JPH0944645A - Image processing method and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image without causing any moire due to interference fringes in an image processing method by which image processing is performed by applying multiplex resolution conversion to the image containing a grid image. SOLUTION: In a resolution demultiplexing processing means 32, an image signal S inputted from an image input means 31 and expressing an image containing the grid image is decomposed into the images of multiple resolutions by the method such as Laplacian pyramid. In this case, a filter for applying filtering processing to an original image is constituted of a filter having characteristics for removing the grid image. The emphasis degree of a desired frequency band in the decomposed image is decided based on the signal value of image in lower frequency band and at an emphasizing processing means 22, emphasizing processing is executed to the image. The emphasizing processed image and the other image are restored at a restoring processing means 34 and a processed image signal S' is obtained. The processed image signal S' is reproduced as a visible image in an image output means 35.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing method and apparatus for performing image processing on an image in a predetermined frequency band of an original image, and in particular, a grid image obtained by shooting using a grid is recorded. The present invention relates to an image processing method and apparatus for processing a processed image.

[0002]

2. Description of the Related Art In various fields, an image signal representing an image is obtained, the image signal is subjected to appropriate image processing, and then the image is reproduced and displayed. For example, in order to improve the diagnostic performance of a radiation image, a method of performing frequency enhancement processing such as blurring mask processing on an image signal has been proposed by the applicant (Japanese Patent Laid-Open No. 55-163772). This frequency processing is a process of adding a product obtained by subtracting the blur mask signal from the image signal representing the original image and multiplying the product by a degree of emphasis, and by doing so, a predetermined spatial frequency component is emphasized in the image. is there.

As another method for performing frequency processing on an image signal, Fourier transform, wavelet transform,
By converting the image into a multi-resolution image by subband conversion, etc., the image signal representing the image is decomposed into signals in multiple frequency bands, and among these decomposed signals, signals in the desired frequency band are emphasized. There has been proposed a method of performing a predetermined image processing such as.

In recent years, in the field of image processing, a method called Laplacian pyramid has been proposed as a new method for converting an image into multiple resolutions (for example, Japanese Unexamined Patent Publication No. H6-6 / 1994).
No. 301766). In this Laplacian pyramid, the original image is masked with a mask similar to a Gaussian function, and then the image is sub-sampled to reduce the number of pixels by half to halve the original image. A blurred image of size is obtained, pixels having a value of 0 are interpolated into the sampled pixels of this blurred image to return to an image of the original size, and this image is further masked by the mask described above. A blurred image is obtained, and the blurred image is subtracted from the original image to obtain a detailed image in a predetermined frequency band of the original image. By repeating this process for the blurred image obtained, N blurred images each having a size of 1/2 ^2N of the original image are created. Here, since an image masked by a mask similar to a Gaussian function is sampled, a Gaussian filter is actually used, but the same processing as when a Laplacian filter is applied is performed. An image is obtained. Since an image in the low frequency band having a size of 1/2 ^2N is sequentially obtained from the image of the original image size in this manner, the image obtained as a result of this processing is called a Laplacian pyramid.

Regarding this Laplacian pyramid, Burt PJ, "Fast Filter Transforms for Image"
Processing ”, Computer Graphics and Image Proces
Sing16, 20-51, 1981; Crowley JL, Stern R.
M., “Fast Computation of the Difference of Low ・ Pass
Transform ”IEEE Trans.on Pattern Analysis and Mach
ine Intelligence, Volume 6, Issue 2, March 1984, Mallat
SG, “A Theory for Multiresolution Signal Decompo
sition ； The Wavelet Representation ”IEEE Trans.on
Pattern Analysis and Machine Intelligence, 11
Volume 7, Issue 1989; Ebrahimi T., Kunt M., "Image
compression by Gabor Expansion ”, Optical Engineer
ing, Vol. 30, No. 7, pp. 873-880, July 1991, and Pi.
eter Vuylsteke, Emile Schoeters, “Multiscale Image
Contrast Amplification ”SPIE Vol.2167 Image Proce
Details are described in ssing (1994), pp551-560.

