Re: png image scrambled

On Fri Aug 23 2019 Pavel Zlatovratskii wrote:
> It's not looks like a bug in libpng and not corrupted image.
> 
> Your image use fully transparent black as background using tRNS
> chunk. Some software use neutral (grey or white) background and
> image looks good. Other ignore transparency (and they are allowed
> to do so as tRNS is an ancillary chunk) and draw background with
> original black colour.
> 
> You can check modified picture: three bytes black to white and
> four bytes of CRC changed.

Thanks a lot to everyone who replied to this thread.  Now I
understand much better how the problem comes about.

The eog viewer lets the user choose a custom color for transparent
parts.  So with eog I happened to get for this picture what I was
expecting to get because my eog was configured to use a white
background.  If I choose black instead, the figure is as "scrambled"
as what I got from rpng.

For GNU Emacs customizability is quite important.  So it seems to me
it would make sense that it allowed the user to choose a custom
color for transparent parts of a png image similar to eog.  I'll
discuss this on an emacs mailing list.  I assume that libpng
supports this.