What does Smith and Blinn (1996) define as the matting equation for constant-colour backings, why is single-backing matting underdetermined, and which failure cases and constraints does it name?
Smith and Blinn show that pulling a matte from a single constant-colour backing is underdetermined (three colour equations, four unknowns per pixel), so practical keyers rely on constraints about foreground colour (such as no blue, which rules out all greys but black, about two-thirds of hues and all pastels) or need triangulation with two different backings; blue spill, flare, backing shadows and impurities are named practical problems. This is why keyer results depend on assumptions and fail on foreground colours near the screen colour.
Smith and Blinn show that pulling a matte from a single constant-colour backing is underdetermined (three colour equations, four unknowns per pixel), so practical keyers rely on constraints about foreground colour (such as no blue, which rules out all greys but black, about two-thirds of hues and all pastels) or need triangulation with two different backings; blue spill, flare, backing shadows and impurities are named practical problems. This is why keyer results depend on assumptions and fail on foreground colours near the screen colour.
Curator qualifications: Paper read 2026-10-22; nothing keyed. Vlahos constant range per producer (not found in extraction).
Limitations: Paper read 2026-10-22; nothing keyed.
Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.
Structured fields
{
"citations": [
{
"url": "https://alvyray.com/Papers/CG/blusig96.pdf",
"note": "Smith and Blinn, Blue Screen Matting (SIGGRAPH 96), abstract and sections on the matting problem"
}
]
}Evidence claims
- [sourced_fact] Smith and Blinn show that pulling a matte from a single constant-colour backing is underdetermined (three colour equations, four unknowns per pixel), so practical keyers rely on constraints about foreground colour (such as no blue, which rules out all greys but black, about two-thirds of hues and all pastels) or need triangulation with two different backings; blue spill, flare, backing shadows and impurities are named practical problems. This is why keyer results depend on assumptions and fail on foreground colours near the screen colour. · locator: Smith and Blinn, Blue Screen Matting (SIGGRAPH 96), abstract and sections on the matting problem source
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