Then, the images in all the frequency bands of the Laplacian pyramid thus obtained are subjected to processing for enhancing the image values, and the images in the respective frequency bands subjected to this enhancement processing are reversed. A method for obtaining a processed image by conversion is described in JP-A-6-301766. Since the image processed in this way is emphasized in each frequency band, the image is substantially the same as the image subjected to the blur mask processing with the masks of a plurality of sizes in the blur mask processing described above.

On the other hand, radiographic images are photographed and recorded on a recording sheet such as an X-ray film or a stimulable phosphor sheet. The radiation scattered by the subject is irradiated on the recording sheet during the photographing and recording. In order to prevent this, radiation is not transmitted at a fine pitch of about 4.0 lines / mm. For example, it is easy to transmit lead and it is easy to transmit. For example, a grid in which aluminum and wood are alternately arranged is placed between the subject and the recording sheet for shooting. Sometimes. When the image is captured using the grid, the radiation scattered by the subject is less likely to irradiate the recording sheet, so the contrast of the radiation image of the subject can be improved, but on the other hand, the recording sheet has a fine striped pattern along with the subject image. A grid image of is recorded.

[0008]

By the way, a radiation image reading apparatus for obtaining an image signal from a recording sheet on which a radiation image is recorded usually reads the light carrying the radiation image information photoelectrically and determines the maximum required as the image information. Spatial frequency (hereinafter, the required maximum spatial frequency is represented by fss)
Is sampled at a sampling interval Δx = 1 / (2 · fss) corresponding to the above to obtain a digital image signal. The image signal obtained in this way is not only useful information representing the radiation image of the object, but is caused by the grid image even if the spatial frequency of the grid image is higher than the required highest spatial frequency fss. It may also contain noise.

FIG. 14 is a graph showing a spatial frequency characteristic of a radiation image (including a grid image) recorded on a recording sheet in a direction orthogonal to the striped pattern of the grid image.

It is assumed here that imaging is performed using a grid of 4.0 lines / mm, the spatial frequency of the grid image is 4 cycles / mm, and the maximum spatial frequency fss required to reproduce the radiation image of the subject is 2.5 cycles / mm. It will be described as mm.

FIG. 15 shows a sampling interval Δx = corresponding to fss = 2.5 (cycle / mm) in order to obtain information on a spatial frequency band of fss = 2.5 (cycle / mm) or less necessary for reproducing a radiation image of a subject. 1 / (2 · fss) = 0.2 (mm), that is, a diagram for explaining a mixed state of noise when sampling is performed 5 times per 1 mm.

In this case, the so-called aliasing noise is mixed in at the position where the graph shown by the solid line in the figure (the same as the graph in FIG. 14) is folded back at fss = 2.5 (cycle / mm). Therefore, in this case, the spatial frequency of the grid image is 4 cycl.
Aliasing of e / mm occurs at 1 cycle / mm.

FIG. 16 shows the sampling interval Δx = 1 /
The spatial frequency characteristic of the radiation image carried by the image signal obtained by sampling at (2 · fss) = 0.2 (mm) is shown.

Noise corresponding to the grid image is mixed in at a position of 1 cycle / mm, and when a visible image is reproduced and recorded, a result appears as a 1 cycle / mm striped pattern in the visible image. When observing a radiation image, even if the grid image is in a spatial frequency band that is not so conspicuous, a stripe pattern appears in the spatial frequency band that is easily conspicuous when an image signal is sampled. The stripe pattern causes interference fringes, which causes moire. This moire sometimes makes the visible image reproduced based on this image data very difficult to see.

Further, in the method described in the above-mentioned JP-A-6-301766, when an image including a grid image is converted into multiresolution, a Gaussian function is used as a filter for converting the image into multiresolution. As the image becomes in the low frequency band, the above-mentioned aliasing repeatedly occurs, and moire becomes very noticeable. Then, even if the image including such a moire is subjected to image processing and the image-processed image is restored by inverse multi-resolution conversion, the restored processed image contains many moire artifacts. It is difficult to see the image.

