JP6429548B2 - Image processing apparatus, control method therefor, and computer program - Google Patents

Description

  The present invention relates to an image processing apparatus, a control method thereof, and a computer program, and more particularly, to a technique for improving contrast reduction due to saturation of an image sensor.

  An X-ray imaging apparatus for medical diagnosis using an X-ray sensor (imaging device) is known. FIG. 1 shows the relationship between the X-ray dose reaching the sensor and the sensor output value. Usually, linearity is maintained between the X-ray dose and the sensor output value. However, if the reaching dose exceeds a certain threshold, the relationship between the X-ray dose and the sensor output value loses linearity. This threshold is called a saturated dose, and a pixel that has reached an X-ray dose exceeding the saturated dose is called a saturated pixel. When the saturation dose is exceeded, the sensor output value gradually approaches a constant value. This is because the outputs of amplifiers, photodiodes (in the case of indirect sensors), etc. in the sensor gradually lose linearity as the X-ray dose increases. The fact that the sensor output value gradually approaches a constant value means that the sensitivity of the sensor output value with respect to the X-ray dose gradually decreases. That is, an image configured using pixels that exceed the saturation dose is an image with a reduced contrast and is not suitable for diagnosis. Therefore, some countermeasure is required for saturated pixels.

  Patent Document 1 describes that an image is formed by fixing an output value to a constant value for a saturated pixel. Patent Document 2 describes that the value of a saturated pixel is corrected based on the output value of a surrounding non-saturated pixel. In the configuration of Patent Document 2, correction is performed by weighting pixels having high correlation with saturated pixels among peripheral pixels. Japanese Patent Application Laid-Open No. 2004-228688 describes that a captured image of a moving image is interpolated using a pixel at the same position in a previous frame and a pixel at the same position in a subsequent frame that are not saturated.

JP 2003-000576 A JP 2012-024344 A JP 2010-045294 A

  If pixels equal to or higher than the saturation dose are fixed to a certain value as in Patent Document 1, information exceeding the saturation dose is lost at all. When the diagnosis area is included, there is no possibility that the diagnosis information is lost and information necessary for the diagnosis cannot be acquired. In the configuration of Patent Document 2, correction is performed by interpolating pixel values from surrounding pixels, so that unique information held by the pixels is not reflected in the image. The configuration of Patent Document 3 not only lacks information as in Patent Document 1 and Patent Document 2, but also uses the information of the previous frame, and thus requires a plurality of frame buffers. For this reason, the system memory may be compressed, and the stability of the system may be reduced. In addition, if the saturation state occurs over a plurality of frames, data for interpolation cannot be acquired, and interpolation itself cannot be performed.

  The present invention has been made in view of the above problems, and is an efficient technique for converting an image including an area photographed exceeding a saturation dose into an image capable of visually reading information included in the area. The purpose is to provide.

In order to achieve the above object, an image processing apparatus according to the present invention comprises the following arrangement. That is,
An image processing apparatus that performs image processing on a photographed image photographed using a plurality of imaging elements,
Decomposition means for decomposing the captured image into a plurality of band limited images limited to different frequency bands;
With respect to the captured image, detection means for detecting a pixel having an incident dose on the image sensor of a predetermined value or more as a saturated pixel,
Adjusting means for adjusting the contrast of the partial image composed of saturated pixels of the band-limited image;
Reconstructing means for reconstructing an image using the plurality of band-limited images whose contrasts are adjusted.

  ADVANTAGE OF THE INVENTION According to this invention, the efficient technique which converts the image containing the area | region image | photographed exceeding the saturated dose into the image which can visually read the information contained in the said area | region can be provided.

