What is the math behind exposure adjustment on photoshop?

Question

I have spent a lot of time on google but couldn't find something useful. I want to set an image's exposure value like photoshop does. So i want to know how to change a bitmap's exposure like photoshop exposure adjustment does?

Answer 1

Theorically for exposure modification x (x being a signed floating point value, 0.0 for non compensation), you have to multiply each pixel luminance value (or each sub-pixel in RVB) by 2 ^ x.

newValue = oldValue * (2 ^ exposureCompensation);

Think about your range of value, to limit value that could be superior to your maximum allowed value (255 in 8bit, 65535 in 16bit). This is what created "burned" part of a picture when you raise the exposure, and this is a part that changed on the new Photoshop process (dubbed '2012)