JP6250988B2 - Image processing method and apparatus - Google Patents

Description

  The present invention relates to an image processing method and apparatus for processing an image acquired by an imaging device in a plurality of gain modes.

  The dynamic range of X-ray detectors is generally narrow. For this reason, when shooting a high-contrast subject, the output may be saturated beyond the dynamic range of the X-ray detector or buried in noise, and subject information may be lost. In order to solve such a problem, an image output in a high sensitivity gain mode with high sensitivity to incident X-rays and an image output in a low sensitivity gain mode with low sensitivity are acquired, and those images are acquired. Is combined to expand the dynamic range.

  Generally, the gain mode is switched by preparing a plurality of capacitors for accumulating charges and increasing or decreasing the number of capacitors actually used for accumulating charges. Therefore, even if one capacitor is defective, it may operate normally in a certain gain mode. That is, the defective pixel and the normal pixel may be switched for each gain mode. Similarly, when the transistor that controls the capacitor is defective, the defective pixel and the normal pixel may be similarly switched. As a result, in an image read out by changing the gain mode, defective pixels appear at different positions for each gain mode. Therefore, an image processing apparatus that performs defective pixel correction needs to grasp the defective pixel position for each gain mode.

  In Patent Literature 1 and Patent Literature 2, defective pixel information for high sensitivity is stored in the high sensitivity mode (high gain mode), and defective pixel information for low sensitivity is stored in the low sensitivity mode (low gain mode). The defective pixel correction is performed using the defective pixel information corresponding to the set sensitivity. Further, Patent Document 3 proposes a method of switching the defect correction method for each gain mode.

JP 2007-306506 A Japanese Patent No. 4391876 JP 2007-129339 A

  In any of the above documents, defective pixel correction is performed by predicting the pixel value of a defective pixel from the peripheral pixels of the defective pixel. Since pixels with missing information are predicted from their peripheral pixels, the more normal peripheral pixels, the more accurate correction can be made. However, if there are many defective pixels in the peripheral pixels of the pixel to be corrected, the prediction accuracy decreases. For example, when there is only one normal pixel around the defective pixel, the pixel value of the defective pixel is only replaced with the pixel value of the only normal peripheral pixel. Furthermore, when there is no normal pixel in the peripheral pixels, the defective pixel cannot be corrected. In addition, when the defective pixel is near the edge and the peripheral pixel having the edge information includes many defective pixels, the correction result does not include the edge information.

  The present invention has been made in view of the above problems, and an object of the present invention is to realize an appropriate correction process even when there are many defective pixels around a defective pixel.

In order to achieve the above object, an image processing apparatus according to a position aspect of the present invention comprises the following arrangement. That is,
An image processing device that processes an image obtained by an imaging device capable of photographing in a first gain mode and a second gain mode different from the first gain mode,
Acquisition means for acquiring first defect information indicating a position of a defective pixel in the first gain mode and second defect information indicating a position of the defective pixel in the second gain mode of the imaging apparatus;
Switching means for switching correction processing of defective pixels in the first image captured by the imaging device in the first gain mode based on the first and second defect information;
The switching means includes a first correction process for correcting the defective pixel using pixels around the defective pixel in the first image, and a second correction image captured by the imaging device in the second gain mode. The selection is switched between the second correction process for correcting the defective pixel using the pixel corresponding to the defective pixel in the image.

  According to the present invention, even when there are many defective pixels around a defective pixel, an appropriate correction process can be realized.

1 is a block diagram showing a configuration example of an X-ray imaging apparatus according to an embodiment. The figure which shows the circuit example of the pixel of an X-ray sensor. The figure which shows the example of the input-output characteristic by two gain modes. The block diagram which shows the function structural example of 1st-3rd embodiment. The flowchart which shows the defect correction process by 1st Embodiment. The figure explaining synthetic defect information. The flowchart which shows the defect correction process by 2nd Embodiment. The figure explaining the subject of the surrounding pixel correction | amendment in an edge area | region. The flowchart which shows the defect correction process by 3rd Embodiment. The block diagram which shows the function structural example by 4th Embodiment. The flowchart which shows the defect correction process by 3rd Embodiment. The block diagram which shows the function structural example of 5th, 6th Embodiment. The flowchart which shows the defect correction process by 5th Embodiment. The flowchart which shows the defect correction process by 6th Embodiment. The block diagram which shows the function structural example of 7th Embodiment. The flowchart which shows the defect correction process by 7th, 8th embodiment. The block diagram which shows the function structural example of 8th Embodiment. The block diagram which shows the function structural example of 9th Embodiment. The flowchart which shows the synthetic | combination process of the pixel by 9th Embodiment. The block diagram which shows the function structural example of 10th, 11th Embodiment. The flowchart which shows the defect correction process by 10th Embodiment. The flowchart which shows the defect process by 11th Embodiment. The figure explaining the production | generation of line defect information. The figure explaining ranking of a defect map.

  Hereinafter, some preferred embodiments of the present invention will be described with reference to the accompanying drawings.

<First Embodiment>
In the embodiment described below, correction of a defective pixel is executed using the pixel value of a defective pixel in a certain gain mode, if the corresponding pixel is a normal pixel in a different gain mode. FIG. 1 is a diagram illustrating a configuration example of an X-ray imaging apparatus 100 according to the embodiment. A control PC 101 that controls the entire X-ray imaging apparatus 100, an X-ray sensor 102 that outputs an electrical signal corresponding to the irradiated X-ray dose, and an X-ray generation apparatus 110 that generates X-rays are connected via an optical fiber 122. Has been. The signal line may not be an optical fiber, and may be, for example, a CAN (Controller Area Network) or a Gigabit Ethernet. An external display device 109, an external storage device 111, and a network interface 112 are further connected to the optical fiber 122. In the control PC 101, for example, a CPU (Central Processing Unit) 103, a RAM (Random Access Memory) 104, and a ROM (Read Only Memory) 105 are connected to the bus 121. An input unit 106, a display unit 107, and a storage unit 108 are further connected to the bus 121.

  The control PC 101 sends commands to the X-ray sensor 102, the external display device 109, the X-ray generator 110, and the like. In the control PC 101, the processing content for each shooting mode is stored as a software module in the storage unit 108, read into the RAM 104 as necessary, and executed by the CPU 103. For example, each block of the functional configuration described later with reference to FIG. 4 is realized by the CPU 103 executing a corresponding software module stored in the storage unit 108. However, a configuration in which a dedicated image processing board for realizing each configuration (function) shown in FIG. 4 is mounted may be used.

  The X-ray sensor 102 is an indirect X-ray detector that can output pixel values with two different gains, a high sensitivity gain and a low sensitivity gain. That is, the X-ray sensor 102 constitutes an imaging apparatus that can perform imaging in the first gain mode and the second gain mode that is different from the first gain mode. FIG. 2 shows a circuit configuration example per pixel of the X-ray sensor 102. In FIG. 2, a photodiode 201 converts light converted by a phosphor into electric charges, and a capacitor 202 accumulates the electric charges. An X-ray image is generated by outputting the accumulated charges from the transistor 203 and the transistor 204. At this time, the transistor 205 is switched so that electric charge flows through the capacitor 206, whereby the capacitor capacity of the entire circuit is changed, and images of different gain modes are generated. However, although FIG. 2 shows a configuration in which two types of gain modes are realized using two types of capacitance, an image having a different gain can be generated by adding a capacitor and a transistor. it can.

  The input / output characteristics representing the relationship between the X-ray dose and the output signal from the sensor in the two types of gain modes acquired by the above configuration are, for example, as shown in FIG. In either gain mode, there is a region where the output signal is linearly related to the dose and a region where the linear relationship does not hold before and after the region. The region where the X-ray dose and the output signal are not in a linear relationship is a region where the signal value is small and buried in noise, or the capacitors 202 and 206 are saturated.

