JP2001218058A - Method and device for image processing and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make both a tumor shadow and a calcified opacity proper images in the case of applying enhancement processing to a mammography image by using a nonlinear conversion function. SOLUTION: Each signal is subjected to nonlinear conversion by using a nonlinear conversion function corresponding to each signal where output contrast about a highest frequency band limitation image signal is double as much as that of a lowest frequency band limitation image signal in a low contrast area (<=10) and in middle and high contrast areas (>=10). Enhancement processing is carried out by adding a signal obtained by estimating the converted signal to an original image signal. The degree of enhancement can be adjusted in accordance with both the frequency area and the image contrast of each signal, the enhancement degree of the tumor shadow can be small, and meanwhile, the enhancement degree of the calcified opacity can be large. Therefore, it is possible to solve the problem that the calcified opacity looks out-of-focus by making the enhancement processing of the tumor shadow equal to the enhancement of the calcified opacity.

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 a contrast changing process such as an emphasis process on an image, and a computer readable program storing a program for causing a computer to execute the image processing method. The present invention relates to a simple recording medium.

[0002]

2. Description of the Related Art In the field of image processing for handling medical images, for example, a response characteristic of an output contrast with respect to an input contrast has a non-linear characteristic (contrast of an image is changed non-linearly). ) May be used.

As one mode of signal processing using this non-linear image processing, for example, the present applicant has disclosed in Japanese Patent Application Laid-Open No. 55-163472.
No. 55-87953, JP-A-3-222577, No. 10-75364,
Nos. 10-75395 and 10-171983, an input image signal is divided into a plurality of band-limited image signals each having a predetermined bandwidth using an unsharp mask image signal (blurred image signal). Performing the non-linear image processing on each band-limited image signal, performing a frequency enhancement process or a dynamic range compression process using each of the converted band-limited image signals subjected to the non-linear image processing, and performing a diagnostic performance of a radiation image. Many image processing methods have been proposed to improve the image quality.

Further, as a method of dividing the image into each band-limited image signal, a method using a multi-resolution conversion such as a wavelet transform or Laplacian pyramid expansion may be used. The present applicant also discloses, for example, JP-A-6-27
No. 4615, No. 6-350989, etc., various image processing methods have been proposed in which each band-limited image signal obtained by wavelet transform is used to emphasize only edge components in an image.

Further, Japanese Patent Application Laid-Open No. Hei 5-244508 proposes an image processing method for performing processing such as enhancing image contrast using each band-limited image signal obtained by Laplacian pyramid expansion.

Incidentally, there is mammography (breast diagnosis) as one use form of the image processing using the converted band-limited image signals subjected to the above-described non-linear image processing. This mammography is mainly for reading a tumor shadow which is a low contrast image and a calcified image which is a high contrast image.

Here, the above-mentioned non-sharp mask image signal is subjected to the non-linear image processing for each band-limited image signal to obtain each of the converted band-limited image signals, and then to the frequency emphasis processing. When processing (also referred to as non-linear image processing using a blurred image signal) is applied to mammography, two types of image processing with different processing contents, such as low-frequency enhancement of a tumor shadow and high-frequency enhancement of a calcified image, are usually performed. The diagnosis is performed using these two images.

On the other hand, the non-linear image processing is performed on each band-limited image signal obtained by using a multi-resolution transform such as a wavelet transform to obtain each of the converted band-limited image signals, and then the frequency emphasis is performed. When applying processing (also called non-linear image processing using multi-resolution conversion) to mammography, a relatively low-frequency component corresponding to a tumor shadow and a relatively high-frequency component corresponding to a calcified image are separately processed. Since the emphasis can be made, there is an advantage that the degree of freedom of the processed image is increased and the diagnostic performance is improved.

[0009]

However, in the case of performing the frequency enhancement processing after performing the non-linear image processing on each band-limited image signal obtained using the above-described various methods, for example, in mammography, a tumor It was found that if the enhancement processing of the shadow (low-frequency band image) is equal to or stronger than the enhancement of the calcified image (high-frequency band image), the calcified image looks blurred.

Further, by performing the above-mentioned non-linear image processing on each band-limited image signal, artifacts such as overshoot and undershoot due to enhancement are suppressed. It has also been found that a new problem arises in that the calcification becomes worse (the shape of the calcification becomes difficult to see). Since the shape of the calcification image of mammography is a measure of malignancy evaluation of calcification (if the calcification shape is jagged, there is a possibility of malignancy), such an artifact suppression process in which the calcification shape is blurred, It is not suitable for calcification diagnosis.

That is, when a process of changing the image contrast such as a frequency emphasis process is performed using each of the converted band-limited image signals subjected to the non-linear image process, depending on the degree of emphasis, the low-frequency band image and the high-frequency band image are changed. There is a problem that an appropriate image is not always obtained in either one or both.

The present invention has been made in view of the above circumstances. For example, when performing a process of changing image contrast such as a frequency emphasis process using a converted band-limited image signal subjected to non-linear image processing, for example, mammography An image processing method and apparatus capable of forming an appropriate image in both the low-frequency band image and the low-frequency band image, such as a tumor shadow and a calcified image, and a computer for executing the image processing method. It is an object of the present invention to provide a computer-readable recording medium on which a program is recorded.

[0013]

According to a first image processing method of the present invention, an image signal is divided into a plurality of band-limited image signals each having a predetermined bandwidth. An image processing method for performing a non-linear conversion process and performing a process of changing image contrast using each converted band-limited image signal subjected to the non-linear conversion process,
The process of changing the image contrast sets the degree of enhancement in the low contrast region with respect to the band-limited image signal having a relatively high frequency band among the band-limited image signals, and sets the degree of enhancement in the relatively low frequency band among the band-limited image signals. It is characterized in that the degree of enhancement is higher than the degree of enhancement in the low contrast area for the band-limited image signal.

