Hi all,

peter sikking schrieb:
> and I do not really follow what you wrote in there.
> I do have the feeling we draw different conclusions.

indeed, obviously we draw different conclusions from the very same specs.
Here's my take on why png bKGD is complementary to any (future) element of XCF:

"" The background color given by bKGD will typically be used to fill
"" unused screen space around the image

this intention is really different vom any XCF intent

"" , as well as any transparent pixels within the image.

transparent XCFs are meant to be transparent, wether or not they are
specified with the help of a bg-color-layer.

"" (Thus, bKGD is valid and useful even when the image does not use 

GIMP bg-color-layer is redundant when the bottom layer is opaque

"" Viewers that have a specific background against which to present the
"" image (such as Web browsers) should ignore the bKGD chunk

giving presentation hints for viewers is outside the scope of XCF,
no part of it is optional when it gets rendered.

> bg-color-layer and png bKGD are about what will the image consumers see.

I think that doesn't really match png bKGD:
in the common web use-case, the png bKGD gets intentionally ignored by the 
so the consumers never see it.
This use-case is in turn why most(?) image viewers and GIMP also do ignore png 
to gauge transparency.

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