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Low level visual equalization of images

Asked by Jonathan on 3 Apr 2012

Hi all,

I'm conducting an experiment using visual stimuli in an fMRI. It is important that all stimuli have the same low level visual parameters i.e. Contrast and Brightness ( all images are greyscaled)

How can this be done in Matlab?

Thanks!

Jonathan

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Jonathan

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2 Answers

Answer by Ashish Uthama on 5 Apr 2012
Accepted answer

You could try using histeq to equalize the histogram of two images.

I was about to say its hard to quantify 'contrast' objectively, but decided to search.. and found this. Some of those definitions needs additional specifications like foreground/background which is pretty specific to the types of images you plan to use.

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Ashish Uthama
Answer by Jurgen on 15 Nov 2012

I'm assuming the resolutions are identical. If images have different content it's hard to give them equal parameters. One could say histogram A is 10% flatter than histogram B and maybe 15% wider. But the surface areas are equal by definition.

If you shape the histograms identically, by definition the contrast and brightness will be equal for both images, but one may look a lot worse than the other (e.g. if equalizing: you may turn 1 'shade' of white on a flower into 5, whereas a rainbow may look more natural).

I happend to see this contribution by Image Analyst: http://www.mathworks.com/matlabcentral/fileexchange/28972-custom-shaped-histogram

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Jurgen

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