In the processing for changing the image contrast in the first image processing method, the degree of enhancement in the low-contrast region with respect to the band-limited image signal having the highest frequency band among the band-limited image signals is determined. It is preferable that the degree of enhancement in the low-contrast region with respect to the band-limited image signal having the lowest frequency band among the signals is at least twice or more.

In contrast to the first image processing method, in the second image processing method according to the present invention, the processing for changing the image contrast is performed by using a band-limited image having a relatively high frequency band among the band-limited image signals. It is characterized in that the degree of enhancement of the signal in the middle-high contrast region is made larger than the degree of enhancement of the band-limited image signal having a relatively low frequency band among the band-limited image signals in the middle-high contrast region. That is, while the first method targets a low contrast region, the second method targets a middle / high contrast region.

In the second image processing method, the image contrast is changed by changing the degree of enhancement of the band-limited image signal having the highest frequency band among the band-limited image signals in the middle-high contrast region by using each band-limited image signal. It is preferable that the degree of enhancement is at least twice as high as the degree of enhancement in the middle and high contrast regions with respect to the band-limited image signal having the lowest frequency band among the image signals.

It is more preferable that the first method and the second method are combined to perform processing for changing image contrast.

In the image contrast, a region having a relatively low contrast is referred to as a low contrast region, and a region having a relatively high contrast is referred to as a medium / high contrast region. Absent. Here, for example, the low contrast region is a region at least 1/100 or less of the maximum contrast of the image signal, and the middle and high contrast region is a region at least 1/100 or more of the maximum contrast of the image signal. Good to do.

A third image processing method according to the present invention divides an image signal into a plurality of band-limited image signals each having a predetermined bandwidth, and performs non-linear conversion processing or linear conversion on each of the band-limited image signals. An image processing method for performing processing and changing image contrast using each of the converted band-limited image signals subjected to the conversion processing, wherein a relatively low frequency band of each band-limited image signal is used. Non-linear conversion processing is performed on the band-limited image signal so that the output contrast is smaller than the input contrast of the image signal, and the band-limited image signal having a relatively high frequency band among the band-limited image signals is And performing a linear conversion process so that the output contrast is higher than the output contrast of the band-limited image signal having a relatively low frequency band.

In the non-linear conversion process in the third image processing method, the output contrast of the band-limited image signal having the lowest frequency band among the band-limited image signals is determined by comparing the output contrast of the band-limited image signal with the lowest frequency band. Preferably, the output contrast is at least 少 な く と も or less of the output contrast of the high band-limited image signal.

In the above description, the processing for changing the image contrast may be any processing as long as it is an emphasis processing for performing each of the above-described methods. Further, any method may be used as a method of the enhancement process itself, and the present invention is applied to various enhancement processes proposed in, for example, JP-A-5-244508 and JP-A-10-75395. can do.

In the above, the degree of enhancement in the low (or middle and high) contrast region with respect to the band-limited image signal having a relatively high (or highest) frequency band is determined by comparing the band-limited image signal with a relatively low (or lowest) frequency band. Is greater than the degree of enhancement in the low (or medium-high) contrast region with respect to low contrast images in relatively low frequency regions regardless of the mode of image contrast changing processing such as enhancement processing or dynamic range compression processing. In other words, the contrast value should be relatively small (meaning the high frequency region) and the contrast value should be relatively large (meaning the low frequency region) for a high contrast image in a relatively high frequency region. Means

A first image processing apparatus according to the present invention is an apparatus for implementing the above-mentioned first image processing method, that is, a band limit for dividing an image signal into a plurality of band-limited image signals each having a predetermined bandwidth. Image signal generating means, converting means for performing non-linear conversion processing on each of the generated band-limited image signals, and processing for changing image contrast using each of the converted band-limited image signals subjected to the non-linear conversion processing. An image processing apparatus comprising: a processing unit configured to determine, in each of the band-limited image signals, a degree of enhancement in a low-contrast region with respect to a band-limited image signal having a relatively high frequency band. It is characterized in that the degree of emphasis in a low-contrast region with respect to a band-limited image signal having a relatively low frequency band in the image signal is increased.

The processing means in the first image processing apparatus comprises:
The degree of enhancement in the low-contrast region with respect to the band-limited image signal having the highest frequency band among the band-limited image signals is set in the low-contrast region with respect to the band-limited image signal having the lowest frequency band among the band-limited image signals. Preferably, the degree of emphasis is at least twice or more.

A second image processing apparatus according to the present invention is an apparatus for implementing the above-mentioned second image processing method, that is, a band limiting apparatus for dividing an image signal into a plurality of band limited image signals each having a predetermined bandwidth. Image signal generating means, converting means for performing non-linear conversion processing on each of the generated band-limited image signals, and processing for changing image contrast using each of the converted band-limited image signals subjected to the non-linear conversion processing. An image processing apparatus comprising: a band-limiting image signal having a relatively high frequency band among the band-limited image signals. It is characterized in that the degree of enhancement of a band-limited image signal having a relatively low frequency band in the image signal is made larger than the degree of enhancement in the middle and high contrast regions. .

The processing means in the second image processing apparatus comprises:
The degree of emphasis in the medium-high contrast region for the band-limited image signal having the highest frequency band of each band-limited image signal is determined in the medium-high contrast region for the band-limited image signal having the lowest frequency band of each band-limited image signal. Preferably, the degree of emphasis is at least twice or more.

An image processing apparatus including both the first and second image processing apparatuses, that is, an image processing apparatus having both processing means in the first image processing apparatus and processing means in the second image processing apparatus A device is more preferable.

