PDF export writes a CMYK image whose opacity mask is a gray image on its
own pixel grid with the mask as the image's soft mask. That path always
asked viewers to smooth the image, so a pixelated piece of an envelope
with Anti-Alias off was still written with /Interpolate when it had such
a mask. It now takes the pixelated flag as images without a mask do, and
caches the smoothed and pixelated versions apart.
An axial or radial shading's stops are the samples that linear
interpolation does not reproduce. An ink that changes nothing in RGB,
such as a varnish, could paint at dropped samples only, and its spot
swatch was then missing. Every sample now marks the inks it paints with
as used; the stops are unchanged.
A DeviceN color with a spot ink at a tint above 0 together with a process
plate or a second ink imports as RGB. The importer returned before marking
those inks as used, and only used inks become spot swatches, so the spot
ink was missing from the document and from every later export. Shading
stops take the same path, so a DeviceN gradient lost its ink the same way.
The art still imports as RGB with the existing warning; each ink it paints
with now becomes a spot swatch with its 100% color.
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