inspection using an appropriate luminance conversion function.
Brief Description of the Drawings
[0023] [Figure 1] It is an external perspective view of an X-ray inspection apparatus according to an embodiment of the present invention. [Figure 2] It is a simplified configuration diagram inside the housing of the X-ray inspection apparatus of FIG. 1. [Figure 3] It is an example of a graph conceptually showing the amount of transmitted X-rays detected by the line sensor of the X-ray inspection apparatus of FIG. 1. [Figure 4] It is a block diagram of the X-ray inspection apparatus of FIG. 1. [Figure 5]This is an example of a histogram created based on the difference image generated by the X-ray inspection apparatus of FIG. 1, and is a diagram conceptually explaining the evaluation of the luminance conversion function by the evaluation unit. [Figure 6] This is an example of a flowchart of a method for evaluating a luminance conversion function by the X-ray inspection apparatus of FIG. 1.
Embodiment for Carrying Out the Invention
[0024] Referring to the drawings, an X-ray inspection apparatus according to an embodiment of the present invention will be described. Note that the following embodiments are specific examples of the present invention and do not limit the technical scope of the present invention.
[0025] (1) Overall Outline The X-ray inspection apparatus 10 is an apparatus that inspects an article P based on a plurality of transmission images (a plurality of transmission images based on detection results of X-rays having different energy bands) obtained by irradiating the article P with X-rays. Although not limiting the inspection content, the X-ray inspection apparatus 10 performs a foreign object inspection for inspecting the presence or absence of foreign objects mixed in the article P.
[0026] The X-ray inspection apparatus 10 is, for example, incorporated into a food production line. For example, an article (food) P to be inspected is conveyed to the X-ray inspection apparatus 10 from an upstream process. The X-ray inspection apparatus 10 inspects the conveyed article P and classifies the article P as a good product or a defective product. The result of the foreign object inspection of the X-ray inspection apparatus 10 is transmitted to a sorting mechanism (not shown) arranged on the downstream side of the X-ray inspection apparatus 10. The article P classified as a good product is sent to the next process (for example, the boxing process), and the article P classified as a defective product is sent to, for example, a defective product collection container.
[0027] (2) Detailed Explanation As shown in FIGS. 1 to 4, the X-ray inspection apparatus 10 mainly includes a housing 11, a conveyor 12, an X-ray irradiator 13, a first line sensor 14 and a second line sensor 15, a display 30, and a controller 20.
[0028] (2-1) Housing The housing 11 is a shielded box that houses the conveyor 12, the X-ray irradiator 13, the first line sensor 14, the second line sensor 15, and the controller 20. A display 30 and various switches (not shown) are located on the upper front of the housing 11.
[0029] Openings 11a (see Figure 1) for loading and unloading articles P are formed on the upstream and downstream sides of the housing 11 in the conveying direction D (see Figure 2) of the conveyor 12.
[0030] (2-2) Conveyor The conveyor 12 is an example of a conveying section that transports an item P as the object to be transported. The conveyor 12 is positioned to pass through both openings 11a of the housing 11.
[0031] (2-3)X-ray irradiator The X-ray irradiator 13 is an example of an X-ray source. The X-ray irradiator 13 irradiates X-rays onto the item P being transported by the conveyor 12. As shown in Figure 2, the X-ray irradiator 13 is positioned above the conveyor 12. The X-ray irradiator 13 irradiates X-rays into a fan-shaped irradiation range Y toward the line sensors 14 and 15 positioned below the conveyor 12. As shown in Figure 2, the irradiation range Y of the X-ray irradiator 13 extends perpendicular to the transport surface of the conveyor 12 and spreads in a direction perpendicular to the transport direction D of the conveyor 12 (the width direction of the conveyor belt 12).
[0032] (2-4) Line Sensor Line sensors 14 and 15 are examples of detection units. Line sensors 14 and 15 detect X-rays irradiated from the X-ray irradiator 13 that have passed through the item P and the conveyor belt 12. The first line sensor 14 and the second line sensor 15 are sensors that detect X-rays of different energy bands (wavelengths). The first line sensor 14 detects X-rays in the first energy band (low energy band with relatively long wavelengths), and the second line sensor 15 detects X-rays in the second energy band (high energy band with relatively short wavelengths).
