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Old 10-08-2013, 07:04 PM   #1
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Russell Fincher
Dallas, USA
Join Date: May 2007
Posts: 269
Convert full spectrum height map to grayscale

I have a full spectrum height map that I need to convert to a 16-bit grayscale height map. Photoshop used to have much better controls for doing this with Gradient Map, and I'm not sure when that changed. Any ideas how to achieve this? For reference, white is the highest point, and blue is the lowest:

Edit: I distinctly remember a tool back in the pre-Creative Suite days where you could map a gradient to the existing colors in your image. All the colors in your image were laid out in a grid of swatches for very specific control. Beginning to think I'm losing my mind.

Last edited by moiremusic : 10-08-2013 at 07:12 PM.
Old 10-08-2013, 07:17 PM   #2
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Russell Fincher
Dallas, USA
Join Date: May 2007
Posts: 269
Hm. The tool I was thinking about is still there... Image>Mode>Color Table. I couldn't get to it because you have to start with an image in Index Color mode.

However, this is not going to work for me since Index Color has such a limited bit depth.

So still looking for a way to convert this map.
Old 10-27-2013, 04:48 PM   #3
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Scott Valentine
Photoshop Author
Join Date: Sep 2004
Posts: 182
Hi - sorry this reply is so late. If you're still working on a solution, why doesn't a gradient map do the trick for you? Here's how I would approach this one...

Add a Black and White adjustment layer (set to Luminosity blending mode) above the map, then add a White to Black Gradient Map adjustment layer. If you want even finer control, add a Selective Color adjustment layer below the B&W and Gradient Map.

Using this method, you can control the input to the gradient map and make any shade brighter or darker. This works because the gradient map converts luminosity (additive result of RGB channels in this case) to a position along the gradient bar. If you change the relative luminosity of a given color, you change its conversion.

I couldn't get a perfect translation, but it was close enough that you could make selections and mask some regions. In particular, I had trouble getting the ridge line to show up at the proper height because it's so saturated that it returns a low luminosity value. But that can be taken care of with another map, perhaps a threshold adjustment to grab just that ridge.
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Old 10-27-2013, 04:48 PM   #4
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