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Some tools like img2pdf refuse PNG images with alpha channel. The suggested option --png-no-alpha will omit the alpha channel so that the PNG output can be used with img2pdf directly.

Signed-off-by: Tormod Volden <debian.tormod@gmail.com>
@tormodvolden
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Or should this happen automatically if --foreground and --background are both set with only RRGGBB (no AA)?

@tormodvolden
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Strictly it is not an alpha channel in this case but a tRNS Transparency chunk so we should maybe say "transparency" instead of "alpha channel".

@lenoleno
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lenoleno commented Dec 7, 2021

This is also relevant when generating PDF/A-1 compliant documents. Preflight fails on PDF/A-1 documents embedding plainqrencodePNG output, since transparency is only supported since PDF/A-2.

@ROBERT-MCDOWELL
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this PR is 3 years old and still open, why is it not merged? it's a very important feature!

@tormodvolden
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tormodvolden commented Apr 4, 2024

The maintainer hasn't committed anything here since 2020 (Feb 2021 on the cygwin branch).

Anyway, I would be happy to modify this PR to use "transparency" instead of "alpha channel" if preferred.

@ROBERT-MCDOWELL
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the most important is your option is working well. I'm now following your fork. here it's dead....

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3 participants