Do it with the GIMPLUT (Look-Up Tables Effects)Brightness and ContrastAnswer

3.1.1. Answer

Increasing or decreasing the brightness involves adding or subtracting a certain amount from the value of each pixel.

The contrast can be increased by plotting an y=mx graph according to the value, where m is greater than 1 to increase the contrast, and less than 1 to decrease it.

Written by Shlomi Fish