The figure which shows the relationship between the X-ray dose which reaches | attains an image sensor, and a sensor output value Block diagram schematically showing a functional configuration example of an X-ray image processing apparatus Block diagram showing a system configuration example including an X-ray image processing apparatus The flowchart which shows the process sequence which X-ray image processing apparatus performs Schematic diagram showing the calculation principle of saturated pixel values Schematic diagram showing the detection principle of saturated pixels Block diagram schematically showing a functional configuration example of an X-ray image processing apparatus The flowchart which shows the process sequence which X-ray image processing apparatus performs Block diagram schematically showing a functional configuration example of an X-ray image processing apparatus The flowchart which shows the process sequence which X-ray image processing apparatus performs The figure which shows the relationship between the number of frames, sensor output value and offset component amount

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

(Configuration of X-ray image processing apparatus)
FIG. 2 is a block diagram schematically showing a functional configuration example of the X-ray image processing apparatus according to the embodiment of the present invention. An X-ray image processing apparatus as an image processing apparatus that performs image processing on captured images captured using a plurality of image sensors includes a detection unit 201, a decomposition unit 202, an adjustment unit 203, and a reconstruction unit 204. Yes. The detection unit 201 inputs an image obtained by performing predetermined preprocessing on an X-ray image acquired by an X-ray sensor (imaging device), detects a pixel (nonlinear pixel) that is a saturated pixel, and outputs a detection result. Output. As will be described later, the detection unit 201 detects, as a saturated pixel, a pixel having an incident dose with respect to the image sensor that is a predetermined value or more. The decomposition unit 202 inputs an image obtained by performing predetermined preprocessing on the X-ray image acquired by the X-ray sensor, decomposes the image into a plurality of band limited images each representing a frequency component limited to a different frequency band, Output. The adjustment unit 203 receives the band limited image and the detection result of the saturated pixel, adjusts the band limited image based on the saturation pixel detection result, and outputs the adjusted band limited image. Specifically, the adjustment unit 203 adjusts the contrast of the partial image including the saturation pixels of the band limited image for each band limited image. The reconstruction unit 204 receives the band-limited image whose contrast has been adjusted, performs reconstruction, and outputs a reconstruction result.

  The X-ray image processing apparatus shown in FIG. 2 can be realized by an information processing apparatus such as a PC (Personal Computer), a workstation, or a tablet terminal. FIG. 3 is a block diagram illustrating a hardware configuration example of an X-ray image processing system including an X-ray image processing apparatus realized by a PC. In FIG. 3, the control PC 301, the X-ray sensor 302, and the X-ray generator 310 are connected by an optical fiber 313. However, the signal lines connecting these devices are not limited to optical fibers, and any network capable of transmitting information, such as CAN (Controller Area Network) or Gigabit Ethernet, can be used. The X-ray generator 310 includes an X-ray tube and irradiates the X-ray sensor 302 with X-rays. The X-ray sensor 302 includes a plurality of image sensors that detect X-rays emitted from the X-ray generator 310 and forms a captured image. Further, a display device 309, a storage device 311, and a network interface (I / F) 312 are connected to the optical fiber 313. The control PC 301 includes components such as a CPU 303, a RAM (Random Access Memory) 304, a ROM (Read Only Memory) 305, an input unit 306, a storage unit 307, and the like. These components are connected to each other by a bus 308. A CPU 303 is a central processing unit (Central Processing Unit), and controls the entire apparatus based on data, computer programs, and the like stored in a RAM 304, a ROM 305, a storage unit 307, and the like. A RAM 304 is a writable memory (Random Access Memory), and is used as a work area for temporarily storing data and programs read from the storage unit 307 and the like. A ROM 305 is a read-only memory, and stores computer programs such as basic I / O programs, data used for basic processing, and the like. The input unit 306 is a component that inputs an instruction from the user, and is realized by an instruction device such as a keyboard, a pointing device, or a touch panel. The storage unit 307 is a device that functions as a large-capacity memory, and is realized by a hard disk device, an SSD, a USB memory, a flash memory, or the like.

  The control PC 301 transmits a command to the X-ray sensor 302, the display device 309, or the like according to an instruction from the user, a processing process, or the like. In the control PC 301, the processing content for each shooting mode is stored in the storage unit 307 as a software module. This software module is read into the RAM 304 and executed in response to an instruction input to the pointing device. The functional elements 201 to 204 in the functional configuration illustrated in FIG. 2 are stored in the storage unit 307 as software modules. Of course, the functional elements 201 to 204 shown in FIG. 2 may not be implemented as software, but may be implemented by hardware such as a dedicated image processing board. Optimal mounting can be performed according to the application and purpose.

  Hereinafter, five exemplary embodiments will be described with respect to details of the X-ray image processing apparatus.

