JPH06339071A - Image processing method - Google Patents

Abstract

PURPOSE:To simplify the arithmetic processing for a density correction and to shorten image processing time in a radiograph processing method. CONSTITUTION:A CPU 50 prepares the histogram of the radiation image signal Sorg inputted in a frame memory 51 and performs the pattern matching with the prescribed histogram stored in the memory 51. An Sk/Gp conversion table performing an Sk/Gp conversion so that the image signal Smin to Smax of the desired image information range obtained by it may be a prescribed density range is written in an Sk/Gp conversion table RAM 53. In the Sk/Gp conversion table RAM 53, the Sk/Gp conversion is performed for the image signal (Srog+DELTAS) where an addition processing is performed for an image signal corrected value DELTAS for the image signal Sorg, and an image processing is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention reads a radiation image from a recording sheet such as a stimulable phosphor sheet on which radiation image information of a subject is recorded to obtain an image signal, and the image signal is subjected to image processing for density. The present invention relates to an image processing method to be applied.

[0002]

2. Description of the Related Art An image signal is obtained by reading a recorded radiation image, and after subjecting this image signal to appropriate image processing,
Reproduction and recording of images are performed in various fields. For example, an X-ray image is recorded using an X-ray film having a low gamma value designed so as to be suitable for later image processing, and the X-ray image is read from the film on which the X-ray image is recorded and converted into an electric signal. By converting and performing image processing on this electric signal (image signal) and reproducing it as a visible image on a copy photograph or the like, a reproduced image with good image quality performance such as contrast, sharpness, and graininess can be obtained. (See Japanese Patent Publication No. 61-5193).

In addition, the applicant of the present invention has conducted radiation (X-ray, α
Radiation, β rays, γ rays, electron rays, ultraviolet rays, etc.), some of this radiation energy is accumulated, and when excitation light such as visible light is subsequently irradiated, accumulation that shows stimulated emission according to the accumulated energy Using fluorescent phosphor (stimulable phosphor),
Radiation image information of a subject such as a human body is once recorded on a sheet-shaped stimulable phosphor, and this stimulable phosphor sheet is scanned with excitation light such as laser light to generate stimulated emission light, and the obtained luminescence is obtained. A radiation image recording / reproducing system has already been proposed which photoelectrically reads out the emitted light to obtain an image signal and outputs a radiation image of a subject as a visible image on a recording material such as a photographic light-sensitive material or a CRT based on the image data. (Japanese Patent Laid-Open Nos. 55-12429, 56-11395, 55-163472, and 56-1)
04645, 55-116340, etc.).

This system has the practical advantage of being able to record images over a very wide radiation exposure area as compared to conventional radiographic systems using silver halide photography. That is, in the stimulable phosphor, it has been recognized that the amount of emitted light stimulated by excitation after storage is proportional to the radiation exposure dose over a very wide range, and therefore the radiation exposure dose varies depending on various imaging conditions. Even if it fluctuates significantly, the amount of stimulated emission light emitted from the stimulable phosphor sheet is read by the photoelectric conversion means with the reading gain set to an appropriate value and converted into an electric signal. Recording material such as photographic light-sensitive material,
By outputting a radiation image as a visible image on a display device such as a CRT, it is possible to obtain a radiation image that is not affected by variations in radiation exposure dose.

In the various systems described above, it is general to perform various image processes on the image signal obtained in order to obtain a visible image suitable for observation and diagnosis as described above. As this image processing, a gradation processing for adjusting the density of a radiation image reproduced according to the level of an image signal is known.

In order to improve the diagnostic performance of radiographic images, the applicant of the present invention has proposed a method of subjecting image signals to frequency enhancement processing such as blur mask processing (Japanese Patent Laid-Open No. 55-163472). JP-A-55-87953). In this frequency processing, the read image signal Sorg is added with a value obtained by subtracting the blur mask signal Sus from the read image signal Sorg and multiplying it by the emphasis degree β, whereby a predetermined spatial frequency component in the image is obtained. Is emphasized. This can be expressed by the following expression (7).