[0033] In this embodiment, as shown in Figure 2, the second line sensor 15 is arranged vertically below the first line sensor 14. Of the X-rays irradiated from the X-ray irradiator 13, X-rays in the first energy band are detected by the first line sensor 14. Of the X-rays that have passed through the first line sensor 14, the intermediate energy band (X-rays in the energy band between the high energy band and the low energy band) is removed by a filter (not shown) placed between the first line sensor 14 and the second line sensor 15. X-rays in the second energy band that have passed through the filter are detected by the second line sensor 15. The first line sensor 14 is mainly composed of a large number of X-ray detection elements 14a (see Figure 2). The second line sensor 15 is mainly composed of a large number of X-ray detection elements 15a (see Figure 2). The X-ray detection elements 14a and 15a are installed horizontally and in a straight line in a direction perpendicular to the conveying direction D of the conveyor 12. Line sensors 14 and 15 detect the amount of X-rays transmitted through the item P or conveyor 12 (transmitted X-ray dose) for X-rays in their respective target energy bands, and output an X-ray transmission signal based on the transmitted X-ray dose (intensity of transmitted X-rays). The brightness (luminance) of the first transmission image, described later, is determined based on the X-ray transmission signal output by the first line sensor 14, and the brightness of the second transmission image, described later, is determined based on the X-ray transmission signal output by the second line sensor 15. In the transmission images (first and second transmission images), areas with a high transmitted X-ray dose are displayed brightly, and areas with a low transmitted X-ray dose are displayed darkly.
[0034] Figure 3 is a graph showing an example of the transmitted X-ray quantity detected by the X-ray detection elements 14a and 15a. Because there are two line sensors 14 and 15 detecting X-rays in different energy bands, a graph of the detection result of the first line sensor 14 (solid line G1) and a graph of the detection result of the second line sensor 15 (dashed line G2) can be obtained. In the graph in Figure 3, the horizontal axis corresponds to the position of each X-ray detection element 14a and 15a (position in the width direction of the conveyor belt 12), and the vertical axis shows the transmitted X-ray quantity (detected amount) detected by the X-ray detection elements 14a and 15a. It is not always necessary to provide two line sensors; for example, a single direct-conversion type line sensor capable of detecting X-rays using a photon counting method may be used. A direct-conversion type line sensor is, for example, a multi-energy sensor that detects X-rays in multiple energy ranges passing through an object, and includes photon detection type sensors such as CdTe semiconductor detectors. In this line sensor, for example, electron-hole pairs are generated when X-ray photons arrive. The generation of this electron-hole pair allows for the detection of energy (photon energy).
[0035] (2-5) Display The display 30 is a liquid crystal display with touch panel functionality. The display 30 is electrically connected to the controller 20 and exchanges signals with the controller 20.
[0036] The display 30 functions as both a display unit and an input unit. The display 30 displays, for example, transparent images or the results of foreign object inspection. The display 30 also accepts various settings and information input from the operator.
[0037] (2-6) Controller As shown in Figure 4, the controller 20 is electrically connected to the conveyor 12, the X-ray irradiator 13, the first line sensor 14, the second line sensor 15, and the display 30.
[0038] The controller 20 controls the operation of each part of the X-ray inspection device 10. The controller 20 also performs foreign object inspection based on the detection results of the X-ray transmission amount from the line sensors 14 and 15.
[0039] The controller 20 mainly comprises a processor including a CPU, auxiliary storage devices such as ROM, RAM, and flash memory, a display control circuit that controls the data display on the display 30, a key input circuit that captures key input data entered by the operator via the display 30, and a communication port that enables connection to external devices and networks such as LANs. As shown in Figure 5, the controller 20 functions as a storage unit 21 and a control unit 22.
[0040] (2-6-1) Storage section The memory unit 21 is composed of ROM, RAM, auxiliary devices, etc., and stores various programs executed by the processor, which functions as the control unit 22, and various settings for controlling each part of the X-ray inspection apparatus 10. The memory unit 21 includes a luminance conversion function storage area 21a and a histogram storage area 21b. The luminance conversion function is stored in the luminance conversion function storage area 21a. The luminance conversion function is information used by the inspection unit 22c of the control unit 22, which will be described later, to correct the luminance of each pixel of the second transmitted image. The luminance conversion function may be replaced by, or in addition to, information used by the inspection unit 22c to correct the luminance of each pixel of the first transmitted image.
[0041] The luminance conversion function is the information described below. To begin the explanation, we will first outline the functions of the control unit 22 (particularly its function as the inspection unit 22c).
