JP2003319260A - Image signal generating method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To avoid occurrence of moire or to shorten a processing time as needed in an image signal generating method and apparatus for generating an image signal by reading a storage type phosphor sheet recorded with radiographic images including a grid image. <P>SOLUTION: Any one of first image reading processing not to apply suppressing processing to suppress a return distortion component caused by a spatial frequency component of the grid image and second image reading processing to apply the suppressing processing is selected based upon a photographing menu, and selected image reading processing is applied upon the radiographic images. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image signal generating method and apparatus for generating an image signal by reading a recording medium on which an original image containing a predetermined periodic pattern is recorded.

[0002]

2. Description of the Related Art Conventionally, a predetermined recording medium (film,
Image reproducing systems in which a reproduced image is output from a printer or the like based on an image signal obtained by reading an original image recorded on paper or the like with a scanner or the like are used in many fields.

Particularly in the medical field, radiation (X-ray, α
Radiation, β-rays, γ-rays, electron rays, ultraviolet rays, etc.), some of this radiation energy is accumulated, and then irradiation with excitation light such as visible light or laser light causes a luminescence according to the accumulated radiation energy. Using a stimulable phosphor that emits exhausted light (stimulable phosphor), for example, radiation that has passed through a subject such as a human body on a stimulable phosphor sheet in which this stimulable phosphor is laminated on a support. By irradiating, the radiation image is once accumulated and recorded, and the stimulable phosphor sheet is irradiated with excitation light such as laser light to generate stimulated emission light,
A technique using a radiation image reading device that photoelectrically converts this stimulated emission light to obtain an image signal is CR (Computed R).
It has been widely used as an adiography).

Here, when the radiation image of the subject is photographed and recorded on the above-mentioned stimulable phosphor sheet, the radiation is scattered at a fine pitch of about 4 lines / mm so that the sheet is not exposed to the radiation scattered by the subject. In some cases, a grid in which non-transmissive lead and the like and aluminum and wood, which are easily transmitted, are alternately arranged between the subject and the sheet may be used. When the image is captured using the grid, the radiation scattered by the subject is less likely to be applied to the sheet, so it is possible to improve the contrast of the radiation image of the subject, but if the image containing this grid image is enlarged or reduced, Aliasing due to folding occurs according to the scaling ratio. Furthermore, if the aliasing overlaps with the spatial frequency of the grid image or the like, a fine striped pattern (moire) occurs, which makes the reproduced image difficult to see.

Therefore, the applicant of the present invention reads an image at a sampling frequency that is at least twice the spatial frequency of the grid image, performs filter processing to remove the harmonic components of the grid image, and then resamples at the desired sampling frequency. By doing so, an image signal generation method for obtaining an image signal without the above-mentioned aliasing or moire is proposed.

[0006]

However, as in the above-described image signal generating method, the spatial frequency of the grid image is reduced to 2
When sampling at a finer sampling frequency such as twice or more, there is an advantage that moire can be prevented as described above, but the processing time for sampling is long and the amount of data also increases, so image processing for that large amount of data The processing time will also be long. Further, there may be a case where the above-mentioned moire does not occur depending on the type and direction of the grid used, or there is no particular problem even if the moire occurs when shooting is performed without using the grid. Therefore, there is a demand for a method capable of avoiding the occurrence of moire as necessary or shortening the processing time without avoiding it.

In view of the above circumstances, it is an object of the present invention to provide an image signal generating method and apparatus capable of selecting a process for avoiding the occurrence of moire and a process for avoiding it.

[0008]

An image signal generating method according to the present invention comprises a first image reading process for obtaining a first image signal by sampling an original image containing a predetermined periodic pattern at a desired sampling frequency, The original image is sampled at a frequency higher than the desired sampling frequency to obtain the initial image signal, and the suppression process is performed to suppress the aliasing distortion component that occurs when the initial image signal is resampled at the desired sampling frequency. One of the second image reading process of re-sampling the suppression-processed image signal having been subjected to the second image signal is selected based on a predetermined input signal, and the selected image reading process is selected. The image reading process is performed on the original image.

