Cross Process

Cross-processing was an accident in a darkroom that became a whole aesthetic. Slide film designed for E-6 chemistry pushed through C-41 gives you blown highlights and surreal, high-contrast color; negative film through E-6 goes cold, pastel, and almost alien. Fashion and music photography in the 90s ran on this stuff. Cross Process bottles both accidents as a two-choice dropdown with a strength slider.

It's one of the smaller nodes in ComfyUI-Darkroom, and that's fine - it's a flavor node. The pack's heavier hitters (Film Stock Color, Halation) build full emulations from physics and measured data; this one is a focused color-shift effect with exactly one job: make the image look like the wrong chemistry went through the wrong soup.

How it works

Both directions are the same mechanism with different color behavior. "E-6 in C-41 (slide → negative)" pushes highlights toward blowout and gives color that strange, hyper-saturated yet grittier look - the famous cross-processed slide signature. "C-41 in E-6 (negative → slide)" is the colder, flatter direction, with muted pastel color and lifted blacks. The node applies its shifts in linear light like everything else in the pack, and the strength slider blends the result with the original, so you can go from "barely there" to "a whole film was destroyed for this."

The inputs that matter

• process_type - the dropdown. E-6 in C-41 (slide → negative) is the famous warm/broken look; C-41 in E-6 (negative → slide) is the cold pastel one. Try both - they're genuinely different images.
• strength - the blend between original (0) and fully cross-processed (1).

That's the whole interface: image in, image out. No hidden menus, no profile hunting. Output is image - wire it to the next node or a Preview.

Install and gotchas

cd ComfyUI/custom_nodes
git clone https://github.com/jeremieLouvaert/ComfyUI-Darkroom
pip install -r ComfyUI-Darkroom/requirements.txt

Or search "Darkroom" in ComfyUI Manager and restart. It's under AKURATE/Darkroom/Film.

The trap with cross-processing as an aesthetic: it's loud. The slide-in-C-41 look at strength 1.0 can nuke skin tones into something nobody asked for. The good news is it's a per-pixel color transform, so it's fully welcome inside a LUT bake chain - throw it between LUT Bake Inject and Extract and export the look as a .cube. Practical tip: run it at 0.4–0.7 and let a Film Stock node underneath carry the tonal weight. Cross-process reads best as a hint of wrong chemistry over an otherwise believable image, not as the whole thing.