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Caveat: I'm not a graphic designer and may be misusing some terminology. Please bear with me. :-)

I'm attempting to add color to some greyscale icons (i.e. all three channels are identical). I want to map the colors such that the brightest grey becomes one specific color, the darkest grey becomes another specific color, and all the greys in between are translated into colors along the "gradient" between those two specific colors.

I've never used GIMP in this manner before and, while it looks like I should be able to use the Colors > Curves tool for this, I can't figure out the specifics even after reading the docs and Googling around a bit.

Perhaps someone who actually knows what they're doing can offer me some advice? ;-)

Update

As per leugim's suggestion, I ended up going with the Gradient Map tool, but there turned out to be two caveats:

  1. It appears to map the full range of possible Values (0.0 through 1.0), not just what's being used in the image. This was easy enough to work around by using the Curves tool to "stretch" my images' Value ranges such that the darkest color became (0, 0, 0) and the brightest color became (255, 255, 255).
  2. It doesn't seem to be exact? The colors I used in my gradient were (7, 7, 11) and (70, 58, 96), but the colors in the final image were (6, 6, 10) and (69, 59, 95). Mind you, no one's holding a colorimeter to my work, so this is plenty close enough! Just thought it a bit odd.
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I always assumed the lightest and the darkest colors of the image were mapped to the gradient! Good to know they aren't. Photoshop and Gimp behave the same way here. I used the levels tool to "stretch" the images value ranges to see if I got the same inaccuracy but got the exact same colors I had chosen before. Maybe the inaccuracy you mention is due to the curves tool? –  leugim Mar 21 '11 at 3:23
    
@leugim — That was my first thought as well, but I went back and checked; it really was pure white and pure black. GIMP's gradients are a bit of a mystery to me anyway, so I'm blaming them for the time being. ;-) –  Ben Blank Mar 21 '11 at 6:32

1 Answer 1

up vote 5 down vote accepted

I think what you are searching for is called Gradient Map.
In Photoshop:

  • In Image -> Adjustments -> Gradient Map

In GIMP if I remember correctly you have to:

  1. Select a gradient or create one in the Gradients dialog. (Ctrl + G)
  2. Go to Colors -> Map -> Gradient Map

Hope this is what you were looking for!

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This did the trick. Thanks for your help! I've updated the question with some details on how it worked out for me. –  Ben Blank Mar 20 '11 at 23:51

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