CMYK Colour Separation using the Gimp
Selby Markham writes a step-by-step to CMYK colour separation for gum bichromate printing – but not with Photoshop – he used the freeware Gimp.
Gimp
How to make digital negatives
An easy way to make interesting negatives with the help of a computer. If you think Photoshop is too expensive – The Gimp is a cheaper program – it’s actually free.