Re: [Gegl-developer] babl roadmap: How do you know which images are sRGB images?

[Elle Stone <ellestone ninedegreesbelow com>]

On 10/14/2014 07:16 AM, Øyvind Kolås wrote:
> On Tue, Oct 14, 2014 at 11:20 AM, Elle Stone
> <ellestone ninedegreesbelow com> wrote:
> > On 10/13/2014 06:36 PM, Elle Stone wrote:
> > So again, upon opening an image, how do you plan to detect whether the image
> > is an sRGB image or not?
>
> > Will you compare MD5 checksums?
> > Will you consult the profile descriptions?
> > Will you examine the profile colorants and TRCs?
>
> Most likely examination of profile colorants/TRCs since that is
> what ICC or other color profile meta-data aware image loaders needs to
> provide down to babl anyways.

You did pick the only plausible answer: check the colorants and TRCs.

> In many
> circumstances it is desirable to to treat almost sRGB as sRGB and
> consider deviance from the real standard a mistake in labeling; for
> instance if it is a low bitdepth image containing dithering - at other
> times assuming that the slight off profile has been applied as is
> earlier in the production pipeline might be desirable.

For most users, for most purposes, you as developer can probably decide 
for the user that "slight off" means "close enough". The trouble is you 
don't know whether "slight off" is a mistake or intentional.

The profile maker might have used something other than Bradford 
adaptation to make the profile. This is allowed by the ICC specs, and 
would result in slightly different colorants.

The artist might be fully aware that the profile is not exactly like the 
GIMP built-in profile, and nonetheless intend to use the embedded sRGB 
profile instead of the GIMP built-in sRGB profile. Perhaps the existing 
gray axis needs to be preserved.

And so on. You think it's OK to second-guess and decide for the artist 
what happens to the artist's RGB data. But it's really not OK.

Elle Stone