05-25-2020, 08:07 PM
Observe this:
when you run Colors > Levels... and change the Channel option to Red, Green or Blue (initially set to Value), you can see the 3 small triangles under the Input Levels histogram.
The black triangle is in the left, the gray triangle is in the middle and the white triangle is in the right.
Now, click the "Auto Input Levels" and observe again the position of the 3 triangles for the 3 RGB channels, they have moved... (or maybe not, depending of the image).
The algorithm implied here is a "contrast strechting" applied independently on each of the RGB channels.
when you run Colors > Levels... and change the Channel option to Red, Green or Blue (initially set to Value), you can see the 3 small triangles under the Input Levels histogram.
The black triangle is in the left, the gray triangle is in the middle and the white triangle is in the right.
Now, click the "Auto Input Levels" and observe again the position of the 3 triangles for the 3 RGB channels, they have moved... (or maybe not, depending of the image).
The algorithm implied here is a "contrast strechting" applied independently on each of the RGB channels.