S = Sorg + β (Sorg−Sus) (7) Further, in order to widen the observation target density range in one image,
The contrast between the high density region or the low density region or the entire image is also reduced so as to narrow the difference between the maximum density and the minimum density, that is, the dynamic range (see, for example, Japanese Patent Laid-Open No. 3-222577).

Further, in the central region to be observed in the radiation image (tomographic image) obtained by a so-called tomographic method (see, for example, Japanese Patent Laid-Open No. 58-67245), the tomographic image to be imaged is obtained. An image processing method is also used for removing an obstacle shadow (hereinafter referred to as a flow image) which is generated on a portion other than the surface where the radiation transmission amount is largely changed along the moving direction of the recording sheet ( For example, Japanese Patent Application No. 2-75880). In this method, a low spatial frequency component corresponding to a flow image is removed from an image signal of a radiographic image obtained by tomography to generate an image from which the flow image is removed.

As described above, image processing such as gradation processing and frequency processing is performed by an image processing apparatus which stores a calculation method dedicated to each of the intended image processing.

However, if a different image processing device is provided for each of a plurality of image processes, the calculation method and the image processing device become complicated, and the number of devices increases.

Therefore, the applicant of the present application has proposed an image processing method and apparatus capable of performing the various image processing described above by a single calculation method and apparatus, and has already filed a patent application (Japanese Patent Application No. No. 345173).

That is, in reproducing an image signal representing a radiation image as a visible image, an image read for each pixel constituting the radiation image in each of pixels in a range of vertical M × horizontal N around the pixel. For the signal Sorg, the blur mask signal Sus is obtained by performing an operation of Sus = ΣSorg / (M × N) (1), and S = γ {K1 × Sorg + β (Sorg) × (K2 × Sorg−D (Sus))} (2) Image processing is performed based on the equation (2). When performing gradation processing, the function γ (x) is an arbitrary function, the function β (Sorg) = 0, and the constant K1 = 1.
When frequency processing is performed, the function γ (x) = x, the function β (Sorg) is an arbitrary function, the function D (Sus) = Sus, and the constant K1 is set.
= K2 = 1 and the number of pixels is set to M = N. When performing dynamic range compression processing,
The function γ (x) = x, the function β (Sorg) = 1, the function D (Sus) as an arbitrary function, and the constant K
1 = 1, the constant K2 = 0, and the number of pixels M =
N may be set, and in the case of performing one-dimensional blurring mask processing, the function γ (x) = x and the function β (Sorg)
Is an arbitrary function, the function D (Sus) = Sus, the constant K1 = K2 = 1, and either one of the numbers M or N of the pixels is set to 1. Further, in performing the various image processing as described above, the image signal Sorg of the read radiation image is formed into a histogram, and the maximum value and the minimum value of the image signal indicating the desired image portion in this histogram are determined, There is also a system for converting an image signal so that the range defined by the maximum value and the minimum value is output as the optimum image density (for example, Japanese Patent Laid-Open No. 60-156055).

This image signal conversion is called Sk / Gp conversion and is not limited to a system using a stimulable phosphor sheet. For example, an image signal is obtained from a radiation image recorded on a recording sheet such as a conventional X-ray film. It is also applied to the system.

Sk / Gp conversion for associating the range of the image signal (including the preread image signal) with the density range of the output image is a photographing part of a subject (a head, a chest, an abdomen when the subject is a human body). For each imaging condition, from the result of statistically processing a large number of image signals obtained from each of a large number of radiographic images classified according to the imaging conditions such as the imaging method (normal imaging, contrast imaging, magnified imaging, etc.) The algorithm is defined in the above, and it is widely performed automatically by using the Sk / Gp conversion table based on the algorithm.

[0015]

However, even in the case of a radiation image obtained by performing various kinds of image processing as described above, in the field of diagnosis, the density of the radiation image reproduced by the above-mentioned image processing is actually used. There may be a slight difference between the image density and the optimum image density for the image reader. It is considered that this is due to individual differences in the sensitivity of individual image interpreters and individual differences in calibration of various processes.