A third image processing apparatus according to the present invention is an apparatus for implementing the third image processing method, that is, a band for dividing an image signal into a plurality of band-limited image signals each having a predetermined bandwidth. A limited image signal generating unit, a converting unit for performing a non-linear conversion process or a linear conversion process on each of the generated band-limited image signals, and an image contrast using each of the converted band-limited image signals subjected to the conversion process. And a processing unit for performing a process of changing the output contrast of the band-limited image signal of a relatively low frequency band among the band-limited image signals. A non-linear conversion process is performed so as to be smaller than the input contrast of the image signal, and a band-limited image signal having a relatively high frequency band among the band-limited image signals is output. Wherein the contrast is to subject the linear conversion process so than larger output contrast of relatively frequency band low band-limited image signals.

The conversion means in the third image processing device may be arranged so that the output contrast of the band-limited image signal having the lowest frequency band among the band-limited image signals is the highest in the frequency band of each band-limited image signal. It is preferable to perform the non-linear conversion process so that the output contrast of the band-limited image signal is at least 1/2 times or less.

The first and second image processing methods according to the present invention may be provided by being recorded on a computer-readable recording medium as a program for causing a computer to execute the method.

[0031]

According to the first and second methods and apparatuses according to the present invention, the degree of emphasis in a low or middle / high contrast region with respect to a band-limited image signal having a relatively high frequency band among the band-limited image signals is determined. Since the degree of emphasis in the low or medium-high contrast region for the band-limited image signal having a relatively low frequency band in each band-limited image signal is set to be larger than that of the band-limited image signal, The degree of emphasis can be adjusted according to both. As a result, if the present invention is applied to, for example, mammography, the calcified image is reduced due to the problem that the calcified image looks blurred by making the enhancement processing of the tumor shadow equal to or stronger than the enhancement of the calcified image and the artifact suppression effect. It is possible to solve the problem that the appearance of the margin becomes poor, and to provide an image in which the extraction power of both the tumor shadow and the calcified image in the mammography image is improved.

Further, according to the third method and apparatus according to the present invention, a non-linear conversion process is performed on a band-limited image signal having a relatively low frequency band among the band-limited image signals, Since the band-limited image signal having a high band is subjected to the linear conversion processing that is larger than the output contrast by the non-linear conversion processing, the artifact suppression processing is not performed in a relatively high frequency band. As a result, the degree of emphasis can be adjusted according to both the frequency domain and the image contrast of each band-limited image signal in substantially the same manner as in the first and second methods and apparatuses. It is possible to obtain substantially the same effects as the method and the device of the second aspect.

[0033]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram illustrating the concept of an image processing apparatus according to the present invention. The image processing apparatus according to the present invention as shown in FIG. 1, blurred image to create an unsharp image signal in the frequency response characteristics from each other on the basis of the input original image signal Sorg is different multiresolution Sus _{k (k} = 1~n) and signal forming means 1, the band-limited image signal forming means 2 for creating a plurality of band-limited image signal on the basis of the unsharp image signal Sus _k created in the unsharp image signal forming means 1, the band-limited image signal forming means 2 A conversion unit for performing a non-linear conversion process on at least one of the plurality of band-limited image signals generated so as to reduce at least a part of the band-limited image signal; Integrating means 4 for integrating the processed band-limited image signal to generate an integrated signal, and multiplying the integrated signal by a predetermined emphasis coefficient and adding the resultant signal to the original image signal Sorg. Consisting frequency emphasis processing means 5 for obtaining a processed image Sproc a high frequency component is emphasized.

First, the processing performed in the blurred image signal creating means 1 will be described. FIG. 2 is a block diagram showing the processing of the blurred image signal creating means 1. As shown in FIG. 2, the digital original image signal Sorg representing the original image is filtered by the low-pass filter in the filtering processing means 10. As the low-pass filter, for example, a filter F substantially corresponding to a one-dimensional Gaussian distribution in a 5 × 1 grid as shown in FIG. 3 can be used. This filter F is expressed by the following equation (1).

(Equation 1) , Σ = 1. Here, the reason why the Gaussian signal is used as the filter F is that the Gaussian signal has good localization in both the frequency space and the real space.

Then, the filtering process is performed by the filter F in the x and y directions of the pixels of the original image, whereby the entire original image signal Sorg is subjected to the filtering process.

In the filtering processing means 10,
A filtering process is performed by such a filter F as follows. FIG. 4 is a diagram illustrating details of the filtering process. As shown in FIG. 4, the original image signal Sor
g is subjected to a filtering process for every other pixel by a filter F shown in FIG. And by this filtering process, the filtering-processed image signal B ₁ is obtained. The filtering-processed image signals _{B 1} represents the size of the original image is a 1/4 (x-direction, respectively in the y-direction 1/2). Then, filtering every other pixel with respect to the filtering-processed image signal B ₁ is applied again by the filter F. The filtering process by the filter F is repeatedly performed, so that the n filtered image signals B
_k (k = 1 to n) is obtained. This filtered image signal _Bk has a size of 1 / ^22k with respect to the original image. At this time, the filtered image signal B _k
Are as shown in FIG. Response of the filtering-processed image signals B _k, as shown in FIG. 5 has assumed a high frequency component is removed as k is large (but is set to k = 1 to 3 in FIG. 5).

In the above embodiment, the one-dimensional filter F shown in FIG.
Although the filtering process is performed in the direction, the filtering process is performed on the original image signal Sorg and the filtered image signal at a time by a 5 × 5 two-dimensional filter as shown in FIG. You may make it.

[0038] Then, such interpolation calculation processing in the interpolation processing unit 11 shown in FIG. 2 with respect to the filtering-processed image signals B _k obtained in is performed, thereby the same original image size multiple A blurred image with a resolution is obtained. Hereinafter, the interpolation calculation processing will be described.

