Gift Chroma Master · 合成预览

A keyed subject composited onto nothing is impossible to judge. On a grey or black backdrop, a bad key hides its own damage: green fringes vanish into the dark, transparent holes read as intentional, and you can't tell whether the edge is a soft glow or a spill disaster. GiftChromaMasterPreview is the suite's answer - a dead-simple node that composites your keyed image onto a checkerboard (or black, white, or a color you pick), giving you the professional standard view for judging a matte.

It takes image and mask (any IMAGE + MASK pair - the chroma chain's foreground_rgb/foreground_alpha, or anything else), and a background dropdown with four choices: checker (the default and the right one for most tuning), black, white, and color - with background_color for the last one. One preview IMAGE comes out. That's the entire interface, and that's a feature: it's not a compositing node, it's a checking instrument.

Why the background choice matters

Checkerboard is the honest view: it shows you both transparent holes and leftover screen-color contamination, because the two look different against the alternating patches. Switch to white when you're hunting for dark fringing or see-through smoke that reads as grey. Switch to black when the concern is bright spill or halos. Pick a real background color when you're testing how the key survives a composite against the actual thing it'll sit on - the classic find: a key that looks fine on checker but falls apart against a bright, colored backdrop. That failure mode is precisely why the suite's background-removal sibling-docs keep hammering "judge against a real background, not a grey preview."

The production discipline

The README is refreshingly blunt about this: don't run your whole long video through the preview. It's for spot-checking frames, not for the full pass - the preview is a render like any other, and you're spending GPU time to look at frames you'll never ship. The recommended flow is to pull a few frames into a preview, tune, disconnect, then run the real batch straight from the chroma node to the composite/encoder. The preview's job is to answer "is this key good?" in ten seconds, not to be a permanent resident of the graph.

Getting it

Standard pack install: ComfyUI Manager (search "ComfyUI-GiftHelperSuite") or git clone https://github.com/lingziwyh/ComfyUI-GiftHelperSuite.git into custom_nodes, restart, no extra pip dependencies. One note on polarity so you don't chase ghosts: the node just composites image using mask as opacity, so feed it the chain's own outputs (foreground_alpha is 1=foreground) and it behaves exactly as intended. And remember the honest summary that applies to the whole suite: this node makes a bad key visible, it doesn't make it good - for that you go upstream to the Keyer/Cleaner/Despill knobs.