There is a demand for finely adjusting the density of the thus reproduced radiographic image to obtain an image having an optimum density for the image interpreter. In this case, usually, the above formula (2) or formula (5) is used. ), Various constants (K1, K2, etc.) and functions (γ (x), β (x), D (x), etc.) are variously changed to obtain an image having an optimum density for the image interpreter. .

However, the above-described density correction method has a drawback in that a great deal of time is required for the arithmetic processing in performing the image processing, and the influence on the reduction of the processing speed is very large.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an image processing method which simplifies the arithmetic processing for density correction and prevents a decrease in image processing time. Is.

[0019]

According to a first image processing method of the present invention, in the following equation (2) showing various image processing, a difference from a desired density (correction value Δ
The image signal (Sorg + ΔS) in consideration of S) is input.

That is, as described in claim 1, in reproducing an image signal representing a radiation image as a visible image, for each pixel forming the radiation image, M pixels in the vertical direction and N pixels in the horizontal direction around the pixel are formed. The blurring mask signal Sus for each pixel is obtained by performing the operation Sus = ΣSorg / (M × N) (1) for the image signal Sorg representing each pixel in the range, and the function for an arbitrary value x is calculated by γ (x ),
The function of the enhancement coefficient for the image signal Sorg is β (S
org), where D (Sus) is an arbitrary function for the blur mask signal Sus, and K1 and K2 are constants, S = γ {K1 × Sorg + β (Sorg) × (K2 × Sorg−D (Sus)) } (2) For the equation (2), the functions γ (x) and β (Sorg
), D (Sus) and the constants K1 and K2, and performing an arithmetic operation for performing image processing on the image signal, the density of the radiation image obtained by the image processing according to the equation (2) and the density Letting ΔS be the image signal correction value according to the difference from the desired density of the radiation image, the above equation (1)
And the image signal Sorg in the equation (2) is applied as an image signal Sorg 'represented by a calculation Sorg' = Sorg + ΔS (3) to perform image processing.

In the second image processing method of the present invention, in the Sk / Gp conversion performed prior to performing image processing such as gradation processing and frequency processing, instead of the image signal Sorg, a desired density is obtained. The image signal (Sorg + ΔS) considering the difference (density correction value ΔS) is input.

That is, according to this method, when the image signal representing the radiation image is reproduced as a visible image, the image signal Sorg representing the pixels forming the radiation image is replaced with the image signal Sorg. The image signal Sorg 'is converted so that the maximum value and the minimum value become predetermined values, and the pixel around the pixel is formed for each pixel forming the radiation image based on the image signal Sorg' after the conversion. Vertical M
Image signal Sorg ′ representing each pixel in the range of N pixels and N pixels in the horizontal direction, Sus = ΣSorg ′ / (M × N) (4) is calculated to obtain the blur mask signal Sus, and the function for an arbitrary value x is γ (X), where the function of the enhancement coefficient for the image signal Sorg ′ is β (Sorg ′), the arbitrary function for the blur mask signal Sus is D (Sus), and the constants are K1 and K2, S ′ = γ {K1 × Sorg ′ + β (Sorg ′) × (K2 × Sorg ′ −D (Sus))} (5) For the expression (5), the functions γ (x) and β (Sorg
′), D (Sus) and the constants K1 and K2 are set, and in the image processing method for performing image processing on the image signal, the radiation obtained by the image processing according to the equation (5) in performing the conversion. The image signal correction value according to the difference between the image density and the desired density of the radiation image is ΔS, and the image signal Sorg before the conversion is represented by the operation Sorg ″ = Sorg + ΔS (6) It is characterized in that image processing is performed by applying it as the image signal Sorg ″.