[0042] The control unit 22 receives the detection results from the first line sensor 14 and the second line sensor 15 of the X-rays irradiated onto the item P being transported by the conveyor 12, and based on the detection results, acquires a first transmission image based on the detection results of X-rays in the first energy band and a second transmission image based on the detection results of X-rays in the second energy band. The control unit 22 performs foreign object inspection of the item P based on the difference image obtained by performing a subtraction process between the first transmission image and the second transmission image. The subtraction process is a process of taking the difference between the brightness of each pixel (referred to as the first pixel) in the first transmission image and the brightness of the pixel (referred to as the second pixel) in the second transmission image that corresponds to each first pixel (based on X-rays that passed through the item P and the conveyor 12 at the position corresponding to each first pixel). The subtraction process here is a process of dividing one of the brightness of each first pixel and the brightness of the second pixel corresponding to each first pixel by the other. The difference image is an image based on the difference result between each first pixel and its corresponding second pixel. Typically, the absorption rates of the first and second energy bands of a foreign object differ from those of the first and second energy bands of object P. Therefore, in the difference image described above, pixels corresponding to the areas where the foreign object is present will appear brighter or darker than pixels corresponding to other areas (areas where the foreign object is absent).
[0043] To perform such an inspection, it is required that when the difference image is generated, the presence of item P is largely removed (erased) from the difference image, and if item P does not contain any foreign matter, the brightness value of each pixel in the difference image should be roughly equal to the brightness value representing the background. Since there is a difference between the absorption rate of the first energy band and the absorption rate of the second energy band in item P, the brightness of each first pixel and the brightness of the second pixel corresponding to each first pixel are not the same, and even if subtraction processing is performed using the first transmission image and the second transmission image (the original image without the correction described later), the image of item P remains in the difference image. Therefore, a brightness conversion function is used to remove the presence of item P from the difference image.
[0044] The luminance conversion function is created by the control unit 22 using the method for creating a luminance conversion table described in, for example, Patent Document 1 (Japanese Patent Application Publication No. 2012-73056). An overview of this process is provided below.
[0045] During initial setup, etc., items P, which are known to be free of foreign matter, are transported to the conveyor 12 multiple times. The same item P may be transported to the conveyor 12 multiple times, or different items P of the same type may be transported multiple times. In this case, if the items P are not uniform and there are individual differences, items P with different shapes, sizes, thicknesses, overlapping of components, and component compositions (weight ratio of each component) are transported to the conveyor 12. Furthermore, items P are transported to the conveyor 12 with changes in transport posture and transport position (the position of the item P on the belt of the conveyor 12 in the width direction).
[0046] Each time an item P is transported on the conveyor belt 12, the control unit 22 receives the detection results from the line sensors 14 and 15, and based on the detection results, acquires a first transmission image based on the detection results of X-rays in the first energy band and a second transmission image based on the detection results of X-rays in the second energy band.
[0047] The control unit 22 uses data from multiple first transmission images to create a histogram of the first energy band showing the luminance distribution of multiple first transmission images, and uses data from multiple second transmission images to create a histogram of the second energy band showing the luminance distribution of multiple second transmission images. Furthermore, the control unit 22 integrates the histogram of the first energy band to calculate the histogram integral curve for the first energy band, and integrates the histogram of the second energy band to calculate the histogram integral curve for the second energy band. Then, the control unit 22 compares the histogram integral curve for the first energy band and the histogram integral curve for the second energy band to create a luminance conversion function that matches or approximates the histogram integral curve for the first energy band. Specifically, the luminance conversion function is obtained by finding the luminance conversion ratio I2 / I1 for each luminance such that the integrated value I2 of the histogram integral curve for the second energy band matches the integrated value I1 of the histogram integral curve for the first energy band. A more detailed method for creating a luminance conversion function is described in Patent Document 1 (Japanese Patent Application Publication No. 2012-73056). The histograms of the first and second energy bands used in creating the luminance conversion function are stored in the histogram storage area 21b. Here, the luminance conversion function is a table that associates the luminance values in the second transmission image with the corresponding corrected luminance values (corrected luminance values). However, the format of the luminance conversion function is not limited as long as it indicates what value to correct each luminance of the pixels in the second transmission image to. The luminance conversion function does not have to be created by the control unit 22, and the luminance conversion function storage area 21a may store a luminance conversion function created outside the X-ray inspection device 10 (input to the X-ray inspection device 10).
[0048] (2-6-2) Control Unit The processor, acting as the control unit 22, functions as a first image generation unit 22a, a second image generation unit 22b, an inspection unit 22c, an evaluation unit 22d, and a determination unit 22e.
[0049] (2-6-2-1) Image generation unit The first image generation unit 22a generates a first transmission image (low-energy transmission image) based on the transmitted X-ray dose of the first energy band X-ray detected by the first line sensor 14. The second image generation unit 22b generates a second transmission image (low-energy transmission image) based on the transmitted X-ray dose of the second energy band X-ray detected by the second line sensor 15.