Here, the above-mentioned "original image" means, for example, a radiation image that may be photographed using a grid, and an image that may include a periodic pattern such as a grid image. To do. Further, not only the grid image but also an image that may include other periodic patterns that generate harmonic components are also included.

The medium on which the "original image" is recorded is, for example, a stimulable phosphor sheet or a solid state detector.

Further, the "folding distortion component" means a folding distortion component generated in response to a predetermined periodic pattern of the grid image or the like and a harmonic component based on the periodic pattern during the resampling.

Further, the "predetermined input signal" is, for example, information such as the photographing conditions of the photographing apparatus and the photographing region when the radiation image is photographed when the original image is the radiation image, and the information of this apparatus. The signal is input by the user using a predetermined input means, and indicates whether or not the second image reading process is necessary.

Further, in the first image reading process, the original image is sampled at a frequency higher than a desired sampling frequency and lower than a frequency used in obtaining the initial image signal in the second image reading process, and then the desired image is obtained. A process of sampling at the sampling frequency can be performed.

The image signal generating apparatus of the present invention is the first image reading process for performing the first image reading process for sampling the original image at the desired sampling frequency to obtain the first image signal, and the original image desired. The initial image signal is obtained by sampling at a frequency higher than the sampling frequency of, and a suppression process is performed to suppress the aliasing distortion component that occurs when the initial image signal is resampled at a desired sampling frequency,
The original image can be selectively subjected to the second image reading process of performing the second image reading process of re-sampling the suppressed image signal subjected to the suppression process to obtain the second image signal. Image reading means, and either the first image reading processing or the second image reading processing of the image reading means is selected based on a predetermined input signal, and the selected image reading processing is performed on the original image. And a selection means.

Further, the shooting menu of the original image can be used as the predetermined input signal.

The "photographing menu" has information on the photographing conditions and photographing parts designated in the photographing device for the original image, and based on these information, the second image reading process is performed. The necessity can be decided.

[0017]

According to the image signal generating method and apparatus of the present invention, either one of the first image reading process and the second image reading process is selected based on a predetermined input signal, and Since the selected image reading process is applied to the original image, if necessary, the reading process giving priority to the processing speed is applied to the original image, or the reading giving priority to the suppression of moire generation based on the aliasing distortion component. The original image can be processed.

Further, when the photographing menu of the original image is used as the predetermined input signal, an appropriate image reading process may be applied to the original image in accordance with the photographing condition and photographing region specified in the photographing device. it can.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A radiation image reading apparatus to which an embodiment of an image signal generating apparatus for carrying out the image signal generating method of the present invention is applied will be described below with reference to the drawings. Figure 1
FIG. 1 is a schematic configuration diagram of the present radiation image reading device.

First, a stimulable phosphor sheet (hereinafter referred to as a phosphor sheet) read in the present embodiment will be described. FIG. 2 is a diagram showing an outline of an example of a radiation image capturing apparatus for recording a radiation image on a phosphor sheet.

The radiation 2 emitted from the radiation source 1 is applied to the phosphor sheet 7 via the subject 3 and further via the grid 4. In the grid 4, lead 4a and aluminum 4b are alternately arranged at a pitch of 4 lines / mm. Radiation 2 is blocked by lead 4a, and aluminum 4
b is transmitted and irradiated to the phosphor sheet 7. Therefore, the phosphor sheet 7 has four lines /
A mm grid image is stored and recorded. The radiation 2a scattered in the subject 3 is obliquely incident on the grid 4 and thus is blocked by the grid 4 or reflected by the grid 4 and is not irradiated onto the phosphor sheet 7, and therefore the phosphor sheet 7 is scattered by radiation. A sharp radiation image with less irradiation is stored and recorded. The spatial frequency of the grid image is 4 cy.
cle / mm.

