Source string usage details

Adjusting color levels scales the given channels to a range specified by the 'low' and 'high' values. These 'low' and 'high' values can be any value between 0 and 1. E.g. assume that 'low' is 0.2 and 'high' is 0.9. Pixels that had a value of 0, will get a value of 0.2 * 255 = 51 and pixels that had a value of 255, will get a value of 0.9 * 255 = 229.

Note that color level adjustment is a mathematical filter and a such doesn't do automatic balancing.