Low level visual equalization of images

Question

Jonathan 2012-4-3

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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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Answer 1

Ashish Uthama 2012-4-5

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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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Answer 2

Jurgen 2012-11-15

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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