JPH0232667B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an image processing device capable of recording and processing grayscale images and displaying the resulting grayscale images in parallel.

[Technical background of the invention and its problems]

Conventionally, in image processing devices that store medical images such as X-ray CT images as digital signals, perform various digital image processing, and display the images for diagnosis, multiple medical images are displayed simultaneously in parallel. Something happened. In order to accurately compare medical images displayed in parallel, it is preferable to make geometric conditions such as the position, direction, and size of the images the same, and this can be easily done. Further, in order to perform accurate comparative examination, it is preferable that the contrast of the plurality of juxtaposed images be the same.

Conventionally, in this type of image processing apparatus, the contrast of a plurality of images has been matched, for example, in the following manner.

For example, if the density gradation handled by an image processing device has an 8-bit configuration, both the processing system and display system within the image processing device will have a density gradation of 0 to 2 ⁸ -1=
It will handle up to 255 data. For example, if the maximum density values of two images to be displayed are Max1 and Max2, respectively (Max1, Max2≦255), the density matching between the images is 2.
The density of each pixel image is set to 255/
Max1, equivalent to multiplying by 255/Max2. In this way, the image is certainly expanded to the maximum density range of the processing system, and an image with uniform density and good contrast can be obtained.

However, the contrast matching described above has the following problems.

Considering a density histogram in which the density of the image is plotted on the X axis and the degree of appearance of pixels corresponding to the density value is plotted on the Y axis, for images such as those shown in Figure 1 a and b, the density histogram is Since it is formed by one peak, the contrast matching results in density histograms as shown in FIGS. 1A and B, and it can be said that the contrast matching was performed satisfactorily. However, in the case shown in FIGS. 2a and 2b, there are two peaks in the density histogram of one image as a whole (there are isolated points caused by noise etc. on the histogram), so the above-mentioned When such contrast matching is performed, Fig. 2A,
As shown in B, the main peak in the density histogram having two peaks and the peaks in the other density histograms are shifted, making it impossible to match the contrast of the two images. This is because only the maximum concentration value was considered.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an image processing device that can perform accurate contrast matching even if an isolated point exists on a density histogram. .

[Summary of the invention]

The outline of this invention for achieving the above object is as follows:
In an image processing device capable of simultaneously displaying a plurality of images in parallel, an averaging means for equalizing the average value of the density gradation of pixels constituting each of the plurality of images; The present invention is characterized in that it includes a density expansion means for expanding the maximum density of pixels in each image to a maximum density within an allowable range, and makes the contrast of each image displayed in parallel equal.

[Embodiments of the invention]

FIG. 3 is a block diagram showing one embodiment of the present invention.

In FIG. 3, reference numeral 1 denotes a first image storage unit that stores a plurality of grayscale images, and is configured to include, for example, a plurality of frame memories. 2
What is indicated by is a grayscale conversion processing unit having a function realizing means described later, which reads out a plurality of grayscale images stored in the first image storage unit 1 pixel by pixel, and calculates the average value of the density in each grayscale image. , and match the average density value of one grayscale image with the larger average density value to the average density value of the other grayscale image,
Next, it has a function of expanding the density of each grayscale image so that the maximum density value of any grayscale image is equal to the maximum density value of the processing system. Reference numeral 3 denotes a second image storage section that stores the gradation image subjected to contrast matching processing by the gradation conversion processing section 2, and is configured, for example, to include a plurality of frame memories. Reference numeral 4 indicates an image processing unit that performs processing such as subtraction processing between a plurality of contrast-matched grayscale images, and reference numeral 5 indicates an image processing unit that performs processing such as subtraction processing between a plurality of contrast-matched grayscale images. This is a display section for displaying a grayscale image of , and a grayscale image processed by the image processing section 4, such as a subtraction image.

As shown in FIG. 4, the gradation conversion processing section 2 includes an averaging section 2A and a density expansion section 2B, and the averaging section 2A includes a first image storage section 1.
For example, each of two gray scale images stored in the memory is read out, the average value of the density of the pixels constituting each gray scale image is calculated, and the calculated average values are compared with each other to find the maximum average value. Calculate the difference between each average value from the average value, and then add the difference to the density value of each pixel of each gray image that has an average value that is not the largest average value to calculate the average value of the density of each gray image. The density expansion means 2B is configured to perform an operation to match the average value of the maximum density, and the density expansion means 2B calculates the maximum value from among the pixels constituting each grayscale image whose average density values are matched, and It has a configuration that calculates a magnification of the maximum allowable value of the processing system with respect to the maximum value of each image, and executes an operation of enlarging the density of each grayscale image by the magnification.

