[dvipdfmx] bug with inclusion of a PNG

[Paulo Ney de Souza]

Philip,

But "identify" from ImageMagic says it is there:

 identify -verbose A.png
 ....
  Colorspace: sRGB
 ....

The specification further says:

An application that writes the sRGB chunk should also write a gAMA chunk
(and perhaps a cHRM chunk) for compatibility with applications that do not
use the sRGB chunk. In this situation, only the following values may be
used:

   gAMA:
   Gamma:         45455

   cHRM:
   White Point x: 31270
   White Point y: 32900
   Red x:         64000
   Red y:         33000
   Green x:       30000
   Green y:       60000
   Blue x:        15000
   Blue y:         6000

When the sRGB chunk is present, applications that recognize it and are
capable of color management [ICC
<http://www.libpng.org/pub/png/spec/1.2/PNG-References.html#B.ICC>] must
ignore the gAMA and cHRM chunks and use the sRGB chunk instead.
and as you can see these are the values that TwekPNG puts out, indicating
that this is either a very big coincidence or the sRGB chunk is there.

Paulo Ney





On Wed, Jan 13, 2021 at 1:49 AM Philip Taylor <
P.Taylor at hellenic-institute.uk> wrote:

> Paulo Ney de Souza wrote:
>
>
> And on another point, reading the PNG specification (
> http://www.libpng.org/pub/png/spec/1.2/PNG-Chunks.html) I saw the
> following text:
>
>         An sRGB chunk or iCCP chunk, when present and recognized,
> overrides the cHRM chunk.
>
> that seems to imply the calibration chunk should be ignore in the presence
> of an sRGB chunk -- which I believe is our case, isn't it?
>
>
> I do not see either an sRGB chunk or an iCCP chunk in "A.png", Paulo :
>
>
>
> That is not to say that neither is there, but "TweakPNG" does not display
> them, so one or both *may* be missing.
> Philip Taylor
>
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