[0023]

According to the image processing method of the present invention, the density of the radiation image obtained by the image processing is finely adjusted to obtain an image having the optimum density for the image reader.
The first image processing method is the above-mentioned equation (1) for performing image processing,
In (2), since the image signal (Sorg + ΔS) corrected by the density correction value ΔS is substituted in place of the image signal Sorg, the equations (1) and (2) of this image processing are simply executed. Each constant (K1, K2, etc.) or function (γ (x), β (x), D
(X) and the like) do not need to be changed, and the arithmetic processing can be simplified.

In the second image processing method, the image signal (Sorg + ΔS) corrected by the density correction value ΔS is substituted for the image signal Sorg in the Sk / Gp conversion before performing the above-mentioned image processing. Therefore, the calculation process can be further facilitated with respect to the first image processing method. That is, the density correction value ΔS is simply added in the Sk / Gp conversion table that determines the correlation between the image signal Sorg and the density. For example, 1000 pixels × 10
In the case of a radiographic image consisting of 00 pixels or 1 million pixels,
According to the first method, the above formulas (1) and (2) are calculated by 100
According to the second method, the number of times corresponding to the gradation (usually about 1024 gradations) of the radiation image,
That is, it is sufficient to execute the calculation about 1000 times, and the efficiency of the arithmetic processing can be improved.

[0025]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view showing an example of a computer system including a radiation image reading apparatus and a radiation image processing apparatus of the present invention. This system is a system using a stimulable phosphor sheet 11.

In a radiation imaging apparatus (not shown), a radiation image of a subject (not shown) is accumulated and recorded on the stimulable phosphor sheet 11. The stimulable phosphor sheet 11 on which the radiation image is recorded is first set at a predetermined position of the radiation image information reading means 100. The stimulable phosphor sheet 11 set at this predetermined position is conveyed (sub-scanned) in the arrow Y direction by the sheet conveying means 13 such as an endless belt driven by the motor 12. On the other hand, a weak light beam 15 emitted from the laser light source 14 is reflected and deflected by a rotary polygon mirror 16 driven by a motor 23 and rotating at a high speed in the arrow direction, and passes through a focusing lens 17 such as an fθ lens, and then a mirror.
The optical path is changed by 18 to enter the sheet 11, and the main scanning is performed in the arrow X direction substantially perpendicular to the sub-scanning direction (arrow Y direction).
From the location of the sheet 11 irradiated with this light beam 15, stimulated emission light 19 having a light amount corresponding to the accumulated and recorded radiation image information is diverged, and this stimulated emission light 19 is guided by a light guide 20. , Photomultiplier (photomultiplier tube) 21
Photoelectrically detected by. The light guide 20 is formed by molding a light guide material such as an acrylic plate, and is arranged so that the linear incident end face 20a extends along the main scanning line on the stimulable phosphor sheet 11. The light receiving surface of the photomultiplier 21 is coupled to the emitting end surface 20b formed in a ring shape. The photostimulated luminescence light 19 that has entered the light guide 20 through the incident end face 20a proceeds by repeating total reflection inside the light guide 20, is emitted from the emission end face 20b, is received by the photomultiplier 21, and is a radiation image. The photomultiplier 21 converts the amount of the stimulated emission light 19 representing the light into an electric signal.

The analog output signal S output from the photomultiplier 21 is logarithmically amplified by the logarithmic amplifier 26,
The image signal Sorg is obtained by being digitized by the A / D converter 27. The signal level of this image signal Sorg is the sheet
It is proportional to the logarithm of the amount of stimulated emission light emitted from each of the 11 pixels.

In reading the image information, the reading conditions, that is, the voltage value applied to the photomultiplier 21 and the logarithmic amplifier so that the radiation energy accumulated in the stimulable phosphor sheet 11 can be read over a wide range.
Amplification factors of 26 are specified.

The obtained image signal Sorg is input to the computer system 40. This computer system 40
Includes a device for carrying out the image processing method of the present invention, a main body 41 having a CPU 50 and an internal memory built therein, a drive unit 42 into which a floppy disk as an auxiliary memory is inserted and driven, and an operator A keyboard 43 for inputting necessary instructions to the computer system 40, and a CRT for displaying necessary information
It is composed of a display 44.

