KR20210077427A - Method for revising fundus photographing image - Google Patents

Abstract

Disclosed is a correction method of a fundus photographed image capable of obtaining a fundus image with a reduced color deviation and brightness deviation by correcting an image of a reflected light reflected from the fundus. The correction method of the fundus photographed image comprises: a step of obtaining a color image of the fundus from an image sensor of the fundus photographing device; a step of separating the color image into R, G, and B channel images; a step of increasing a contrast of the R, G, and B channel images by expanding a brightness distribution for each of the separated R, G, and B channel images; and a step of integrating an image of R, G, and B channels with increased contrast back into one color image.

Description

Method for revising fundus photographing image

The present invention relates to a method for correcting a photographed fundus image, and more particularly, to a method for correcting a photographed fundus image by correcting an image of reflected light reflected from the fundus to obtain a fundus image with reduced color deviation and brightness deviation will be.

The fundus imaging device irradiates strong illumination light into the eyeball through the pupil of the eye to be examined, and captures the weak reflected light reflected from the fundus inside the eyeball. It is an ophthalmic examination device for observing 1 is a view showing the configuration of a conventional fundus imaging apparatus. As shown in FIG. 1 , a typical fundus imaging apparatus includes an illumination optical system 10 and an imaging optical system 20 . The illumination optical system 10 includes an illumination light source 12 that generates illumination light, and a ring-shaped slit is formed in a mask to adjust the illumination light irradiated from the illumination light source 12 to a ring shape. A mask 14, a hole mirror 16 and the hole mirror 16 that reflect the ring-shaped illumination light by a mirror part on the outer periphery and transmit the reflected light reflected from the fundus through a hole in the center and an objective lens 22 for irradiating the ring-shaped illumination light reflected from the eye to the fundus of the eye to be examined (E). The illumination optical system 10 may further include a focusing lens 18 and the like for imaging the ring-shaped illumination light onto the retina of the eye E under examination. The photographing optical system 20 includes an objective lens 22 for imaging reflected light reflected from the fundus of the eye to be examined, an aperture 24 through which the imaged reflected light passes, and an image sensor for detecting an image of reflected light passing through the aperture 24 (26). The photographing optical system 20 may further include a focusing lens 28 that is movable left and right to adjust the focus of the reflected light. The image sensor 26 is mainly a two-dimensional image element, and the image signal formed by the image sensor 26 is transmitted to a calculation unit such as a PC through various interfaces such as USB, Camera Link, GigaNet, Wifi, and Bluetooth, and the calculation unit Digitized image information can be obtained from

The fundus image obtained by the fundus photographing apparatus shown in FIG. 1 has several disadvantages as follows. First, since the light reflectance of the fundus (retina) is different for each patient and the size of the pupil is also different, the brightness of the fundus image is different. For example, if the patient's pupil size is small and the light reflectance of the fundus (retina) is low, the fundus image contains dark or unclear areas. Second, the image sensor 26 cannot realistically reflect the reflection contrast ratio of the retina of the eyeball, which is the subject. Specifically, since the dynamic range of the fundus image detected by the image sensor 26 is very wide, it is difficult to obtain an image that clearly expresses the brightest part and the darkest part at the same time. In particular, microscopic changes in the blood vessels in the optic disc with heavy light reflection or the macula where light absorption is severe are often not properly expressed. Although the light reflectance of the retina's optic disc is several thousand times higher than that of other retinal areas, the area is only a fraction of the total retinal area. Accordingly, in the image detected by the image sensor 26, only the optic disk area appears white, and the rest of the image appears black and dark, so it is difficult to easily check the retinal state.

US Patent No. 7,248,736

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for correcting a fundus photographed image in which color deviation and brightness deviation are reduced to obtain a fundus image in which color and brightness are uniformly distributed.

Another object of the present invention is to provide a method of correcting a photographed fundus image capable of more easily diagnosing the condition of the fundus.

In order to achieve the above object, the present invention, the step of obtaining a color image of the fundus from the image sensor of the fundus photographing apparatus; separating the color image into R, G, and B channel images; increasing the contrast of the R, G, and B channel images by enlarging the brightness distribution for each of the separated R, G, and B channel images; and re-integrating the R, G, and B channel images having the increased contrast into one color image.

