JPH0484930A - Method and device for correcting shading image - Google Patents

Abstract

PURPOSE:To correct the shading area without being influenced even if an abnormal density area exists in the outside of the shading area by outputting a corrected image shose shading area is corrected from an inputting image and a shading correction mask image. CONSTITUTION:A smoothing processing is executed to all picture elements of an original eyeground image A containing a bright nipple part H and a dark shading area L by applying a smoothing filter F, for instance, of a size of 15X15 picture elements, and also, an eyeground image B in which other area than the shading area is a flat density distribution is obtained. Subsequently, the maximum value WAX of a density level of the average image B is selected, a normalization processing for dividing the level of all picture elements of the eyeground image B by the maximum value MAX is executed, and an eyeground image C is obtained. Next, an eyeground image D being a specific image obtained by dividing all picture element level of the original eyeground image A by a level of a picture element in the corresponding position of the eyeground image C is obtained. That is, in other area than the shading area L of the original eyeground image A, the density is not varied, the density of the shading area L rises and the area becomes bright. The eyeground image D can be displayed on an image monitor.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a shading image correction method and a correction apparatus for, for example, a fundus image (monochrome or color) output from a fundus camera.

[Prior Art] Conventionally, when a dark region or shading partially exists in an input image such as a fundus image, it is necessary to correct the shading to make the image brighter as a whole and output the image.

For this purpose, a blurred image obtained by smoothing the input image is used as a shading correction mask image, and shading correction is performed by obtaining a ratio image with the input image, or a fixed shading correction mask according to the imaging optical system is used. An image is prepared, and shading correction is performed by obtaining a ratio with the input image, that is, a ratio image.

[Problems to be Solved by the Invention] However, in the case of fundus images, etc., if there is an area in the image that is much brighter than other areas in the image, such as a papilla, in an area other than the dark area that should be corrected for shading, shading may occur. The correction mask image is high in the nipple and low in areas other than the nipple. As a result, the corrected image as a ratio image becomes brighter as a whole except for the papilla. That is, there is a problem that areas other than areas requiring shading correction become brighter.

[Means for Solving the Problems] An object of the present invention is to provide a shading image correction method and a correction device that solve the above-mentioned problems. a second step of setting a shading correction mask image in which areas other than the shading area have a flat density distribution; and outputting a corrected image in which the shaved area has been shading corrected from the input image and the shading correction mask image. The method is characterized in that it has a third step.

[Operation] If the input image is a black and white image, shading correction is performed by setting a mask image for shading correction in which areas other than the shading area have a flat density distribution.

If the input image is a color image, the RGBB color image is converted to a color space image, and shading correction is performed on at least one image other than the hue image (for example, a brightness image) so that the area other than the shading area has a flat density distribution. A mask image is set, shading correction is performed, and the image is then converted to an RGBB color image.

[Example] FIG. 1 shows a configuration diagram when the present invention is applied to an ophthalmological measuring device. The fundus camera 1 is equipped with a CCD camera 2, and an A/D controller 3 connected to the CCD camera 2 is provided.
An image processor 4 is connected to the image processor 4, and an image memory 5 and an image monitor 6 are connected to the image processor 4.

Then, the fundus is photographed by the CCD camera 2 of the fundus camera 1, and the obtained fundus image is digitized via the A/D converter 3 and stored in the image memory 5, and then the operations shown in the flowchart of FIG. Perform processing.

In the flowchart of FIG. 1g2, first, in step 11, an inlaid fundus image A as shown in FIG. 3, which has already been stored in the image memory 5, is read into the image processing processor 4.
Next, in step 12, in the image processing processor 4, all pixels of the inlaid fundus image A including the bright papilla H and the dark shading area are processed, for example, by 15 pixels as shown in FIG.
Smoothing in which a smoothing filter F with a size of x15 pixels is moved to the right and each pixel level of the inlaid fundus image A is replaced with the average value of all pixel levels in a pixel area of 15 x 15 pixels centered on that pixel. The process is further performed to obtain a fundus image B in which areas other than the shading area have a flat density distribution. Thereby, a mask image for shading correction using the inlaid fundus image A can be obtained.

Next, in step 13, the maximum value MAX among the density levels of all pixels of this average image B is selected, and in step 14, a normalization process is performed in which the level of all pixels of fundus -tB is divided by the maximum value MAX. good. This average density value may be obtained from a density histogram, or the density at a position recognized by the operator as an average density may be used.

In this way, in step 15, an unprocessed fundus image of the inlay, which is stored in the image memory 5, is obtained.

By performing this division process, the density of the areas other than the shading area of the fundus image A does not substantially change, and the density of the shading area increases and becomes brighter. This fundus image can then be displayed on the image monitor 6. The above image processing process is shown in FIGS. 5(a) to 5(d).

Next, the case of an input image or a color image is as follows.

That is, since the normally obtained fundus color image is an RGB image, this is converted into a color space image including a hue image, a brightness image, and a chroma image. Examples of this conversion are HSV, HSI
, HSL is al.