The computer system 40 will be described below with reference to the block diagram shown in FIG.

The image signal Sorg input to the computer system 40 is temporarily stored in the frame memory 51 provided in the main body 41. Next, the CPU 50 creates a histogram of the image signal Sorg according to the amount of stimulated emission light shown in FIG. 3 based on the image signal Sorg stored in the frame memory 51. This created histogram is subjected to pattern matching with the histogram which is obtained in advance from various image data and stored in the memory 52, whereby the minimum stimulated emission light amount S ₁ and the minimum stimulated emission light amount S in FIG. 3 are obtained. Range L from ₁ to the specified stimulated emission light intensity value
Then, the maximum stimulated emission light amount Smax and the minimum stimulated emission light amount Smin in the range L are determined.

On the other hand, in the output image after the image processing, there is a density range suitable for observation / interpretation. Generally, the appropriate density range (Dmax to Dmin) is predetermined and stored in the memory 52. .

Here, the CPU 50 creates a Sk / Gp conversion table in which the above-mentioned maximum stimulated emission light amount Smax and minimum stimulated emission light amount Smin are associated with appropriate density ranges Dmax to Dmin, and this Sk / Gp conversion is performed. Table Sk /
Write to the Gp conversion table RAM53.

Next, the CPU 50 causes the image signal Sorg stored in the frame memory 51 to be sequentially output to the Sk / Gp conversion table RAM 53, and the Sk / Gp conversion table RAM.
At 53, Sk / Gp conversion is performed on all the image signals Sorg, and the result is sent to the image processing unit 54. Where Sk
The signal correction value ΔS which is initially set to zero is added to the image signal Sorg in the / Gp conversion table RAM53.

Sk / sent to the image processing unit 54 in this way
The image signal (Sorg + ΔS) after Gp conversion is subjected to image processing such as frequency processing and gradation processing represented by the following expression (2) in the image processing unit 54. Here, the operator selects a desired image processing and inputs it from the keyboard 43, so that the constants K1 and K2 and the function γ of the following equation (2) are input.
(X), β (x) and D (x) are determined and desired image processing is performed. The image signal thus subjected to the image processing by the image processing unit 54 is sent to the laser printer 60, and the laser printer 60 outputs an image having a density corresponding to the image signal subjected to the image processing. As a result, the output image has the optimum density for observation and interpretation.

S = γ {K1 × (Sorg + ΔS) + β (Sorg + ΔS) × (K2 × (Sorg + ΔS) −D (Sus))} (2) Here, the Sk / Gp conversion is automatically performed as described above. Then, after that, the density D of the output image obtained by performing the above image processing
However, if the image density is not optimal for the observer,
The operator inputs the image signal correction value .DELTA.S corresponding to the density difference .DELTA.D between the density D'of the output image desired by the observer and the density D of the image-processed output image by the operator through the keyboard 43 to easily correct the density. It can be performed.

That is, as shown in the block diagram of FIG.
Each image signal Sorg is input to the Sk / Gp conversion table RAM53, and the image signal correction value ΔS input from the keyboard 43 is added to the image signal Sorg in this Sk / Gp conversion table RAM53, and this signal correction value ΔS is added. The image processing unit 54 for the processed image signal (Sorg + ΔS)
By performing the image processing in (1), it is possible to obtain an output image having the optimum density for observation and interpretation by the observation and interpretation person.

As described above, the Sk / Gp conversion table RAM
In 53, by correlating the image signal (Sorg + ΔS) obtained by adding the correction signal for density correction instead of the image signal Sorg to the density D, the density correction of the output image can be easily performed, and the main body section The arithmetic processing in 41 is simplified.

