WO2019150731A1

WO2019150731A1 - Image processing device and image processing method and program

Info

Publication number: WO2019150731A1
Application number: PCT/JP2018/043717
Authority: WO
Inventors: 竹中　克郎; 尚志郎猿田; 聡太鳥居
Original assignee: キヤノン株式会社
Priority date: 2018-02-02
Filing date: 2018-11-28
Publication date: 2019-08-08
Also published as: JP2019134387A

Abstract

The image processing device is provided with: an acquisition unit for acquiring a radiographic image including a pixel to be corrected; a calculation unit for calculating the respective priorities of two directions intersecting with each other at the pixel to be corrected; and a determination unit for determining a pixel value of the pixel to be corrected by applying greater weighting to the pixel values of pixels along the direction of higher priority with respect to the pixel to be corrected and applying lesser weighting to the pixel values of pixels along the direction of lower priority with respect to the pixel to be corrected. When, for the calculation of the respective priorities of the two directions, the direction of calculation out of the two directions is defined as a first direction and the other direction as a second direction, the calculation unit uses the pixel values of multiple pixels including first pixels adjacent to the pixel to be corrected, second pixels adjacent to the first pixels in the first direction, and third pixels located on the opposite side from the first pixels or the second pixels with respect to a straight line extending in the second direction through the pixel to be corrected.

Description

Image processing apparatus, image processing method, and program

The present invention relates to an image processing apparatus, an image processing method, and a program.

As an imaging apparatus used for medical image diagnosis and nondestructive inspection, there is a radiation imaging apparatus including an imaging panel in which pixels in which a combination of a conversion element that converts radiation into electric charge and a switching element such as a thin film transistor (TFT) are arranged in an array It's being used. In such a radiation imaging apparatus, there is a defective pixel that does not output a normal signal due to an abnormality of the conversion element or the switch element. In addition, an optical black pixel is also formed by providing a light shielding layer on the conversion element. Patent Document 1 describes a technique for correcting such defective pixels and optical black pixels by image processing.

JP 2002-33964 A

In Patent Document 1, curvature information is used to determine a pixel direction to be prioritized when correcting a target pixel. The curvature information is calculated using information on a pixel that is one pixel away from the correction target pixel. For this reason, the correction direction may not be correctly calculated for an image with many high-frequency components. One aspect of the present invention provides a technique for accurately correcting a target pixel.

In view of the above problems, an image processing apparatus, an acquisition unit that acquires a radiation image including a correction target pixel, and a calculation unit that calculates the respective priorities of two directions intersecting each other with respect to the correction target pixel; Assigning a large weight to the pixel value of the pixel in the higher priority direction for the correction target pixel, and assigning the small weight to the pixel value of the pixel in the lower priority direction to the correction target pixel And determining means for determining a pixel value of the correction target pixel, wherein the calculation means sets the direction of the calculation target among the two directions in calculating the priority of each of the two directions. A first pixel adjacent to the correction target pixel, a second pixel adjacent to the first pixel in the first direction, and a front direction when the first direction is a second direction and the other direction is a second direction. Image processing using pixel values of a plurality of pixels including the first pixel or a third pixel on the opposite side of the second pixel with respect to a straight line passing through the correction target pixel in the second direction An apparatus is provided.

By the above means, a technique for accurately correcting the target pixel is provided.

Other features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings. In the accompanying drawings, the same or similar components are denoted by the same reference numerals.

The accompanying drawings are included in the specification, constitute a part thereof, show an embodiment of the present invention, and are used to explain the principle of the present invention together with the description.
The figure which shows the structural example of the radiation imaging system which concerns on 1st Embodiment. The figure which shows the structural example of the imaging panel of the radiation imaging device which concerns on 1st Embodiment. The figure which shows the structural example of the cross section of the pixel of the radiation imaging device which concerns on 1st Embodiment. The timing chart which shows operation | movement of the radiation imaging device which concerns on 1st Embodiment. The figure which shows the operation | movement flow of the radiation imaging device which concerns on 1st Embodiment. The figure explaining the correction method of the radiation imaging device concerning a 1st embodiment. The figure explaining the effect of correction of the radiation imaging device concerning a 1st embodiment. The figure explaining the effect of correction of the radiation imaging device concerning a 1st embodiment. The figure explaining the effect of correction of the radiation imaging device concerning a 1st embodiment. The figure explaining the effect of correction of the radiation imaging device concerning a 1st embodiment. The figure which shows the structural example of the imaging panel of the radiation imaging device which concerns on 2nd Embodiment. The figure which shows the structural example of the cross section of the pixel of the radiation imaging device which concerns on 2nd Embodiment. The figure which shows the structural example of the cross section of the pixel of the radiation imaging device which concerns on 2nd Embodiment. The figure which shows the operation | movement flow of the radiation imaging device which concerns on 2nd Embodiment. The figure explaining the correction method of the radiation imaging device concerning a 2nd embodiment.

<First Embodiment>
Hereinafter, specific embodiments of a radiation imaging apparatus according to the present invention will be described with reference to the accompanying drawings. In the following description and drawings, common reference numerals are given to common configurations throughout the drawings. Therefore, a common configuration is described with reference to a plurality of drawings, and a description of a configuration with a common reference numeral is omitted as appropriate. In this specification, the radiation includes α-rays, β-rays, γ-rays, and the like, which are beams generated by particles (including photons) emitted by radiation decay, such as X-rays, It can also include particle beams, cosmic rays, and the like.