In view of the above circumstances, the present invention is an image processing method for performing image processing by performing multi-resolution conversion on an image including a grid image, and can obtain an image in which moire due to interference fringes does not occur. It is an object of the present invention to provide an image processing method and device capable of performing the image processing.

[0017]

According to an image processing method and apparatus of the present invention, an original image on which a grid image is recorded is repeatedly subjected to a filtering process by a predetermined filter to convert the original image into a multi-resolution space. Image processing is performed on an image of a desired frequency band among images obtained by converting the plurality of frequency bands, and the image of the frequency band subjected to the image processing and an image of another frequency band are demultiplexed. In an image processing method and apparatus for obtaining a processed image by converting into a resolution space, at least the predetermined filter at the time of performing the filtering process is a grid image removing filter for removing the grid image. It is what

[0018]

In the image processing method and apparatus according to the present invention, when the original image is subjected to the filtering process to be converted into the multi-resolution, at least the filter to be subjected to the filtering process is the filter having the characteristic of removing the grid. Even if the image is converted into multiple resolutions, the converted image will have the grid image removed in all frequency bands. Therefore, the image in the desired frequency band is subjected to image processing to obtain the inverse multiresolution. The processed image signal obtained by performing the conversion can be an easy-to-see image without the moire due to interference fringes, in which the grid image is erased.

[0019]

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

FIG. 1 is a diagram showing an outline of an example of the radiation image capturing apparatus. Here, an example in which the above-described stimulable phosphor sheet is used as a recording sheet will be described.

The radiation 2 emitted from the radiation source 1 irradiates the stimulable phosphor sheet 11 via the subject 3 and the grid 4. In the grid 4, lead 4a and aluminum 4b are alternately arranged at a pitch of 4 lines / mm.
The radiation 2 is blocked by the lead 4a and transmitted through the aluminum 4b to irradiate the sheet 11. Therefore, a striped grid image of 4 lines / mm is accumulated and recorded on the sheet 11 together with the subject image. The radiation 2a scattered in the subject 3 is in the grid 4
Since it is obliquely incident on the sheet 11 and is shielded by the grid or reflected by the grid 4, the sheet 11 is not irradiated, and therefore a clear radiation image with little irradiation of scattered radiation is accumulated and recorded on the sheet 11.

FIG. 2 shows a subject image (shaded areas in the drawing) and a striped grid image (vertical stripes in the drawing) stored and recorded in the stimulable phosphor sheet 11 by photographing using a grid. It is the figure shown. In this manner, a radiation image on which the subject image 5 and the striped pattern 6 are superimposed is recorded on the sheet 11.

FIG. 3 is a perspective view of an embodiment of a radiation image reading apparatus using the embodiment of the image processing method of the present invention.

The stimulable phosphor sheet 11 on which the radiation image is set at a predetermined position of the reading unit 10 which is an example of the reading unit is transferred by a sheet conveying unit 15 such as an endless belt driven by a driving unit (not shown). , Are conveyed (sub-scanning) in the arrow Y direction. On the other hand, the light beam 17 emitted from the laser light source 16 is reflected and deflected by a rotary polygon mirror 18 driven by a motor 24 and rotating at a high speed in the arrow direction, and fθ
After passing through a converging lens 19 such as a lens, the optical path is changed by a mirror 20 to enter the sheet 11, and main scanning is performed in an arrow X direction substantially perpendicular to the sub-scanning direction (arrow Y direction). Light beam
From the location of the sheet 11 irradiated with 17, the stimulated emission light 21 of the amount of light according to the radiation image information stored and recorded is diverged, this stimulated emission light 21 is guided by the light guide 22,
It is detected photoelectrically by a photomultiplier (photomultiplier tube) 23. The light guide 22 is formed by molding a light guide material such as an acrylic plate, and is arranged so that the linear incident end face 22a extends along the main scanning line on the stimulable phosphor sheet 11. And the injection end face 22 formed in an annular shape
The light receiving surface of the photomultiplier 23 is coupled to b. The photostimulated luminescent light 21 that has entered the light guide 22 through the incident end face 22a travels through the inside of the light guide 22 by repeating total reflection, and then exits from the exit end face 22b to exit the photomultiplier 23.
The photostimulated luminescent light 21 representing the radiation image is converted into an electric signal by the photomultiplier 23.