  FIG. 4 shows a functional configuration example for realizing the X-ray image processing method (defect correction processing method) in the first embodiment. As shown in FIG. 4, the functional configuration for realizing the X-ray image processing method of the first embodiment includes a peripheral pixel analysis unit 401, a defect information comparison unit 402, and a correction method determination unit 403. The peripheral pixel analysis unit 401 inputs an image (X-ray image (A) 51) obtained by subjecting the X-ray image acquired by the X-ray sensor 102 to predetermined preprocessing and defect information (defect information (A) 61). And outputs the result of analyzing the peripheral pixels for each defective pixel. The defect information comparison unit 402 receives at least two types of gain defect information (defect information (A) 61 and defect information (B) 62) and determines whether or not each pixel is a defective pixel in all gain modes. Is output. The correction method determination unit 403 determines a defect correction method to be adopted for each defective pixel based on the analysis result of the peripheral pixel by the peripheral pixel analysis unit 401 and the comparison result (composite defect information) of the defect information comparison unit 402. To do. A correction processing unit (not shown) corrects defective pixels using the defect correction method determined by the correction method determination unit 403. In the present embodiment, it is assumed that the X-ray image and defect information are stored in the external storage device 111, but the present invention is not limited to this.

  The defect correction method according to the first embodiment will be described with reference to the functional configuration diagram of FIG. 4 and the flowchart of FIG. The peripheral pixel analysis unit 401 acquires the X-ray image (A) 51 photographed in the gain mode A from the external storage device 111 (step 501). The X-ray image (A) 51 is an image on which necessary preprocessing is performed. Here, the pre-processing is processing for correcting sensor characteristics such as offset correction, log conversion, and gain correction, and the correlation between the value of each pixel and the value of surrounding pixels is maintained by the pre-processing. Become. Next, the peripheral pixel analysis unit 401 acquires defect information (A) 61 in the gain mode A of the X-ray sensor 102 from the external storage device 111 (step 502). The defect information (A) 61 indicates the position of the defective pixel in the X-ray sensor 102 in the same gain mode A as the X-ray image acquired in step 501.

  Next, the correction method is switched based on the defect information (A) 61 and the defect information (B) 62 for each of the defective pixels indicated by the defect information (A) 61 in the processing loop after step 503. First, the peripheral pixel analysis unit 401 grasps the position of the defective pixel (defect position) from the acquired defect information (A) 61 and analyzes the peripheral pixels of the defective pixel. Then, the peripheral pixel analysis unit 401 notifies the correction method determination unit 403 of the analysis result for determining the correction method of the defective pixel at each defect position. The peripheral pixel analysis unit 401 according to the first embodiment counts the number of normal pixels among peripheral pixels used for correcting defective pixels (step 504). For example, when a defective pixel is corrected from adjacent 8 pixels using the number 1 described below, the number of normal pixels among the adjacent 8 pixels is counted. The correction method determination unit 403 compares the count result with the threshold value 53 (step 505). When the number of normal pixels is equal to or smaller than the threshold value 53, the correction method determination unit 403 determines that the accuracy reduction of the correction using the peripheral pixels exceeds the allowable range, and the pixel of the image captured in another gain mode (in this example, Consider the use of a correction method using pixels of an image captured in gain mode B. Hereinafter, this correction method is referred to as “correction using different gain modes”. On the other hand, if the number of normal pixels exceeds the threshold value 53, it is determined that the accuracy of correction using the peripheral pixels can be maintained, and the correction method determination unit 403 determines the peripheral pixels of the defective pixel in the X-ray image (A) 51. Then, the peripheral pixel correction for correcting the defective pixel is selected (step 506). The peripheral pixel correction method is the correction method assumed in step 504 (a correction method using eight pixels around the defective pixel). In this case, for example, an integer of 1 to 8 is set for the threshold 53.

ここで、Ｓ（ｘ，ｙ）は座標（ｘ、ｙ）での画素値、Ｓ’（ｘ，ｙ）は補正された画素値である。ｗ（ｘ，ｙ）は座標（ｘ，ｙ）の画素が欠陥画素であるか否かのフラグである。欠陥画素であればｗ（ｘ，ｙ）＝０、正常画素であればｗ（ｘ，ｙ）＝１である。Ｐｎｏｒｍは正常画素フラグの総数であり、正常画素の総数を表すことになる。数１では周辺画素に欠陥画素があれば、その画素情報は使わずに補正値が算出される。 Many methods have been proposed for defective pixel correction (peripheral pixel correction) using the peripheral pixels selected in step 506, and any of them may be used. For example, a correction method as shown in the following equation 1 can be used.

Here, S (x, y) is a pixel value at coordinates (x, y), and S ′ (x, y) is a corrected pixel value. w (x, y) is a flag indicating whether or not the pixel at coordinates (x, y) is a defective pixel. For defective pixels, w (x, y) = 0, and for normal pixels, w (x, y) = 1. Pnorm is the total number of normal pixel flags, and represents the total number of normal pixels. In Equation 1, if there is a defective pixel in the surrounding pixels, the correction value is calculated without using the pixel information.

  On the other hand, when the process proceeds from step 505 to step 507 in order to consider the adoption of “correction using different gain modes”, the correction method determination unit 403 inputs the composite defect information 63 from the defect information comparison unit 402 (step 507). 507). The defect information comparison unit 402 acquires the defect information (A) 61 in the gain mode A and the defect information (B) 62 in the gain mode B from the external storage device 111 in advance (steps 521 and 522). Then, as shown in FIG. 6, the defect information comparison unit 402 merges the defect information (A) 61 and the defect information (B) 62 to generate new combined defect information 63 (step 523). As shown in FIG. 6, the composite defect information 63 includes pixels that are defective in both gain mode A and gain mode B, pixels that are defective in either mode, and pixels that are not defective in either mode. Is included.

  The correction method determination unit 403 checks whether or not the defective pixel to be corrected is a normal pixel in mode B from the composite defect information 63 (step 508). If the corresponding pixel of the image obtained in the gain mode B is a normal pixel, the value of the corresponding pixel is used to correct the defective pixel. That is, “correction using different gain modes” is selected (step 509). Note that when pixel values in different gain modes are used, it is necessary to correct the gain difference, details of which will be described in the fifth embodiment. On the other hand, if the corresponding pixel of the image obtained in the gain mode B is also a defective pixel, “correction using a different gain mode” cannot be performed, so the peripheral pixels from the peripheral pixels of the X-ray image (A) 51 A correction method is selected (step 506).

  Thereafter, according to the correction method determined (selected) by the correction method determination unit 403, correction of defective pixels is executed by a correction processing unit (not shown). That is, when “peripheral pixel correction” is selected, the pixel value of the defective pixel is generated using the peripheral pixel of the defective pixel in the X-ray image (A) 51. When “correction using different gain modes” is selected, the defective pixel of the X-ray image (A) 51 is corrected using the corresponding pixel of the X-ray image (B) 52. The above processing is executed for each defective pixel in the X-ray image (A). Also, when correcting defective pixels in the X-ray image (B), the same correction processing as described above is performed using the X-ray image (A) as an image in a different gain mode.

  As described above, according to the first embodiment, when the number of usable peripheral pixels is insufficient in the correction process for correcting the value of the defective pixel using the values of the peripheral pixels, another gain mode is used. The pixel value obtained in (1) was used. Therefore, even when there are few normal pixels around the defective pixel, there is a high possibility that correction with accuracy is realized.

Second Embodiment
In the first embodiment, the number of defective pixels included in the peripheral pixels of the defective pixel is used for correction method switching control (steps 504 and 505). On the other hand, in the second embodiment, switching of the correction method is controlled according to the determination result of whether or not the defective pixel portion is an edge region. The configuration of the X-ray imaging apparatus 100 of the second embodiment and the circuit configuration per pixel of the X-ray sensor 102 are the same as those of the first embodiment (FIGS. 1 and 2). Hereinafter, correction processing according to the second embodiment will be described with reference to the functional configuration diagram of FIG. 4 and the flowchart of FIG. 7. Steps 701 to 703 are the same as steps 501 to 503 in the first embodiment (FIG. 5).

The peripheral pixel analysis unit 401 extracts an edge from the pixel area used when correcting the defective pixel from the peripheral pixels (step 704). For the edge extraction, for example, an extraction method using a Sobel operator as described below can be used. Equation 2 shows the Sobel operator.