The configuration and operation of the radiation imaging apparatus according to the first embodiment will be described with reference to FIGS. FIG. 1 is a diagram illustrating a configuration example of a radiation imaging system 200 using the radiation imaging apparatus 210 in the first embodiment. The radiation imaging system 200 is configured to electrically capture an optical image converted from radiation and obtain an electrical signal (radiation image data) for generating a radiation image. The radiation imaging system 200 includes, for example, a radiation imaging apparatus 210, a radiation source 230, an exposure control unit 220, and a computer 240.

The radiation source 230 starts radiation emission according to an exposure command (radiation command) from the exposure control unit 220. The radiation emitted from the radiation source 230 passes through a subject (not shown) and is irradiated on the radiation imaging apparatus 210. The radiation source 230 also stops radiation emission according to a stop command from the exposure control unit 220.

The radiation imaging apparatus 210 includes an imaging panel 212 and a control unit 214 that controls the imaging panel 212. The control unit 214 generates a stop signal for stopping radiation emission from the radiation source 230 based on a signal obtained from the imaging panel 212. The stop signal is supplied to the exposure control unit 220. The exposure control unit 220 sends a stop command to the radiation source 230 in response to the stop signal. The controller 214 is, for example, a PLD (Programmable Logic Device) such as an FPGA (Field Programmable Gate Array), an ASIC (Application Specific Integrated Circuit), a general-purpose computer in which a program is incorporated, or all or one of them. It can be configured by a combination of parts.

The computer 240 controls the radiation imaging apparatus 210 and the exposure control unit 220. In addition, the computer 240 receives the radiation image data output from the radiation imaging apparatus 210 and processes the radiation image data to generate a radiation image. Therefore, the computer 240 functions as an image processing device. The computer 240 includes a processor 241 and a memory 242. The processor 241 functions as a CPU that controls the overall operation of the computer 240. The processor 241 controls the radiation imaging apparatus 210 and the exposure control unit 220 described above and generates a radiation image. The memory 242 holds a program. When the processor 241 executes the program held in the memory 242, processing by the computer 240 is performed.

The exposure control unit 220 has an exposure switch (not shown) as an example. When the exposure switch is turned on by the user, the exposure control unit 220 sends an exposure command to the radiation source 230 and starts indicating the start of radiation emission. A notification is sent to the computer 240. Upon receiving the start notification, the computer 240 notifies the control unit 214 of the radiation imaging apparatus 210 of the start of radiation emission in response to the start notification.

FIG. 2 shows a configuration example of the imaging panel 212. The imaging panel 212 includes a pixel array 112. The pixel array 112 includes conversion elements S11 to S44 (hereinafter collectively referred to as conversion elements S) and switch elements T11 to T44 (hereinafter collectively referred to as switch elements T) arranged in a two-dimensional array for detecting radiation. ) Including a plurality of pixels PIX. The pixel array 112 includes a plurality of column signal lines Sig1 to Sig4 along the column direction (vertical direction in FIG. 2) for outputting the signal generated by the conversion element S. Further, the imaging panel 212 includes a drive circuit (row selection circuit) 114 that drives the pixel array 112 and a readout circuit 113 for detecting a signal that appears on the column signal line Sig of the pixel array 112. In the configuration shown in FIG. 2, for simplification of description, the pixel array 112 is configured by 4 rows × 4 columns of pixels PIX, but in reality, more pixels PIX can be arranged. In one example, the imaging panel 212 may have dimensions of 17 inches and may have approximately 3000 rows by approximately 3000 columns of pixels PIX.

Each pixel PIX includes a conversion element S for detecting radiation, and a switch element T that connects the conversion element S and a column signal line Sig (a signal line Sig corresponding to the conversion element S among the plurality of signal lines Sig). Including. Each conversion element S outputs a signal corresponding to the amount of incident radiation to the column signal line Sig. The conversion element S may be, for example, a MIS photodiode that is disposed on an insulating substrate such as a glass substrate and uses amorphous silicon as a main material. Further, the conversion element S may be a PIN photodiode. In the present embodiment, the conversion element S can be configured as an indirect element that detects light after the radiation is converted into light by the scintillator layer. In the indirect element, the scintillator layer can be shared by a plurality of pixels PIX (a plurality of conversion elements S).

The switch element T can be constituted by a transistor such as a thin film transistor (TFT) having a control terminal (gate) and two main terminals (source, drain), for example. The conversion element S has two main electrodes, one main electrode of the conversion element S is connected to one of the two main terminals of the switch element T, and the other main electrode of the conversion element S is common. Are connected to a bias power source via a bias line Bs. The bias power supply supplies a bias voltage. The control terminal of the switch element T of each pixel PIX arranged in the first row is connected to the gate line Vg1 arranged along the row direction (lateral direction in FIG. 2). Similarly, the control terminals of the switches S of the pixels PIX arranged in the second to fourth rows are connected to the gate lines Vg2 to Vg4, respectively. A gate signal is supplied to the gate lines Vg1 to Vg4 by the drive circuit 114.

