RC Threshold

Sometimes you don't want a photo, you want a silhouette. Threshold takes an image and makes every pixel either black or white based on one value - the oldest trick in image processing, and the direct route to high-contrast line art, stencil looks, and extraction masks. RC_Threshold is the RC Image Compositor pack's version, and it's refreshingly complete for a node this simple: five calculation methods, an invert switch, and alpha preservation so your transparent layers stay transparent.

How it works

It converts the image to a single grayscale value per pixel, compares it against your threshold, and outputs pure black or white. The question is how "gray" is computed, and that's the method dropdown:

• luminance (default) - perceptual luminance, 0.299R + 0.587G + 0.114B. This is the "how bright does it look" calculation, and it's the right default for photos.
• average - plain (R+G+B)/3. Flatter, less perceptually correct, but predictable if you're comparing raw channel sums.
• red / green / blue - use a single channel. Want to threshold by how red something is? Pick red and everything with low red goes black.

The rest:

• threshold (0–1) - pixels below become black, above become white.
• invert - flips it, black becomes white and vice versa. One click for the negative look.

Output is a single IMAGE of pure black/white - and if the input had alpha, the alpha is preserved, so a transparent PNG stays transparent while its content goes binary.

Installing it

ComfyUI Manager → search "RC Image Compositor" → install, restart. Manual:

cd ComfyUI/custom_nodes
git clone https://github.com/kj863257/ComfyUI_RC_Image_Compositor
cd ComfyUI_RC_Image_Compositor
pip install -r requirements.txt

Dependencies: pillow, numpy, opencv-python. Nothing to download.

Where people get burned

• Threshold is global, not local. One value for the whole image. If your image has a bright background and a dark subject, no single threshold separates them cleanly - you'll get noise speckles where the values cross. That's inherent to the operation, not a bug.
• The output is pure black/white, no gray. If you wanted soft edges, this node is binary by design - run a feather (the pack's MaskApply) or a blur on the result if you need antialiased edges.
• luminance vs average matter more than you'd think. On saturated colors, average and luminance disagree visibly - a bright blue flips at different thresholds. If your result looks "wrong" compared to a reference, try the other method.
• Don't use it on JPGs with compression artifacts. Blocky noise at the threshold line is a JPEG problem; threshold makes it loud. Clean source in, clean binary out.

Threshold is the node you reach for when you need a mask from a photo, a stencil from a render, or a high-contrast graphic look in two seconds. It's the simplest node in the pack - and sometimes the simplest node is the one that saves the workflow.