[0050] Specifically, the first image generation unit 22a acquires X-ray transmission signals corresponding to the intensity of X-rays that have passed through the object P, etc., output from each X-ray detection element 14a of the first line sensor 14 at fine time intervals, and generates a first transmission image based on the acquired X-ray transmission signals. The first image generation unit 22a generates the first transmission image by concatenating the data on the intensity of X-rays obtained from each X-ray detection element 14a at fine time intervals in a matrix in a time series. The second image generation unit 22b is the same as the first image generation unit 22a except that it uses the X-ray transmission signals output from each X-ray detection element 15a of the second line sensor 15, so a detailed explanation is omitted.
[0051] (2-6-2-2) Inspection Department The inspection unit 22c determines whether or not foreign matter is present in the item P based on the first and second transmission images. Specifically, the inspection unit 22c performs the following processing:
[0052] When the inspection unit 22c acquires a first transmission image and a second transmission image of the item P to be inspected, it corrects the brightness of the second transmission image using a brightness conversion function stored in the brightness conversion function storage area 21a. In practice, the inspection unit 22c also performs processing such as sizing the first transmission image and the second transmission image (see Patent Document 1 (JP 2012-73056)), but this explanation is omitted here. Next, the inspection unit 22c performs subtraction processing using the first transmission image and the corrected second transmission image (referred to as the corrected second transmission image) to generate a difference image. If there is no foreign matter mixed in the item P, the brightness values of each pixel in the difference image will be approximately the same value (brightness value indicating the background). If there is foreign matter mixed in the item P, a difference will occur between the brightness value of the first transmission image and the brightness value of the corrected second transmission image at the pixel corresponding to the position of the foreign matter. The inspection unit 22c inspects for the presence of foreign matter in the item P based on the difference in the difference image due to the presence or absence of foreign matter.
[0053] The inspection results from the inspection unit 22c are displayed on the display 30. The inspection results from the inspection unit 22c are also transmitted to, for example, a sorting mechanism located downstream of the X-ray inspection device 10.
[0054] (2-6-2-3) Evaluation Department As mentioned above, the inspection unit 22c uses a brightness conversion function to erase (remove) the presence of item P in the difference image. However, if the brightness conversion function is inappropriate, foreign objects may also be erased in addition to item P in the difference image, or the image of item P may remain in the difference image, causing the inspection unit 22c to mistakenly identify the image of item P as a foreign object. Therefore, the X-ray inspection device 10 is required to use an appropriate brightness conversion function. However, it is not easy for operators with little knowledge or experience to determine whether the brightness conversion function is appropriate or not.
[0055] Therefore, in the X-ray inspection apparatus 10, the evaluation unit 22d evaluates the brightness conversion function. The evaluation unit 22d evaluates the brightness conversion function based on the difference image of the item P, which is known to be free of foreign matter (hereinafter referred to as the first difference image), and the brightness value of the background of the first difference image. For example, the evaluation unit 22d evaluates the first difference image based on the distribution information of brightness values in the first difference image and the brightness value of the background of the first difference image.
[0056] An example of an evaluation method by the evaluation unit 22d is described below. Here, for ease of understanding, the evaluation method is explained using a graph, but the evaluation unit 22d does not need to create the graph itself.
[0057] The evaluation unit 22d counts the number of pixels for each brightness level within the region where the item P exists in the first difference image. The region where the item P exists can be determined by performing a process to extract the contour of the item P in the first or second transparent image (for example, a process in which binarization is performed in the first transparent image at a predetermined brightness value (threshold) and the binary boundary portion is extracted as the edge of the item P).
[0058] In other examples, the evaluation unit 22d may count the number of pixels for each brightness level in the entire first difference image.
[0059] If we create a histogram with the brightness value on the horizontal axis and the number of pixels on the vertical axis, based on the count results of the number of pixels for each brightness level, ideally all pixels would have a predetermined brightness value (the brightness value indicating the background, hereafter referred to as the background brightness value), and the histogram would be a straight line as shown by the solid line in Figure 5. However, in reality, the distribution will be as shown by the dashed-dot line or the double-dashed line in Figure 5.
[0060] Conceptually, the evaluation unit 22d evaluates the performance of the luminance conversion function used to create the histogram as better the closer the luminance values of all pixels are to the background luminance values.
