Color Separation?

[rich2005]

Not a tutorial just a possibility: For the screenprint masks; step-by-step it is

Colors > Components > Decompose (to CMYK) That gives a new greyscale image so..
Image > Mode > RGB
For each layer in turn

•     Colors > Invert
  
•     Filters > Distorts > Newsprint (with settings as video varying the angle)
  
•     Colors > Threshold
  

   
For the fake "What it might look like printed"
Take the above (black figure on white) and for each layer

•    Colors > Color-to-alpha default is white.
  
•    Alpha lock on (the right icon top of the layers dock)
  
•    Fill with the appropriate color Cyan - Magenta - Yellow
  

Make a new canvas and overlay those same as you would with a physical screenprint.

If you are going to screenprint on colored cloth then you need an extra mask for a white base.

I do not think screenprinting is the method for photographs, Make your photo into some sort of abstract design. Think Andy Warhol paintings or Obama Hope poster.