Various methods such as a B-spline method can be used for the interpolation operation. In the embodiment of the present invention, since the filter F based on the Gaussian signal is used as the low-pass filter, the interpolation operation is performed. It is assumed that a Gaussian signal is also used as an interpolation coefficient for performing. Here, the interpolation coefficient using the Gaussian signal is represented by the following equation (2).

(Equation 2) In the above, an approximation of σ = 2 ^k−1 is used.

[0040] When the interpolating operation for the filtering-processed image signals _{B 1} represents, a sigma = 1 since a k = 1. In the above equation (4), a filter for performing interpolation when σ = 1 is a 5 × 1 one-dimensional filter as shown in FIG. First filtering-processed image signals B ₁ by a value 1 pixel every other filtering-processed image signal B ₁ is interpolated by one pixel 0 is enlarged to the same size as the original image. Thus the filtering-processed image signal B ₁ having pixels interpolated values 0 are shown in one-dimensionally FIG. The filter F shown in FIG. 7 described above with respect to the interpolated filtering image signals B _1
1 performs a filtering process.

[0041] Here, the filter _{F 1} shown in FIG. 7 is 5 ×
It is a first filter, the filtering-processed image signals B ₁ as shown in FIG. 8 is a pixel value in every other pixel is 0 is interpolated. Therefore, the filtered image B
Filtering processing performed by the filter F ₁ with respect to ₁ is substantially 2 × 1 filter (0.5, 0.5) in and 3 × 1 filters (0.1, 0.8, 0.1) by two filters, facilities This is equivalent to the filtering process performed. And by this filtering process, the original image signal Sorg and the same number of data or signals Sus ₁ of the original image and the same size of the blurred image is obtained.

Next, the filtered image signal B
_{2 is} subjected to a filtering process. In the interpolating operation for the filtering-processed image signal B ₂ are the k = 2, the sigma = 2. In the above equation (4), σ =
The filter for performing the interpolation when 2 is used is an 11 × 1 one-dimensional filter as shown in FIG. Then, the filtering-processed image signal B ₂ by a value in every other pixel is interpolated by the three pixels of 0 as shown in FIG. 11 is enlarged to the same size as the original image is first with respect to the filtering-processed image signal B ₂ You. Value filtering process by the filter F ₂ shown in FIG. 9 described above is carried out on the filtering-processed image signal B ₂ which pixels are interpolated zero.

[0043] Here, the filter _{F 2} shown in FIG. 9 11
Is a filter × 1, the filtering-processed image signal B ₂ as shown in FIG. 10 is a pixel value in every other pixel is 0 is by three interpolated. Therefore, the filtering process performed on the filtered image signal B ₂ by the filter F ₂ is substantially a 2 × 1 filter (0.5, 0.5) and a 3 × 1 filter (0.3, 0.65,
0.05), (0.13, 0.74, 0.13) and (0.05, 0.65,
0.3) It is equivalent to the filtering process performed by the four types of filters. And by this filtering process, the original image signal Sorg and the same number of data of the blurred image signal Sus ₂ is obtained.

Such filtering processing is performed
Filtering image signal B _kDone against
You. Filtered image signal B_kWhen interpolating
Is 3 × 2 based on the above equation (4).^k -1 of length
Create a filter and filter image signal B_k
2 pixels with a value of 0 between each pixel^k Interpolate one by one
As a result, the image is enlarged to the same size as the original image. This value
Filtered image signal B in which the pixel of 0 is interpolated
_k3 × 2^k With a filter of length -1,
Filtering processing is performed.

Here, the filtering process performed by the filter having a length of 3 × 2 ^k −1 is equivalent to the filtering process performed by a filter having a length of 2 or 3 in a ^2k cycle. . And by this filtering process, n number of unsharp image signals Sus _k is obtained. Expressing this unsharp image signal Sus _k as a visible image,
As a result, blurred images having different resolutions, that is, multi-resolution blurred images having different frequency response characteristics are obtained. As described above, although the filter becomes longer, the filtering amount is substantially the same as that in which the filtering process is performed by the filter having the length of 2 or 3, so that the calculation amount does not become so large even if the filter becomes longer. Things. For this reason, the calculation amount is reduced, and the multi-resolution blurred image signal Sus
_k can be created at high speed.

In this embodiment, the length is 3
× 2^k The one-dimensional filter of -1 allows the
Filtering is applied in the x and y directions
However, a two-dimensional filter is created in advance and
Filter on the filtered image
By applying the filtering process, the blurred image signal Sus _k
 May be obtained. In this case, the filter
Filter for performing interpolation operation on the scanned image
The filter used for ring processing is (3 × 2^k-1) ×
(3 × 2^k -1), but the above-mentioned first order
As with the original filter, this is 2^k period
Filter applied by a 2 × 2 or 3 × 3 filter
Is equivalent to the one-dimensional filtering described above.
Filter size, as in the case of using
Even so, the amount of computation for performing the filtering process is
Qualitatively, it is not so large.

The blurred image signal Sus thus obtained
FIG. 11 shows the frequency characteristic of _k . As shown in FIG. 11, the larger the value of k of the unsharp image signal Sus _k,
The original image signal Sorg is a signal from which high frequency components have been removed.

FIG. 12 is a diagram showing the overall configuration of an embodiment of the image processing apparatus of the present invention including the blurred image signal creating means of FIG. 2, as shown in FIG. Each of the blurred image signals generated by the blurred image signal creating means 1 is then converted to a band-limited image signal creating means 2.
And the conversion means 3. As shown in FIG. 12, first, the original image signal Sorg and the unsharp image signals a plurality of unsharp image signals created in the creation unit 1 Sus _k
Although the band-limited image signal is generated on the basis of, this band-limited image signal subtracter 21, obtained by performing a subtraction of the unsharp image signal Sus _k frequency bands adjacent to each other. In other words, Sorg -Sus _1, Sus ₁ -
By sequentially calculating Sus ₂ ,... Sus _N−1 −Sus _N , a plurality of band-limited image signals are obtained. FIG. 13 shows the frequency characteristics of the band-limited image signal. As shown in FIG. 13, the band-limited image signal unsharp image signal Sus _k
As the value of k becomes larger, the signal becomes a signal representing the band of the low frequency component of the original image signal Sorg.