[0061] Specifically, for example, the evaluation unit 22d evaluates the performance of the luminance conversion function used to create the histogram as better the closer the representative value of the luminance (for example, the mode of the luminance value (the luminance value with the most pixels), the median of the luminance value, or the mean of the luminance value) is to the background luminance value. Also, for example, the evaluation unit 22d evaluates the performance of the luminance conversion function used to create the histogram as better the smaller the variation in luminance values. Specifically, for example, the evaluation unit 22d evaluates the performance of the luminance conversion function used to create the histogram as better the smaller the standard deviation of the luminance values. Also, for example, the evaluation unit 22d evaluates the performance of the luminance conversion function used to create the histogram as better the smaller the difference between the maximum luminance value and the background luminance value, or the difference between the minimum luminance value and the background luminance value. Also, for example, the evaluation unit 22d may evaluate the luminance conversion function based on the number of extreme value points (maximum and minimum values). For example, if there are multiple extreme value points (for example, multiple local maximums), the evaluation unit 22d may evaluate that the performance of the luminance transformation function used to create the histogram is poor.
[0062] For example, in the example shown in Figure 5, the graph shown with a dashed line has an average brightness value that is closer to the background brightness value and exhibits less variation in brightness values than the graph shown with a double dashed line. Therefore, the evaluation unit 22d evaluates the brightness conversion function used to obtain the graph shown with a dashed line as having relatively better performance.
[0063] The evaluation unit 22d may evaluate the luminance conversion function based on multiple indicators. A specific method for evaluating the luminance conversion function by the evaluation unit 22d (a method for evaluating the luminance conversion function using the mode and standard deviation) will be explained with reference to the flowchart in Figure 6. The various numerical values described herein are for illustrative purposes only and do not limit the present invention.
[0064] The background brightness value here is, for example, a measured value. Specifically, the background brightness value is, for example, the average of the brightness values of the difference image obtained by subtraction processing using the first and second transmission images acquired when the conveyor 12 is not transporting anything. The background brightness value may also be a theoretically calculated value or a value based on the experience of the worker, etc.
[0065] <Specific examples of evaluation based on multiple indicators> The control unit 22 acquires a first and second transmission image of an item P that is known to be free of foreign matter, and the evaluation unit 22d generates a difference image (first difference image) obtained by performing subtraction processing using the first transmission image and the second transmission image corrected by the brightness conversion function. Furthermore, the evaluation unit 22d counts the number of pixels for each brightness within the region where item P is present in the first difference image (step S1). The region where item P is present in the first difference image can be determined using, for example, the method described in the description of the inspection unit 22c.
[0066] Next, the evaluation unit 22d calculates a score of 10 for the luminance conversion function used to generate the first difference image if the mode of luminance deviates significantly from the background luminance value (for example, 60) (for example, if the mode of luminance is 30 or less or 90 or more) (steps S2, S2a).
[0067] Furthermore, if there are many pixels that deviate significantly from the background brightness value (e.g., 60) (for example, if 30% or more of all pixels have a brightness value of 30 or less or 90 or more), the evaluation unit 22d calculates a score of 20 for the brightness conversion function used to generate the first difference image (steps S3, S3a).
[0068] If both step S2 and step S3 are No, the evaluation unit 22d subtracts the difference between the mode of luminance and the background luminance value from a certain reference value (e.g., 100) (step S4). For example, if the mode of luminance is 54, the evaluation unit 22d subtracts the difference (6) between the background luminance value (60) and the mode of luminance (54) from the reference value 100 to calculate a value A of "94".
[0069] Furthermore, the evaluation unit 22d subtracts the standard deviation of luminance from the value A (90 in this case) calculated in S4 (step S5). For example, if the standard deviation of luminance is 17, the standard deviation (17) is subtracted from the value A of "94" to calculate the value "77" as the score of the luminance conversion function. In this example, a higher score indicates a higher evaluation of the luminance conversion function.
[0070] The control unit 22 displays the evaluation result (in this case, a score) of the brightness conversion function by the evaluation unit 22d on the display unit 30, which is an example of a display unit (step S6).
[0071] In this example, the evaluation of the luminance conversion function by the evaluation unit 22d is shown as a score. However, the evaluation does not have to be done with a score; for example, the evaluation unit 22d may evaluate the luminance conversion function in steps (for example, in 5 steps).
[0072] (2-6-2-4) Judgment section The control unit 22 may have a judgment unit 22e in addition to the evaluation unit 22d. The judgment unit 22e determines the suitability of the brightness conversion function based on the evaluation results of the evaluation unit 22d. Determining the suitability of the brightness conversion function means determining whether the inspection unit 22c can perform inspection using the evaluated brightness conversion function. If the judgment unit 22e is present, even an operator without knowledge or experience can set an appropriate brightness conversion function for the X-ray inspection device 10.
[0073] The determination unit 22e determines that the luminance conversion function is appropriate if the evaluation of the luminance conversion function by the evaluation unit 22d is high, and that the luminance conversion function is inappropriate if the evaluation is low. Specifically, if the evaluation of the luminance conversion function by the evaluation unit 22d is performed using a score, the determination unit 22e determines that the luminance conversion function is appropriate if the score is above a certain threshold.