According to the method for correcting a photographed fundus image according to the present invention, since the color deviation and brightness deviation are reduced, it is possible to obtain a fundus image in which color and brightness are uniformly distributed, so that the condition of the fundus can be more easily diagnosed.

1 is a view showing the configuration of a conventional fundus imaging apparatus.
2 is a flow chart for explaining a method of correcting a photographed fundus image according to an embodiment of the present invention.
3 is a photograph showing a color image of the fundus obtained from the image sensor of the fundus photographing apparatus.
4 is a photograph in which the color image of the fundus is separated into R, G, and B channel images.
5 is a brightness distribution histogram for explaining a process of increasing the contrast of separated R, G, and B channel images.
6 is a photograph showing images of R, G, and B channels with increased contrast.
7 is a photograph showing a fundus image with improved contrast by integrating images of R, G, and B channels with increased contrast.
8 is a photograph showing an example of the fundus image before correction obtained from the image sensor of the fundus photographing apparatus.
9 is a photograph showing a process of creating a scan line on the fundus image before correction.
10 is a photograph showing the change in brightness on the scan line of the fundus image before and after correction.

Hereinafter, with reference to the accompanying drawings, the present invention will be described in detail.

2 is a flowchart for explaining a method of correcting a fundus photographed image according to an embodiment of the present invention. As shown in FIG. 2 , according to the method for correcting a photographed fundus image according to the present invention, first, a color image of the fundus is obtained from the image sensor 26 of a conventional fundus photographing apparatus as shown in FIG. 1 (S) 10). An example of such a digital image of the fundus is shown in FIG. 3 . As shown in FIG. 3 , when the patient's pupil is small or the light reflectance of the fundus is low, the digital image of the fundus obtained from the image sensor 26 includes a dark or unclear area. Next, as shown in FIG. 4 , the color image is divided into R, G, and B channel images, respectively (S 20, split).

Next, for each of the separated R, G, and B channel images, the intensity distribution is expanded (stretching) to increase the contrast of the R, G, and B channels (S 30). To expand the brightness distribution, in each R, G, and B channel image, the brightness of each pixel is proportionally adjusted according to the brightness of each pixel, so that the difference between the brightness of the pixel with low brightness and the brightness of the pixel with high brightness is reduced. is to expand Each of the R, G, and B channel images separated in step S 20 has a predetermined brightness distribution, which is referred to as an intensity histogram. An example of a brightness distribution histogram for such a specific channel (R, G, or B) is shown in FIG. 5A . In the brightness distribution histogram shown in FIG. 5(A), pixels of the corresponding channel mainly have medium brightness (x to y), and pixels in a low-brightness area (less than x) or high-brightness area (greater than y) are almost nonexistent That is, although the corresponding channel has a medium brightness, since the difference in brightness of the pixels is small, the regional contrast of the pixels is low. Accordingly, as shown in FIG. 5B , the brightness distribution is stretched for each R, G, and B channel. If the brightness distribution is stretched in this way, the contrast of brightness becomes large, and thus clearer identification is possible. In the example shown in FIG. 5B, the brightness (eg, x) of a pixel with low brightness is decreased, and the brightness (eg, y) of a pixel with high brightness is increased, so that the difference in brightness ( contrast) is magnified. In this way, images of R, G, and B channels having increased contrast are shown in FIG. 6 . If the average brightness of the corresponding channel is small (in the case of FIG. 4), both the average brightness and the contrast are increased by the brightness distribution stretching (in the case of FIG. 6), and if the average brightness of the corresponding channel is large, by the brightness distribution stretching The average brightness decreases and the contrast increases. In the brightness distribution histogram, determining the degree of brightness distribution is said to determine the "kernel size". When the “kernel size” is small, the stretching level is small, and when the “kernel size” is large, the stretching level is applied large.

