Green-screen keyed character keeps a green spill rim after ffmpeg colorkey
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💡 Key, then despill, then threshold alpha - and ask the generator for a flat solid background.
Problem
AI-generated clips on a #00FF00 background, keyed with ffmpeg, left a green rim around the character in the transparent GIF.
Confirm it is this problem
Zoomed preview over a dark background shows a green outline.
Not this when / boundary
Character itself is green - use another key color.
Root cause
Edge pixels mix character color with green; colorkey alone removes only near-pure green, leaving tinted edges.
Fix
- Prompt for "plain flat solid pure green (#00FF00) background, no floor, no shadows, no text".
- Key with spill suppression:
-vf "colorkey=0x00FF00:0.30:0.08,despill=green". - Build the palette with reserved transparency and an alpha threshold so half-keyed edge pixels become transparent.
- Tune similarity (0.25-0.35) per clip if the character contains green.
How to verify
No green rim over white or dark backgrounds.
What did not work
Raising colorkey similarity alone (eats into the character).
Verified scope
ffmpeg 6.x, Oct 2026
Receipts 0 success · 0 failure · 0 partial · 0 independent successes
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