[0074] The control unit 22 notifies the notification unit of the judgment result of the judgment unit 22e regarding the suitability of the brightness conversion function. For example, the notification unit is the display 30. Alternatively, the notification unit may be a speaker that outputs the judgment result of the suitability of the brightness conversion function as sound. If the judgment result of the judgment unit 22e regarding the brightness conversion function is unsuitable, and the control unit 22 has created the brightness conversion function using the method described above, the control unit 22 may correct the brightness conversion function or create a new brightness conversion function as follows. If the evaluation unit 22d determines that the brightness conversion function is unsuitable, the control unit 22 acquires a first transmission image and a second transmission image based on the detection results of the line sensors 14 and 15 that irradiate the item P being transported by the conveyor 12 from the X-ray irradiator 13. If the judgment result of the brightness conversion function is unsuitable, the control unit 22 may automatically switch to the mode for performing this processing, or it may switch to the mode for performing this processing as a result of an operation on the display 30 or the like by the operator. Furthermore, the control unit 22 may determine how many times the process of obtaining additional difference images is performed. For example, the control unit 22 may determine how many times the process of obtaining additional difference images is performed, such that the number of times increases as the evaluation by the evaluation unit 22d decreases. Alternatively, the operator may determine how many times the process of obtaining additional difference images is performed.
[0075] The control unit 22 counts the number of pixels with each luminance value for the multiple first and second transmission images. The control unit 22 then adds the count results of the number of pixels with each luminance value obtained for the multiple first and second transmission images to the histogram information of the first energy band and the histogram information of the second energy band already stored in the histogram storage area 21b of the storage unit 21, respectively, and creates a luminance conversion function in the manner described in the description of the storage unit 21 (correcting any luminance conversion functions deemed unsuitable).
[0076] In this explanation, we have described the case where the histogram information used when creating the brightness conversion function is stored in the histogram storage area 21b. However, instead, the storage unit 21 may store data of multiple first and second transmission images used when creating the brightness conversion function that the judgment unit 22e determined to be unsuitable, as information related to the first and second transmission images. However, if image data is stored in the storage unit 21, the required storage capacity of the storage unit 21 tends to be large.
[0077] The above describes the case in which the luminance conversion function is corrected (by using information about the first and second transmission images used when the judgment unit 22e created a luminance conversion function that it determined to be unsuitable). However, the control unit 22 may also create a new luminance conversion function (without using information stored in the storage unit 21).
[0078] Specifically, if the control unit 22 determines that the brightness conversion function is unsuitable, it may perform a process multiple times to acquire a new first transmission image and a second transmission image based on the detection results of the line sensors 14 and 15 of the X-rays irradiated from the X-ray irradiator 13 onto the item P being transported by the conveyor 12, and then create a new brightness conversion function based on the multiple newly acquired first transmission images and second transmission images (only) using the method described in the description of the storage unit 21.
[0079] When using a method that corrects the brightness conversion function, there is an advantage in that it can shorten the time required to acquire data (X-ray transmission images) because it utilizes existing data.
[0080] On the other hand, if the evaluation of the luminance conversion function by the evaluation unit 22d (e.g., score) is quite low, it may be better to acquire new data (X-ray transmission images) rather than using data that yields only such a low-accuracy luminance conversion function. Therefore, the control unit 22 may choose between correcting the luminance conversion function and creating a new luminance conversion function, depending on the score of the evaluation of the luminance conversion function by the evaluation unit 22d. The operator may decide which process to perform.
[0081] The corrected luminance conversion function and the newly created luminance conversion function should be evaluated again by the evaluation unit 22d, and their suitability should be determined by the judgment unit 22e.
[0082] In this explanation, we have described cases in which the luminance conversion function is corrected or a new luminance conversion function is created when the judgment unit 22e determines that the luminance conversion function is unsuitable. However, even if the judgment unit 22e is not provided, the operator may, at their discretion, have the control unit 22 correct or create a new luminance conversion function in the manner described above.
[0083] (3) Features (3-1) The X-ray inspection apparatus 10 includes a conveyor 12 as a transport unit, an X-ray irradiator 13 as an X-ray source, line sensors 14 and 15 as detection units, and a control unit 22. The conveyor 12 transports an item P as an object to be inspected. The X-ray irradiator 13 irradiates the item P being transported by the conveyor 12 with X-rays. The line sensors 14 and 15 detect X-rays of a first energy band and X-rays of a second energy band irradiated onto the item P. The control unit 22 acquires a first transmission image based on the detection result of the X-rays of the first energy band and a second transmission image based on the detection result of the X-rays of the second energy band. The control unit 22 corrects at least one of the first transmission image and the second transmission image based on a brightness conversion function, and after correction, inspects the item P based on a difference image obtained by performing subtraction processing using the first transmission image and the second transmission image. The control unit 22 evaluates the luminance conversion function based on the difference image (in particular, the first difference image for item P, which is known not to contain foreign matter) and the luminance value of the background of the difference image (first difference image).