Next, the conversion means 3 performs a non-linear conversion process on the band-limited image signal obtained in this manner in accordance with the image contrast (input contrast) and the frequency domain indicated by the band-limited image signal. In the non-linear conversion processing, the converter 22 has a non-linear conversion function f as shown in FIG. 14, for example, when the absolute value (input contrast) of the band-limited image signal is smaller than the threshold Th1, the gradient is a predetermined fixed value. If the threshold value is larger than the threshold value Th1, the inclination is smaller than the fixed value, and the threshold value T
When the value becomes much larger than h1, the function is performed by using a function such that the inclination becomes 0 (constant at a predetermined value).

The converted band-limited image signal converted by the non-linear conversion function f is input to the arithmetic unit 23 including the integrating means 4 and the frequency enhancement processing means 5 described above. In the arithmetic unit 23, the following processing is performed. First, the converted band-limited image signal converted by the function f as described above is integrated in the arithmetic unit 23 to obtain a signal (integrated signal) Fusm required for the frequency emphasizing process, and further, a predetermined coefficient β is added to the signal Fusm. After being multiplied by (Sorg), it is added to the original image signal Sorg to generate a processed image signal Sproc.

The processing performed by the band-limited image signal creating means 2, the converting means 3, the integrating means 4, and the frequency emphasizing processing means 5 is expressed by the following equation (3). Sproc = Sorg + β (Sorg) · Fusm (Sorg, Sus 1, Sus 2, ... Sus N) Fusm (Sorg, Sus 1, Sus 2, ... Sus N) = {f 1 (Sorg -Sus 1) + f 2 (Sus ₁₋ Sus ₂ ) +... + F _k (Sus _k−1 −Sus _k ) +... + F _N (Sus _N−1 −Sus _N )｝ (3) (where, Sproc: an image signal Sorg in which high-frequency components are emphasized) : original image signal Sus _{k (k} = 1~N): unsharp mask image signals f _{k (k} = 1~N): a function for converting the band-limited image signals, f ₁ is the highest frequency band-limited image signal f _N is a lowest frequency band-limited image signal beta (Sorg): emphasis coefficient determined based on the original image signal)

Here, the frequency band necessary for diagnosis differs depending on the imaging site at the time of obtaining the original image. For example, in a double-contrast image of the lung and the stomach, it is preferable that the lung emphasizes relatively low-frequency components, and that the stomach emphasizes relatively high-frequency components in order to observe folds in the stomach wall. On the other hand, in images containing metals such as bones and artificial bones,
It is necessary to prevent artifacts due to over-emphasis of these edge parts, but for an image that does not include edge parts such as bones such as mammography,
Artifacts are unlikely to occur, and there is also a problem in that if a frequency component is emphasized similarly to an image including a bone, a portion necessary for observation becomes difficult to see. Therefore, it is desirable to change the shape of the function f shown in FIG. 14 according to the imaging site when obtaining the original image.

For example, in an image including a bone, the function f is set to B to suppress the high frequency component of the band-limited image signal so that an artifact does not easily occur at an edge portion. In an image that does not include the image, the high-frequency component is also emphasized by setting the function f as A, so that the nonlinear conversion processing is performed so that the absolute value of the band-limited image signal becomes large.

Further, when an enhancement process is performed on an image, generally, the degree of enhancement in the low contrast area (the relationship between the input value and the output value) mainly contributes to the balance of the entire image. Contributes to the balance between the appearance of tumor shadows and the appearance of calcified images.
Becomes difficult. On the other hand, the degree of enhancement in the middle-high contrast region contributes to artifact suppression, and as described in the section of the related art, when the artifact suppression is strengthened (more artifact suppression) in the middle-high frequency band with a large amount of calcification information, It becomes difficult to diagnose the shape of the chemical image. In addition, in the low frequency band, since the boundary between the skin and the X-ray part is included in addition to the tumor shadow, if the suppression of the artifact is weakened, a large artifact occurs at the skin boundary. Therefore, artifact suppression in the low frequency band is strong,
It is preferable to set a nonlinear conversion function so that artifact suppression in a high-frequency band is weakened. It is desirable to change the shape of the function f shown in FIG. 14 according to the frequency band (frequency domain) of the band-limited image signal.

From the above, for example, for application to mammography, a different fixed value (slope) is used for the function f shown in FIG. 14 according to the frequency band of each band-limited image signal, and The lower the frequency band, the smaller the fixed value, that is, the smaller the slope.

FIG. 15 shows an example of a non-linear conversion function set to be applied to mammography based on such considerations, and differs according to the frequency domain of each band-limited image signal. FIG. 9 is a diagram illustrating an aspect using a nonlinear conversion function having characteristics. It is assumed that the maximum contrast of the input image is 1023. Also,
The low contrast area has the maximum contrast (1023)
, Where the contrast is 10 or less, and the medium-high contrast area is 1/100 or more of the maximum contrast (1023), where the contrast is 11 to 1023. .