In each pixel PIX arranged in the first column, the main terminal of the switch element T that is not connected to the conversion element S is connected to the column signal line Sig1 in the first column. Similarly, in each pixel PIX arranged in the second to fourth columns, the main terminal on the side not connected to the conversion element S of the switch element T is connected to the column signal lines Sig2 to Sig4 in the second to fourth columns, respectively. The

The read circuit 113 has a plurality of column amplifiers CA so that one column amplifier CA corresponds to one column signal line Sig. Each column amplifier CA may include an integrating amplifier 105, a variable amplifier 104, a sample hold circuit 107, and a buffer circuit 106. The integrating amplifier 105 amplifies the signal appearing on the column signal line Sig. The integrating amplifier 105 can include an operational amplifier and an integrating capacitor and a reset switch connected in parallel between the inverting input terminal and the output terminal of the operational amplifier. A reference potential Vref is supplied to the non-inverting input terminal of the operational amplifier. The integration capacitor is reset by turning on the reset switch, and the potential of the column signal line Sig is reset to the reference potential Vref. The reset switch can be controlled by a reset pulse RC supplied from the control unit 214.

The variable amplifier 104 amplifies the signal output from the integrating amplifier 105 with a set amplification factor. The sample hold circuit 107 samples and holds the signal output from the variable amplifier 104. The sample hold circuit 107 can be configured by a sampling switch and a sampling capacitor. The buffer circuit 106 buffers the signal output from the sample hold circuit 107 (impedance conversion) and outputs the result. The sampling switch can be controlled by a sampling pulse SH supplied from the control unit 214.

Further, the readout circuit 113 includes a multiplexer 108 that selects and outputs signals from a plurality of column amplifiers CA provided in correspondence with each column signal line Sig in a predetermined order. The multiplexer 108 includes, for example, a shift register. The shift register performs a shift operation in accordance with the clock signal CLK supplied from the control unit 214, and one signal from the plurality of column amplification units CA is selected by the shift register. Read circuit 113 further includes a buffer 109 for buffering (impedance conversion) the signal output from multiplexer 108 and an AD converter 110 for converting an analog signal output from buffer 109 into a digital signal. sell. The output of the AD converter 110, that is, radiation image data is transferred to the computer 240.

FIG. 3 schematically shows an example of a cross-sectional structure of the pixel PIX having the conversion element S. Here, a configuration in which radiation is incident from the upper side of the drawing will be described, but radiation may be incident from the lower side of the drawing.

The conversion element S of each pixel PIX is disposed on an insulating substrate 310 such as a glass substrate. Each pixel PIX includes a conductive layer 311, an insulating layer 312, a semiconductor layer 313, an impurity semiconductor layer 314, and a conductive layer 315 in order from the side closer to the substrate 310 on the substrate 310. The conductive layer 311 constitutes a gate electrode of a transistor (for example, TFT) constituting the switch element T. The insulating layer 312 is disposed so as to cover the conductive layer 311, and the semiconductor layer 313 is disposed on a portion of the conductive layer 311 that constitutes the gate electrode with the insulating layer 312 interposed therebetween. The impurity semiconductor layer 314 is disposed on the semiconductor layer 313 so as to constitute two main terminals (source and drain) of the transistor constituting the switch element T. The conductive layer 315 constitutes a wiring pattern connected to each of two main terminals (source and drain) of the transistor constituting the switch element T. A part of the conductive layer 315 constitutes the column signal line Sig, and the other part constitutes a wiring pattern for connecting the conversion element S and the switch element T.

Each pixel PIX further includes an interlayer insulating film 316 that covers the insulating layer 312 and the conductive layer 315. The interlayer insulating film 316 is provided with a contact plug 317 for connecting to a portion of the conductive layer 315 constituting the switch element T. Each pixel PIX includes a conversion element S disposed on the interlayer insulating film 316. In the example illustrated in FIG. 3, the conversion element S is configured as an indirect conversion element that converts light converted from radiation in the scintillator layer 904 into an electrical signal. The conversion element S includes a conductive layer 318, an insulating layer 319, a semiconductor layer 320, an impurity semiconductor layer 321, a conductive layer 322, and an electrode layer 325 stacked on the interlayer insulating film 316. A protective layer 323 and an adhesive layer 324 are disposed on the conversion element S. The scintillator layer 904 is disposed on the adhesive layer 324 so as to cover the incident surface side of the substrate 310.

The conductive layer 318 constitutes the lower electrode of the individual conversion element S. In addition, the conductive layer 322 and the electrode layer 325 constitute an upper electrode of the individual conversion element S. The conductive layer 318, the insulating layer 319, the semiconductor layer 320, the impurity semiconductor layer 321, and the conductive layer 322 constitute a MIS type sensor as the conversion element S. For example, the impurity semiconductor layer 321 is formed of an n-type impurity semiconductor layer.

The scintillator layer 904 can be formed using a material such as GOS (gadolinium oxysulfide) or CsI (cesium iodide). These materials can be formed by bonding, printing, vapor deposition, or the like.

In the present embodiment, the conversion element S is an example using a MIS type sensor, but is not limited thereto. The conversion element S may be, for example, a pn type or PIN type photodiode.

Next, operations of the radiation imaging apparatus 210 and the radiation imaging system 200 will be described with reference to FIG. Here, the operation of the radiation imaging apparatus 210 having the imaging panel 212 including the pixel PIX of 4 rows and 4 columns each including the conversion element S illustrated in FIG. 2 will be described as an example. The operation of the radiation imaging system 200 is controlled by the computer 240. The operation of the radiation imaging apparatus 210 is controlled by the control unit 214 under the control of the computer 240.

First, the control unit 214 causes the drive circuit 114 and the readout circuit 113 to perform a reset operation until radiation of radiation from the radiation source 230, in other words, irradiation of radiation to the radiation imaging apparatus 210 is started. The reset operation is an operation in which the driving circuit 114 sequentially drives the gate signals supplied to the gate lines Vg1 to Vg4 in the respective rows of the pixel array 112 to the active level to reset the dark charges accumulated in the conversion elements S. That is. Here, during the reset operation, the reset pulse RC of the active level is supplied to the reset switch of the integrating amplifier 105, and the column signal line Sig is reset to the reference potential. The dark charge is a charge that is generated even though no radiation is incident on the conversion element S.

The control unit 214 can recognize the start of radiation emission from the radiation source 230 based on, for example, a start notification supplied from the exposure control unit 220 via the computer 240. Further, the radiation imaging apparatus 210 may be provided with a detection circuit that detects a current flowing through the bias line Bs or the column signal line Sig of the pixel array 112. The controller 214 can recognize the start of radiation irradiation from the radiation source 230 based on the output of the detection circuit.

When irradiated with radiation, the control unit 214 controls the switch element T to be in an open state (off state). As a result, charges generated in the conversion element S due to radiation irradiation are accumulated. The control unit 214 stands by in this state until radiation irradiation is completed.

Next, the control unit 214 causes the drive circuit 114 and the read circuit 113 to perform a read operation. The read operation is an operation in which the drive circuit 114 drives the gate signals supplied to the gate lines Vg1 to Vg4 in each row of the pixel array 112 to the active level. Then, the readout circuit 113 reads out the electric charge accumulated in the conversion element S via the column signal line Sig, and outputs it as radiation image data to the computer 240 through the multiplexer 108, the buffer 109, and the AD converter 110.

Next, the acquisition of offset image data will be described. The conversion element S continues to accumulate dark charges even in a state where no radiation is irradiated. For this reason, the control part 214 acquires offset image data by performing the same operation | movement as acquiring radiation image data, without irradiating a radiation. By subtracting the offset image data from the radiation image data, the offset component due to the dark charge can be removed.

Next, the image processing flow in this embodiment will be described with reference to FIG. First, in step S910, after performing the above-described reset operation, the control unit 214 performs control so as to accumulate charges generated by the conversion element S during radiation irradiation in order to acquire radiation image data. Next, in step S911, the control unit 214 causes the drive circuit 114 and the readout circuit 113 to perform a readout operation, and reads out radiation image data. In step S911, radiation image data is output to the computer 240. Next, the control unit 214 performs an accumulation operation for acquiring offset image data in step S912. In step 913, the control unit 214 causes the drive circuit 114 and the readout circuit 113 to read the offset image data, and causes the computer 240 to output the offset image data.

Next, in step S914, the processor 241 of the computer 240 performs offset correction by subtracting the offset image data acquired in step S913 from the radiation image data acquired in step S911. In step S915, the processor 241 performs gain correction by dividing the image data after the offset correction by the gain correction image data acquired in advance. In this way, the processor 241 acquires a radiation image. As will be described later, this radiation image includes correction target pixels. The correction target pixel is a significant pixel such as a defective pixel that outputs an abnormal pixel value generated when the pixel array 112 or the scintillator layer 904 is manufactured, or an optical black pixel that is intentionally arranged. A pixel that does not have a value. The processor 241 may acquire a radiation image by reading out a radiation image generated by the radiation imaging apparatus 210 and then stored in an external storage device.

Subsequently, in step S916, the processor 241 corrects the correction target pixel included in the radiation image. Specifically, in step S917, the processor 241 calculates the priorities of the two directions that intersect each other for the correction target pixel. Thereafter, in step S918, the processor 241 determines the pixel value of the correction target pixel based on the calculated priority.

First, the priority calculation method will be described in detail with reference to FIG. FIG. 6 is a diagram focusing on a portion including the correction target pixel in the radiation image. As shown in FIG. 6, pixels a to m and reference numerals are attached. The pixel values of the pixels a to m are also represented by a to m, respectively. For the sake of explanation, in the part shown in FIG. 6, it is assumed that the pixel to be corrected is only the pixel e, and the other pixels have significant pixel values.

The processor 241 calculates the priorities of the horizontal direction indicated by the arrow 601 and the vertical direction indicated by the arrow 602 for the pixel e. Specifically, the processor 241 calculates the horizontal priority X using the difference absolute value as follows.

ave1 = (a + b + c) / 3
ave2 = (g + h + i) / 3
S1 = | a-ave1 | + | b-ave1 | + | c-ave1 |
S2 = | g-ave2 | + | h-ave2 | + | i-ave2 |
S = (S1 + S2) / 2
X = 1 / S
In this equation, S1 is the sum of the absolute values of the differences between the pixel values of the three pixels a, b, and c and their average value ave1. That is, S1 indicates the degree of variation in pixel values of the three pixels a, b, and c arranged in the horizontal direction. The smaller the S1, the smaller the variation in the pixel values of the three pixels a, b, c. The larger the S1, the larger the variation in the pixel values of the three pixels a, b, c. S is the variation in the pixel values of the three pixels a, b, c arranged horizontally in the upper side of the pixel e, and the pixels of the three pixels g, h, i arranged horizontally in the lower side of the pixel e. It is an average with the degree of dispersion of values. That is, S indicates the degree of variation in the horizontal direction of the pixel values of the pixels around the pixel e.

Similarly, the processor 241 calculates the priority Y in the horizontal direction using the difference absolute value as follows.

When determining the pixel value of the pixel e based on the pixel values of the pixels around the pixel e, the pixel value of the pixel located in the direction with less variation is preferentially used to correct the pixel value with high accuracy. it can. Therefore, the priorities X and Y are the reciprocals of S and T, respectively. Taking the reciprocal is one method for giving negative correlation to the priorities X, Y and S, T, and other methods may be used.

Subsequently, a method for determining the pixel value of the correction target pixel based on the calculated priority will be described. Specifically, the processor 241 assigns a large weight to the pixel value of the pixel in the higher priority direction with respect to the correction target pixel, and decreases the pixel value of the pixel in the lower priority direction with respect to the correction target pixel. By assigning a weight, the pixel value of the correction target pixel is determined.

For example, the processor 241 calculates the pixel value of the pixel e by the following formula.

e = α × (d + f) / 2 + β × (b + h) / 2
However, the weights α and β are values that satisfy α + β = 1 and coincide with the magnitude relationship between the priorities X and Y.

For example, in one example, when X> Y (that is, the priority in the horizontal direction is high), α = 1 and β = 0 (that is, only the pixel values of the pixels d and f positioned in the horizontal direction of the pixel e are used). ). When X <Y (that is, the priority in the vertical direction is high), α = 0 and β = 1 (that is, only the pixel values of the pixels b and h positioned in the vertical direction of the pixel e are used). When X = Y, α = β = 0.5.

In another example
α = X / (X + Y)
β = Y / (X + Y)
To do. In this method, the weights α and β are determined according to the priority in each direction.

In order to calculate S1 indicating the degree of variation in the horizontal direction, the processor 241 uses pixel values of a plurality of pixels including the following pixels. A pixel b adjacent to the pixel e in the vertical direction, which is a direction different from the calculation target, a pixel a adjacent to the pixel b in the horizontal direction, and a pixel on the opposite side of the pixel a with respect to a straight line passing through the pixel e and extending in the vertical direction a plurality of pixels including c. The pixels g, h, i used for calculating S2 also satisfy this property. Since the pixels used for calculating the priority include the pixels adjacent to the correction coping pixels, it becomes easy to consider the influence of the high frequency component. Moreover, the influence of a stripe pattern can be included by including two or more pixels continuous in the horizontal direction. Furthermore, by including two pixels on the opposite side of the pixel a with respect to a straight line extending in the vertical direction through the pixel e, the influence of the continuity of the high-frequency component including the correction target pixel can be taken into consideration. Similarly, when calculating T1 indicating the degree of variation in the vertical direction, the processor 241 uses pixel values of a plurality of pixels including the following pixels. A pixel d adjacent to the pixel e in the horizontal direction, which is different from the calculation target, a pixel a adjacent to the pixel d in the vertical direction, and a pixel on the opposite side of the pixel a with respect to a straight line passing through the pixel e and extending in the horizontal direction g.

The effect of the correction according to the present embodiment will be described with reference to FIGS. 7A to 7D. FIG. 7A shows a radiation image that does not include a correction target pixel. Of this radiation image, the pixel value of one pixel (the black pixel at the center of the frame portion) is corrected from the pixel values of surrounding pixels by determining the priority in each direction by various methods. . FIG. 7B shows a radiographic image obtained by determining priority using a plurality of pixels (hatched pixels) that are one or more pixels away from the correction target pixel. FIG. 7C shows a radiographic image obtained by determining priority using a plurality of pixels (hatched pixels) on only one side of the correction target pixel. FIG. 7D shows a radiographic image obtained by determining priorities according to this embodiment. It can be seen that the radiographic image shown in FIG. 7D is closer to the original radiographic image (FIG. 7A) than the radiographic images shown in FIGS. 7B and 7C.

In order to calculate the priorities X and Y, the processor 241 may use the standard deviation, variance, and curvature of the pixel values of surrounding pixels in addition to the above-described absolute difference value. The processor 241 may calculate the priorities X and Y by combining at least one of these. For example, the processor 241 uses the following expression when calculating the priorities X and Y using the curvature.

X = | a−2 × b + c | + | g−2 × h + i |
Y = | a−2 × d + g | + | c−2 × f + i |
Since the pixel value of surrounding pixels has higher linearity as the curvature is smaller, the pixel value of the correction target pixel can be accurately corrected using the surrounding pixels.