[0084] This X-ray inspection apparatus 10 allows even operators with limited knowledge and experience in X-ray inspection to perform accurate X-ray inspections using an appropriate brightness conversion function. For example, the control unit 22 evaluates the brightness conversion function based on the distribution information of brightness values in the difference image and the brightness values of the background of the difference image. The distribution information used to evaluate the brightness conversion function includes, for example, at least one of the following: mode, standard deviation, maximum value, minimum value, median, mean value, and number of extreme value points of the brightness values in the difference image.
[0085] (3-2) The X-ray inspection apparatus 10 has a display 30 as an example of a display unit that displays the evaluation results of the brightness conversion function. By displaying the evaluation results on the display 30, the operator can easily understand the evaluation of the brightness conversion function.
[0086] (3-3) In the X-ray inspection device 10, the control unit 22 determines the suitability of the brightness conversion function based on the evaluation results of the brightness conversion function. By having the control unit 22 determine the suitability, accurate X-ray inspections can be performed using an appropriate brightness conversion function, regardless of the operator's level of knowledge or experience.
[0087] The X-ray inspection apparatus 10 may have a notification unit (for example, a display 30 that displays the judgment result, or a speaker that outputs the judgment result as sound) that notifies the control unit 22 of the judgment result of whether the brightness conversion function is appropriate or not.
[0088] (3-4) The X-ray inspection apparatus 10 has a storage unit 21 that stores a histogram used to create the brightness conversion function as information about the first and second transmission images. The control unit 22 performs a process multiple times to acquire additional first and second transmission images based on the detection results of line sensors 14 and 15 of X-rays irradiated from the X-ray irradiator 13 onto the item P being transported by the conveyor 12 (for example, when the judgment unit 22e determines that the brightness conversion function is unsuitable). The control unit 22 corrects the brightness conversion function based on the information about multiple first and second transmission images already stored in the storage unit 21 (for example, used to create the brightness conversion function that the judgment unit 22e determined to be unsuitable) and the additionally acquired multiple first and second transmission images.
[0089] The information regarding the first and second transparent images stored in the memory unit 21 may be the first and second transparent images used to create the (uncorrected) luminance conversion function, rather than the histogram used to create the luminance conversion function.
[0090] Furthermore, the control unit 22 may, for example, if the judgment unit 22e determines that the brightness conversion function is unsuitable, and especially if the evaluation unit 22d evaluates the brightness conversion function poorly, perform the process of acquiring a first transmission image and a second transmission image multiple times based on the detection results of the line sensors 14 and 15 of the X-rays irradiated from the X-ray irradiator 13 onto the item P being transported by the conveyor 12, and then create a new brightness conversion function based on the multiple newly acquired first transmission images and second transmission images. With this configuration, for example, if the evaluation of the brightness conversion function is extremely poor, data unsuitable for creating the brightness conversion function can be excluded, and an appropriate brightness conversion function can be created. Even if the control unit 22 does not make a judgment on the suitability of the brightness conversion function, the control unit 22 may, in response to the operator's instructions, perform the above-mentioned process of correcting the brightness conversion function or the process of creating a new brightness conversion function.
[0091] (4) Variations The following are modifications of the above embodiment. These modifications may be combined with other modifications to the extent that they do not contradict each other.
[0092] (4-1) Variation A In the above embodiment, the evaluation unit 22d was described as performing an evaluation of the luminance conversion function based on a difference image including the item P (first difference image) and the luminance value of the background (background luminance value). However, the evaluation unit 22d may also perform the evaluation of the luminance conversion function in the following manner.
[0093] In modified example A, the evaluation unit 22d may compare the brightness value of each pixel in the difference image containing the item P (first difference image) with the brightness value of the corresponding pixel in the difference image containing only the background (a difference image obtained by acquiring the first and second transparent images without the item P being transported by the conveyor 12, and using the first transparent image and the second transparent image corrected with the brightness conversion function; hereafter referred to as the background difference image), and evaluate the brightness conversion function based on how much the brightness values differ between corresponding pixels in the two difference images. For example, the evaluation unit 22d may highly evaluate the brightness conversion function if the accumulated difference between the brightness value of each pixel in the first difference image and the brightness value of the corresponding pixel in the background difference image is less than a threshold, or if the maximum difference between the brightness value of each pixel in the first difference image and the brightness value of the corresponding pixel in the background difference image is less than a threshold.
