Re: [Gimp-developer] Why the endless background conversions between linear and regular sRGB TRC?

[Michael Natterer <mitch gimp org>]

On Thu, 2012-08-30 at 07:55 -0400, Elle Stone wrote:
> On 8/30/12, Jon Nordby <jononor gmail com> wrote:
> > On 30 August 2012 01:01, Elle Stone <l elle stone gmail com> wrote:
> >> Regarding sRGB and rendering to the screen:
> >> Could you explain more about what you mean by "rendering to the screen
> >> is done using sRGB"? What about the actual monitor profile?
> >
> > Cairo, the library used for rendering to the screen in GTK and GIMP
> > expects its input as sRGB*. See app/display/gimpdisplayshell.c for
> > example of how we use this library. The Babl format "cairo-ARGB32" is
> > short for "R'aG'aB'aA u8": 8 bit unsigned integer gamma-corrected,
> > pre-multiplied alpha. The LCMS plugin is used before this step to do
> > the conversion with the actual monitor profile.
> 
> So if I understand what you are saying (I don't think I do):
> First the lcms plugin converts the image to the actual monitor display profile.
> Then "something" converts the image to sRGB and sends the image to Cairo?
> And then Cairo sends the image to the screen?
> 
> I don't think that is what really happens. If it were happening, all
> images displayed by Gimp would have a magenta color cast as displayed
> on my monitor. And they don't. Perhaps Cairo just sends RGB numbers to
> the screen (and doesn't care what these numbers "mean"), and Gimp is
> sending the monitor profile RGB numbers to Cairo.

Don't work under the assumption that anything in git master works as it
should. It's safe to assume that *nothing* works as it should, and
needs to be fixed. So if something doesn't seem to work, the bug could
be in many places.

--mitch