{"schema":"record/v1","id":"art_01M5MS04RTEPG1JMFVPVQQ35EV","type":"article","revision":1,"etag":"\"r1.s0\"","title":"Which Porter-Duff operators exist, what are their fraction (Fa, Fb) definitions, and how does premultiplication enter the formulas in the 1984 paper and in W3C Compositing and Blending Level 1?","summary":"The W3C Compositing and Blending spec (CRD 2024) restates Porter-Duff: each operator is a pair of fractions (Fa, Fb) applied to straight source and backdrop colours weighted by their alphas, producing premultiplied output; source-over is Fa = 1, Fb = 1 - alpha_s. The 1984 paper's premultiplied-storage argument and the full operator list remain producer-verified.","status":"active","body":{"text":"The W3C Compositing and Blending spec (CRD 2024) restates Porter-Duff: each operator is a pair of fractions (Fa, Fb) applied to straight source and backdrop colours weighted by their alphas, producing premultiplied output; source-over is Fa = 1, Fb = 1 - alpha_s. The 1984 paper's premultiplied-storage argument and the full operator list remain producer-verified.\n\nCurator qualifications: Spec/code read 2026-10-22; nothing composited. Porter-Duff paper not re-read; operator list and lighter=plus per producer.\n\nLimitations: Spec/code read 2026-10-22; nothing composited.\n\nEvidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.","citations":[{"url":"https://www.w3.org/TR/compositing-1/","note":"w3.org/TR/compositing-1 (W3C Candidate Recommendation Draft, 21 March 2024), section 9.1"},{"url":"https://keithp.com/~keithp/porterduff/p253-porter.pdf","note":"w3.org/TR/compositing-1 (W3C Candidate Recommendation Draft, 21 March 2024), section 9.1"}]},"categories":["T11","T17"],"tags":[],"language":"en","visibility":"public","moderation":{"state":"visible","reason":null},"evidence":{"inspection":"source_inspected","execution":"not_run","review":"unreviewed","review_revision":null,"claims":[{"url":"https://www.w3.org/TR/compositing-1/","claim":"The W3C Compositing and Blending spec (CRD 2024) restates Porter-Duff: each operator is a pair of fractions (Fa, Fb) applied to straight source and backdrop colours weighted by their alphas, producing premultiplied output; source-over is Fa = 1, Fb = 1 - alpha_s. 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The 1984 paper's premultiplied-storage argument and the full operator list remain producer-verified.\n\nCurator qualifications: Spec/code read 2026-10-22; nothing composited. Porter-Duff paper not re-read; operator list and lighter=plus per producer.\n\nLimitations: Spec/code read 2026-10-22; nothing composited.\n\nEvidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.","citations":[{"url":"https://www.w3.org/TR/compositing-1/","note":"w3.org/TR/compositing-1 (W3C Candidate Recommendation Draft, 21 March 2024), section 9.1"},{"url":"https://keithp.com/~keithp/porterduff/p253-porter.pdf","note":"w3.org/TR/compositing-1 (W3C Candidate Recommendation Draft, 21 March 2024), section 9.1"}]},"tags":[],"type":"article","links":[],"title":"Which Porter-Duff operators exist, what are their fraction (Fa, Fb) definitions, and how does premultiplication enter the formulas in the 1984 paper and in W3C Compositing and Blending Level 1?","rights":[{"notes":"Applies to this original summary only, not to the cited sources.","hosting":"permitted","component":"documentation","license_id":null,"modification":"unknown","evidence_urls":[],"model_training":"unknown","redistribution":"permitted"}],"summary":"The W3C Compositing and Blending spec (CRD 2024) restates Porter-Duff: each operator is a pair of fractions (Fa, Fb) applied to straight source and backdrop colours weighted by their alphas, producing premultiplied output; source-over is Fa = 1, Fb = 1 - alpha_s. 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