[0094] In this case, the evaluation is based on the difference in brightness values for each pixel, rather than the distribution information of brightness values for all pixels. Therefore, it is possible to cancel out the influence of the local background and perform a highly accurate evaluation of the brightness conversion function. This method allows for an even more accurate evaluation of the brightness conversion function, even when the evaluation of the brightness conversion function is already relatively high.
[0095] (4-2) Modification B In the above embodiment, the evaluation unit 22d was described as performing an evaluation of the luminance conversion function based on a difference image including the item P (first difference image) and a background luminance value (background luminance value) that has been set in advance by some method. However, the background luminance value may be the luminance value of an area in the first difference image where the item P does not exist (for example, the average value of the luminance values of an area in the first difference image where the item P does not exist). By using the background luminance value in the first difference image in this way, it is possible to perform an accurate evaluation of the luminance conversion function.
[0096] (4-3) Modification C When the evaluation unit 22d uses the same evaluation criteria (evaluation method), depending on the type of item P, it may be more likely to produce a high score or a low score. For example, in the case of item P with little individual variation, the absolute value of the score calculated by the evaluation unit 22d tends to be high. However, even if the absolute value is relatively high, because item P tends to produce high scores, the luminance conversion function may not be considered good in relative terms.
[0097] In contrast, the evaluation unit 22d has multiple evaluation criteria (evaluation methods) for the luminance conversion function, allowing it to appropriately evaluate the luminance conversion function according to the type of item P. [Explanation of Symbols]
[0098] 10 X-ray inspection equipment 12. Conveyor (transport section) 13 X-ray irradiator (X-ray source) 14. First line sensor (detection unit) 15. Second line sensor (detection unit) 21 Memory section 22 Control Unit 30. Display (display unit, notification unit) P Article (object to be inspected) [Prior art documents] [Patent Documents]
[0099] [Patent Document 1] Japanese Patent Publication No. 2012-73056
Claims
1. A transport unit that transports the object to be inspected, An X-ray source that irradiates the object to be inspected, which is being transported by the transport unit, A detection unit for detecting X-rays in a first energy band and X-rays in a second energy band irradiated onto the object to be inspected, A control unit that acquires a first transmission image based on the detection results of X-rays in the first energy band and a second transmission image based on the detection results of X-rays in the second energy band, corrects at least one of the first transmission image and the second transmission image based on a brightness conversion function, and then performs subtraction processing using the first and second transmission images to inspect the object under inspection based on the difference image obtained, Equipped with, The control unit evaluates the brightness conversion function based on the difference image and the brightness value of the background of the difference image. X-ray inspection equipment.
2. The control unit evaluates the luminance conversion function based on the distribution information of luminance values in the difference image and the luminance value of the background of the difference image. The X-ray inspection apparatus according to claim 1.
3. The distribution information includes at least one of the following for the luminance values in the difference image: mode, standard deviation, maximum value, minimum value, median, mean value, and number of extreme points. The X-ray inspection apparatus according to claim 2.
4. The system further includes a display unit for displaying the evaluation results of the brightness conversion function. The X-ray inspection apparatus according to claim 1 or 2.
5. The control unit determines whether the brightness conversion function is appropriate based on the evaluation result of the brightness conversion function. The X-ray inspection apparatus according to claim 1 or 2.
6. The control unit further includes a notification unit that notifies the result of the determination of whether the brightness conversion function is appropriate or not. The X-ray inspection apparatus according to claim 5.
7. The system further includes a storage unit for storing information relating to the first transparent image and the second transparent image, The control unit, If the brightness conversion function is deemed unsuitable, the process of acquiring the first and second transmission images is performed multiple times based on the detection result of the X-rays irradiated from the X-ray source onto the object to be inspected being transported by the transport unit, as detected by the detection unit. Based on the information regarding the multiple first and second transmission images already stored in the memory unit, and the additionally acquired multiple first and second transmission images, the brightness conversion function that was deemed unsuitable is corrected. The X-ray inspection apparatus according to claim 5.
8. The control unit, If the brightness conversion function is deemed unsuitable, the process of acquiring the first and second transmission images is performed multiple times based on the detection result of the X-rays irradiated from the X-ray source onto the object to be inspected, which is being transported by the transport unit, by the detection unit. Based on the newly acquired first and second transmission images, a new luminance conversion function is created. The X-ray inspection apparatus according to claim 5.
9. The control unit has multiple evaluation criteria for the brightness conversion function. The X-ray inspection apparatus according to claim 1 or 2.