なお、上述のソーベルオペレータを用いたエッジ抽出方法は一例であり、その他のエッジ抽出方法を用いてもよい。 Edge components in the X and Y directions are extracted from the Sobel operator. When the gradient strength is calculated as shown in Equation 3, the edge strength can be obtained. The obtained edge strength is compared with a specific threshold value to determine whether an edge exists or not. Therefore, in the second embodiment, the threshold value 53 is a threshold value of edge strength.

Note that the edge extraction method using the Sobel operator described above is an example, and other edge extraction methods may be used.

  The correction method determination unit 403 selects a defect correction method according to the presence / absence of an edge (whether the strength of the edge exceeds the threshold value 53) (step 705). If there is an edge, the process proceeds to step 707 to consider “correction using different gain modes” using pixels in gain mode B. If correction using peripheral pixels is performed in a region where an edge exists, information before and after the edge with large pixel variation is mixed as shown in FIG. 8, for example, and accurate correction cannot be performed. That is, it is assumed that an image such as a defect occurrence image 82 is obtained because a defective pixel (x mark) is present in a subject photographing in which an image such as an image 81 having no defect is originally obtained as an image including an edge region. . In this case, when the correction using the peripheral pixels (Equation 1) is performed, “5” is calculated as the value of the defective pixel, and the image quality of the edge portion is degraded (defect correction image 83). The edge is often clinically important information, and it is not desirable that the information be lost. Therefore, the edge is stored using “correction using different gain modes” as much as possible. On the other hand, in a region where there is no edge, since pixel variation is small, peripheral pixel correction is selected (step 705 → step 706). The processing from step 707 to step 709 is the same as that from step 507 to step 509 of the first embodiment.

  As described above, according to the second embodiment, an appropriate correction method is selected according to the characteristics of the image in the area where the defective pixel exists. Note that the determinations in step 504 and 505 of the first embodiment (selection of a correction method according to the number of defective pixels around the defective pixel) may be used together.

<Third Embodiment>
In the third embodiment, a configuration for controlling the switching of the correction method based on the amount of noise in the peripheral area of the defective pixel will be described. The configuration of the X-ray imaging apparatus 100 of the third embodiment and the circuit configuration per pixel of the X-ray sensor 102 are the same as those of the first embodiment (FIGS. 1 and 2). Hereinafter, correction processing according to the third embodiment will be described with reference to the functional configuration diagram of FIG. 4 and the flowchart of FIG. 9. Steps 901 to 903 are the same as steps 501 to 503 in the first embodiment (FIG. 5).

  The peripheral pixel analysis unit 401 calculates the amount of noise from the peripheral region centered on the defective pixel (step 904). The peripheral area may be the same size as an area used for peripheral pixel correction (for example, a 3 × 3 pixel area centered on a defective pixel) or a different size. For example, the noise can be calculated using variance as shown in Equation 4 below. Equation 4 shows the noise amount σ ^ 2 using variance.

（ｘ、ｙ）が欠陥画素位置を示し、ｋが周辺領域のサイズとなる。ｗは、ｗ（０，０）で０、その他では１となる変数で、欠陥画素位置を省いた計算をするためのものである。なお上記のような分散を用いたノイズ算出方法は一例であり、その他のノイズ算出法方法を用いてもよい。

(X, y) indicates the defective pixel position, and k is the size of the peripheral region. w is a variable which is 0 for w (0,0) and 1 for others, and is used for calculation without the defective pixel position. Note that the noise calculation method using the above variance is an example, and other noise calculation methods may be used.

  The correction method determination unit 403 selects a defect correction method according to the amount of noise calculated in step 904 (step 905). If the amount of noise is greater than the threshold value 53, the process proceeds to step 907 to consider adopting “correction using a different gain mode” that uses a pixel in gain mode B. The threshold value 53 is a noise amount threshold value in the third embodiment.

  The peripheral pixel correction as shown in Equation 1 becomes a moving average filter excluding the central pixel. In other words, it has a function of reducing noise and the graininess is changed. Since the influence of the graininess reduction is small in the area where the noise is not conspicuous, the change in graininess is not felt. However, in the area where noise is conspicuous, only the defective pixel position becomes an image with little noise, and an artifact is generated. If the defective pixel is not an isolated defect but a connected defect such as a line defect or a block defect, such an artifact becomes more prominent. Artifacts interfere with diagnosis and their presence is undesirable. On the other hand, in the region where the amount of noise is small, the influence of noise reduction is small, so the peripheral pixel correction method is selected (step 906). The processing from step 907 to step 909 is the same as the processing from step 507 to step 509 of the first embodiment.

  As described above, according to the third embodiment, the occurrence of artifacts can be reduced by switching the correction method according to the amount of noise in the peripheral area of the defective pixel to be corrected. In step 905 for selecting a defect method, the number of defective pixels to be connected may be used as a branching index. The larger the number of connections, the larger the noise-reduced area. Therefore, the correction method determination unit 403 desirably selects step 907. In addition, you may use together the determination by step 504,505 of 1st Embodiment, and the determination by step 704,705 of 2nd Embodiment.

<Fourth embodiment>
In the fourth embodiment, a configuration is described in which when a defective pixel is corrected using pixel values of images in different gain modes, the correction result can be used for correction of other defective pixels. The configuration of the X-ray imaging apparatus 100 of the fourth embodiment and the circuit configuration per pixel of the X-ray sensor 102 are the same as those of the first embodiment (FIGS. 1 and 2).

  An example of the functional configuration of an X-ray imaging apparatus that implements the X-ray image processing method according to the fourth embodiment is shown in FIG. The peripheral pixel analysis unit 401, the defect information comparison unit 402, and the correction method determination unit 403 are as described in the first embodiment (FIG. 4). Further, the defect information update unit 1001 updates the defect information (A) 61 referred to by the peripheral pixel analysis unit 401 based on the correction method selected by the correction method determination unit 403.

  The process of the fourth embodiment will be described below using the configuration diagram of FIG. 10 and the flowchart of FIG. The processing from step 1101 to step 1109 is the same as that from step 501 to step 509 of the first embodiment.

  The defect information update unit 1001 is the defect pixel currently focused on in the defect information (A) 51 acquired by the peripheral pixel analysis unit 401 in step 1102 (defective pixel in which “correction using a different gain mode” is selected in step 1109. ) Is updated to normal pixels (step 1113). That is, in step 1109, the correction based on the pixel value in the gain mode B is selected, and the defective pixel subjected to the correction is regarded as having the same amount of information as the normal pixel in the gain mode A, and is normal in the subsequent processing. Treat as a pixel. Thereafter, the peripheral pixel analysis unit 401 refers to the updated defect information (A) 51 when counting the number of normal pixels. In addition, when performing defect correction from peripheral pixels, if there are pixels corrected with pixel values in different gain modes in the peripheral pixels, the corrected pixel values are used as defect pixel values for defect correction. .

  As described above, according to the fourth embodiment, the pixel value after correction of a defective pixel can be used for “peripheral pixel correction” of other defective pixels. In steps 1104 and 1105, the count result of the normal pixels around the defective pixel is used for the determination. However, the present invention is not limited to this. For example, as described in the second embodiment or the third embodiment, the edge extraction result or the noise amount calculation result in the peripheral region of the defective pixel may be used, or these may be combined.

<Fifth Embodiment>
In the first to fourth embodiments, when “correction using different gain modes” is executed, whether or not a pixel value that functions as a normal pixel in different gain modes is adopted is determined. Absent. However, even if it is a normal pixel in an image in a different gain mode, as shown in FIG. 3, there is a region that does not have linearity in its characteristics, a saturated region, or the like, so only a gain difference is corrected. Then, there are cases where the defective pixel cannot be corrected accurately. Therefore, in the following fifth to ninth embodiments, the linearity of the input / output characteristics of the X-ray sensor 102 is corrected and the range that can be used for “correction using different gain modes” is limited. Some examples of the configuration will be described.

