Image equalisation

I have an image. I would like to equalize histogram using histeq. But, I want only certain portion of the image be equalized and the rest part be displayed as it is. I could display the whole 开发者_运维问答image and equalized image in two different plots but I want them to be in the same image such that certain portion of the image is different.

figure
imshow(a)
figure
b = a(1:100, 1:100);
b = histeq(b)
imshow(b)

Now how do I merge both these figures into one.

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Is the region to be equalized a(1:100, 1:100)?

If so, just set a(1:100, 1:100) = b.