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I'm working with Risograph (sort of automatized silk screen printing for paper) and I'm trying to find solution for effect I want to achieve. I'm trying to edit photographs to look something like this: Duotone image example

Note: I'm not interested in halftone effect, just focus on colors.

I want to make only some parts of the image blue, and the rest red. I tried to use Duotone mode in Photoshop but no matter what I can't achieve this. Here are two of my failed attempts:

  1. I opened image I'm working on, then changed to duotone mode. In duotone popup menu I selected desired colors red and blue, but when I try to pick blue in color panel all I can get is variations of purpleish color (mix of red and blue). And I can't figure out how to use pure blue or red.
  2. I tried making blue monotone image and mask out what I don't need, than do the same with red monotone image. Then I tried making red-blue duotone file and placing this 2 previously made monotone images, but it's doesn't work, it won't get imported.

It is really important for me to actually work with spot colors, I know exactly how to do this in CMYK/RGB mode. But then I need to do the color separations in order to prepare files for printing and I end up with 4 channels, but I have only 2 available.

Only solution that's working for me right now is to make 2 separate monotone files for blue part of the picture and the red one. Than I would place them in Indesign and position them on top of each other. This works but it's quite hard to manipulate image later, I would have to change 2 separate PSD files by hart and go back and forward with changes.

Best solution for me would be to have only one PSD file, that I'm able to select 2 colors I'm working with, and to be able to mix those to colors (than in print overprint those parts for purple color). And than to be able to import that PSF file in Indesign and print separations with ease. Seems to me that duotone mode is maybe not perfect for this.

I hope I was clear enough. I would appreciate all your help!

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It's not a duotone. I think what you want to create is a Multichannel image with spot colour channels.

Basically, start with a desaturated RGB image, then all you need to do is create spot channels in the channels panel, and then copy and paste each separation in to the channel. Then delete the RGB channels.

enter image description here

As for getting the separations into InDesign, save as a DSC2.0 EPS from Photoshop. Although I think InDesign might also be able to handle it as a regular PSD.

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    Thank you! This will save me many hours in future! This sounds like a great solution. I knew my approach was bad. :D – Trombolo Nov 27 '17 at 19:50

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