(Embodiment 1)
A process flow of the X-ray image processing apparatus will be described with reference to the configuration diagram of FIG. 2 and FIG. 4. FIG. 4 is a flowchart showing a processing procedure executed by the X-ray image processing apparatus. Each step in FIG. 4 is executed based on the control of the CPU 303.

  First, an original image input to the detection unit 201 and the decomposition unit 202 is created through S401 and S402. That is, the X-ray sensor 302 in FIG. 3 acquires an X-ray image (S401). The control PC 301 performs preprocessing on the acquired X-ray image (S402). The preprocessing may include processing for correcting sensor characteristics such as offset correction, log conversion, gain correction, and defect correction, and grid stripe suppression processing for suppressing grid moire. If necessary, processing for improving S / N, such as processing for reducing random noise, may be performed. The image that has been preprocessed in this way becomes the original image.

Next, the detection unit 201 detects nonlinear pixels from the original image. The non-linear pixel is a pixel in which the reached X-ray dose and the sensor output value are not in a linear relationship. The aforementioned saturated pixel is an example of a nonlinear pixel. Here, first, a saturated pixel value for determining a saturated pixel is determined (S403). The saturated pixel value is a value indicating a non-linear characteristic between the incident dose and the output value when the dose greater than the saturated pixel value is incident on the image sensor. The saturated pixel value is calculated by thresholding a value obtained by differentiating the sensor output value with the X-ray dose. FIG. 5 shows a method for determining a saturated pixel value. When the relationship between the sensor output value F and the X-ray dose u is as shown in FIG. 5A, linear approximation is performed in the low-dose region (region in which linearity is reliably maintained) to obtain an approximate expression. Here, M is the slope of the approximate expression. Next, when the sensor output value is differentiated by the X-ray dose as shown in FIG. 5B, the differential value decreases in the X-ray dose range where the linearity cannot be maintained. Therefore, to detect the smallest u that satisfies Equation 1 as saturated dose u _s.

If necessary, calculates a sensor output value corresponding to the saturation dose u _s as in FIG. 5 (c), may be calculated that value as the saturated pixel value F _s. The saturated pixel value is not a value that changes every time shooting is performed, and is difficult to calculate during shooting. Therefore, in actual operation, the saturated pixel value is calculated in advance and stored in the storage unit 307 and the like. You may make it read the value. When the saturated pixel value F _s is determined, all pixels having a pixel value greater than or equal to the saturated pixel value in the original image are detected as saturated pixels (S404).

Next, the decomposition unit 202 creates a band-limited image having a plurality of frequencies (spatial frequencies) from the original image (S405). Methods for creating a plurality of band limited images include a method using Laplacian pyramid decomposition, a method using wavelet transform, a method using an unsharp mask, and the like. When the unsharp mask is used, if the original image is S _org and the blurred image is S _UsLv , the band limited image H _Lv is as shown in _Equation 2.

Lvは帯域制限画像のインデックスである。周波数応答特性の異なるボケ画像を作成することで、様々な帯域制限画像を得ることができる。

Lv is an index of the band limited image. Various band limited images can be obtained by creating blurred images with different frequency response characteristics.

  Next, the adjustment unit 203 detects a saturated pixel on the band-limited image using the detection result of the saturated pixel in S404 (S406). The saturated pixel on the band limited image is a pixel on the band limited image at the position of the pixel value in the blurred image generated using the pixel value of the saturated pixel of the original image. In this embodiment, a blurred image is used to create a band limited image.

  When the filter size of the blurred image is N, the saturated pixel is an N × N region centered on the saturated pixel of the original image. FIG. 6 is a diagram schematically showing a procedure for detecting saturated pixels on a band limited image. FIG. 6 shows an example in which a 3 × 3 filter is applied as a blurred image. When the 3 × 3 filter is applied to the saturated pixels of the original image 601, the pixel positions affected by the saturated pixels are as shown in FIG. 6 on the blurred image 602. All these pixels are treated as saturated pixels on the band limited image 603.