  The configuration of the X-ray imaging apparatus 100 of the fifth embodiment and the circuit configuration per pixel of the X-ray sensor 102 are the same as those of the first embodiment (FIGS. 1 and 2). An example of the functional configuration for realizing the X-ray image processing method according to the fifth embodiment is shown in FIG. The functional configuration of the fifth embodiment includes a correction method selection unit 1201, a defect information comparison unit 1202, an evaluation unit 1203, and a defect correction unit 1204. The correction method selection unit 1201 selects a correction method based on the combined defect information 63 acquired from the defect information comparison unit 1202. Note that the correction method selection unit 1201 performs correction using the pixel value in the other gain mode when the pixel corresponding to the defective pixel is a normal pixel in the other gain mode, and in other cases, the surrounding pixel is corrected. It is set as the structure which performs the used correction | amendment. However, the correction method selection unit 1201 may use the correction selection method described in the first to third embodiments.

  The evaluation unit 1203 receives input / output characteristics with respect to the dose of the X-ray image acquired by the X-ray sensor, and corrects the pixel value of the defective pixel with accuracy when a pixel value in another gain mode is used. The evaluation result of whether or not is output. That is, the evaluation unit 1203 applies “correction using pixel values of other gain modes” to each defective pixel based on the input / output characteristics of the gain mode A and the gain mode B as described below. Judge the suitability of application. The defect correction unit 1204 determines a correction method to be finally adopted based on the selection result of the correction method by the correction method selection unit 1201 and the evaluation result by the evaluation unit 1203, and is obtained according to the determined correction method. Output the pixel value.

  The fifth embodiment will be described with reference to the functional configuration diagram of FIG. 12 and the flowchart of FIG. The evaluation unit 1203 and the defect correction unit 1204 acquire the X-ray image (A) 51 imaged in the gain mode A and the X-ray image (B) 52 imaged in the gain mode B from the external storage device 111 (step 1301). ). Note that the X-ray image (A) 51 and the X-ray image (B) 52 are pre-processed images. The preprocessing is processing for correcting sensor characteristics such as offset correction, log conversion, and gain correction, which are performed to maintain a correlation with surrounding pixels. Further, the defect information comparison unit 1202 and the evaluation unit 1203 acquire the defect information (A) 61 in the gain mode A and the defect information (B) 62 in the gain mode B from the external storage device 111 (step 1302). Further, defect information (A) 61 is input to the correction method selection unit 1201. Further, the evaluation unit 1203 acquires the input / output characteristic (A) 71 of the gain mode A and the input / output characteristic (B) 72 of the gain mode B from the external storage device 111 (step 1303).

  Further, the evaluation unit 1203 inputs an evaluation threshold value 73 (step 1304). The evaluation threshold 73 is a threshold relating to the correction rate. In order to correct a defect using a pixel in a different gain mode, it is necessary to multiply the pixel in a different gain mode by a correction factor and correct it before use. However, this correction is performed in the same manner for both signals and noise. Since the noise includes system noise that is not proportional to the X-ray dose, the S / N becomes worse as the correction factor increases. Therefore, the maximum correction rate at which the S / N does not affect the diagnosis is set, and this is set as the evaluation threshold 73.

  Next, the correction method selection unit 1201 grasps the defect position from the acquired defect information (A) 61 (step 1305), and determines the correction method with reference to the composite defect information 63 provided from the defect information comparison unit 1202. (Steps 1306 and 1307). In the present embodiment, it is determined whether or not the defective pixel indicated by the defect information (A) 61 is a normal pixel in another gain mode (in this case, gain mode B) by referring to the composite defect information 63. (Step 1307). If it is a normal pixel in another gain mode, it is determined to try to adopt “correction using a different gain mode”. When the correction method selection unit 1201 selects to consider the use of “correction using different gain modes”, the process proceeds to step 1308 to consider correction using the pixels in the gain mode B.

  On the other hand, if the defective pixel is also a defective pixel in other gain modes, correction using different gain modes cannot be used, and correction using peripheral pixels of the X-ray image (A) 51 is performed. To decide. When it is determined to perform correction from surrounding pixels, the defect correction unit 1204 executes correction of defective pixels (peripheral pixel correction) using the peripheral pixels (step 1311).

When it is selected to consider the use of correction using different gain modes, the evaluation unit 1203 uses the X-ray image (B) 52, the input / output characteristics (A) 71, and the input / output characteristics (B) 72. A correction factor is calculated (step 1308). The correction rate is a rate for converting the gain mode B pixel value into the gain mode A pixel value. An input value (X dose) for the pixel value S _B (x, y) in the gain mode B is obtained from the X-ray image (B) 52 and the input / output characteristic (B) 72, and the pixel in the gain mode A corresponding to this input value. The value S _A (x, y) is calculated from the input / output characteristic (A) 71. Accordingly, the correction factor r (x, y) is as shown in Equation 5.

  The evaluation unit 1203 compares the obtained correction rate r (x, y) with the evaluation threshold 73 (step 1309). If the correction rate is smaller than the evaluation threshold 73, the defect correction unit 1204 executes “correction using different gain modes” by correcting the defective pixel using the correction rate as it is (step 1310). On the other hand, if the correction rate is equal to or higher than the evaluation threshold 73, the S / N may be deteriorated as described above, and thus the defect correction unit 1204 corrects the defective pixel using the peripheral pixels (step 1311).

  As described above, according to the fifth embodiment, the suitability of the correction value is evaluated using the magnitude of the correction rate in determining whether to use the correction using the pixel value of another gain mode. . When it is determined that the image quality deterioration due to the correction using the pixel value in another gain mode is significant (in the above embodiment, the correction rate r exceeds the evaluation threshold), the pixel value in the other gain mode is used. The correction using peripheral pixels in the same gain mode is employed without adopting the correction that was performed. Therefore, the image quality of the image after correcting the defective pixel is maintained satisfactorily.

<Sixth Embodiment>
In the fifth embodiment, when the pixel value of the defective pixel in the gain mode A is corrected using the pixel value in the gain mode B, how much the pixel value in the gain mode B needs to be corrected ( Whether or not the pixel value can be used in the gain mode B is determined based on the correction rate. On the other hand, in the sixth embodiment, whether or not to adopt the pixel value in the gain mode B is determined based on the linearity in both the gain modes A and B. The configuration of the X-ray imaging apparatus 100 according to the sixth embodiment and the circuit configuration per pixel of the X-ray sensor 102 are the same as those in the first embodiment (FIGS. 1 and 2). The processing of the sixth embodiment will be described below with reference to the functional configuration diagram of FIG. 12 and the flowchart of FIG. Steps 1401 to 1403 are the same as steps 1301 to 1303 of the fifth embodiment (FIG. 13).

The evaluation unit 1203 inputs the input / output characteristic (A) 71 of the gain mode A and the input / output characteristic (B) 72 of the gain mode B, and calculates an approximate expression for performing a linear approximation thereof (step 1404). Since the linearity of the input / output characteristics is lost with respect to the dose, the evaluation unit 1203 approximates using the linearity γ so that the correction can be easily performed. In the present embodiment, for example, approximation such as Equation 6 is performed on the input / output characteristics for each gain mode.

  The approximation to Expression 6 is calculated from a plurality of sampling points by the least square method or the like. The residual is calculated from the calculated result and the base sampling point, and the result obtained by multiplying the residual in the gain mode A by the residual in the gain mode B, that is, the error amount by approximation is set as the approximation accuracy. Therefore, the higher the approximation accuracy, the smaller the approximation accuracy value (error amount). This approximate accuracy (error amount) is stored in the memory as a table for the input pixel value. Next, the evaluation unit 1203 inputs an evaluation threshold value 73 (step 1405). In the sixth embodiment, the evaluation threshold 73 is a threshold relating to the approximation accuracy. The processing in steps 1406 to 1408 is the same as that in steps 1305 to 1307 in the fifth embodiment (FIG. 13).

  If the correction method selection unit 1201 selects to consider the adoption of “correction using different gain modes”, the process proceeds to step 1409 to examine the adoption of a correction method using pixels in the gain mode B. The evaluation unit 1203 acquires the pixel value of the pixel corresponding to the defective pixel to be processed from the X-ray image (B) 52, refers to the approximate accuracy (table) calculated in step 1404, and corresponds to the pixel value. Get the approximation accuracy. Then, the evaluation unit 1203 compares the acquired approximate accuracy with the evaluation threshold 73 (step 1409). If the approximation accuracy is equal to or greater than the evaluation threshold 73, the peripheral pixel correction is executed with the X-ray image 71 as an input (step 1412). The fact that the approximation accuracy (error amount) is large is a place where the linearity is remarkably lowered and it can be said that it is a region where correction is difficult. Therefore, the correction using the surrounding pixels of the defective pixel is employed without using different gain mode values.