In the analog output signal S _A output from the photomultiplier 23, the highest first space in the spatial frequency band in the desired range necessary for reproducing and outputting a good radiation visible image is used. Information on the spatial frequency band higher than the frequency fss = 2.5 cycles / mm, particularly information on the grid image 6 shown in FIG. 2 is also included. The information on the grid image 6 is one of the causes of making the visible image difficult to see when observing the visible image, and is information that needs to be removed.

The analog output signal S _A is logarithmically amplified by the log amplifier 26, then sampled at a predetermined sampling interval by the A / D converter 28 and digitized to obtain a digital image signal S. The image signal S is temporarily stored in the storage unit 29.

FIG. 4 is a diagram showing sampling points on the stimulable phosphor sheet 11. The horizontal direction (x direction) in the figure corresponds to the X direction (main scanning direction) in FIG. 3, and the vertical direction (y direction) corresponds to the Y direction (sub scanning direction) in FIG. In the figure, the mark * represents each sampling point in the initial image signal, and the mark ◯ represents each sampling point after resampling.
In the present embodiment, these sampling points are desired in order to read the radiation image recorded on the stimulable phosphor sheet 11 in both the x direction (main scanning direction) and the y direction (sub scanning direction). Which is half the sampling interval 2 · Δ = 1 / (2 · fss) = 0.2 (mm) corresponding to the highest spatial frequency fss = 2.5 cycles / mm of the spatial frequency band Sampling interval Δ corresponding to the spatial frequency fsw = 5.0 (cycle / mm), which is twice the highest spatial frequency fss = 2.5 (cycle / mm)
= 1 / (2 · fsw) = 0.1 (mm). The adjustment of the sampling interval is performed by adjusting the sampling time interval of the A / D converter 28 (see FIG. 3) in the x direction (main scanning direction) and the like in the y direction (sub scanning direction). This is performed by adjusting the transport speed of the sheet 11 by the sheet transport means 15 (see FIG. 3).

The image signal S obtained in this way and having a sampling interval (0.1 mm interval) shown by point of FIG.
It carries information of less than or equal to 5.0 (cycle / mm), and therefore carries information of the striped pattern 6 shown in FIG. 2 (4.0 cycle / mm). Further, in this embodiment, aliasing of the striped pattern 6 does not occur.

The image signal S is temporarily stored in the storage unit 29 shown in FIG. 3 and then input to the image signal processing means 30 to be subjected to image processing as follows.

FIG. 5 is a block diagram showing the outline of an apparatus for carrying out the image processing method according to the present invention. As shown in FIG. 5, the apparatus for carrying out the image processing method according to the present invention includes an image input unit 31 such as the image reading unit shown in FIG. 3 for inputting an image into the apparatus, and the input image. A multi-resolution decomposition processing means (32) for performing a multi-resolution decomposition processing on the image, and among the images decomposed into a plurality of frequency bands by the multi-resolution decomposition processing means (32), an enhancement as will be described later for an image in a predetermined frequency band. Enhancement processing means 33 for performing processing, restoration processing means 34 for restoring the image in the frequency band subjected to the enhancement processing by the enhancement processing means 33 and the image in another frequency band to obtain a processed image, and restoration processing The image output means 35 for reproducing the processed image restored by the means 34 as a visible image.

Next, the operation of the image processing method according to the present invention will be described. FIG. 6 is a block diagram for explaining the processing performed in the multi-resolution image decomposition processing means 32 in FIG. In this embodiment, it is assumed that the image signal S is decomposed into a multi-resolution image by the Laplacian pyramid method. As shown in FIG. 3, the digital image signal S representing the original image is processed by the multi-resolution decomposition processing means 32.
When input to, the following filtering process is first performed.

That is, the filtering means shown in FIG.
In 40, the filter L _G as shown in FIG. 7, performs filtering processing on the image signal S. That is, in the pixel value aij (i, j = 1,2 ...) Shown in FIG.

