Riso CMYK and CMY Compositor in Blender

I made an alternative option to Photoshop’s Split Channels feature in Blender to create black and white CMYK spot color image files that could be used to create thermal screens or also known as ‘Masters’ in Riso printing. My biggest issue with the current Split Channels feature is that when you put an image file in, the colors tend to desaturate overall when you go from RGB to CMYK and there is a lot of back and forth between splitting the channels, adjusting the values and then having to setup layers to stack and multiply spot colors over each other to check how the values affect the mixing of color. This previous conversion lacks an intermediary level of control on adjustments for the spot colors that is required for Riso printmaking.

What’s included is a .blend file with a compositor node setup that simulates conversion of RGB into a CMYK or CMY so that a visual preview mockup can easily be toggled for different two -, three - or four - color passes on the same image. 

By inserting the hex values of the Riso colors for the individual color passes, you will be able to preview how certain standard Riso colors might mix as a print. This compositing process works for all images, not just Blender renders. Black and White value color ramps are used as controllable exposure adjustments to the original image so that more saturation of the Riso ink can be applied per color pass. There are file output nodes at each color pass after adjusting the exposure that you can set up to file locations of your PC to save to after you click Render Image. 

Through trial and error, Riso artists have found a way to control their saturation of printed Riso ink by matching the incremental value percentages to how the color ink looks when physically printed through reference charts. With the use of my eye and charts I’ve collected from people; like Natalie Andrewson, PrintedPony, Ryan Cecil, I notice that saturation loads more when the values start reaching 70%-100% so I try to adjust the color ramps with the Riso hex colors gradation in a way that matches this snowballing gradation.

I decided to keep the node setup the way as it is, so everything is transparent and can be customized depending on your process.

It’s a little tricky to get from an RGB additive method of image making to a controllable CMYK or CMY subtractive preview but I'm hoping this saves you some time and opens up some options! As a Riso printmaker, you often can't just rely on having a single button do all the conversion without adjusting your values so I hope this helps, part of the fun is how creative you can be adjusting your CMY or CMYK process! Some things I recommend through trial and error is combining some spot colors to reduce the number of color passes you do, omitting some color passes completely, try swapping out Riso colors for other ones! https://www.stencil.wiki/colors The preview mockups allows you to see what the effect might look like for different passes and can be quickly toggled through!

I recommend adding the free Node Wrangler Add-on to your setup so you can quickly toggle outputs with ‘Ctrl-Shift-Left Click’.  

Caution: Exact color outputs might vary depending on individual printers and may differ from your preview mockup and depend on user input. You are free to adjust this through the nodes!   

I may continue to work on the node setup to improve it, and any future edited iterations will be included with the existing purchase and noted below. Purchases directly help me continue development. :)

Edits:

12/17/2024 - I added a .pdf Troubleshooting Q & A styled guide for common issues/questions you might run into when trying out the node setup for the first time!

2/27/2024 - I added a .pdf manual explaining the node setup a little more step by step!