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Image processing: finding transfer function of histogram equalization

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John Snow
John Snow 2013-11-18
评论： Image Analyst 2015-5-3
Hello, lets say I have an image then I adjusted the contrast by using histogram equalization (histeq) Is there a way to plot or get an image of the transfer function that this command uses ?

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Image Analyst
Image Analyst 2013-11-18
Just take the histogram of the original image, then call cumsum on the pixel counts and plot it.
[pixelCounts, grayLevels] = imhist(grayImage);
cdf = cumsum(pixelCounts); % Make transfer function (look up table).
cdf = cdf / sum(cdf); % Normalize
plot(grayLevels, cdf, 'b-');
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Image Analyst
Image Analyst 2015-5-3
Huh? That has nothing to do with equalization, though equalization can use the cdf just like a lot of other functions do. This is just general purpose code that will compute the cdf regardless of your histogram. What do you mean by "other CDF"? What other CDF functions might there be?

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Anand
Anand 2013-11-18
Or use the two argument syntax for histeq.
[histIm,T] = histeq(grayImage);
plot(T,'b-')
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Image Analyst
Image Analyst 2013-11-18
I didn't know it had that output - I guess I should have looked. Of course like I warn people histogram equalization gives a nonlinear stretch which usually looks pretty crummy and unnatural. imadjust() almost always gives a better looking image.

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