FIG. 3 shows a radiation image in which a grid image (vertical stripes in the figure) is superimposed on a subject image (shaded areas in the figure), which is stored and recorded in the phosphor sheet 7 by photographing using a grid. FIG. In this way, the radiation image in which the subject image 5 and the grid image 6 are superimposed is recorded on the sheet 7.

Next, a radiation image reading apparatus using the image signal generating apparatus of the present invention will be described. As shown in FIG. 1, the radiation image reading apparatus includes a reading device 20 that reads a radiation image recorded on the phosphor sheet 7 and an image signal generation that generates a desired digital signal based on an analog signal output from the reading device 20. And a device 30.

First, the reading device 20 will be described. As shown in FIG. 1, the phosphor sheet 7 is set on the sheet conveying means 10 so that the conveying direction (Y direction) is orthogonal to the grid image 6. The phosphor sheet 7 set as described above is transferred by a sheet conveying means 10 such as an endless belt driven by a driving means (not shown).
It is transported (sub-scanning) in the direction of arrow Y. On the other hand, the light beam 14 emitted from the laser light source 12 is driven by a motor 18 to be reflected and deflected by a rotary polygon mirror 22 which rotates at a high speed in the arrow direction, and after passing through a focusing lens 23 such as an fθ lens, the optical path is changed by a mirror 17. Instead, the light enters the phosphor sheet 7 and is subjected to main scanning in an arrow X direction substantially perpendicular to the sub-scanning direction (arrow Y direction). From the portion of the phosphor sheet 7 irradiated with the light beam 14, stimulated emission light 16 having a light amount corresponding to the stored and recorded radiation image is emitted, and the stimulated emission light 16 is guided by the light guide 24, It is detected photoelectrically by a photomultiplier (photomultiplier) 25. Then, the stimulated emission light 16 representing the radiation image is converted into an electric signal by the photomultiplier 25, the analog signal S0 is logarithmically amplified by the log amplifier 26, and then output to the image signal generation device 30 in the subsequent stage. .

Next, the image signal generating device 30 will be described. The image signal generating device 30 is finally
An image signal having a pixel density of pixels / mm is obtained. The image signal generating device 30 includes a reading device 20 as shown in FIG.
An analog signal S0 output from the A / D converter 27 for sampling the analog signal S0 at a predetermined sampling frequency and outputting a digital signal;
Enlargement processing means 29 for performing processing for suppressing the aliasing distortion component due to the spatial frequency of the grid image on the digital signal output from the / D converter 27, and filtering means 31.
And an image reading unit 40 including a resampling unit 32, a selecting unit 28 for selecting an image reading process to be performed on the analog signal S0, and a grid removing unit 33 for removing the spatial frequency of the grid image.

The analog signal S0 output from the reading device 20 is an A / D converter 27 in the image signal generating device 30.
Entered in.

Here, in the image signal generating device 30, as shown in FIG. 4, either one of the first image reading process and the second image reading process is selected by the selecting means 28 based on a predetermined input signal. Then, the selection means 28 outputs a signal to the image reading means 40 so that the selected processing is applied to the analog signal S0. What is the first image reading process?
For an analog signal based on a radiographic image captured without using a grid or a radiographic image based on a radiographic image captured using a grid image but allowing the spatial frequency and aliasing distortion component based on the grid image This is the sampling process performed. Also, the second
The image reading process is a sampling process performed on an analog signal based on a radiographic image captured by using a grid, and is a process of suppressing a aliasing distortion component caused by a spatial frequency of a grid image. First and second
Details of the image reading process will be described later.

The selecting means 28 selects the first image reading process or the second image reading process based on a predetermined input signal. The predetermined input signal is, for example, an imaging menu having an imaging region and imaging conditions selected at the time of capturing a radiation image in the radiation image capturing apparatus, and is output from the radiation image capturing apparatus to the image signal generating apparatus 30. It is something. Then, the selection means 28 has a table as shown in FIG. 5, which shows information indicating whether or not each imaged region is compatible with the stationary grid. In addition, in the shooting menu shown in FIG. 5, a mark with a circle corresponding to a still grid means that the image is shot using the still grid and it is necessary to perform a process of suppressing the aliasing distortion component caused by the still grid, The ones marked with “X” corresponding to the stationary grid mean that the images have not been captured using the stationary grid, or that have been captured using the stationary grid but do not require the processing for suppressing the aliasing distortion component.

