[Libreoffice-bugs] [Bug 134213] Changed transparency handling in Draw breaks export to PNG of transparent objects over pictures with just default Layout layer, forces use of additional layer(s) for transparent shape(s)

bugzilla-daemon at bugs.documentfoundation.org bugzilla-daemon at bugs.documentfoundation.org
Sat Jun 27 04:26:08 UTC 2020


https://bugs.documentfoundation.org/show_bug.cgi?id=134213

--- Comment #18 from V Stuart Foote <vstuart.foote at utsa.edu> ---
(In reply to mwtjunkmail from comment #17)
> That's confusing, because the two images in the side-by-side example are
> identical in size, and in the same document just different slides, so sorry
> for me being dense, but I'm not understanding why one slide's content would
> would be resampled but the other not. I can play with it and see what's
> going on.

The source PNG is held in the ODF archive. Unzip it and look in the /Pictures
directory. If the source PNG is not the size of the drawing page it is being
scaled.

When filter parsed onto canvas, or when canvas selection is filter exported to
a new PNG (or other format), it is being resampled. Resulting pixels are not
the same size as the original, and color bands for each resulting pixel will
also change depending on the sampling type and also for any filter applied
(color, gamut, transparency).

So, to eliminate effects of scaling (and isolate the filtering) the drawing
page size would have to match the size of the source PNG.  

But that is not the issue here of changed handling of transparency on the
'Layout' layer.

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