[0033]

[Equation 1]

The filtering process is performed so that Here, the filter L _G shown in FIG. 7 has a characteristic that the transfer characteristic of 4 cycle / mm becomes 0 as shown in FIG. 8, and therefore, by performing the filtering process by the filter L _G shown in FIG. The image signal S does not carry the information of the striped pattern 6. The filter L _G is disclosed in JP-A-3-14039.

The image signal S filtered by such a filter L _G is sampled every other pixel by the filtering means 40 to obtain a striped pattern removed image g ₁ . The striped pattern removed image g ₁ is 1/4 of the original image.
The size has become. Next, the interpolating means 41 interpolates pixels having a value of 0 in the sampled intervals of the striped pattern removed image g ₁ . This interpolation is performed by removing the striped pattern image g ₁
This is done by inserting rows and columns with a value of 0 for each column and row. In this way, the striped pattern removed image g ₁ in which the pixels having the value of 0 are interpolated, the pixels having the value of 0 are inserted every other pixel, so that the change in the signal value is not smooth.

After the interpolation is performed in this way,
Further, the interpolated striped pattern removed image g _{1 is} filtered again by the filter L to obtain a low resolution approximate image g ₁ ′. This low-resolution approximate image g ₁ ′ has a smoother signal value change than the striped pattern removed image g _{1 on} which the above-described interpolation is performed. In addition, it is an image in which high frequencies higher than half of the original image are disappeared in terms of frequency band. This is because the size of the image is reduced to ¼ and pixels having a value of 0 are interpolated every other pixel, and filtering processing is performed by the filter L, so that an image in a frequency band in which the spatial frequency is higher than half is blurred. The reason is that it seems to have been destroyed.

Next, in the subtractor 42, the low resolution approximate image g ₁ ′ is subtracted from the original image to obtain the detailed image b ₀ . This subtraction is performed between the signals of the pixels corresponding to the original image and the low-resolution approximate image g ₁ ′. Here, since the low-resolution approximate image g ₁ ′ is an image in a frequency band higher than half of the spatial frequency of the original image as described above, the detailed image b ₀ is less than half of the original image. The image shows only the upper frequency band.
That is, as shown in FIG. 9, the detailed image b ₀ represents an image in the frequency band of N / 2 to N of the Nyquist frequency N of the original image.

Next, the striped pattern removed image g ₁ is input to the filtering means 40 and is filtered by the low pass filter L in the filtering means 40. This low-pass filter substantially corresponds to a two-dimensional Gaussian distribution on a 5 × 5 grid as shown in FIG. This low-pass filter L is applied to images of all subsequent resolutions.

The striped pattern removed image g ₁ filtered by such a low-pass filter is sampled every other pixel by the filtering means 40, and a low resolution approximate image g ₂ is obtained. This low resolution approximate image g ₂
Is 1/4 of the striped pattern removed image g ₁ , that is, 1 / of the original image
It has a size of 16. Next, in the interpolating means 41,
Pixels having a value of 0 are interpolated in the sampled intervals of the low resolution approximate image g ₂ . This interpolation is performed by inserting rows and columns having a value of 0 for each column and each row of the low-resolution approximate image g ₂ . In this way, the low-resolution approximate image g ₂ in which the pixel of which the value is 0 is interpolated is blurred, but the pixel of which the value is 0 is inserted at every other pixel, so that the change in the signal value is not smooth. Has become.

After the interpolation is performed in this way,
Further, the low-resolution approximate image g ₂ thus interpolated is filtered again by the low-pass filter L shown in FIG. 10 to obtain a low-resolution approximate image g ₂ ′. The low-resolution approximate image g ₂ ′ has a smoother change in signal value than the low-resolution approximate image g _{2 on} which the above-described interpolation is performed. Further, as compared with the striped pattern removed image g ₁ , the image in the frequency band higher than half is disappeared.

