how to correct shading of an image?

Hi there; i am new at image processing and specially in Matlab. in a homework our teacher asked us to correct shading of an image( like shading correction figure-2-29 of Image processing Book by Gonzales and Woods). but i didn't find any track to solve this problem in Google. I'll be glad of any help.

Answer 1

[Afsaneh]

thanks for helpful link. i did it by dividing the main image with a shading pattern. without knowing how to get the shading pattern!!! is there a way to produce that shading pattern?

[Image Analyst]

Well somehow you got it because you said you did it. There are a variety of ways depending on what the objects and background look like. I mentioned two of them in my answer, such as taking points known to be in the background and doing a fit to a 2D polynomial, or by using locally adaptive histogram equalization, or the mrohpological technique MATLAB used in their demo. Whether you do background subtraction of background division depends on how you acquired your image. If you have x-ray or fluorescence images you do subtraction and for most other types of images you do division.

Answer 2

[Image Analyst]

See the Demo of it: http://www.mathworks.com/help/images/examples/correcting-nonuniform-illumination.html. If that way doesn't work, then post your image so I can recommend other methods, such as CLAHE or a 2D fitted model or something. CLAHE is done by adapthisteq() in the Image Processing Toolbox.