The processor 241 may calculate the horizontal priority X and the vertical priority Y for the pixel e as follows.

ave5 = (k + d + f + l) / 4
S = | k-ave5 | + | d-ave5 | + | f-ave5 | + | l-ave5 |
X = 1 / S
ave6 = (j + b + h + m) / 4
T = | j-ave6 | + | b-ave6 | + | h-ave6 | + | m-ave6 |
Y = 1 / T
In this equation, in order to calculate S indicating the degree of variation in the horizontal direction, the processor 241 uses pixel values of a plurality of pixels including the following. A pixel d adjacent to the pixel e in the horizontal direction, which is the direction to be calculated, a pixel k adjacent to the pixel d in the horizontal direction, and a pixel l on the opposite side of the pixel k with respect to a straight line passing through the pixel e and extending in the vertical direction. In order to calculate T indicating the degree of variation in the vertical direction, the processor 241 calculates the pixel b adjacent to the pixel e in the vertical direction, which is the calculation target direction, the pixel j adjacent to the pixel b in the vertical direction, and the pixel e. The pixel values of a plurality of pixels including a pixel m on the opposite side of the pixel j with respect to a straight line passing through and extending in the horizontal direction are used.

In the first embodiment, the priority in the two directions of the vertical direction and the horizontal direction is calculated. However, the priority in the diagonal direction is calculated, and the pixel of the correction target pixel is calculated using the pixel located in the diagonal direction of the correction handling pixel. The value may be determined.

<Second Embodiment>
The configuration and operation of the radiation imaging apparatus according to the second embodiment will be described with reference to FIGS. A description of the same parts as those in the first embodiment is omitted. A configuration example of the radiation imaging system is the same as that shown in FIG.

9A and 9B show a configuration example of the imaging panel 212. FIG. Differences between the imaging panel 212 of the first embodiment and the imaging panel 212 of the second embodiment will be described below. On the imaging panel 212, a scintillator layer that converts radiation into visible light covers both the incident surface side on which radiation is incident and the back surface opposite to the incident surface so as to cover the respective surfaces. Arranged. The conversion element S included in each pixel PIX includes two types of conversion elements S. In the configuration shown in FIG. 8, the conversion elements S11, S12, S13, S22, S23, S24, S31, S32, S34, S41, S42, S43, and S44 receive light from scintillator layers disposed on both sides of the substrate. Arranged. Hereinafter, when a conversion element that receives light from the scintillator layers on both sides of the conversion element S is specified, it is referred to as a conversion element 901. In the conversion elements S14, S21, and S33, a light shielding layer 903 is disposed between one scintillator layer and each of the conversion elements S. Accordingly, the conversion elements S13, S21, and S33 are arranged so that light from one scintillator layer is blocked and light from the other scintillator layer is received. In the following, these conversion elements S are referred to as conversion elements 902 when a conversion element that blocks light from one scintillator layer of the conversion elements S is specified. The light-shielding layer 903 is a layer that shields light emitted from the scintillator layer, and it is only necessary to shield between the conversion element 902 and any one of the scintillator layers covering the incident surface side or the back surface side of the substrate.

In this embodiment, it is assumed that the light shielding layer 903 is disposed between the scintillator layer disposed on the incident surface side of the substrate and the conversion element 902. Of the radiation incident from the incident surface side of the substrate, the low energy component is absorbed by the scintillator layer covering the incident surface side of the substrate, converted into visible light, and incident on each pixel PIX. Since the conversion element 902 is shielded from the incident surface side of the substrate, light emitted from the scintillator layer on the incident surface side of the substrate does not enter. Therefore, light converted from a component having low radiation energy does not enter the conversion element 902. On the other hand, since the light shielding layer 903 is not disposed in the conversion element 901, light converted from a component having low radiation energy is incident.

Also, of the radiation, high energy components that are not absorbed by the scintillator layer disposed on the incident surface side of the substrate are absorbed by the scintillator layer covering the back surface side of the substrate and converted into visible light. In the conversion element 901 and the conversion element 902, since the back side of the substrate is not shielded, light converted from a component having high energy in the radiation enters both the conversion element 901 and the conversion element 902.

Thus, the conversion element 901 can acquire a signal due to a high energy component and a low energy component of radiation, and the conversion element 902 can acquire a signal due to a high energy component of radiation. That is, the information of different radiation energy can be held in the pixels PIX adjacent to each other. By holding information acquired from radiation of different energy components in adjacent pixels PIX in this way, energy subtraction can be performed using a method described later.

9A and 9B schematically show examples of cross-sectional structures of the pixel PIXA having the conversion element 901, the pixel PIXB having the conversion element 902, and the pixel PIXC. Here, the radiation is described as being incident from the upper side of the drawing, but the radiation may be incident from the lower side of the drawing. In FIG. 9A, the conversion element 901 and the conversion element 902 are arranged between the substrate 310 and the scintillator layer 904 that covers the incident surface side of the substrate 310, and in the pixel PIXB, the light shielding layer 903 includes the conversion element 902 and the scintillator layer 904. The case where it is arranged between is shown. 9B is the same as FIG. 9A in that the conversion element 901 and the conversion element 902 are arranged between the substrate 310 and the scintillator layer 904 that covers the incident surface side of the substrate 310. On the other hand, in the configuration of FIG. 9B, the pixel PIXC shows a case where the light shielding layer 903 is disposed between the conversion element 902 and the scintillator layer 905 covering the back surface opposite to the incident surface of the substrate 310.

