adjust bitmap image brightness/contrast using c++

Question

adjust image brightness/contrast using c++ without using any other 3rd party library or dependancy

Answer 1

Read in the image with a library just as the Independent JPEG library. When you have raw data, you can convert it from RGB to HSL or (preferably) CIE Lab*. Both contrast and brightness will basically just involve adjustments to the L channel -- to adjust brightness, just adjust all the L values up or down by an appropriate amount. To adjust contrast, you basically adjust the difference between a particular value and the center value. You'll generally want to do this non-linearly, so values near the middle of the range are adjusted quite a bit, but values close to the ends or the range aren't affected nearly as much (and any that are at the very ends, aren't changed at all).

Once you've done that, you can convert back to RGB, and then back to a normal format such as JPEG.