On the other hand, if the approximation accuracy is smaller than the evaluation threshold 73, correction in different gain modes is performed, so that a correction rate for correcting the gain mode B pixel value to the gain mode A pixel is calculated (step 1410). The correction factor can be obtained by, for example, Equation 5 described above. That is, an input value for the gain mode B pixel value SB (x, y) is obtained from the X-ray image (B) 52 and the input / output characteristic (B) 72, and the gain mode A pixel value SA corresponding to the input value is obtained. (X, y) is calculated from the input / output characteristic (A) 71. Then, the correction factor is calculated by S _A (x, y) / S _B (x, y). The defect correction unit 1204 corrects the defect using the correction rate obtained in step 1410 (step 1411).

  As described above, according to the sixth embodiment, in determining whether to employ correction using pixel values in other gain modes, the correction value is referred to by referring to the approximation accuracy to the straight line of the input / output characteristics. Appropriateness is evaluated, and use of pixel values in other gain modes is prevented in a portion where the approximation accuracy is low. Thereby, deterioration of the image quality of the corrected image can be prevented. Note that the correction value calculated in step 1413 may be further determined as to whether the correction value is appropriate based on the magnitude of the correction rate described in the fifth embodiment. Note that the residual of the approximate value obtained from Equation 6 in each of the gain mode A and the gain mode B is obtained and multiplied to obtain the approximate accuracy, but the residual in either one of the gain modes is approximate accuracy. It is good. For example, when the pixel value of the gain mode B is adopted in the correction of the defective pixel in the gain mode A, the approximation accuracy obtained from the residual in the gain mode B may be referred to.

<Seventh embodiment>
In the fifth embodiment and the sixth embodiment, a fixed value is used as the evaluation threshold value to be compared with the correction factor and the approximation accuracy. However, in the seventh embodiment, depending on whether the defective pixel is in the subject area or outside the subject area. A configuration for changing the evaluation threshold will be described. The configuration of the X-ray imaging apparatus 100 according to the seventh embodiment and the circuit configuration per pixel of the X-ray sensor 102 are the same as those in the first embodiment (FIGS. 1 and 2). The processing of the seventh embodiment will be described below with reference to the functional configuration diagram of FIG. 15 and the flowchart of FIG. The processing of steps 1601 to 1608 is the same as that of steps 1401 to 1408 of the sixth embodiment (FIG. 14).

  In FIG. 15, in the functional configuration according to the seventh embodiment, a peripheral pixel analysis unit 1501 is added to the functional configuration according to the sixth embodiment (FIG. 12). Further, the evaluation unit 1203 uses the adaptive threshold value 75 output from the surrounding pixel analysis unit 1501 instead of the evaluation threshold value 73 for comparison with the approximation accuracy.

  When the correction method selection unit 1201 selects to consider the adoption of “correction using different gain modes”, the process proceeds to step 1609 to examine the adoption of a correction method using pixels in the gain mode B. The peripheral pixel analysis unit 1501 receives the X-ray image (B) 52 as an input, corrects the evaluation threshold 73, and calculates an adaptive threshold 75 (step 1609). In calculating the adaptive threshold 75, the surrounding pixel analysis unit 1501 calculates a correction coefficient. The peripheral pixel analysis unit 1501 extracts a subject area from the X-ray image (B) 52 and determines whether the defective pixel (position) notified from the correction method selection unit 1201 is inside or outside the subject area. . As a method for extracting the subject area, for example, an analysis method using a histogram can be cited. For example, the peripheral pixel analysis unit 1501 creates a cumulative histogram of the X-ray image (B) 52. When it is considered that there is a range where X-rays are directly incident on the sensor in the high luminance region and there is a range where X-rays are prevented from entering the sensor by the collimator in the low luminance region, the cumulative frequency is α% of the total number of pixels. To 100-α% (0 <α <50). If the defective pixel (position) is within the range, the peripheral pixel analysis unit 1501 determines that the pixel is in the subject area, and multiplies the correction coefficient so that the evaluation threshold 73 becomes smaller to obtain the adaptive threshold 75. That is, the approximation accuracy is tightened for the pixels in the subject area. This is because it is within the subject and is an area useful for diagnosis, and its accuracy is strictly required.

  On the other hand, if it is a defective pixel outside the subject range, the peripheral pixel analysis unit 1501 sets the evaluation threshold value 73 as a value obtained by multiplying the evaluation threshold value 73 by a correction coefficient so as to increase the value, or an unchanged value as the adaptive threshold value 753. To provide. The fact that the subject is outside the subject is because information that is useful for diagnosis is often not included and accuracy is not so high. Note that the peripheral pixel analysis unit 1501 does not have to execute the extraction of the subject area every time in the loop for processing each defective pixel, and the subject area extracted first may be used in the subsequent loops. The subsequent steps 1610 to 1613 are the same as steps 1409 to 1412 of the sixth embodiment (FIG. 14) except that the adaptive threshold 75 is used for comparison with the approximation accuracy.

  As described above, according to the seventh embodiment, in the process of switching the correction process according to the approximation accuracy (correction using the peripheral pixels of the defective pixel / correction using pixel values in different gain modes) The threshold value for comparison is changed depending on whether or not it is within the subject area. Therefore, the correction process can be switched more appropriately. In the above embodiment, the X-ray image (B) is used to determine whether or not the position of the defective pixel is in the subject area. However, the X-ray image (A) may be used. Note that the threshold value changing process according to the seventh embodiment may be applied to the threshold value of the correction factor used in the fifth embodiment.

<Eighth Embodiment>
In the seventh embodiment, the threshold is adjusted according to whether or not the position of the defective pixel to be corrected is in the subject area, but the adjustment of the threshold is not limited to this. In the eighth embodiment, the threshold value is adjusted according to the type of image processing application (for example, imaging such as CT or general fluoroscopic imaging). The configuration of the X-ray imaging apparatus 100 of the eighth embodiment and the circuit configuration per pixel of the X-ray sensor 102 are the same as those of the first embodiment (FIGS. 1 and 2). The processing according to the eighth embodiment will be described below with reference to the functional configuration diagram of FIG. 17 and the flowchart of FIG. The processing in steps 1601 to 1608 is the same as that in the sixth embodiment (FIG. 14).

  The application analysis unit 1701 receives the evaluation threshold 73, corrects the evaluation threshold 73 according to the application in use, and calculates an adaptive threshold 75 (step 1612). In calculating the adaptive threshold 75, the application analysis unit 1701 calculates a correction coefficient to be multiplied by the evaluation threshold 73. The application analysis unit 1701 changes the value of the correction coefficient depending on what application is running. For example, when the application is CT or tomosynthesis, the error is largely propagated to the reconstructed image. Therefore, the adaptive threshold 75 is obtained by multiplying the correction coefficient so that the evaluation threshold 73 becomes small. On the other hand, when the application is general fluoroscopy, the S / N is poor because of low-dose imaging, and the influence of the error is considered to be small. Therefore, in general fluoroscopic imaging, the value obtained by multiplying the correction coefficient so that the evaluation threshold 73 becomes large or the value as it is of the evaluation threshold 73 is output as the adaptive threshold 75. Note that the application analysis unit 1701 does not need to execute the extraction of the subject area every time in the loop for processing each defective pixel, and the determination result of the application performed first may be used in the subsequent loops.

  As described above, according to the eighth embodiment, in the process of switching the correction process according to the approximation accuracy, the threshold for comparison with the approximation accuracy is changed according to the running application. Therefore, the correction process can be appropriately switched according to the type of imaging such as CT or tomosynthesis imaging or general fluoroscopic imaging. Note that the threshold value changing process according to the eighth embodiment may be applied to the threshold value of the correction factor used in the fifth embodiment.

