Re: [Gegl-developer] [Gimp-developer] Don't make an architectural mistake based on a groundless premise

[Elle Stone <ellestone ninedegreesbelow com>]

On 10/10/2014 01:41 PM, Øyvind Kolås wrote:
> On Fri, Oct 10, 2014 at 6:36 PM, Elle Stone
> <ellestone ninedegreesbelow com>  wrote:
> > >  On 10/09/2014 07:52 PM, Michael Henning wrote:
> > > >>On Thu, Oct 9, 2014 at 7:22 PM, Elle Stone
> > >So where in the conversion to XYZ and then to LAB (or any other reference
> > >color space) will "sRGB as PCS" fit in?

> This conversion would be User_RGB -> "sRGB PCS" -> LAB.

You cannot get from User_RGB to "sRGB as PCS" without going through XYZ. 
XYZ is the PCS ("Profile Connection Space") for converting between RGB 
color spaces. sRGB is not a Profile Connection Space.

You cannot get from "sRGB as PCS" to LAB without first converting from 
"sRGB as PCS" to XYZ. LAB is a mathematical transform of XYZ, not sRGB.

This is the normal path from User_RGB to LAB: User_RGB -> XYZ -> LAB. 
Two conversions.

You want to take this path, yes? User_RGB -> XYZ -> "sRGB as PCS" -> XYZ 
-> LAB. Four conversions, going through XYZ twice.

Why is the second path preferable?

With respect,
Elle Stone