Then, when the selecting means 28 receives from the radiographic image capturing apparatus an image capturing menu of an image capturing site that does not correspond to the still grid, it selects the first image reading process by referring to the above table, and selects the first analog signal S0. A signal is output to the image reading means 40 so that the image reading process of (1) is performed. The A / D converter 27 in the image reading means 40 is
At this time, sampling processing is performed with a sampling pitch of 10 pixels / mm in both the main scanning direction and the sub scanning direction. Then, an image signal of 10 pixels / mm is output. Therefore, when the selection unit 28 selects the first image reading process, the image signal generation device 30 outputs the image signal in which the spatial frequency based on the grid image and the aliasing distortion component are still included.

On the other hand, when the reading processing control means 28 receives the information of the imaging menu of the imaging region corresponding to the stationary grid from the radiation image capturing apparatus, it refers to the above table and selects the second image reading processing, and the second The signal is output to the image reading means 40 so that the image reading process of (1) is performed on the analog signal S0.

The second image reading process in the present embodiment is a process for generating image data having a pixel density of 10 pixels / mm so that the aliasing distortion component due to the spatial frequency based on the grid image is 3 cycles / mm or more. Is.
As described above, processing is performed so that the aliasing distortion component is 3 cycles / mm or more. In medical images, there are many effective signal components at frequencies lower than the spatial frequency of 3 cycles / mm. This is because the noise of 1 does not significantly affect the image diagnosis.

The analog signal S0 obtained by reading the sheet 7 photographed using the grid of 4 lines / mm as described above includes the spatial frequency 4 cycle of the grid image.
/ Mm and its second harmonic 8 cycle / mm and 3
It contains 12 cycles / mm of the second harmonic. Note that the frequency characteristics of the analog signal S0 are as shown in FIG. 6 if the response of the third and higher harmonics is so small that it can be ignored.

The A / D converter 27 samples the analog signal S0 at a sampling interval of 10 pixels / mm in the main scanning direction, and 15 pixels / mm in the sub-scanning direction by changing the carrying speed in the sub-scanning direction. Sampling is performed at the sampling interval of.

Regarding the sampling in the main scanning direction, 10 pixels / m which is a particularly desired sampling interval.
The reason why the sampling is performed at a sampling interval smaller than m is that the signal is obtained as a continuous analog signal in the main scanning direction, and therefore the aliasing distortion component can be suppressed by the analog filter. This is because it is not necessary to perform sampling at a sampling interval smaller than the interval.

Then, the digital signal S2 sampled as described above is output to the enlargement processing means 29.
At this time, the frequency characteristic of the digital signal S2 output from the A / D converter 27 is as shown in FIG. In the frequency characteristics shown in FIGS. 7, 9 and 10, only the spatial frequency component of the grid image, its harmonic component and the aliasing distortion component are indicated by arrows. When the sampling is performed at a sampling interval of 15 pixels / mm, the Nyquist frequency is 7.5 cycle / mm, and therefore the aliasing distortion is caused by the spatial frequency component 4c of the grid image as shown in FIG.
11 cycle / mm for Cycle / mm, 7 cycle / m for 2nd harmonic component 8 Cycle / mm
m, 3c for 3rd harmonic component 12 cycle / mm
A component of cycle / mm will appear.

Next, in order to obtain image data having a pixel density of 10 pixels / mm from the digital signal S2 output from the A / D converter 27, 2/3 reduction processing is performed. This 2 /
The 3 reduction processing is performed by doubling the digital signal S2, performing filtering processing, and then performing 1/3 thinning (1/3 reduction).