Here, the image signal Sor in the histogram is
The minimum stimulated emission amount S ₁ of g may be a true minimum stimulated emission amount as shown in FIG. 3, may be a value determined by a predetermined threshold value, or may be low stimulation. When there is a noise component due to scattered radiation in the emitted light amount region, the minimum stimulated emitted light amount of the histogram portion from which the noise component is removed may be used. When the irradiation field is narrowed with respect to the stimulable phosphor sheet 11, scattered rays of radiation are incident on the area outside the irradiation field, and this comes out in the low stimulated emission amount area on the histogram. It is preferable to use the minimum stimulated emission light amount in the histogram in the irradiation field as the minimum stimulated emission light amount S ₁ of the histogram by recognizing the irradiation field.

As described above, according to the image processing method of the present invention, it is possible to facilitate the density correction processing, simplify the calculation processing related to the density correction processing, and shorten the time required for the calculation processing. You can

In this embodiment, instead of adding the image signal correction value ΔS to the image signal Sorg in the Sk / Gp conversion table RAM 53, as shown in FIG.
The image signal correction value ΔS may be added in the image processing unit 54 to the image signal Sorg Sk / Gp converted by the Gp conversion table RAM 53.

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of a radiation image reading apparatus and a computer system.

FIG. 2 is a block diagram showing details of a computer system.

FIG. 3 is a diagram showing a histogram of a read image signal.

FIG. 4 is a block diagram showing another aspect of the computer system.

[Explanation of symbols]

 11 Accumulative phosphor sheet 15 Laser beam 19 Photostimulated emission light 21 Photomultiplier 26 Logarithmic amplifier 27 A / D converter 40 Computer system 41 Main body 43 Keyboard 50 CPU 51 Frame memory 52 Memory 53 Sk / Gp conversion table RAM 54 Image processing unit 60 Laser printer 100 Reading means

Claims (2)

[Claims] 1. When reproducing an image signal representing a radiation image as a visible image, an image representing each pixel in the range of M pixels in the vertical direction and N pixels in the horizontal direction around the pixel, which constitutes the radiation image. For the signal Sorg, Sus = ΣSorg / (M × N) (1) is performed to obtain the blur mask signal Sus, and the function for an arbitrary value x is γ (x), and the image signal S
The function of the enhancement coefficient for org is β (Sorg), the arbitrary function for the blur mask signal Sus is D (Sus),
When the constants are K1 and K2, S = γ {K1 × Sorg + β (Sorg) × (K2 × Sorg−D (Sus))} (2) For the equation (2), the function γ (x), β (Sorg
), D (Sus) and the constants K1 and K2, and performing an operation of performing image processing on the image signal, the density of the radiation image obtained by the image processing according to the equation (2) and the density Letting ΔS be the image signal correction value according to the difference from the desired density of the radiation image, the above equations (1) and (2)
The image processing method is characterized in that image processing is performed by applying the image signal Sorg in the above as an image signal Sorg ′ represented by an operation Sorg ′ = Sorg + ΔS (3). 2. When reproducing an image signal representing a radiation image as a visible image, an image signal Sorg representing pixels forming the radiation image is generated by setting a maximum value and a minimum value of the image signal Sorg to predetermined values. Image signal Sorg so that
Image signal Sor which represents M pixels in the vertical direction and N pixels in the horizontal direction around the pixel for each pixel constituting the radiation image based on the image signal Sorg 'after the conversion.
For g ′, Sus = ΣSorg ′ / (M × N) (4) The blur mask signal Sus is calculated, and the function for an arbitrary value x is γ (x), and the image signal S
The function of the enhancement coefficient for org 'is β (Sorg'), and the arbitrary function for the blur mask signal Sus is D (Su
s), where K1 and K2 are constants, S ′ = γ {K1 × Sorg ′ + β (Sorg ′) × (K2 × Sorg ′ −D (Sus))} (5) The functions γ (x) and β (Sorg
′), D (Sus) and the constants K1 and K2 are set, and the image processing is performed on the image signal, the radiation obtained by the image processing according to the equation (5) in performing the conversion. The image signal correction value according to the difference between the image density and the desired density of the radiation image is ΔS, and the image signal Sorg before the conversion is represented by the operation Sorg ″ = Sorg + ΔS (6) An image processing method characterized by performing image processing by applying it as an image signal Sorg ″.