Image processing: finding transfer function of histogram equalization
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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
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-');
3 个评论
John Snow
2013-11-18
Royi Avital
2015-5-3
This will work for Equalization. What if I want any other CDF function?
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
2013-11-18
Or use the two argument syntax for histeq.
[histIm,T] = histeq(grayImage);
plot(T,'b-')
2 个评论
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.
John Snow
2013-11-18
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