First, the digital signal S2 is processed by the enlargement processing means 2
The data is output to 9 and is doubled in size. This double expansion process is performed by inserting a zero-value pixel between each pixel. This 2 × enlargement processing converts the digital signal S2 into 30 pixels /
Since the sampling interval of mm corresponds to resampling, the Nyquist frequency changes to 15 cycles / mm, but the frequency characteristic does not change from that shown in FIG. 7.

The digital signal S3 subjected to the enlargement processing by the enlargement processing means 28 is output to the filtering means 29. Here, the filtering unit 29 removes frequency components of 8 cycles / mm or more by performing filtering processing with a filter having a frequency characteristic as shown in FIG. 8, for example. This is 8 cycles / mm
This is because the presence of the above frequency components causes the aliasing distortion component of 3 cycles / mm or less at the time of resampling described later. Therefore, the frequency characteristic of the digital signal S4 obtained by performing the filtering process on the digital signal S3 is as shown in FIG.

The digital signal S4 output from the filtering means 29 is input to the resampling means 30. The resampling means 30 can obtain a digital signal S5 having a pixel density of 10 pixels / mm by subjecting the digital signal S4 to 1/3 decimation processing. In addition,
The ⅓ thinning processing is performed by the digital signal S so that the size of the image represented by the digital signal S4 becomes ⅓.
4 is a process of thinning out the number of pixels in the main / sub scanning direction to 1/3, which is a process corresponding to resampling at a frequency of 10 cycle / mm (Nyquist frequency of 5 cycle / mm). Therefore, at this time, FIG.
As shown in Fig. 3, a fold-back distortion of 6 cycle / mm occurs for a frequency component of 4 cycle / mm, but 3 cycle
It is possible to avoid the occurrence of folding distortion of le / mm or less.

The digital signal S5 in which the aliasing distortion component is suppressed as described above is output to the grid removing means 33. In the grid removing means 33, the spatial frequency of the grid image included in the digital signal S5 is 4 cyc.
le / mm and 3 cycle / m which is the aliasing distortion component
A process for removing frequency components of m, 6 cycle / mm and 7 cycle / mm is performed.

Therefore, when the second image reading processing is selected by the selecting means 28, the above-described processing is applied to the analog signal S0 to suppress the spatial frequency and aliasing distortion component of the grid image. The signal is output from the image signal generation device 30.

According to the radiation image reading apparatus using the image signal generating apparatus of the present invention, one of the first image reading process and the second image reading process is selected based on the photographing menu. Since the selected image reading process is applied to the radiation image, the reading process giving priority to the processing speed according to the imaging menu such as the imaging condition and the imaging region is performed on the radiation image, or the aliasing distortion component is added. It is possible to perform a reading process on the radiation image, which gives priority to the suppression of moire generation based on the radiation image.

In the above embodiment, the selection means 28
Is configured to select either the first image reading process or the second image reading process based on the imaging menu output from the radiation image capturing apparatus. However, the present invention is not limited to this and, for example, When the user inputs a predetermined signal to the selecting means 28 using an input means such as a keyboard, the selecting means 28 selects either the first image reading process or the second image reading process in response to this signal. You may do it.

Further, in the above embodiment, the grid removing process is performed only on the suppression-processed image signal which has been subjected to the second image reading process. However, as shown in FIG. 11, it is selected by the selecting means 28. It is also possible to select whether to perform grid removal processing on the processed image signal after the first image reading processing or the suppression processed image signal after the second image reading processing based on the information.

Further, as shown in FIG. 12, the grid removing process may be applied to the processed image signal after the first image reading process or the suppression processed image signal after the second image reading process. .

Further, the presence or absence of a periodic pattern such as a grid image is recognized by the method of Japanese Patent Application No. 2002-029737 or Japanese Patent Laid-Open No. 8-293020, and the grid removal processing is performed only when the periodic pattern exists. You may

In the above embodiment, the case where the stimulable phosphor sheet is read to obtain an image signal has been described as an example.
Not limited to this, the image signal generation method and apparatus of the present invention can be applied to the case where an image signal is obtained by a solid-state radiation detector or the like.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a radiation image reading apparatus to which an embodiment of an image signal generating apparatus according to the present invention is applied.