The non-linear conversion function shown in FIG. 15A is an example of a non-linear conversion function for a band-limited image having the lowest frequency band (lowest frequency band-limited image signal).
The non-linear conversion function shown in FIG. 5 (B) is an example of a non-linear conversion function for a band-limited image having the highest frequency band (highest frequency band-limited image signal). FIG. 15 (A), (B)
In the example shown in FIG. 7, the output contrast of the lowest frequency band limited image signal is 5 with respect to the input contrast 10 as the low contrast region, and the output contrast of the highest frequency band limited image signal is 10
It is. Also, the output contrast of the lowest frequency band limited image signal is 10 with respect to the input contrast 100 as the middle and high contrast area, and the output contrast of the highest frequency band limited image signal is 2
0. FIG. 15C shows an example in which only the highest frequency band limited image signal is not subjected to the non-linear conversion processing, and the output contrast is equal to the input contrast (that is, a one-to-one linear conversion function).

Therefore, for example, FIG.
By using one of (B) or a combination of both, or by using FIGS. 15 (A) and 15 (C) in combination, both the frequency domain and the image contrast of each band-limited image signal are used. , The degree of emphasis can be adjusted. For example, the degree of enhancement in a low-contrast region (contrast value less than 10) for a band-limited image signal having a relatively high frequency band is made larger than that in a low-contrast region for a band-limited image signal having a relatively low frequency band. In particular, in this example, the degree of enhancement in the low contrast region with respect to the highest frequency band limited image signal is two times the degree of enhancement in the low contrast region with respect to the lowest frequency band limited image signal.
It can be about twice (or more). Further, the emphasis degree in a medium-high contrast region (contrast value of 10 or more) with respect to a band-limited image signal having a relatively high frequency band is expressed by:
It is possible to increase the degree of enhancement in the middle-high contrast region for the band-limited image signal having a relatively low frequency band, and in this example, in particular, the degree of enhancement in the middle-high contrast region for the highest frequency band-limited image signal,
It can be set to about twice (or more) the degree of enhancement of the lowest frequency band limited image signal in the middle and high contrast areas.

In the above description, the setting of each nonlinear conversion function for the highest frequency band limited image signal and the lowest frequency band limited image signal has been described. However, for the band limited image signal located in the intermediate frequency region between them. However, it is preferable to set each nonlinear conversion function so that the degree of artifact suppression gradually decreases from the lowest frequency band to the highest frequency band.

Further, by using the mode in which FIGS. 15A and 15C are combined, it is possible to set the artifact suppression only in the highest frequency band to be weak (not to suppress it at all in the example of FIG. 15). In both the contrast region and the middle-high contrast region, the degree of emphasis on a band-limited image signal having a relatively high frequency band can be made larger than that of a band-limited image signal having a relatively low frequency band. In particular, the degree of enhancement for the highest frequency band limited image signal when the input contrast is 100 or more can be extremely increased.

As described above, according to the image processing apparatus having the above configuration, the degree of emphasis can be adjusted in accordance with both the frequency domain and the image contrast of each band-limited image signal, and the low level of the relatively low frequency domain can be adjusted. While the degree of enhancement for a contrast image is reduced, the degree of enhancement for a high-contrast image in a relatively high frequency region can be increased. For example, in mammography, the degree of enhancement can be reduced for a tumor shadow that appears as a relatively low-frequency component and a low-contrast image, while the degree of enhancement can be reduced for a calcified image that appears as a relatively high-frequency component and a high-contrast image. The problem that the calcified image looks blurry can be solved by making the enhancement processing of the tumor shadow equal to or stronger than the enhancement of the calcified image.

Further, in the above embodiment, the degree of enhancement of the calcified image is set to about twice the degree of enhancement of the tumor shadow, so that the calcified image is not excessively enhanced.

Further, since at least each band-limited image signal except for the highest frequency band-limited image signal is always subjected to non-linear image processing, artifacts such as overshoot and undershoot due to enhancement can be suppressed. The calcified image (high-contrast image of the medium-frequency component) has a relatively higher degree of emphasis (about twice as large in this example) than the tumor shadow. It is also possible to solve the problem that the appearance of the periphery of the image becomes poor (the shape of the calcification becomes difficult to see).

As described above, according to the present invention, an image suitable for observation can be obtained without being affected by the image contrast even if the frequency emphasis processing is performed. For example, the present invention can be applied to mammography. By providing an image that is easy to diagnose both the tumor shadow and the calcified image,
Diagnosis can be performed with one image, and diagnostic performance and efficiency can be dramatically improved.

Although the preferred embodiment of the present invention has been described above, the present invention is not necessarily limited to the above-described embodiment.

For example, in the above embodiment, the above equation (3)
To obtain the processed image signal Sproc,
For example, the frequency emphasis processing may be performed using another equation described in Japanese Patent Application Laid-Open No. 10-75395.

In the above embodiment, the nonlinear conversion functions having different characteristics according to the frequency domain of the band-limited image signal are used, so that the degree of enhancement is determined according to both the frequency domain and the image contrast of each band-limited image signal. Was adjusted, but is not necessarily limited to this. In short, various methods can be used as long as the degree of enhancement for a low-contrast image in a relatively low-frequency region can be reduced while the degree of enhancement for a high-contrast image in a relatively high-frequency region can be increased. For example, the emphasis coefficient β may be made frequency-dependent, that is, a nonlinear conversion function having the same characteristic may be used for each band-limited image signal, while the emphasis coefficient β may be different depending on the frequency domain of each band-limited image signal. Good.

In the above embodiment, the frequency emphasis processing using the wavelet transform as the multi-resolution conversion has been described. However, the Laplacian pyramid may be used. A frequency enhancement process using a blurred image signal (unsharp mask image signal) proposed by the applicant in Japanese Patent Application Laid-Open No. 10-75395 may be used.

