Gimp->colors->levels->values

Software GIMP
1

If I set the Gimp->colors->levels->values menu to 15 at menu left and 245 at menu right, is that equivalent to making the same settings individually to all of red green and blue?

2

Yes it is (assuming GIMP 2.8). You can test it if you want by:

  1. Duplicated image a couple of times.
  2. Apply 15/245 to Value on bottom copy.
  3. Apply 15/245 to each RGB on top copy.
  4. Set top copy layer mode to Subtract.
  5. New From Visible and inspect (should be completely black).
    Check the histogram or Colors > Info > Colorcube Analysis.
1 Like
3

Thank you. I suspected as much. I even did the test you suggested and saw
no apparent difference between the images. But I’m old and have failing
eyesight, and images do vary.

Understanding what goes on underneath the hood better than the black magic,
trial-and-error menu poking approach.

I recently made the switch from UFRAW to RawTherapee, and feel quite stupid
for not doing so sooner (I’m a Linux guy so I don’t do no LightRoom).

2 Likes
4

Me too. :slight_smile: That’s why I suggest using the Colorcube Analysis to actually see a report of the layer colors.

image

It helps me not to rely on these tired old eyes…