Luminosity Masking

Luminosity masks are one of those Photoshop tricks that feel like cheating the first time you use them. Instead of selecting an object by shape, you select by brightness - pull a mask that covers only the shadows, or only the highlights, and grade that band without touching anything else. JHPixelProLuminosityMasking brings exactly that to ComfyUI, and it does it properly: the three bands sum to ~1.0 at every pixel (a partition of unity), so shadows + midtones + highlights ≈ 100% with no gaps and no double-counting.

Why you'd reach for it: split-tone grading (push warm into the shadows only), denoising just the dark regions where the noise actually lives, or a subtle local-contrast bump in the midtones. It's a mask generator, so the output feeds any mask consumer - an ImageBlend, a LUT apply, a compositor, a SetLatentNoiseMask. Selection by luminance band, not by shape, is the whole game.

How it works: the node computes a luminance channel from your image, then builds three smooth masks with smoothstep transitions at the band boundaries. The luminance_source dropdown matters more than you'd think:

• lab_l (default) - the perceptual L channel, matching Photoshop's default. ~120 ms at 2K on CPU.
• ycbcr_y - the fast path, ~7 ms at 1024 on CPU. Use it for realtime previews or CPU-bound work.
• hsv_v - simple max-RGB, the least perceptual of the three.

The two bounds you'll actually set:

• shadow_end - where the shadow band stops (default 0.33).
• highlight_start - where highlights begin (default 0.67). Must be greater than shadow_end or the node raises.

soft_edge (default 0.1) controls the transition width: smaller means sharper band edges, larger means smoother blends.

Outputs are three MASKs: mask_shadows, mask_midtones, mask_highlights. A classic move: multiply a color LUT through mask_midtones only, and you get split-tone grading without touching shadows or highlights.

Install is the shared pack install - one clone covers every PixelPro node:

cd ComfyUI/custom_nodes
git clone https://github.com/jetthuangai/ComfyUI-JH-PixelPro.git
cd ComfyUI-JH-PixelPro
pip install -r requirements.txt

Or ComfyUI Manager → search "ComfyUI-JH-PixelPro" → Install → restart. This node lives under ComfyUI-JH-PixelPro/color.

Troubleshooting: with very small soft_edge (< 0.03), the partition isn't exactly unity near band edges - you'll see a thin blend zone. The node rescales to keep it honest, so it's cosmetic, not a bug. On CPU, lab_l at 2K costs ~120 ms per call; if that's your environment, switch to ycbcr_y for interactive work. And it's RGB-only - feed it a 4-channel image and things get weird. None of the mask nodes in this pack need a model download, so this one is a light, immediate install.