The adjustment unit 203 calculates the average power in each band using the saturated pixel detection result of the band limited image in S406 (S407). The average power is the root mean square of the pixel values of the band limited image. As the average power, in the present embodiment, calculates the average power P _Lvs in the saturation pixel regions, the average power two of the P _Lvn in normal pixel region (image other than the partial image is a saturated pixel area). Here, the saturated pixel region refers to a partial image composed of saturated pixels of the band limited image. Also, let sb _Lv (x, y) be a function representing the saturation pixel detection result at coordinates (x, y). sb _Lv (x, y) takes a value of 1 for saturated pixels and 0 for normal pixels. _Assuming that the image size of the band limited image is w _Lv × h _Lv , the average power is expressed by the following equations (3) and (4).

ただし、Ｎ_sはsb_Lv＝１となる画素の総数、Ｎ_nはsb_Lv＝０となる画素の総数である。

Here, N _s is the total number of pixels where sb _Lv = 1, and N _n is the total number of pixels _where sb _Lv = 0.

Next, the adjustment unit 203 adjusts the saturated pixels of the band limited image using the average power obtained in S407 (S408). Since the contrast of the saturated pixel region is lower than the contrast of the normal pixel region, the value of the saturated pixel is adjusted so as to maintain the same contrast as the normal pixel region. Specifically, when the adjusted band limited image is H _Lv ′, the contrast of the band limited image is adjusted based on Equation 6.

すなわち、調整部２０３は、帯域制限画像の飽和画素からなる部分画像の各画素値に対してＰ_Lvn／Ｐ_Lvsを乗じることにより該画素値を調整する。

That is, the adjustment unit 203 adjusts the pixel value by multiplying each pixel value of the partial image including the saturated pixels of the band limited image by P _Lvn / P _Lvs .

Next, the reconstruction unit 204 reconstructs the entire image using the band limited image H _Lv ′ adjusted in S408 (S409). Specifically, the original image is reconstructed by adding the decomposed band-limited images. That is, by adding the adjusted band-limited images, an original image S _org ′ with reduced influence of saturated pixels is reconstructed. Assuming that the image with the lowest band-limited frequency is L, the relationship with the original image S _org ′ in which the influence of saturated pixels is reduced is as shown in _Equation 6.

ただし、LvMaxは最大分解レベルである。再構成された画像Ｓ_org'は、図３に示すコントロールＰＣ３０１が幾何変換等の後処理を行い（Ｓ４１０）、表示装置３０９やネットーワークＩ／Ｆ３１２を介して外部装置等へ出力する（Ｓ４１１）。

However, LvMax is the maximum decomposition level. The reconstructed image S _org ′ is subjected to post-processing such as geometric transformation by the control PC 301 shown in FIG. 3 (S410), and is output to an external device or the like via the display device 309 or the network I / F 312 (S411). .

  As described above, the X-ray image processing apparatus according to the present embodiment detects, as a saturated pixel, a pixel having an incident dose with respect to an imaging element equal to or greater than a predetermined value for a captured image, and the contrast of a partial image including the saturated pixel is captured. adjust. In the present embodiment, the captured image is decomposed into a plurality of band limited images that are limited to different frequency bands, the contrast is adjusted for each of the band limited images (except for the image with the lowest frequency), and the image is reproduced again. Configure. As described above, in this embodiment, the contrast of the saturated pixel region is adjusted for each band-limited image, so that the contrast adjustment can be performed efficiently and effectively. Therefore, as a result of adjusting the contrast of saturated pixels to the contrast of normal pixels in each band limited image, an image in which a decrease in contrast due to saturated pixels is reduced is generated.

(Embodiment 2)
In the first embodiment, the type of pixel is classified into two, that is, a saturated pixel and a normal pixel in S404, but in this embodiment, the saturation pixel is classified more finely, thereby realizing an appropriate correction more suitable for the characteristics of the pixel. To do. The processing procedure of this embodiment will be described along the flow of processing using the configuration diagram of FIG. 2 and the overall flow of FIG.

The processing in S401 and S402 is the same as that in the first embodiment. In S403, the detection unit 201 determines a saturated pixel value. Although one saturated pixel value is detected in the first embodiment, a plurality of saturated pixel values are detected in the present embodiment. Similar to the first embodiment, the relationship between the sensor output value F and the X-ray dose u is approximated to obtain an approximate expression of the slope M. Then, the sensor output value is differentiated by the X-ray dose. Let N _max be the number of saturated pixel values to be detected, and N = 1, 2,. . . , N _max , the minimum u satisfying Equation 7 is defined as a saturation dose u _s (N).

