What is the math behind offset slider in exposure adjustment on photoshop?

Question

I'm trying to understand the formula or the math behind the "offset slider".
As found in Image -> Adjustments -> Exposure.

I'm working on a project for detecting shadows in an image and I need to understand how this slider work. I spent a week comparing photos and pixel values but I couldn't understand the formula behind it.

Nudism

Answer 1

For anyone searching for an answer to this question: it can be found in this web article: https://geraldbakker.nl/psnumbers/exposure.html

This is an in-depth study of the Exposure adjustment in Photoshop, including a lot of math and explanation what happens behind the scenes!

Key points discussed:

• Exposure is designed for working in 32-bit
• A short summary of 8-, 16- and 32-bit coding in Photoshop
• The meaning of gamma corrections
• All formulas for the Exposure sliders (Exposure, Offset, Gamma), in 8-bit and in 32-bit mode (they are different)
• Some oddity with the eyedroppers on the Exposure window

Lots of math, pretty technical, but very exhaustive.

Polytypic

Hi, Gerald, and welcome to StackOverflow. Since rot-link can happen, would you mind summarizing some of his key points? It would make your answer more valuable to the SO community. – Asseveration

Answer 2

Formula for exposure: out = in * 2^(exposure);

Formula for offset: out = in + offset;

Formula for gamma: out = in ^ 1/gamma;

note that these assumes floating point values, and is not clipping on 1.0 with no curve correction, you might want to apply correction by in ^= 2.2 and out ^= 1/2.2 before and after applying the above formulas, respectively.

Determinable