Next, in the subtractor 42, the low-resolution approximate image g ₂ ′ is subtracted from the striped pattern removed image g ₁ to obtain the detailed image b ₁ . This subtraction is performed between the signals of the pixels corresponding to the striped pattern removed image g ₁ and the low resolution approximate image g ₂ ′. Here, since the low-resolution approximate image g ₂ ′ is a blurred image in a frequency band higher than half of the spatial frequencies of the striped pattern removed image g ₁ as described above, the detailed image b ₁ is a striped pattern. This is an image showing only the frequency band above half of the removed image g ₁ . That is, as shown in FIG. 9, the detail image b ₁ is only in the frequency band above half of the striped pattern removal image g ₁ , that is, in the frequency band N / 4 to N / 2 of the Nyquist frequency N of the original image. It represents an image. As described above, the low-pass filter L having the Gaussian distribution is used to perform the filtering process to obtain the detail image. However, since the image subjected to the filtering process is subtracted from the low-resolution approximate image, it is substantially Laplacian. The result is the same as when the filtering process is performed by the filter.

Then, the above-mentioned processing is performed by filtering means.
The low-resolution approximate image g _k (k = 1 to N) filtered and sampled by 40 is sequentially repeated, and n detailed images b _k (k = 1) are obtained as shown in FIG.
~ N) and the residual image g _L of the low resolution approximate image.
Here, the resolution of the detailed image b _k decreases in order from b ₀ , that is, the spatial frequency of the image decreases.
Against the Nyquist frequency N of the original image, detail images b _k represents the frequency band of ^{N / 2 k + 1 ~N /} 2 k, the size of the image is a 1/2 ^2k times the original image. That is, the highest resolution detail image b ₀ has the same size as the original image, which is a quarter of the size of the next high resolution detail image b ₁ original image detail image b _0. As described above, since the detail image becomes smaller from the one having the same size as the original image, and the detail image is substantially the same as the one to which the Laplacian filter is applied, the multi-resolution conversion according to the present embodiment is performed. Is called the Laplacian Pyramid. Further, the residual image g _L can be regarded as an approximate image having a very low resolution of the original image, and in an extreme case, the residual image g _L is composed of only one image representing the average value of the original image. Becomes The detailed image b _k and the residual image g _L thus obtained are stored in a memory (not shown).

Then, the detailed image b thus obtained
Of the _k , the detail processing b _k of the desired frequency band is subjected to the enhancement processing by the enhancement processing means 33. This enhancement processing is performed, for example, by multiplying a detailed image b _{k in} a certain frequency band by a certain enhancement coefficient.

Next, the detail image b _{k in} the frequency band and the detail image in the other frequency band that have been subjected to the emphasis process are inversely transformed. This inverse conversion processing is performed in the restoration processing means 34 as follows.

FIG. 11 is a diagram showing details of the inverse transformation of the detailed image. First, the residual image g _L is interpolated between the pixels by the interpolating means 44 to obtain an image g _L ′ having a size four times the original size.
It is said. Next, in the adder 45, the interpolated image g
_L 'and perform the addition at the lowest resolution detail image b _n-1 of the corresponding pixels comrades addition image (g _L' get + b _n-1). Then, this added image (g _L ′ + b _n−1 ) is interpolated.
It is input to 44, and the interpolation means 44 interpolates between the respective pixels to obtain an image b _n-1 ′ having a size four times the original size.

Next, this image b _n-1 ′ is subjected to addition of pixels corresponding to the one-step high-resolution image b _n-2 of the detailed image b _{n-1 in} the adder 45, and the added addition is performed. The signal (b _n-1 ′ + b _n-2 ) is interpolated by the interpolating means 44 at each pixel interval, and the image b having a size four times as large as the detail image b _n-2 is obtained.
_n-2 .

The above processing is repeated and the same processing is applied to the emphasized image b _kp . That is, addition of the emphasized image b _kp and the one-step low resolution image b _k-1 ′ subjected to the above-described processing is performed in the adder 45, and the addition signal (b
_kp + b _k-1 ′) is interpolated between the pixels in the interpolating means 44 to obtain an interpolated signal b _kp ′. Then, this processing is sequentially performed on the high-frequency detail image, and finally, in the adder 45, the interpolation image b ₁ ′ and the highest resolution detail image b are added.
Addition with ₀ is performed to obtain the processed image signal S '.