N = 1, 2,. . . , N _max , a sensor output value for the saturated dose u _s (N) is calculated, and the value is set as a saturated pixel value Fs (N). Here, since the sensor output value F generally increases monotonously with respect to the X-ray dose u, the value of Fs (N) increases as N increases. When a plurality of saturated pixel values are determined, a pixel value having a value not less than the saturated pixel value Fs (N) and less than Fs (N + 1) in the original image is detected as the saturated pixel N (S404). There is no upper limit for the maximum N (N _max ). That is, a pixel having a pixel value greater than or equal to Fs (N _max ) is detected as the saturated pixel N _max . For example, when N = 2, first and second predetermined values are determined in advance as saturated pixel values, and pixels whose incident dose is greater than or equal to the first predetermined value and less than the second predetermined value are first saturated. A pixel having an incident dose equal to or higher than the second predetermined value is detected as a second saturated pixel.

S405 is the same as that in the first embodiment. In S406, the adjustment unit 203 detects a saturated pixel on the band limited image for each of N _max types of saturated pixels. Although the detection method is the same as that in the first embodiment, in the present embodiment, when there are pixels of a blurred image affected by a plurality of types of saturated pixels, the saturated pixel having the greatest influence is selected. For example, the maximum number of types existing in the filter may be selected, or the largest N that most affects the contrast may be selected.

In S407, the adjustment unit 203 calculates the average power P _Lvs (N) of each saturated pixel region for each of N _max types of saturated pixels. In step S <b> 408, the adjustment unit 203 adjusts the value of each saturated pixel so that the same contrast as that of the normal pixel region is maintained for each of N _max types of saturated pixel regions. S409 to S411 are the same as those in the first embodiment.

  As shown in the sensor characteristics of FIG. 1, since the gradient in the saturated pixel region is not constant, the reduction in contrast is not uniform. Therefore, rather than correcting the contrast uniformly, it is possible to correct more appropriately by dividing the correction into a plurality of saturated pixel ranges in this way.

(Embodiment 3)
FIG. 7 is a block diagram illustrating a functional configuration of the X-ray image processing apparatus according to the present embodiment. The X-ray image processing apparatus of this embodiment includes a detection unit 701, a decomposition unit 702, an adjustment unit 703, a reconstruction unit 704, and an area division unit 705. Functions of the functional elements 701 to 704 are the same as those of 201 to 204 in FIG. An area dividing unit 705 receives an image obtained by performing predetermined preprocessing on the X-ray image acquired by the X-ray sensor 302 in FIG. 3, divides the image into a plurality of areas, and outputs a division result. The area dividing unit 705 is stored in the storage unit 307 as a software module, similarly to 701 to 704. Of course, all or part of 701 to 705 may be mounted as a dedicated image processing board. Appropriate implementation may be performed according to the purpose and purpose.

  In the first and second embodiments, the average power of the saturated pixel region is calculated in S407, and the value of the saturated pixel is adjusted so that the same contrast as that of the normal pixel region is maintained in S408. In the present embodiment, a more appropriate correction is realized by dividing the saturated pixel region and the normal pixel region in more detail according to the characteristics of the image. The processing procedure in the present embodiment will be described along the processing flow with reference to the configuration diagram of FIG. 7 and the entire flow of FIG.

  S801 to S804 are the same as S401 to S404 of the first embodiment. In step S805, the area dividing unit 705 divides the original image into a plurality of areas. The regions to be divided are basically a collimation region, a blank region, and a subject region, and the subject region is further divided anatomically based on pixel values. The anatomical division of an image means that a divided region is defined according to an organ (for example, lung field, mediastinum, bone, organ, etc.) constituting a human body as a subject, and the image is divided for each organ. . The method of area division is not particularly limited, and any method can be used.