Further, in the above-described embodiment, as an example of the processing for changing the image contrast, the frequency emphasis processing has been described. However, the present invention is not limited to this.
For example, a dynamic range compression process proposed in No. 64 or the like may be used. In this case, the degree of suppression for a low-contrast image in a relatively low-frequency region may be increased, while the degree of suppression for a high-contrast image in a relatively high-frequency region may be reduced. That is, according to the present invention, the contrast value is relatively relative to the low-contrast image in the relatively low-frequency area (relative to the high-frequency area), regardless of the mode of the image contrast changing processing such as the enhancement processing and the dynamic range compression processing. It is sufficient if the contrast value is relatively large (meaning the low-frequency region) for a high-contrast image in a relatively high-frequency region.

[Brief description of the drawings]

FIG. 1 is a diagram showing the concept of an image processing apparatus according to the present invention.

FIG. 2 is a diagram illustrating details of a blurred image signal creating unit.

FIG. 3 is a diagram illustrating a filter (one-dimensional) used in a blurred image signal creating unit.

FIG. 4 is a diagram showing details of a filtering process.

FIG. 5 is a diagram illustrating frequency characteristics of a filtered image signal.

FIG. 6 is a diagram showing a filter (two-dimensional) used in the filtering processing means.

7 is a diagram representing the filter used in interpolation calculation of the filtering-processed image signals B ₁

FIG. 8 is a diagram showing details of an interpolation operation.

Diagram illustrating a filter used in interpolation calculation of Figure 9 the filtering-processed image signal B ₂

FIG. 10 is a diagram showing details of an interpolation operation.

FIG. 11 is a diagram illustrating frequency characteristics of a blurred image signal.

FIG. 12 is a diagram showing an entire configuration of an image processing apparatus according to an embodiment of the present invention;

FIG. 13 is a diagram illustrating frequency characteristics of a band-limited image signal.

FIG. 14 is a diagram illustrating an example of conversion processing of a band-limited image signal in a conversion unit.

FIG. 15 illustrates an example of a conversion function.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 blur image signal creating means 2 band limited image signal creating means 3 converting means 4 integrating means 5 frequency emphasizing processing means 10 filtering processing means 11 interpolation arithmetic processing means 21 subtractor 22 converter 23 arithmetic unit 24 converter 25 multiplier 25 addition vessel

Claims (21)

