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Image processing

Can anybody help me with this: pic1.png
Original post by john212
Can anybody help me with this: pic1.png


Can't say as I know anything about this, but from a small bit of Google'ing, I would suggest, since your gamma transform is an increasing function, then the highest value input will map to the highest value output. Since this is 255 in each case (assuming it maps onto the whole interval), we have:

255=c(255)γ255= c(255)^\gamma

And rearrange to make "c" the subject.

Best guess!
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john212
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Ok, thanks very much!
Original post by ghostwalker
Can't say as I know anything about this, but from a small bit of Google'ing, I would suggest, since your gamma transform is an increasing function, then the highest value input will map to the highest value output. Since this is 255 in each case (assuming it maps onto the whole interval), we have:

255=c(255)γ255= c(255)^\gamma

And rearrange to make "c" the subject.

Best guess!
As it happens, I know rather a lot about this, but what you say is absolutely correct.

It's a bit of a weird question through, I think the most common way of doing it is to scale 0-255 to the range 0-1, do the γ\gamma exponentiation, and then scale back up to the rang 0-255. Reduces the potential for getting scarily large values when raising 255 to an arbitrary power etc.

[Note also that any "real" image processing app will use a 256 entry lookup table to avoid actually doing calculations for every pixel in the image].

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