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denaliprinting
Joined: 05 Nov 2006
Posts: 3
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 Posted: Sun Nov 05, 2006 10:47 am Post subject: Grayscale separation... |
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I need help with separating a grayscale image into dark and light channels. Specifically what I am trying to do is take a grayscale image and divide it into two (or more) channels representing the lower and upper percentages of black. I am doing this so that I can create a black and light gray spot color separation. In screen printing, the lower values of gray tend not to come out and get dropped when burning the film onto the screen. Additionally with dot gain being what it is in screen printing (30%+), it is advantagous to split the gray channel into two channels with only the upper half (50% or more black) into one channel, and the lower half (less then 50% black) into another channel. I have tried to eliminate both upper and lower halfs without altering the other half but can't figure it out. To explain another way, imagine completely elimimating 50% black or more from the histogram without altering the 49% and lower values or compressing them, and then again in reverse, keeping the 50%+ and completely eliminating the lower half.
Anybody tough enough to answer how this could be done would impress the hell out of me. |
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swanseamale47
Joined: 23 Nov 2004
Posts: 1478
Location: Swansea UK
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| Posted: Mon Nov 06, 2006 2:46 am Post subject: |
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Did you try image/ajustment/posturise and type in 2 ? that will give you just black and white, you could then select each colour and make a seperate image from each. Wayne |
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denaliprinting
Joined: 05 Nov 2006
Posts: 3
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| Posted: Mon Nov 06, 2006 10:36 pm Post subject: |
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Wayne,
Thanks for the tip. I had actually also figured a way to that using custom curves just prior to your post. I tried your method and it works just as well, and then I was able to further refine the split using threshold instead of posterize which gave me the ability to split the histogram at places other than 50%. Thanks again. |
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lasa
Joined: 08 Aug 2005
Posts: 1090
Location: Florida
PS Version: CS
OS: MS XP
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| Posted: Tue Nov 07, 2006 7:11 am Post subject: |
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If you can use the Threshold you might want to try
the gradient map. Using the default B/W, simply pull the sliders until the meet in the middle. It gives alot of control from thru all the grays to black..
Lasa
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Lasa
My hobbie: www.angulo-webdesign-templates.threefooter.com
Treat people the way you want to be treated... |
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