<Ninth Embodiment>
Next, processing for extending the dynamic range using images with different gains will be described. The configuration of the X-ray imaging apparatus 100 of the ninth embodiment and the circuit configuration per pixel of the X-ray sensor 102 are the same as those of the first embodiment (FIGS. 1 and 2). In order to extend the dynamic range, pixel values acquired in the high gain mode and the low gain mode can be synthesized according to the dose. In the input / output characteristics shown in FIG. 3, the pixel value area covered by the two gain modes has an expanded dynamic range. The processing of the ninth embodiment will be described below with reference to the functional configuration diagram of FIG. 18 and the flowchart of FIG.

  The pixel value correction unit 1801 acquires an X-ray image (A) 51 imaged in the gain mode A and an X-ray image (B) 52 imaged in the gain mode B (step 1901). Here, the X-ray image (A) 51 and the X-ray image (B) 52 are images that have undergone preprocessing. Pre-processing is processing for correcting sensor characteristics such as offset correction, log conversion, and gain correction, and image data is in a state in which a correlation with surrounding pixels is maintained by pre-processing.

  Subsequently, the pixel value correction unit 1101 acquires the input / output characteristic (A) 71 of the gain mode A and the input / output characteristic (B) 72 of the gain mode B (step 1902). The input / output characteristic (A) 71 is an input / output characteristic in the same gain mode A as the X-ray image (A) 51 acquired in step 1201, and the input / output characteristic (B) 72 is an X-ray image acquired in step 1201 ( B) Input / output characteristics in the same gain mode B as 52.

  Also, the evaluation unit 1802 inputs or sets the threshold value 76 (step 1903). The threshold value 76 is a threshold value regarding the correction rate. The correction factor is a coefficient for aligning linearity between different gain modes. To synthesize using pixels in different gain modes, it is necessary to synthesize after aligning linearity. Therefore, it is necessary to multiply the pixels in different gain modes by the correction factor. However, the multiplication of the correction factor is performed for both the signal and the noise. Since the noise includes system noise that is not proportional to the X-ray dose, the larger the correction factor, the worse the S / N. Therefore, the maximum correction rate at which the S / N does not affect the diagnosis is set, and is set as the threshold value 76.

ｗの範囲は０以上１以下である。ｗはＸ線量の値の増加に応じて増加する増加関数であれば、その形状は線形でもシグモイドでもよい。各画素について以上のような合成処理を繰り返すことにより、合成画像が生成される。なお、上記では欠陥画素とするか否かの判定を補正率の大きさに基づいて行ったが、これに限られるものではなく、たとえば、第６実施形態の近似精度を用いた判定を利用してもよい。 Next, the evaluation unit 1802 and the image synthesis unit 1803 perform the process of synthesizing images with different gains for the number of pixels (step 1904). First, the evaluation unit 1802 calculates a correction factor for each pixel (step 1905). The correction factor is calculated using, for example, Formula 5 described in the fifth embodiment. Next, the evaluation unit 1802 compares the obtained correction factor with the threshold 76 (step 1906). If the correction rate is larger than the threshold value 76, it is determined that highly accurate correction cannot be obtained, and the evaluation unit 1802 determines that the pixel to be processed is a defective pixel (step 1907). On the other hand, if the correction rate is smaller than the threshold value 76, the evaluation unit 1802 determines that there is no problem in the correction accuracy. If it is determined that there is no problem with the correction accuracy, the image composition unit 1803 composes an image with the corrected pixel values (step 1908). Assuming that the corrected pixel value in the gain mode A is S _A (x, y), the pixel value S _B (x, y) in the gain mode B, and the combining coefficient is w, become that way.

The range of w is 0 or more and 1 or less. If w is an increasing function that increases as the value of the X-ray dose increases, the shape thereof may be linear or sigmoid. A combined image is generated by repeating the above combining process for each pixel. In the above, the determination as to whether or not the pixel is a defective pixel is made based on the magnitude of the correction factor, but the present invention is not limited to this. For example, the determination using the approximation accuracy of the sixth embodiment is used. May be.

<Tenth Embodiment>
In the following tenth and eleventh embodiments, a configuration for reducing the influence on subsequent processing due to correction by pixels acquired in different gain modes will be described. For example, there is a process for restoring grid stripes that have been lost due to defect correction. The defect correction from the peripheral pixels requires a restoration process because the grid stripes are lost. However, since the defect correction results in different gain modes have the grid stripes, there is no need to restore the grid stripes. Therefore, it is checked whether information necessary for subsequent processing (for example, information on grid stripes) remains due to defect correction performed using pixels acquired in different gain modes. Then, according to the check result, the defect information referred to in the subsequent image processing (for example, grid stripe correction) is updated.

  The processing of the tenth embodiment will be described using the functional configuration diagram of FIG. 20 and the flowchart of FIG. The line defect extraction unit 2003 has the configuration used in the eleventh embodiment, and will be described in the eleventh embodiment. The configuration of the X-ray imaging apparatus and the circuit configuration of each pixel of the X-ray sensor 102 are as described with reference to FIGS. The correction method selection unit 2001 acquires an X-ray image (A) 51 imaged in the gain mode A and an X-ray image (B) 52 imaged in the gain mode B (step 2101). The X-ray image (A) 51 and the X-ray image (B) 52 are images that have been preprocessed. Pre-processing is processing for correcting sensor characteristics such as offset correction, log conversion, and gain correction, and image data is in a state in which correlation with peripheral pixels is maintained by pre-processing.

  The correction method selection unit 2001 acquires the defect information (A) 61 in the gain mode A, and the evaluation unit 2004 and the defect information comparison unit 2002 acquire the defect information (A) 61 and the defect information (B) 62 (step 2102). ). Further, the evaluation unit 2004 acquires the input / output characteristic (A) 71 of the gain mode A and the input / output characteristic (B) 72 of the gain mode B (step 2103). That is, the input / output characteristic (A) 71 is an input / output characteristic in the same gain mode A as the X-ray image (A) 51 acquired in step 2101, and the input / output characteristic (B) 72 is acquired in step 2101. This is an input / output characteristic in the same gain mode as that of the X-ray image (B) 52.

  Next, the correction method selection unit 2001 acquires the composite defect information 63 from the defect information comparison unit 2002 (step 2104). The generation of the composite defect information 63 by the defect information comparison unit 2002 is as described in the first embodiment (FIG. 5B, FIG. 6). In other words, the composite defect information 63 is used to discriminate pixels that are defective in both gain mode A and gain mode B, pixels that are defective in either gain mode, and pixels that are not defective in either gain mode. It contains information that is attached.

  The evaluation unit 2004 refers to the composite defect information 63 for all the defective pixels of the X-ray image (A) 51 indicated by the defect information (A) 61, and the corresponding pixels in the gain mode B are normal pixels. It is checked whether or not (Steps 2105 and 2106). When the corresponding pixel in the gain mode B is also a defective pixel, “correction using different gain modes” cannot be used. Therefore, the defect correction unit 2005 performs correction using the peripheral pixels of the defective pixel in the same gain mode A. This correction method is as described in the first embodiment using Equation 1 (step 2110). Then, the defect information update unit 2006 registers the correction target pixel as a defective pixel, and updates the defect information 91 referred to in the subsequent image processing (step 2111). On the other hand, when the gain mode B is a normal pixel, a correction method in a different gain mode using the pixel of the gain mode B is selected (step 2106 → step 2107).

In a correction method in a different gain mode, first, a process for correcting the gain is performed. First, approximate equations of the input / output characteristic (A) 71 and the input / output characteristic (B) 72 are calculated. Since the linearity is lost with respect to the dose, the input / output characteristics are approximated using linearity γA and γB so that the correction can be easily performed. It approximates like several 8 and several 9 for every gain mode.

  The approximations to Equations 8 and 9 are calculated by a least square method or the like from a plurality of sampling points in each gain mode. Next, the corresponding pixel value of the X-ray image (B) 52 is input, and a correction result is calculated. That is, the input value is calculated from the pixel value of the X-ray image (B) 52 using the inverse transformation of Equation 9. The correction corresponding to the gain is completed by obtaining the corrected pixel value using Equation 8 for the obtained input value.

