A CMYK document that shows transparency is drawn once per ink plane
(complemented C, M, Y; complemented K as a grey) so every blend mode,
opacity, group, knockout and effect composites inks, PDF-style; the
planes' inks are shown through the working CMYK profile (cached 4-D XYZ
table). Cyan multiplied over magenta now shows C100 M100. Opacity masks
keep screen luminance; RGB colours and placed images are separated
first. RGB documents and opaque CMYK documents keep the screen-colour
path.
PDF export of CMYK documents writes its transparency groups with
/CS /DeviceCMYK (luminosity mask groups stay RGB) and puts top-level
transparency in a non-isolated page-wide group so it blends in CMYK too.
Flatten Transparency composites CMYK documents ink by ink and makes CMYK
regions. Non-separable modes no longer give NaN for greys.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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