  An example of a method for recognizing a collimation region is described in Japanese Patent Publication No. 5-049143. The collimation region refers to a region (outside of the irradiation field) where X-rays are not irradiated by the collimator. In this method, the X axis and the Y axis are set along two adjacent sides of the outline of the rectangular field, and the image data is added and summed in the set X axis direction and Y axis direction. Here, the addition total data in the irradiation field is higher than that in the irradiation field where X-rays are hardly irradiated. Therefore, a position on the Y axis where the sum total data in the X axis direction is equal to or greater than a predetermined threshold TH and a position on the X axis where the sum total data in the Y axis direction is equal to or greater than the predetermined threshold TH are calculated. Then, a rectangular area surrounded by the straight line in the X-axis direction at the calculated position on the Y-axis and the straight line in the Y-axis direction at the position on the X-axis is set as the irradiation field, and the others are set as the collimation areas.

  Next, an example of extracting the background region will be described. The blank region is a region where the irradiated X-rays reach the sensor directly without passing through the subject. For example, when an image histogram is calculated, the background missing area is concentrated in the high pixel value area. Therefore, an area of several percent from the high pixel value side of the histogram range corresponds to the blank area. By removing such a region, the blank region can be removed. In this way, the remainder obtained by removing the obtained collimation area and the missing area from the original image becomes the subject area.

  Furthermore, the subject area can be divided anatomically based on the pixel values. For example, segmentation may be performed depending on the pixel value using Otsu's discriminant analysis method (binarization of Otsu) or the like. Alternatively, the subject region may be divided by a method of performing clustering such as k-means from an image feature amount or a method using a learning type algorithm.

Steps S806 and S807 are the same as steps S405 to S406 of the first embodiment, and thus are omitted. In S808, the adjustment unit 703 calculates the average power in each band using the region division result in S805 and the saturated pixel detection result of the band limited image in S807. That is, the average power P _Lvs (K, N) in the saturation pixel region divided within the region for each region and the average power P _Lvn (K, N) in a normal pixel region (saturation pixel region out) is calculated . Here, if the number of area divisions is K _max and the number of detected saturated pixel values is N _max , K = 1, 2,. . . , K _max , N = 1, 2,. . . , N _max .

In step S809, the adjustment unit 703 adjusts the value of each saturated pixel so that the same contrast as that of the normal pixel region is maintained for each saturated pixel region having the division number K _max and the detection number N _max . Steps S810 to S812 are the same as steps 409 to 411 of the first embodiment, and will be omitted.

  The contrast in the image differs depending on the irradiation field in the image, the position of the subject, and the area occupied by the organs constituting the human body. Therefore, rather than correcting the contrast uniformly, the input image is divided into a plurality of regions as in the present embodiment, and the contrast of the band-limited image is adjusted for each region, so that more appropriate correction can be performed. it can.

(Embodiment 4)
FIG. 9 is a block diagram illustrating a functional configuration of the X-ray image processing apparatus according to the present embodiment. The X-ray image processing apparatus of this embodiment includes a detection unit 901, a decomposition unit 902, an adjustment unit 903, a reconstruction unit 904, and a difference unit 905. Reference numerals 901 to 904 are the same as 201 to 204 in the configuration diagram of FIG. The difference unit 905 receives two images obtained by performing predetermined preprocessing on the X-ray image acquired by the X-ray sensor 302 in FIG. 3, performs difference processing between the images, and outputs a difference image. The difference unit 905 is stored in the storage unit 307 as a software module, similarly to 901 to 904. Of course, 901 to 905 may be mounted as a dedicated image processing board. What is necessary is just to perform the optimal mounting according to the objective.

  In the first to third embodiments, the processing for the original image has been described. In the present embodiment, image processing using a difference image will be described. The difference image is a time difference image or a DSA (Digital Subtraction Angiography) image. The image processing using the difference image will be described along the flow of processing using the configuration diagram of FIG. 9 and the entire flow of FIG. In the present embodiment, a case will be described in which a difference image is acquired based on two images acquired at a short interval for the same subject. For example, a difference image can be acquired from a mask image and a live image in DSA.

S1001 to S1004 perform the same processing as S401 to S404 of the first embodiment, but in S1001, two images are acquired by the X-ray sensor 302, and each image is individually processed. When the original image 1 and the original image 2 are output in S1002, the difference unit 905 generates a difference image by subtracting the original image 2 from the original image 1 in S1005. _Assuming that the original image 1 is S _org1 and the original image 2 is S _org2 , the difference image D is as shown in _Equation 8.