FIG. 2 is a diagram showing an example of a radiation image capturing apparatus.

FIG. 3 is a diagram showing a radiation image obtained by performing imaging using a grid.

FIG. 4 is a diagram illustrating selection of an image reading process in an image signal generation device.

FIG. 5 is a table showing the relationship between the shooting menu and still grid correspondence.

FIG. 6 is a frequency characteristic of an analog signal obtained by reading a phosphor sheet photographed using a grid of 4 lines / mm.

FIG. 7 is a frequency characteristic of image data when an analog signal is sampled at a sampling interval of 15 pixels / mm.

FIG. 8 is a diagram showing characteristics of a filter that removes frequency components of 8 cycle / mm or more.

9 is a frequency characteristic of image data filtered by the filter shown in FIG.

10 is a frequency characteristic of the image data shown in FIG. 9 after resampling processing.

FIG. 11 is a diagram illustrating grid removal processing in the image signal generation device.

FIG. 12 is a diagram illustrating grid removal processing in the image signal generation device.

[Explanation of symbols]

1 Radiation source 2 radiation 3 subject 4 grid 5 subject image 6 grid image 7 Storage phosphor sheet 10 Transport means 12 Laser light source 14 light beam 16 Bright emission light 17 mirror 18 motor 20 reader 22 rotating polygon mirror 23 Focusing lens 24 light guide 25 Photo Multiplier 26 log amplifier 27 A / D converter 28 Selection means 29 Enlargement processing means 30 image signal generator 31 Filtering means 32 resampling means 33 Grid removal means 40 image reading means

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H013 AC03 AC06                 4C093 AA26 AA28 CA06 CA13 CA29                       EB05 EB24 FA13 FD01 FD05                       FF03 FF13                 5C072 AA01 BA09 BA18 CA06 DA02                       DA04 EA02 UA06 UA09 VA01

Claims (5)

[Claims] 1. A first image reading process for obtaining a first image signal by sampling an original image at a desired sampling frequency; and an initial image obtained by sampling the original image at a frequency higher than the desired sampling frequency. A signal is obtained, and the initial image signal is subjected to a suppression process of suppressing a aliasing distortion component that occurs when resampled at the desired sampling frequency, and the suppression-processed image signal subjected to the suppression process is resampled. One of the second image reading process for obtaining the second image signal and the other image reading process is selected based on a predetermined input signal, and the selected image reading process is performed on the original image. Image signal generating method. 2. The first image reading process, wherein the original image is higher than the desired sampling frequency and the second image
2. The image signal generation method according to claim 1, wherein the image reading process is a process of sampling at a frequency lower than a frequency used when obtaining the initial image signal and then sampling at the desired sampling frequency. 3. A first image reading process for performing a first image reading process for sampling an original image at a desired sampling frequency to obtain a first image signal; and the original image having a frequency higher than the desired sampling frequency. Sampling at a high frequency to obtain an initial image signal, the initial image signal is subjected to a suppression process that suppresses a aliasing distortion component that occurs when resampled at the desired sampling frequency, and the suppression process that has been subjected to the suppression process has been performed. An image reading unit capable of selectively performing a second image reading process of performing a second image reading process of re-sampling the image signal to obtain a second image signal, and a predetermined image reading unit. One of the first image reading process and the second image reading process of the image reading means is selected based on an input signal, and the selected image reading process is applied to the original image. Image signal generating apparatus characterized by comprising a select means. 4. The first image reading process, wherein the original image is higher than the desired sampling frequency and the second image
4. The image signal generation according to claim 3, wherein the sampling is performed at a frequency lower than the frequency used when the initial image signal is obtained in the image reading processing of FIG. apparatus. 5. The image signal generating device according to claim 3, wherein the predetermined input signal is a shooting menu of the original image.