  Next, the evaluation unit 2004 determines whether correction of defective pixels by the correction process is appropriate or inappropriate based on the spectrum obtained from the X-ray image (A) after correction by the correction process using different gain modes. To evaluate. In the present embodiment, in consideration of the grid stripe correction in the subsequent stage, it is evaluated whether or not the grid stripe is maintained based on the spectrum obtained from the X-ray image (A). If the correction process is appropriate and is not maintained, it is evaluated as inappropriate. In the present embodiment, the ratio of the spectral values of a specific frequency (in this embodiment, the peak frequency of the grid stripes) in two orthogonal directions passing through the position of the defective pixel, and the two orthogonal directions not passing through the position of the defective pixel. A comparison is made with the ratio of the spectral values of a particular frequency with respect to the direction. Hereinafter, more detailed description will be given.

First, the evaluation unit 2004 includes a corrected pixel that has been corrected in a different gain mode, includes a defective pixel after the correction, a spectrum S1 in a direction perpendicular to the grid stripe direction, and the same direction as the grid stripe direction. A spectrum S2 is calculated. Further, the reference spectrum RS1 in the direction perpendicular to the grid stripe direction and the reference spectrum RS2 in the same direction as the grid stripe direction around the correction target defective pixel are calculated. When the peak frequency by the grid pattern was fg, reference peak ratio _{P RS} by peak ratio _{P S} and the reference spectrum RS1, RS2 by spectrum S1, S2 is as shown in Equation 10 and Equation 11.

The peak ratio is output as a large value corresponding to the grid stripes. It can be determined whether or not the grid stripe information is missing based on whether this value is equal to the surrounding area. Evaluation unit 2004 compares the reference peak ratio P _RS and the peak ratio P _S, calculates their difference or ratio as an evaluation value (step 2108), the evaluation value is checked whether within a predetermined range (Step 2109). If the evaluation value is within the predetermined range, it is determined that the grid stripe information has been accurately corrected, and the defect correction unit 105 outputs the correction result as the defect correction result. In the subsequent processing, the correction target pixel is used as a normal pixel. When “correction using different gain modes” is employed, the defect information update unit 2006 registers the defective pixel as a normal pixel in the defect information 91 for grid stripe correction (step 2111). Thus, the pixels corrected by the correction process in different gain modes are excluded from the grid stripe correction target.

On the other hand, if the evaluation value does not fall within the predetermined range in step 2118, the evaluation unit 2004 determines that the grid stripe information cannot be corrected accurately. Evaluation unit 2004 receives the decision to perform the correction using the peripheral pixels of the same gain mode A to the defect correction unit 2005 (correction using the number 1 of the first embodiment) (Step 2110). In this case, the correction target pixel is used as a defective pixel. Therefore, the defect information update unit 2006 registers the defect pixel in the defect information 91 for grid stripe correction (step 2110). When a defective pixel is registered in the defect information 91, it is necessary to perform a special defect correction in consideration of the grid stripe as preprocessing when performing grid stripe correction. Absent. According to this embodiment, since there is no need to perform defect correction in consideration of the grid stripes (when the grid stripes is maintained on the basis of peak ratio) different if the gain mode can perform the correction, High speed processing is expected.

<Eleventh embodiment>
Next, processing of the eleventh embodiment will be described with reference to the functional configuration diagram of FIG. 20 and the flowchart of FIG. In the eleventh embodiment, a portion (line defect portion) where a predetermined number or more of defective pixels continue in a line is processed as a group. The configuration of the X-ray imaging apparatus and the circuit configuration of each pixel of the X-ray sensor 102 are as described with reference to FIGS. Further, the processing of steps 2201 to 2204 is the same as that of steps 2101 to 2104 of the tenth embodiment (FIG. 21).

  The line defect extraction unit 2003 acquires the line defect definition 79 (step 2205). The line defect definition 79 is, for example, that three or more defective pixels are connected. Then, the correction method selection unit 2001 reads the line defect information 65 from the line defect extraction unit 2003 (step 2206). The line defect information 65 is generated by the line defect extraction unit 2003. In the extraction of the line defect information 65, the line defect extraction unit 2003 acquires the defect information (A) 61 in the gain mode A and the defect information (B) 62 in the gain mode B. Then, the line defect extraction unit 2003 generates line defect information based on the defect information.

  FIG. 23 is a diagram showing an example of the line defect extraction method according to the present embodiment. If the defect information in the gain mode A is defect information (A) 61 and the defect information in the gain mode B is defect information (B) 62, the line defect information becomes line defect information 65 (step 2211). That is, a defective pixel in the defect information (A) 61 but a normal pixel in the defect information (B) 62 is a line defective portion where a predetermined number or more of pixels are continuously in a line shape. Extracted as The standard for extracting as a line defect is set based on the line defect definition 79 described above. For example, as described above, when the line defect definition 79 is “3 or more defective pixels to be connected”, those having 3 or more defective pixels connected in the same direction are extracted as line pixels. .

  The evaluation unit 2004 checks whether or not the corresponding pixel in the gain mode B is a normal pixel from the combined defect information 63 for all defective pixels in the gain mode A (steps 2207 and 2208). When the gain mode B is a defective pixel, correction using a different gain mode cannot be executed. For this reason, the defect correction unit 2005 performs peripheral pixel correction using Equation 1, for example (step 2209). Then, the defect information update unit 2006 registers the correction target pixel as a defective pixel, and generates defect information 91 for grid correction (step 2215). That is, pixels that have not been corrected by “correction using different gain modes” are subjected to grid stripe correction processing in the subsequent stage.

  On the other hand, if the gain mode A is a defective pixel but the gain mode B is a normal pixel, the use of correction using a different gain mode using a gain mode B pixel is considered. In the eleventh embodiment, correction using different gain modes is performed in units of line defects indicated by the line defect information obtained in step 2206 (step 2210). Correction using different gain modes (step 2211) and peak ratio calculation (step 2212) are the same as steps 2107 and 2108 of the tenth embodiment.

  The evaluation unit 2004 obtains the difference (or ratio) between the peak ratio calculated in step 2212 and the reference peak ratio, and ranks the line defects within the line defects (step 2213). FIG. 24 shows an example of ranking. FIG. 24 shows an example of processing for a line defect in which seven defective pixels are arranged in the vertical direction, as shown in FIG. Each defect pixel constituting the line defect is corrected by the pixel value of the corresponding pixel in a different gain mode by the process of step 2211, and the corrected peak ratio and reference peak error are calculated by the process of step 2212. The one is shown in (b). Then, (c) shows a state in which the peak ratio errors are ranked in ascending order by the processing of step 2213. In step 2221, a pixel having a low rank among them, that is, a pixel having a small peak ratio error is determined as a normal pixel, and the defect map is updated until it does not apply to the line defect definition 79. In the case of FIG. 8, by determining that the pixels in the third rank are normal pixels, there are no defective pixels corresponding to the line defect definition having three or more connected states as line defects.

  Therefore, in this case, the defect information update unit 2006 sets the pixels having the third rank as normal pixels, and the defect correction unit 2005 outputs these correction results (results obtained in Step 2211) as defect correction results. Further, the defect information 91 for grid correction is updated so as to indicate that these pixels are determined to be normal pixels (step 2215). These pixels are excluded from the target of grid stripe correction at the subsequent stage. On the other hand, since the fourth and higher ranks are determined as defective pixels in grid correction, the defect correction unit 2005 performs peripheral pixel correction using, for example, Equation 1 (step 2209). Then, the defect information update unit 2006 registers those pixels (pixels in the fourth and subsequent ranks) as defective pixels (step 2215).

  As described above, according to the eleventh embodiment, it is possible to reduce the influence on the image quality by preferentially treating a pixel with a small error as a normal pixel.