Next, the operation of the above configuration will be explained.

For convenience of explanation, two grayscale images f(x,
y) and g(x, y) will be explained.

Grayscale image f stored in the first image storage unit 1
(x, y) and g(x, y) are sequentially read out to the gray scale conversion processing unit 2 pixel by pixel. In the gradation conversion processing section 2, as shown in FIG.
Then, the average values μf and μg of the density of each grayscale image are calculated, and then the two average values μf and μg are compared.
For example, if μf > μg, the difference μf − μg between the average values is calculated and the grayscale image g (x, y) is
The concentration of and the difference μf−μg between the average values are added,
As shown in FIGS. 6B and 6B, grayscale images g'(x, y) and f(x, y) having equal density average values are obtained. Next, the density expansion means 2B generates a density image g'(x,
The maximum density values Maxf and Maxg at each pixel of pixel y) and f(x, y) are detected. In addition, at this time, the difference between the frequency on the verge of appearance of the maximum value Maxf ₁ detected in the grayscale image g'(x, y) and the frequency on the verge of occurrence of the density value one smaller than the maximum value Maxf ₁ is outside the allowable range. In some cases, the maximum value Mxf ₁ is discarded as noise, and the maximum value Maxf ₂ is selected from among the densities of pixels excluding the maximum value Maxf ₁ .
Next, the maximum concentration value Maxd allowed by the processing system
and the enlargement magnification from the maximum values Maxf and Maxg.
Maxd/Maxf and Maxd/Maxg are calculated, and the gray scale images g'(x, y) and f(x, y) are multiplied by the magnification to form a density histogram, as shown in Figure 6c and C. The grayscale images g″(x,y), f(x,y) whose maximum values of the main peaks match each other are obtained, and the grayscale images g″(x,y), f( x,
y). Also, when μf<μg,
Similarly, gray scale images g(x, y) and f″(x, y) are obtained and stored in the second image storage unit 3.

Grayscale image stored in the second image storage unit 3
g″(x, y), f(x, y) or g(x, y),
f″(x, y) are displayed in parallel on the display unit 5.
In addition, when each of the grayscale images is an image before contrast medium administration and an image when the contrast medium reaches a predetermined part of the subject, the grayscale images g''(x, y), f
(x, y) or g(x, y), f″(x, y) is transferred to the image processing unit 4, where subtraction processing is performed, and the subtraction image from the image processing unit 4 is displayed on the display unit 5. The subtraction image will be displayed.

Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment, and can be implemented with appropriate modifications within the scope of the gist of the invention. Needless to say.

[Effects of the Invention] As detailed above, the density gradation of a plurality of grayscale images that need to be displayed in parallel on the display surface of an image display device and a plurality of grayscale images that need to be subjected to subtraction processing can be improved. No matter what, the average value of the density of each of the plurality of grayscale images is made to match the maximum average value, and the density of the plurality of grayscale images is
Since the maximum value of the density is shifted as a whole so as to match the maximum value allowed by the processing system, the density contrast can be appropriately adjusted, and an image processing apparatus with higher diagnostic performance is provided.

[Brief explanation of drawings]

Figures 1a and b are density histograms of grayscale images, Figures 1A and B are density histograms obtained when the contrasts of grayscale images having the density histograms are matched, and Figures 2a and b are density histograms of grayscale images. Each of them is a density histogram of a grayscale image with one or two peaks on the verge of appearance, and Figures 2A and B respectively show the results when the contrasts of grayscale images with the density histograms of Figures 2a and b are matched. It is a concentration histogram, and the third
The figure is a block diagram showing an embodiment of the present invention, FIG. 4 is a block diagram showing the function realizing means of the grayscale conversion processing section in the embodiment, and FIG. 5 shows the processing procedure in the function realizing means. FIGS. 6A, 6B, 6C, A, B, and C are explanatory diagrams showing changes in the density histogram during the density conversion process according to the processing procedure described above. 2A...Averaging means, 2B...Concentration expansion means.

Claims (1)

[Claims] 1. In an image processing device capable of simultaneously displaying a plurality of images in parallel, averaging means for equalizing the average value of the density gradation of pixels constituting each of the plurality of images, and a plurality of averaging means for equalizing the average value of the density gradation of pixels constituting each of the plurality of images; 1. An image processing apparatus comprising: a density expanding means for expanding the maximum density of a pixel in each of the images to a maximum density within an allowable range, and equalizing the contrast of each of the images displayed in parallel.