The processed image signal S ′ thus obtained is input to the image output means 35 and displayed as a visible image. The image output means 5 may be a display means such as a CRT, a recording device for performing optical scanning recording on a photosensitive film, or for that purpose, an image signal is temporarily stored in an image file such as an optical disk or a magnetic disk. It may be a device.

The inverse transform filter is a low-pass filter (interpolating means 41 in FIG. 6) used for obtaining the image g _n ′.
The original image can be completely restored by using the same filter as that used in (1). Also besides the above-mentioned embodiment also, the image g ₁ during conversion 'as a filter for obtaining the, case of using a filter L _G, the interpolation image b _1' may be used L _G is as a filter for obtaining the.

Further, in the above-mentioned embodiment, the filter L _G (see FIG. 7) having the frequency characteristic as shown in FIG. 8 is used as the filter for removing the grid of the processed signal. However, the present invention is not limited to this, and for example, a filter L _G ′ (see FIG. 12) having a frequency characteristic as shown in FIG. 13 may be used.

[Brief description of drawings]

FIG. 1 is a diagram showing an image capturing apparatus that captures a radiographic image using a grid.

FIG. 2 is a diagram showing a radiographic image obtained by using a grid.

FIG. 3 is a diagram showing a radiation image reading device.

FIG. 4 is a diagram showing sampling points on a stimulable phosphor sheet.

FIG. 5 is a diagram for explaining an image processing method according to the present invention.

FIG. 6 is a diagram showing details of multi-resolution decomposition processing means.

FIG. 7 is a diagram showing a grid image removal filter.

FIG. 8 is a diagram showing frequency characteristics of a grid image removal filter.

FIG. 9 is a diagram showing detailed images for each of a plurality of frequency bands that have been subjected to Laplacian pyramid processing.

FIG. 10 is a diagram showing a low-pass filter.

FIG. 11 is a diagram showing details of restoration processing means.

FIG. 12 is a diagram showing another grid image removal filter.

FIG. 13 is a diagram showing frequency characteristics of another grid image removal filter.

FIG. 14 is a diagram showing spatial frequency characteristics in a direction orthogonal to the striped pattern of the grid image.

FIG. 15 is a graph showing the graph of FIG. 14 and aliasing of an image signal sampled at a sampling interval corresponding to 2.5 cycles / mm.

16 is a diagram showing a spatial frequency characteristic of a radiographic image carried by an image signal sampled at the same sampling intervals as in FIG.

[Explanation of symbols]

 11 Accumulative phosphor sheet 17 Light beam 23 Photomultiplier 26 Log amplifier 27 Analog filter 28 A / D converter 29 Storage unit 30 Image processing means 31 Image input means 32 Multi-resolution decomposition processing means 33 Enhancement processing means 34 Restoration processing means 35 Image output means 40 Filtering means 41 Interpolation means 42 Subtractor 44 Interpolation means 45 Adder

Claims (2)

[Claims] 1. An original image on which a grid image obtained by photographing using a grid is recorded is repeatedly subjected to filtering processing by a predetermined filter to convert the original image into a multi-resolution space. Image of each of the plurality of frequency bands is obtained, image processing is performed on an image of a desired frequency band among the images of each of the plurality of frequency bands, and the image of the frequency band subjected to the image processing and other frequencies An image processing method for obtaining a processed image by converting an image of a band into an inverse multi-resolution space, wherein the predetermined filter at the time of first performing the filtering process on the original image is the grid image. An image processing method, which is a grid image removal filter for removing the image. 2. An original image on which a grid image obtained by photographing using a grid is recorded is repeatedly subjected to filtering processing by a predetermined filter to convert the original image into a multi-resolution space. Multi-resolution conversion means for obtaining an image for each of a plurality of frequency bands, an image processing means for performing an image processing on an image of a desired frequency band among the images for each of the plurality of frequency bands, and an image processing for performing the image processing. An image processing apparatus including an inverse conversion unit that obtains a processed image by converting an image of a frequency band and an image of another frequency band into an inverse multi-resolution space, and at least first with respect to the original image. The image processing apparatus characterized in that the predetermined filter at the time of performing the filtering process is a grid image removing filter for removing the grid image. Place.