[Poppler-bugs] [Bug 80998] New: Overprintmode and shadings

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=80998

          Priority: medium
            Bug ID: 80998
          Assignee: poppler-bugs at lists.freedesktop.org
           Summary: Overprintmode and shadings
          Severity: normal
    Classification: Unclassified
                OS: All
          Reporter: Thomas.Freitag at alfa.de
          Hardware: Other
            Status: NEW
           Version: unspecified
         Component: splash backend
           Product: poppler

Created attachment 102365
  --> https://bugs.freedesktop.org/attachment.cgi?id=102365&action=edit
PDF which shows the problem

If using overprintmode (OPM) together with overprint switched on, the CMYK
values have to examined for each channel. If the channel value is != 0, it
knocks out the background channel, otherwise the background channel remains
unchained.
The actual implementation will not work with shadings: here we have dynamic
patterns and the comparison have to be done with the result of
pattern->getColor(), but it does it only once with the actual fill color which
is completely wrong because the fill color has nothing to do with the shading
colors.
The attached PDF shows the effect: the yellow N is painted greenish if the
jpegcmyk or overprint option is used (only available if compiled with
SPLASH_CMYK)

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