by ʇolɐǝz ǝɥʇ qoq

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I have two images that are the same, except that one has an adjustment in its brightness.

Is there a way to compute the difference of these images in Photoshop somehow to see what has changed from one image to another?

Image 1:


Image 2 (with brightness adjustment):

with brightness adjustment

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What exactly are you looking for as the output? A map of the pixels that have changed? A numeric value representing the amount of change (perhaps in "stops"?) Or something else? What do you want to do with this information once you have it? – mattdm Oct 6 '13 at 18:57
@mattdm I want to the brightness factor that transforms the one into the other image. – confile Oct 6 '13 at 20:15

If you layer those in Photoshop and use subtract or difference blend modes, you'll end up with a result that should show the relative difference of each pixel.

Use that result to create a mask (Image > Apply Image, target layer mask)

Then starting with the first image, add an exposure adjustment layer, and use the above mask - I would expect you'd get something close to the second image.

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