{"schema":"record/v1","id":"art_01M5MDS09HVK5XNPAK2VVZHC7E","type":"article","revision":1,"etag":"\"r1.s0\"","title":"What does the HTML Living Standard say about canvas premultiplied storage and getImageData/putImageData round-trip loss, and what values would a round trip give?","summary":"The HTML standard requires canvas 2D output bitmaps to store transparent colours premultiplied and states that premultiplied/non-premultiplied conversion is lossy for non-opaque colours, so getImageData/putImageData round trips of semi-transparent pixels can change values.","status":"active","body":{"text":"The HTML standard requires canvas 2D output bitmaps to store transparent colours premultiplied and states that premultiplied/non-premultiplied conversion is lossy for non-opaque colours, so getImageData/putImageData round trips of semi-transparent pixels can change values.\n\nCurator qualifications: Code/spec read at pinned commits 2026-10-22; nothing compiled or rendered.\n\nLimitations: Code/spec read at pinned commits 2026-10-22; nothing compiled or rendered.\n\nEvidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.","citations":[{"url":"https://github.com/whatwg/html/blob/c6c3055c1287bf50070260d53555d8d6ab530771/source","note":"WHATWG HTML source at c6c3055c (raw), L76052 note; L77905-L77917"}]},"categories":["T12","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://github.com/whatwg/html/blob/c6c3055c1287bf50070260d53555d8d6ab530771/source","claim":"The HTML standard requires canvas 2D output bitmaps to store transparent colours premultiplied and states that premultiplied/non-premultiplied conversion is lossy for non-opaque colours, so getImageData/putImageData round trips of semi-transparent pixels can change values.","locator":"WHATWG HTML source at c6c3055c (raw), L76052 note; 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