  In S1006, the decomposition unit 902 creates a plurality of frequency band-limited images from the difference image D calculated in S1005. This process is the same as S405. In step S1007, the adjustment unit 903 detects a saturated pixel on the band-limited image using the detection result of the saturated pixel in step S1004. The saturated pixel on the band limited image is a pixel in which the pixel generated using the saturated pixel of the difference image is in the same position in the blurred image used to create the band limited image. It is assumed that the saturation pixel of the difference image is a logical sum of the saturation pixel of the original image 1 and the saturation pixel of the original image 2. That is, of the pixels of the original image 1 or the pixels of the original image 2, pixels having an incident dose equal to or higher than a predetermined value are detected as saturated pixels. Assuming that the filter size of the blurred image is N, an N × N region centered on the saturation pixel of the difference image is set as the saturation pixel. In steps S1008 to S1012, the same processing as that in steps S407 to S411 of the first embodiment is performed on one of the original image 1 and the original image 2.

  The influence of saturated pixels in the difference image is affected by the saturated pixels of the two images. Therefore, as in this embodiment, a plurality of band limited images are generated based on the difference image between two consecutive captured images, and the contrast is adjusted for each saturated pixel of the two captured images in each of the plurality of band limited images. . As described above, in the present embodiment, more optimal correction can be performed by considering the influence of two images.

(Embodiment 5)
In the fourth embodiment, the value of each saturated pixel is adjusted so that the same contrast as that of the normal pixel region is maintained for all band limited images in S1009. However, in this embodiment, the degree of correction is changed for each band limited image. To do. The processing procedure of this embodiment will be described along the flow of processing with reference to the configuration diagram of FIG. 9 and the entire flow of FIG.

  Steps S1001 to S1008 are the same as those in the fourth embodiment, and will be omitted. In S1009, the adjustment unit 903 adjusts the value of each saturated pixel so that the same contrast as that of the normal pixel region is maintained for each saturated pixel region.

  When X-ray images are acquired continuously like a moving image, all the charges accumulated in the (N-1) th frame may remain in the Nth frame without being released. When the X-ray sensor 302 of FIG. 3 is a sensor that needs to perform intermittent dark correction, this residual charge is added to the dark image of the Nth frame. In the present embodiment, this added amount is used as an offset component. If an offset component exists in the dark image, the value of the X-ray image output after dark correction becomes smaller by the offset component. Assuming that the sensor output value when the offset component is not present is the sensor output value 1, and the sensor output value when the offset component is present is the sensor output value 2, the relationship is as shown in FIG. In FIG. 11, the horizontal axis represents the number of frames, and the vertical axis represents the sensor output value. In the example of FIG. 11, the X-ray dose increases at a constant amount as the number of frames increases. Therefore, the sensor output value 1 approaches a constant value from the frame in which the X-ray dose exceeds the saturation dose. On the other hand, when the sensor output value 2 exceeds the saturation dose for a while, the sensor output value decreases. This is because the offset component increases while the amplifier and the photodiode are saturated, resulting in a decrease in the sensor output value. In such a case, the output value exceeding the saturation dose is difficult to use for diagnosis. However, when a differential image such as a DSA image is used, the information on the difference value is used instead of the information on the output value itself.

  Therefore, in this embodiment, when adjusting the contrast in S1009, the contrast is adjusted by weighting each band-limited image so as not to be affected by the output value. When the weight is wgt, the following formula 9 is obtained.

  As the weight wgt, for example, a function that approaches 1 as the value of Lv decreases and approaches 0 as the value of Lv increases and that has a shape like a sigmoid function that is inverted up and down can be used. The high frequency component including detailed position information is increased, and the low frequency component that is easily affected by the pixel value information is decreased. The low frequency component may be zero. In that case, a method may be used in which the reconstruction unit performs reconstruction in S1010 except for the band-limited image in the low frequency band. Since S1010 to S1012 are the same as those in the fourth embodiment, a description thereof will be omitted.

  In the case of an X-ray sensor that requires intermittent dark correction, it is affected by an offset component. Therefore, more appropriate correction can be performed by considering the influence when adjusting the contrast in the band-limited image. That is, in the present embodiment, it is possible to make it easier to visually read the information included in the saturated pixel region by adjusting the contrast of the band limited image of a larger frequency band to a greater degree.