[Claims] An image signal is divided into a plurality of band-limited image signals each having a predetermined bandwidth, and each band-limited image signal is subjected to a non-linear conversion process. An image processing method for performing a process of changing an image contrast using a converted band-limited image signal, wherein the process of changing the image contrast is performed by using a band-limited image signal having a relatively high frequency band among the band-limited image signals. The degree of enhancement in the low contrast area for
An image processing method, wherein a degree of enhancement of a band-limited image signal having a relatively low frequency band in each of the band-limited image signals is made larger than a degree of enhancement in a low contrast region. 2. A process for changing the image contrast, comprising: determining a degree of enhancement in a low contrast region with respect to a band-limited image signal having the highest frequency band among the band-limited image signals; 2. The image processing method according to claim 1, wherein the degree of emphasis in the low contrast region for the band-limited image signal having the lowest frequency band is at least twice or more. 3. An image signal is divided into a plurality of band-limited image signals each having a predetermined bandwidth, and each band-limited image signal is subjected to a non-linear conversion process. An image processing method for performing a process of changing an image contrast using a converted band-limited image signal, wherein the process of changing the image contrast is performed by using a band-limited image signal having a relatively high frequency band among the band-limited image signals. Wherein the degree of emphasis in the medium-high contrast region is larger than the degree of emphasis in the medium-high contrast region for the band-limited image signal having a relatively low frequency band among the band-limited image signals. Processing method. 4. A process for changing the image contrast, wherein the emphasis degree in the middle-high contrast region with respect to the band-limited image signal having the highest frequency band among the band-limited image signals is determined by changing the degree of emphasis in each of the band-limited image signals. 4. The image processing method according to claim 3, wherein the degree of emphasis of the band-limited image signal having the lowest frequency band in the middle and high contrast areas is at least twice or more. 5. A process for changing the image contrast by arbitrarily combining any one of claims 1 and 2 with the image processing method according to any one of claims 3 and 4. An image processing method characterized by performing the above. 6. The image signal is divided into a plurality of band-limited image signals each having a predetermined bandwidth, and a non-linear conversion process or a linear conversion process is performed on each of the band-limited image signals. An image processing method for performing a process of changing an image contrast using each of the converted band-limited image signals, wherein the band-limited image signal having a relatively low frequency band among the band-limited image signals is output. A non-linear conversion process is performed so that contrast is smaller than the input contrast of the image signal. For each of the band-limited image signals, for a band-limited image signal having a relatively high frequency band, the output contrast is relatively low An image processing method, wherein a linear conversion process is performed so as to be larger than an output contrast of a band-limited image signal having a low band. 7. The non-linear conversion process includes: outputting the output contrast of the band-limited image signal having the lowest frequency band among the band-limited image signals to the band-limiting image having the highest frequency band among the band-limited image signals. 7. The image processing method according to claim 6, wherein the output contrast is set to at least 1/2 or less of the output contrast of the image signal. 8. A band-limited image signal generating means for dividing an image signal into a plurality of band-limited image signals each having a predetermined bandwidth, and performing a non-linear conversion process on each of the generated band-limited image signals. An image processing apparatus comprising: a conversion unit; and a processing unit configured to perform a process of changing image contrast using each of the converted band-limited image signals subjected to the non-linear conversion process. The degree of emphasis in a low contrast region for a band-limited image signal having a relatively high frequency band in the signal is emphasized in a low contrast region for a band-limited image signal having a relatively low frequency band in each of the band-limited image signals. An image processing apparatus characterized in that the degree is larger than the degree. 9. The image processing apparatus according to claim 1, wherein the processing unit determines a degree of enhancement in a low contrast region with respect to a band-limited image signal having the highest frequency band among the band-limited image signals, and 9. The image processing apparatus according to claim 8, wherein the degree of emphasis in a low-contrast region with respect to the low-band-limited image signal is at least twice or more. 10. A band-limited image signal generating means for dividing an image signal into a plurality of band-limited image signals each having a predetermined bandwidth, and performing a non-linear conversion process on each of the generated band-limited image signals. An image processing apparatus comprising: a conversion unit; and a processing unit configured to perform a process of changing image contrast using each of the converted band-limited image signals subjected to the non-linear conversion process. The degree of emphasis in the medium-high contrast region for the band-limited image signal having a relatively high frequency band in the signal is emphasized in the middle-high contrast region for the band-limited image signal having a relatively low frequency band in each of the band-limited image signals. An image processing apparatus characterized in that the degree is larger than the degree. 11. The image processing apparatus according to claim 1, wherein the processing unit determines a degree of enhancement in a medium-high contrast region with respect to the band-limited image signal having the highest frequency band among the band-limited image signals, and 11. The image processing apparatus according to claim 10, wherein the degree of emphasis of the low band-limited image signal in the middle and high contrast areas is at least twice or more. 12. An image comprising a processing unit according to any one of claims 7 and 8 and a processing unit according to any one of claims 9 and 10. Processing equipment. 13. A band-limited image signal generating means for dividing an image signal into a plurality of band-limited image signals each having a predetermined bandwidth, and a non-linear conversion process or a linear conversion process for each of the generated band-limited image signals. An image processing apparatus comprising: a conversion unit that performs a conversion process; and a processing unit that performs a process of changing image contrast using each of the converted band-limited image signals that have been subjected to the conversion process. For each of the band-limited image signals, a non-linear conversion process is performed on the band-limited image signal having a relatively low frequency band so that the output contrast is smaller than the input contrast of the image signal. The output contrast of the band-limited image signal having a relatively high frequency band is an output code of the band-limited image signal having a relatively low frequency band. The image processing apparatus characterized in that performing the linear conversion process to be larger than the Trust. 14. The band-limited image having the highest frequency band among the band-limited image signals, wherein the conversion means outputs the band-limited image signal having the lowest frequency band among the band-limited image signals. 2. The method according to claim 1, wherein the non-linear conversion processing is performed so that the output contrast is at least 1/2 times or less of a signal output contrast.
3. The image processing device according to 3. 15. A method of dividing an image signal into a plurality of band-limited image signals each having a predetermined bandwidth;
An image processing method comprising: performing a non-linear conversion process on each band-limited image signal; and performing a process of changing image contrast using each of the converted band-limited image signals subjected to the non-linear conversion process. In a computer-readable recording medium image processing method in which a program to be executed by a computer is recorded, the step of performing the process of changing the image contrast includes the step of limiting a relatively high frequency band of each of the band-limited image signals. The enhancement degree in the low contrast region for the image signal is set to be larger than the enhancement degree in the low contrast region for the band-limited image signal having a relatively low frequency band among the band-limited image signals. Recording medium. 16. The image processing apparatus according to claim 1, wherein the step of performing the process of changing the image contrast comprises: determining a degree of enhancement in a low contrast region with respect to a band-limited image signal having the highest frequency band among the band-limited image signals. 16. The recording medium according to claim 15, wherein the degree of enhancement in a low contrast region with respect to a band-limited image signal having the lowest frequency band among the signals is at least twice or more. 17. A method of dividing an image signal into a plurality of band-limited image signals each having a predetermined bandwidth;
An image processing method comprising: performing a non-linear conversion process on each band-limited image signal; and performing a process of changing image contrast using each of the converted band-limited image signals subjected to the non-linear conversion process. In a computer-readable recording medium image processing method in which a program to be executed by a computer is recorded, the step of performing the process of changing the image contrast includes the step of limiting a relatively high frequency band of each of the band-limited image signals. The enhancement degree in the middle-high contrast area for the image signal is set to be larger than the enhancement degree in the middle-high contrast area for the band-limited image signal having a relatively low frequency band among the band-limited image signals. Recording medium. 18. The step of performing the process of changing the image contrast includes the step of determining a degree of enhancement in a medium-high contrast region with respect to a band-limited image signal having the highest frequency band among the band-limited image signals. At least two emphasis levels in the middle and high contrast regions for the band-limited image signal having the lowest frequency band among the signals.
18. The recording medium according to claim 17, wherein the recording medium is set to be twice or more. 19. A procedure for performing the processing for changing the image contrast according to any one of claims 15 and 16, and changing the image contrast according to any one of claims 17 and 18. And a computer-readable recording medium storing a program for causing a computer to execute an image processing method having a procedure of performing a process of performing the following processing. 20. A method for dividing an image signal into a plurality of band-limited image signals each having a predetermined bandwidth;
An image having a procedure of performing a non-linear conversion process or a linear conversion process on each band-limited image signal, and a process of performing a process of changing image contrast using each converted band-limited image signal subjected to the conversion process In a computer-readable recording medium recording a program for causing a computer to execute the processing method, a procedure for performing the non-linear conversion processing or the linear conversion processing
For each of the band-limited image signals, a non-linear conversion process is performed on the band-limited image signal having a relatively low frequency band so that the output contrast is smaller than the input contrast of the image signal. Of the band-limited image signals having a relatively high frequency band,
A recording medium for performing a linear conversion process such that an output contrast is higher than an output contrast of the band-limited image signal having a relatively low frequency band. 21. The non-linear conversion process according to claim 16, wherein the output contrast of the band-limited image signal having the lowest frequency band among the band-limited image signals is determined by changing the output contrast of the band-limited image signal having the highest frequency band. 21. The recording medium according to claim 20, wherein the output contrast is at least 倍 or less the output contrast of the image signal.