  The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

Claims (27)

An image processing device that processes an image obtained by an imaging device capable of photographing in a first gain mode and a second gain mode different from the first gain mode,
Acquisition means for acquiring first defect information indicating a position of a defective pixel in the first gain mode and second defect information indicating a position of the defective pixel in the second gain mode of the imaging apparatus;
Switching means for switching correction processing of defective pixels in the first image captured by the imaging device in the first gain mode based on the first and second defect information;
The switching means includes a first correction process for correcting the defective pixel using pixels around the defective pixel in the first image, and a second correction image captured by the imaging device in the second gain mode. An image processing apparatus, wherein selection is switched between a second correction process for correcting the defective pixel using a pixel corresponding to the defective pixel in the image. A counter for counting the number of normal pixels around the defective pixel from the first defect information;
The image processing apparatus according to claim 1, wherein the switching unit further switches correction processing based on the number of normal pixels counted by the counting unit.   When the number of normal pixels counted by the counting unit is less than a threshold value and the defective pixel is determined to be a normal pixel in the second image from the second defect information, the switching unit is The image processing apparatus according to claim 2, wherein the second correction process is selected. A determination unit configured to determine whether the defective pixel is included in an edge region based on an image around the defective pixel in the first image;
The image processing apparatus according to claim 1, wherein the switching unit further switches correction processing based on a determination result by the determination unit.   The switching unit determines that the defective pixel is included in an edge region by the determining unit, and determines that the defective pixel is a normal pixel in the second image from the second defect information. The image processing apparatus according to claim 4, wherein the second correction process is selected. A calculation means for calculating a noise amount from an image around the defective pixel of the first image;
The image processing apparatus according to claim 1, wherein the switching unit further switches correction processing based on a noise amount calculated by the calculation unit.   When the noise amount calculated by the calculating unit exceeds a threshold value and the defective pixel is determined to be a normal pixel in the second image from the second defect information, the switching unit is The image processing apparatus according to claim 6, wherein the correction processing is selected.   2. The image processing apparatus according to claim 1, further comprising update means for updating the first defect information so as to indicate that the pixel corrected by the second correction processing in the first image is a normal pixel. 8. The image processing device according to any one of items 7 to 7.   The switching means selects the second correction process when a pixel at a position corresponding to the defective pixel indicated by the first defect information is indicated as a normal pixel by the second defect information; 2. The image processing apparatus according to claim 1, wherein the first correction process is selected. Based on a first input / output characteristic indicating the correspondence between the X-ray dose and the output signal in the first gain mode, and a second input / output characteristic indicating the correspondence between the X-ray dose and the output signal in the second gain mode. , Further comprising evaluation means for evaluating the suitability of application of the second correction process,
The image processing apparatus according to claim 1, wherein the switching unit further switches correction processing based on an evaluation result of the evaluation unit. The evaluation means converts the pixel value of the second image into the pixel value of the defective pixel of the first image based on the first input / output characteristic and the second input / output characteristic. Determine whether the correction rate exceeds the evaluation threshold,
The image processing apparatus according to claim 10, wherein the switching unit selects the first correction process when it is determined that the correction rate exceeds the evaluation threshold. The evaluation unit obtains an error amount of linear approximation based on the first input / output characteristic and the second input / output characteristic, and the error amount in a pixel value of the second image corresponding to the defective pixel. Determine whether or not exceeds the evaluation threshold,
The image processing apparatus according to claim 10, wherein the switching unit selects the first correction process when it is determined that the error amount exceeds the evaluation threshold.   The evaluation means changes the evaluation threshold based on whether or not the position of the defective pixel is within a subject area in the first or second image. The image processing apparatus described.   The image processing apparatus according to claim 13, wherein the evaluation unit is configured such that the evaluation threshold when the position of the defective pixel is within the subject region is smaller than the evaluation threshold when the position is outside the subject region.   The image processing apparatus according to claim 11, wherein the evaluation unit changes the evaluation threshold based on a type of an active image processing application. Based on the spectrum obtained from the first image after the defective pixel is corrected by the second correction process, it is determined whether the correction of the defective pixel by the second correction process is appropriate or inappropriate. An evaluation means for generating an evaluation value for
The switching means adopts the correction result by the second correction process when it indicates that the evaluation value is appropriate, and the correction result by the first correction process when it indicates that the evaluation value is inappropriate. The image processing apparatus according to claim 1, wherein the image processing apparatus is employed.   The image processing apparatus according to claim 16, wherein the evaluation unit generates an evaluation value indicating whether grid stripes are maintained based on the spectrum.   The evaluation means includes a ratio of spectral values at specific frequencies for two orthogonal directions passing through the position of the defective pixel, and a specific frequency at two specific directions not passing through the position of the defective pixel. The image processing apparatus according to claim 16, wherein the evaluation value is generated by comparison with a ratio of spectral values.   The image processing apparatus according to claim 18, wherein the specific frequency is a peak frequency of a grid stripe, and one of the two orthogonal directions is a direction along the grid stripe. In the first gain mode, the evaluation means has a good evaluation value for a line defect portion in which a predetermined number of pixels or more are continuous among the pixels that are defective pixels in the first gain mode but are normal pixels in the second gain mode. Rank the defective pixels in order,
The switching means selects a defective pixel in the ranked order and applies the second correction process to treat it as a normal pixel, and the defective pixels do not continue to be more than the predetermined number in the line defect portion. The image processing apparatus according to claim 16, wherein the image processing apparatus repeats the process until the process is repeated.   21. The image processing apparatus according to claim 16, wherein a defective pixel in which a correction value obtained by the second correction process is adopted is excluded from defect information referred to by subsequent image processing. . A control method for an image processing device for processing an image obtained by an imaging device capable of photographing in a first gain mode and a second gain mode different from the first gain mode,
An acquisition step of acquiring first defect information indicating a position of a defective pixel in the first gain mode and second defect information indicating a position of the defective pixel in the second gain mode of the imaging device;
A switching step of switching correction processing of defective pixels in the first image captured by the imaging device in the first gain mode based on the first and second defect information,
In the switching step, a first correction process that corrects the defective pixel using pixels around the defective pixel in the first image, and a second correction that the imaging device has captured in the second gain mode. A control method for an image processing apparatus, wherein selection is switched between a second correction process for correcting the defective pixel using a pixel corresponding to the defective pixel in an image. An image processing device that processes an image obtained by an imaging device capable of photographing in a first gain mode and a second gain mode different from the first gain mode,
Each pixel is synthesized using the pixel value acquired in the first gain mode and the pixel value acquired by converting the pixel value acquired in the second gain mode into the pixel value in the first gain mode. A synthesis means to
For each pixel to be combined, whether or not to convert the pixel value in the second gain mode into the pixel value in the first gain mode is input / output in each of the first and second gain modes. An evaluation means for evaluating based on characteristics ,
An image processing apparatus according to claim 1, wherein the synthesizing unit generates a synthesized image by synthesizing a pixel evaluated as inappropriate by the evaluation unit as a defective pixel and combining the pixels evaluated as appropriate.   The evaluation means is a correction factor for converting the pixel value of the second gain mode into the pixel value of the first gain mode based on the input / output characteristics of the first and second gain modes. 24. The image processing apparatus according to claim 23, wherein if the value exceeds a threshold value, the conversion is evaluated as inappropriate.   The evaluation unit obtains an error amount from linear approximation for each input / output characteristic of the first and second gain modes, and uses the pixel value of the second gain mode as the pixel value of the first gain mode. 24. The image processing apparatus according to claim 23, wherein whether or not to convert to an image is evaluated based on the error amount in the pixel value.   The evaluation unit evaluates whether or not the pixel value of the second gain mode is converted to the pixel value of the first gain mode based on a spectrum obtained from the image synthesized by the synthesis unit. The image processing apparatus according to claim 23, wherein: A control method for an image processing device for processing an image obtained by an imaging device capable of photographing in a first gain mode and a second gain mode different from the first gain mode,
Each pixel is synthesized using the pixel value acquired in the first gain mode and the pixel value acquired by converting the pixel value acquired in the second gain mode into the pixel value in the first gain mode. A synthesis process to
For each pixel to be combined, whether or not to convert the pixel value in the second gain mode into the pixel value in the first gain mode is input / output in each of the first and second gain modes. An evaluation process for evaluating based on characteristics,
In the composition step, a pixel evaluated as inappropriate in the evaluation step is used as a defective pixel, and a composite image is generated by combining pixels evaluated as appropriate.

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