The conversion element S of each pixel PIX is disposed on an insulating substrate 310 such as a glass substrate that transmits light emitted from the scintillator layers 904 and 905. The scintillator layer 904 is disposed on the adhesive layer 324 so as to cover the incident surface side of the substrate 310. The scintillator layer 905 is disposed so as to cover the back surface side of the substrate 310. The scintillator layers 904 and 905 can be formed using a material such as GOS (gadolinium oxysulfide) or CsI (cesium iodide). The scintillator layer 904 and the scintillator layer 905 may use the same material, or may use different materials depending on the energy of radiation to be acquired. The scintillator layer 904 and the scintillator layer 905 are arranged so as to sandwich the substrate 310.

Next, the arrangement of the light shielding layer 903 disposed on the conversion element 902 in order to block light incident from the scintillator layer 904 or the scintillator layer 905 will be described. 9A, the conversion element 902 of the pixel PIXB includes a conductive layer 318 that forms a lower electrode from the incident surface side of the substrate 310 toward the scintillator layer 904, a semiconductor layer 320, and a conductive layer 322 that forms an upper electrode. And in this order. The conductive layer 322 constituting this upper electrode functions as the light shielding layer 903. Specifically, the conductive layer 322 functions as the light shielding layer 903 by forming the conductive layer 322 using a material that is opaque to light emitted from the scintillator layer 904, such as Al, Mo, Cr, or Cu. In the configuration shown in FIG. 9B, the conversion element 902 of the pixel PIXC includes a conductive layer 318 that forms the lower electrode from the incident surface side of the substrate 310 toward the scintillator layer 904, a conductive layer that forms the upper electrode and the semiconductor layer 320. The layer 322 and the electrode layer 325 are included in this order. The conductive layer 318 constituting this lower electrode functions as the light shielding layer 903. Specifically, the conductive layer 318 functions as the light shielding layer 903 by forming the conductive layer 318 using a material that is opaque to light emitted from the scintillator layer 905 such as Al, Mo, Cr, or Cu.

On the other hand, in the conversion element 901 of the pixel PIXA, a material transparent to light emitted from the scintillator layer 904 such as ITO (indium tin oxide) is used for the conductive layer 318 and the electrode layer 325. Accordingly, signals having different energy components can be acquired between the adjacent pixel PIXA and the pixel PIXB or the pixel PIXC.

In the present embodiment, an example in which the conductive layer 322 of the pixel PIXB and the conductive layer 318 of the pixel PIXC have a single-layer structure is shown, but the present invention is not limited to this. For example, in the conductive layer 322 of the pixel PIXB and the conductive layer 318 of the pixel PIXC, a transparent material and an opaque material may be stacked. In that case, the light shielding amount is determined by the area of the opaque material. In this embodiment, the conductive layer 322 of the pixel PIXB and the conductive layer 318 of the pixel PIXC function as the light shielding layer 903. However, the arrangement of the light shielding layer 903 is not limited thereto. For example, in the pixel PIXB, a dedicated light shielding layer 903 using Al, Mo, Cr, Cu, or the like may be disposed in the protective layer 323 for light incident from the scintillator layer 904. In this case, the light shielding layer 903 may be fixed at a constant potential.

Next, the image processing flow in this embodiment will be described with reference to FIGS. Steps S910 to S915 are the same as in the first embodiment.

In step S921, the processor 241 converts the gain-corrected radiation image into a double-sided incident image based on signals obtained by the plurality of conversion elements 901 and a single-sided incidence image based on signals obtained by the plurality of conversion elements 902. To separate.

These two radiation images will be described with reference to FIG. The image on the left side of FIG. 11 is a radiation image obtained from the radiation imaging apparatus 210, that is, an image based on both the signal from the conversion element 901 and the signal from the conversion element 902. In this image, pixels without hatching correspond to the conversion element 901, and pixels with hatching correspond to the conversion element 902. The processor 241 uses the radiation image based on the double-sided incident image (upper side) based on the signals obtained by the plurality of conversion elements 901 and the signals obtained by the plurality of conversion elements 902, as shown on the right side of FIG. Separated into a single-sided incident image (lower side). The both-side incident image is an image including high energy and low energy information among the radiation incident on the radiation imaging apparatus 210. The one-side incident image is an image including low energy information and not including high energy information. Alternatively, the one-side incident image may be an image that includes high energy information and does not include low energy information. In the both-side incident image, the pixel corresponding to the conversion element 902 is the correction target pixel, and in the one-side incident image, the pixel corresponding to the conversion element 901 is the correction target pixel. The number of correction target pixels included in the both-side incident image is smaller than the number of correction target pixels included in the one-side incident image.

Subsequently, the processor 241 corrects the correction target pixels of the double-side incident image with a small number of correction target pixels, and thereafter corrects the correction target pixels of the one-side incident image. In steps S922 to S924, the processor 241 corrects the correction target pixels of the both-side incident image in the same manner as steps S916 to S918 in FIG.

Subsequently, in step S925, the processor 241 corrects the correction target pixel of the one-side incident image. A case where the pixel value of the pixel q that is the correction target pixel of the one-side incident image of FIG. 11 is determined will be described. In the one-side incident image, since there are few pixels having a significant pixel value around the pixel q, it is difficult to accurately calculate the priority in each direction. Therefore, the processor 241 calculates the priority in each direction using the both-side incident images.

