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I have a gold handprint that I want to set up as a spot for printing. Since it was done with one substance, it should be possible to convert the image to only the gold spot and black.

I've searched for such a tutorial on the internet, but I just don't know how to separate black and gold as layers so that I can remove RGB/CMYK.

How do I do this?

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I'd like to know more on how this will be printed, you said 'set up as a spot for printing,' so will you be taking this to a commercial printer for posters or to a screen printer for t-shirts or something similar? If so, what exactly does the printer need -- can you let us know what his requirements are? Then we could give you a better idea how to get there from here. –  David Rouse Dec 10 '10 at 16:32
    
When I go to print, I want to be able to specify a metallic color to for the hand print so it's shiny. In particular, I'd change the gold to silver. I'd also like to retain the black element as a channel in case I decide to do CMYK printing instead. –  Stephen Dec 10 '10 at 20:17
    
Strangely, I think this is the same issue I encountered here: photo.stackexchange.com/questions/2359/…. I could use Gimp's "Colour to Alpha" tool and then convert the alpha layer to Gold, and then I'd be left with the black elements to extract to another layer. –  Stephen Dec 10 '10 at 20:21
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1 Answer

up vote 3 down vote accepted

Go to the "select" menu and click on "color range". Here you can choose a specific colour and produce a selection based on that colour. You can sample different tones of gold and add them to the selection, and adjust the tolerance. What's even better is that you can preview your selection in realtime if you chose "grayscale" or "black mask" from the preview dropdown menu.

alt text

Here I am selecting just the gold colour.

Press OK once you are happy and that will create a selection. If you save the selection to a channel, then copy and paste the channel into a layer you'll have a greyscale image representing the amount of gold. If necessary you can convert this to a pure black/white image using the threshold tool.

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I've got that far, but I'm wanting to split the image selection into the parts that are gold, and the parts that are black. Then I can adjust each separately; notably to be able to change the gold to silver etc. –  Stephen Dec 10 '10 at 12:17
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I'm not sure I understand, once you have the gold selected you can do what you like with it. If you invert the selection and then press delete, it will isolate the gold on that layer permanently, you can then add a plain black layer behind it to edit each selectively if that's what you're after. –  Matt Grum Dec 10 '10 at 19:32
    
Matt has it nailed...once you create a color range selection, you can either cut the selection and paste it, which would put the gold hand into a new layer. Or, you can invert the selection, and hit delete, which will eliminate the black and leave only the gold behind. You could then create a pure black layer behind that, or use the hand on a variety of backgrounds. If you put the hand on another type of background, best to use a blending mode that blends out black (like multiply). –  jrista Dec 12 '10 at 3:45
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