Hi
Can anyone tell me what gamma correction does. In photo editing when I want to lighten or darken a picture I can use “Brightness” or “Gamma” both seem to do the job but there must be a difference otherwise why have them but I can’t see it. 
Can some one help?
Thanks.
Basically, increasing the brightness shifts the value of each pixel up by a fixed amount, ie. if a pixel has value x before brightness adjustment, it has value (x+y) after, and y is the same for all pixels. Adjusting gamma changes the values of pixels in a non-linear way, where the increase is dependent on the value the pixel had before adjustment.
Several sites exist that can give a better explanation than me.
I don’t know whether you’re looking for a mathematical definition of what gamma is for writing computer programs, or for a layman’s explanation of what gamma is for touching up images, but see Primer_dimer’s links for the former. For the latter, I would explain it this way: gamma correction distributes the light and/or color intensities in an image more evenly, especially in the midtones. Very generally speaking, the typical “ideal” way to correct any image is to correct first the brightness so that you have the darkest possible darks and the lightest possible lights. Then, adjust the gamma until the midtones “pop out” at you.
Yea! Sorry :smack: should have been more specific I was just looking for laymans explanation. To have “the darkest possible darks and the lightest possible lights” wouldn’t that be contrast??? I have in fact done that, correct the contrast then finish of with Gamma which seems to give about the best result - for me anyway. The links are noted thanks 