Next, when images of R, G, and B channels having increased contrast are re-integrated into one color image (S 40, merge), a fundus image with improved regional contrast can be obtained. The fundus image after the color fundus image is corrected in this way is shown in FIG. 7 . To summarize, the color fundus image before correction shown in FIG. 3 is divided into R, G, and B channels, respectively, as shown in FIG. 4, and as shown in FIG. 5, each of the separated R, G, B channels , by expanding the brightness distribution, increasing the contrast of the R, G, and B channels to obtain the corrected R, G, and B channel images shown in FIG. 6, and then integrating them as shown in FIG. , the contrast of each channel is increased to obtain a corrected color fundus image in which the deviation for each channel is reduced.

In the method for correcting a photographed fundus image according to the present invention, since the difference in brightness of the photographed fundus image is very large for each location, correction may be additionally performed to prevent a decrease in the contrast difference between the actual observation area. 8 is a photograph showing an example of the fundus image before correction obtained from the image sensor 26 of the fundus photographing apparatus. As shown in FIG. 8 , in the fundus image before correction, the brightness of most areas except for the optic disc is too dark to identify the fundus image. In order to solve the problem caused by the difference in brightness, as shown in FIG. 9, a scan line passing through the optical disc is created, and as shown in FIG. 10, the change in intensity on the scan line is profiled. . Since the optic disc and the macula are present on the scan line, the scan line can be divided into the lightest optic disc and the darkest macula and other regions (see FIG. 10 ). In the fundus image correction according to the present embodiment, the brightness of each pixel is corrected along the scan line, but the region in which the optical disk is located and the region in which the optical disk is not located are non-linearly corrected. For example, if the brightness of each pixel is amplified as the distance from the area where the optical disk is located, the relative between the area where the optical disk is located and the area where the optical disk is not located, as shown in the brightness profile after correction in FIG. The brightness difference can be reduced. That is, by relatively reducing the brightness of the area where the optical disk is located, the relative brightness difference between the area where the optical disk is located and the area where the optical disk is not located can be reduced. When the scan line is created at a predetermined angle with the optical disk as the center and the above-described nonlinear correction is sequentially performed, a fundus image with reduced contrast for the entire fundus can be obtained. This nonlinear correction for each fundus position may be performed before the correction step through the above-described R, G, and B channel separation.

The present invention overcomes the inherent limitations of the fundus imaging device by correcting the color image of the fundus obtained by the image sensor 26 of the fundus imaging device by software, and enables an ophthalmologist to more accurately diagnose fundus lesions. Accordingly, the method for correcting the fundus image according to the present invention may be implemented by a software module that processes the fundus image.

Although the present invention has been described with reference to exemplary embodiments above, the present invention is not limited to the above-described embodiments. The scope of the following claims should be construed to cover all modifications, equivalent constructions and functions of the exemplary embodiment.

Claims (5)

obtaining a color image of the fundus from the image sensor of the fundus photographing apparatus;
separating the color image into R, G, and B channel images;
increasing the contrast of the R, G, and B channel images by enlarging the brightness distribution for each of the separated R, G, and B channel images; and
A method of correcting a fundus photographed image, comprising the step of re-integrating images of R, G, and B channels with increased contrast into one color image. The method according to claim 1, wherein the expansion of the brightness distribution of the R, G, and B channel images is performed by proportionally adjusting the brightness of each pixel in each of the R, G, and B channel images, so that A method for correcting a fundus photographed image, which is to enlarge a difference in brightness between pixels with high brightness. The method of claim 1 , wherein the expansion of the brightness distribution of the R, G, and B channel images reduces the brightness of pixels with low brightness and increases the brightness of pixels with high brightness, thereby increasing the difference in brightness between pixels. , Correction method of fundus photographed image. The method of claim 1, further comprising: creating a scan line passing through an optic disc in the color image of the fundus, and profiling a change in brightness on the scan line; and
The method of claim 1 , further comprising correcting the brightness of each pixel along the scan line, but non-linearly correcting an area in which the optical disk is located and an area in which the optical disk is not located. The fundus of claim 1 , wherein the non-linear correction reduces the relative brightness difference between an area in which the optical disk is located and an area in which the optical disk is not located by relatively decreasing the brightness of an area in which the optical disk is located. How to correct a shot image.

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