[Poppler-bugs] [Bug 66056] pdftops – avoid excessive or unnecessary rasterization

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=66056

--- Comment #1 from Adrian Johnson <ajohnson at redneon.com> ---
I started looking at what would be involved in implementing finer-grained
fallbacks in PSOutputDev. The first problem I found is how do we handle color
spaces?

In cairo PS output everything is in the DeviceRGB color space. When a fallback
image is adjacent to vector graphics the colors match exactly. In PSOutputDev
each object can have a different color space. When pdftops outputs a fallback
image the DeviceRGB color space is used (except for certain cases like -level1
or the separation modes where DeviceGray or DeviceCMYK is used).

What color space should the fallback images use to ensure that the colors match
vector objects that intersect the images?

As for implementation of finer-grained fallbacks I'm not planning to do
anything fancy like handle drawing translucent colors on top of opaque colors.
I would implement something similar to the way I implemented finer-grained
fallbacks in cairo. ie when there is nothing under an object, blend it into
white. When there is something else under the object, add the bounding box of
the object to the region(s) to be emitted as fallback images. After outputting
all the vector objects, draw the fallback images on top.

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