Specifically, in step S926, the processor 241 uses the pixel values of the pixels around the pixel f of the double-side incident image for each pixel f of the double-side incident image at the same position as the pixel q of the single-side incident image. The priority of is calculated. The calculation of the priority may be performed in the same manner as in the first embodiment, for example, according to the following formula.

X = | a−2 × b + c | + | e−2 × f + g | + | i−2 × j + k |
Y = | a−2 × e + i | + | b−2 × f + j | + | c−2 × g + k |
Here, the pixel value of the pixel e is the value determined in step S924.

Subsequently, in step S927, the processor 241 determines the pixel value of the correction target pixel using the calculated priority. The pixel value may be determined in the same manner as in the second embodiment, for example, according to the following formula.

q = α × (t + u) / 2 + β × (r + s) / 2
As described above, the weights α and β are values that satisfy α + β = 1 and coincide with the magnitude relationship between the priorities X and Y.

After that, the processor 241 performs energy subtraction processing using the corrected double-side incident image and single-side incident image in S928.

As mentioned above, although embodiment which concerns on this invention was shown, it cannot be overemphasized that this invention is not limited to these embodiment, In the range which does not deviate from the summary of this invention, embodiment mentioned above can be changed and combined suitably. Is possible.

(Other examples)
The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

The present invention is not limited to the above embodiment, and various changes and modifications can be made without departing from the spirit and scope of the present invention. Therefore, in order to make the scope of the present invention public, the following claims are attached.

This application claims priority on the basis of Japanese Patent Application No. 2018-017576 filed on Feb. 2, 2018, the entire contents of which are incorporated herein by reference.

Claims

An image processing apparatus,
An acquisition means for acquiring a radiographic image including a correction target pixel;
Calculation means for calculating the priority of each of the two directions intersecting each other with respect to the correction target pixel;
A large weight is assigned to the pixel value of the pixel in the higher priority direction for the correction target pixel, and a small weight is assigned to the pixel value of the pixel in the lower priority direction for the correction target pixel. Determining means for determining a pixel value of the correction target pixel,
In the calculation of the priority in each of the two directions, the calculation unit is configured to correct the correction target when the direction of the calculation target is the first direction and the other direction is the second direction. A first pixel adjacent to the pixel; a second pixel adjacent to the first pixel in the first direction; and the first pixel or the second with respect to a straight line passing through the correction target pixel and extending in the second direction. An image processing apparatus using pixel values of a plurality of pixels including a third pixel on the opposite side of the pixel.
The image processing apparatus according to claim 1, wherein the first pixel is adjacent to the correction target pixel in the first direction.
The image processing apparatus according to claim 1, wherein the first pixel is adjacent to the correction target pixel in the second direction.
4. The calculation unit according to claim 1, wherein the calculation unit calculates the priority based on at least one of a standard deviation, a difference absolute value, and a curvature of pixel values of the plurality of pixels. The image processing apparatus according to item 1.
The acquisition means acquires a first radiation image and a second radiation image,
The calculation means calculates the priority for the second radiographic image using the first radiographic image,
5. The determination unit according to claim 1, wherein the determination unit determines a pixel value of a correction target pixel of the second radiographic image using the priority calculated using the first radiographic image. The image processing apparatus according to item 1.
6. The image processing apparatus according to claim 5, wherein the number of correction target pixels included in the first radiation image is smaller than the number of correction target pixels included in the second radiation image.
The first radiation image is an image including information on the first energy and the second energy among the radiation incident on the radiation imaging apparatus,
The image processing apparatus according to claim 5, wherein the second radiation image is an image that includes the information of the first energy and does not include the information of the second energy.
The radiation imaging apparatus includes:
A substrate having a plurality of first conversion elements and a plurality of second conversion elements;
A first scintillator layer and a second scintillator layer arranged to sandwich the substrate;
A light shielding layer disposed between each of the plurality of second conversion elements and the first scintillator layer,
The plurality of first conversion elements receive light generated in the first scintillator layer and light generated in the second scintillator layer,
The plurality of second conversion elements receive light generated in the second scintillator layer,
The first radiation image is generated based on signals obtained by the plurality of first conversion elements,
The image processing apparatus according to claim 7, wherein the second radiation image is generated based on signals obtained by the plurality of second conversion elements.
An image processing method comprising:
An acquisition step in which an acquisition unit acquires a radiation image including a correction target pixel;
A calculating step in which the calculation means calculates the priority of each of the two directions intersecting each other with respect to the correction target pixel;
The determination unit assigns a large weight to the pixel value of the pixel in the higher priority direction with respect to the correction target pixel, and decreases the pixel value of the pixel in the lower priority direction of the correction target pixel. Determining a pixel value of the correction target pixel by assigning a weight; and
In the calculation of the priority in each of the two directions, when the direction to be calculated is the first direction and the other direction is the second direction, the second direction adjacent to the correction target pixel. One pixel, a second pixel adjacent to the first pixel in the first direction, and a line extending through the correction target pixel in the second direction on the opposite side of the first pixel or the second pixel An image processing method using pixel values of a plurality of pixels including a third pixel.
A program for causing a computer to function as each unit of the image processing apparatus according to any one of claims 1 to 8.