Optional ReadonlyfpsFrames per second for an animated format.
Optional ReadonlyframePer-frame durations in milliseconds, one per written page.
Optional ReadonlyloopHow many times an animation plays. Absent plays it forever.
Optional ReadonlylosslessEncode WebP without loss.
Optional ReadonlymatteThe colour transparency is flattened against, for a format with no alpha.
Optional ReadonlypageWhich page is written, counting from zero.
Not only for a single-page format. Naming a page wins over a format that would otherwise gather them all, so a GIF asked for page 1 of three is a one-frame GIF and a PDF asked for one page is a one-sheet PDF. Left out, a spanning format writes every page and every other format writes the last one.
An index past the last page is refused rather than clamped.
Optional ReadonlyqualityLossy quality from 0 to 1, read by JPEG, WebP and AVIF.
Quality and container settings that only some formats read.
A format that ignores a field ignores it. The timing fields are the exception: naming a frame rate for a format with no clock is an error rather than something quietly dropped, because a caller who wrote
fpsand got a still image asked for something that did not happen.