Next, the brightness image (V) and the chroma image (S) are averaged using a smoothing filter to create a mask image for shading correction. The appropriate number of times of averaging is several times to several thousand times. Then, each corrected image is created by processing similar to that described above.

That is, corrected image (V)=brightness image (V)/.

Normalized mask image (V) Corrected image (S) = Saturation image (S) / Obtain a normalized mask image (S).

Based on the corrected images (V) and (S) obtained here and the hue image (H) of the cliff, the corrected RG is converted into an RGB image.
Obtain B image.

This corrected RGB image has the same hue as the image before correction, and the shading area is corrected to be brighter.

In addition to using the corrected images (V) and (S), one of them, for example, only the corrected image (V) may be used.

Incidentally, in the above embodiment, a fundus image in which a papilla is present has been described, but it goes without saying that the present invention can also be applied to a fundus image in which a papilla is not present.

Note that if a smoothing filter with a size larger than the 15x15 pixel smoothing filter F used in the above embodiment is used, effective smoothing processing can be performed in a shorter time. There is no practical problem even with the smoothing filter of the example size, and a more preferable image can be obtained by repeating the smoothing process a plurality of times.

Furthermore, the inlaid fundus image A to be processed may not be an image taken by the CCD camera 2 of the fundus camera 1 as in the above embodiment, but may be a fundus image digitally input into the image memory 5 from a slide scanner. Fundus images recorded on analog bodies such as still videos and video recorders A/
The fundus image may be digitally input to the image memory 5 after D conversion.

The present invention is applicable not only to fundus images but also to any general images including other medical images.

[Effects of the Invention] According to the present invention, even if there is an abnormal density area outside the shading area, the shading area is corrected without being affected by the abnormal density area. This makes areas other than the abnormal density area other than the shading area less likely to be affected by the presence of the abnormal density area.

Furthermore, if the present invention is applied to a color image, the hue will not change even after shading correction, and an image with high diagnostic properties can be obtained.

[Brief Description of the Drawings] Figure 1 is a block diagram of an apparatus using the present invention for fundus image processing;
Figure 2 is a flowchart of the process, Figure 3 is a diagram of the input fundus image, Figure 4 is an explanatory diagram of the smoothing filter, and Figure 5 is a diagram of the input fundus image.
Figures (a) to (d) are explanatory diagrams of the image processing process. Symbol l is a fundus camera, 2 is a CCD camera, 3 is an A/D converter, 4 is an image processing processor, 5 is an image memory,
6 is an image monitor.

Claims (1)

[Claims] 1. A first step of inputting a predetermined image, and a second step of setting a shading correction mask image in which areas other than the shading area have a flat density distribution for the input image. A shading image correction method, comprising: a third step of outputting a corrected image in which a shading area is subjected to shading correction based on the input image and the shading correction mask image. 2. The shading image correction method according to claim 1, wherein the second step smoothes the input image and then smoothes the area other than the shading area. 3. The shading image correction method according to claim 1, wherein the input image is a fundus image. 4. In the third step, the shading correction mask image is normalized by being divided by the maximum value or average density value among the density levels of all pixels, and the difference between the image and the input image is 4. A shading image correction method according to claim 1, wherein a ratio image is output as a corrected image. 5. A first step of inputting an RGB three-color image, a second step of converting the input image into a color space image including a hue image, and converting at least one image other than the hue image among the color space images. On the other hand, a third step of setting a shading correction mask image in which areas other than the shading area have a flat density distribution; A shading image correction method comprising: a fourth step of outputting; and a fifth step of converting the color space image into an RGB three-color image based on the corrected image and the remaining image including the hue image. 6. The shading image correction method according to claim 5, wherein the color space image includes a brightness image and a saturation image in addition to the hue image, and the shading correction mask image is set corresponding to the brightness image. 7. The shading image according to claim 5, wherein the color space image includes a brightness image and a saturation image in addition to the hue image, and the shading correction mask image is set corresponding to the brightness image and the saturation image, respectively. Correction method. 8. The shading image correction method according to claim 5, wherein in the third step, after smoothing the at least one image, areas other than the shading area are made to have a flat density distribution. 9. The shading image correction method according to claim 8, wherein the input image is a fundus image. 10. In the fourth step, the shading correction mask image is normalized by being divided by the maximum value or average density value among the density levels of all pixels, and the difference between the shading correction mask image and the at least one image is 10. The shading image correction method according to claim 5, wherein the ratio image is output as the corrected image. 11. Means for setting a shading correction mask image with a flat density distribution in areas other than the shading area for an input image, and means for outputting an image subjected to shading correction using the shading correction mask image. A shading image correction device comprising: 12. A means for converting an input RGB three-color image into a color space image including a hue image, and making an area other than the shading area a flat density distribution for at least one image other than the hue image among the color space images. means for setting a shading correction mask image; and means for converting a color space image into an RGB three-color image based on an image subjected to shading correction using the shading correction mask image and the remaining image including the hue image. A shading image correction device characterized by: