png-mng-misc

[Glenn Randers-P. <gl...@gm...>]

I'm working on some applications that read various image formats
that might have embedded iCC sRGB color profiles, and convert
to and from png.

In theory, it's supposed to be OK to recognize the sRGB
profile and just write the sRGB profile in the PNG.

Now comes the rub: when we read a PNG with an sRGB
chunk and write to a format that doesn't have the equivalent
of the sRGB  chunk but does allow embedded color
profiles, which sRGB profile should the application write?
There are two version-2 profiles (with and without blackpoint
compensation) and one version-4 profile which is much
larger and claimed by ICC to produce better-looking results.

I am leaning toward providing an option for the user to
select version 2 or version 4.  What should be the default?
v4 has been out for 10 years, and ICC seems to recommend
using v4 (see http://www.color.org/v4spec.xalter).

What to do about the black-point compensated one?

Currently I am recognizing these profiles by their length
and by the presence of "sRGB" at a certain offset.
I think there are other sRGB profiles floating around
that won't be recognized this way.

Glenn