  As described above, in each embodiment of the present invention, it is possible to output an image suitable for diagnosis by appropriately adjusting the contrast of pixels exceeding the saturation dose.

<< Other Embodiments >>
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, etc.) of the system or apparatus reads the program. It is a process to be executed.

201: detection unit, 202: decomposition unit, 203: adjustment unit, 204: reconstruction unit

Claims (12)

An image processing apparatus that performs image processing on a photographed image photographed using a plurality of imaging elements,
Decomposition means for decomposing the captured image into a plurality of band limited images limited to different frequency bands;
With respect to the captured image, detection means for detecting a pixel having an incident dose on the image sensor of a predetermined value or more as a saturated pixel,
Adjusting means for adjusting the contrast of the partial image composed of saturated pixels of the band-limited image;
An image processing apparatus comprising: a reconstruction unit configured to reconstruct an image using the plurality of band-limited images whose contrasts are adjusted.   The predetermined value is a value indicating a non-linear characteristic between an incident dose and an output value when the dose greater than the predetermined value is incident on the image sensor. An image processing apparatus according to 1. The adjusting unit is configured to determine a partial image including the saturated pixels based on an average power P _{Lvs of a} partial image including the saturated pixels of the band limited image and an average power P _Lvn of an image other than the partial image of the band limited image. The image processing apparatus according to claim 1, wherein the pixel value is adjusted. 4. The image according to claim 3, wherein the adjustment unit adjusts the pixel value by multiplying each pixel value of a partial image including saturated pixels of the band-limited image by P _Lvn / P _Lvs. Processing equipment. The detection means detects a pixel having an incident dose to the image sensor of a first predetermined value or more and less than a second predetermined value as a first saturated pixel, and detects a pixel having an incident dose of a second predetermined value or more. 2 as a saturated pixel,
The said adjustment means adjusts contrast about each of the partial image which consists of a said 1st saturated pixel, and the partial image which consists of a said 2nd saturated pixel, The any one of Claim 1 to 4 characterized by the above-mentioned. The image processing apparatus according to item. Further comprising a dividing means for dividing the photographed image into a plurality of regions in accordance with organs constituting a human body as a subject;
The image processing apparatus according to claim 1, wherein the adjustment unit adjusts a contrast of the band-limited image for each region.   The image processing apparatus according to claim 1, wherein the adjustment unit adjusts the contrast to a greater degree for a band-limited image having a larger frequency band. The decomposing means decomposes the first captured image into a plurality of band-limited images based on the difference between the first and second captured images captured continuously,
The detection means detects, as a saturated pixel, a pixel having an incident dose equal to or higher than the predetermined value among the pixels of the first photographed image or the pixels of the second photographed image,
The adjustment unit adjusts the contrast of the partial image including the saturated pixels for the band limited image of the first captured image,
The image processing according to any one of claims 1 to 7, wherein the reconstruction unit reconstructs an image using the band-limited image of the first photographed image whose contrast has been adjusted. apparatus.   The image processing apparatus according to claim 1, wherein the reconstructing unit reconstructs an image by adding a plurality of the band limited images whose contrasts are adjusted. An X-ray generator for irradiating X-rays;
An X-ray sensor comprising a plurality of image sensors for detecting X-rays emitted from the X-ray generator, and forming a captured image;
An image processing system comprising: the image processing apparatus according to claim 1, which performs image processing on a captured image formed by the X-ray sensor. A control method for an image processing apparatus that performs image processing on a captured image captured using a plurality of image sensors,
A decomposing step of decomposing the captured image into a plurality of band limited images limited to different frequency bands;
A detecting step for detecting, as a saturated pixel, a pixel having an incident dose on the image sensor of a predetermined value or more with respect to the captured image;
An adjusting step for adjusting the contrast of the partial image composed of saturated pixels of the band-limited image;
A method for controlling an image processing apparatus, comprising: a reconstruction unit configured to reconstruct an image using the plurality of band-limited images whose contrasts are adjusted.   The computer program for functioning a computer as each means with which the image processing apparatus of any one of Claim 1 to 9 is provided.

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