On Fri, Oct 10, 2014 at 6:36 PM, Elle Stone <ellestone@xxxxxxxxxxxxxxxxxxxx> 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? > Of course you could convert from User_RGB to XYZ, from XZY to "sRGB as PCS", > from "sRGB as PCS" back to XYZ, and then, finally, to LAB. But I don't see > the point of doing such an odd sequence of conversions. This conversion would be User_RGB -> "sRGB PCS" -> LAB. While Linear User_RGB to Linear User_RGB2, might end up being just be Linear User_RGB -> Linear User_RGB2. The choice of XYZ or linear sRGB or any other linear RGB as a PCS should not have an impact on either the results you get or the number of conversions happening - when converting between RGB spaces. Any linear RGB space is a matrix multiplication away from XYZ, this includes the PCS of babl. Two such matrix multiplication steps can be combined into a single step by multiplying the matrices corresponding to the steps. Thus the number of operations to do per pixel is the same when going from from babl PCS -> XYZ -> some linear RGB, as if you do XYZ -> some linear RGB. This matrix will be stored in the specific BablModel for this color space; and available in code paths for doing conversions to/from PCS or directly between such models. It is only for CIE Lab and related spaces we end up with a longer sequence of conversions (the CIE color models are the type of spaces that need a bit more special treatment, which is why those color models have an implementation of XYZ to/from linear sRGB.). Most algorithms and editing is RGB centric; thus this is a fair compromise. The CIE Lab code if refactored could also be a single step away from the PCS. Given that the choice of PCS, is any suitable RGB space. We are left with looking for other redeeming qualities to make a choice. A lot of - yes legacy; but we have code integrating with such libraries file formats and more; 8bit images around, and some 16bit images as well do use sRGB. And sRGB continues to be the recommended format on the web and elsewhere. /pippin _______________________________________________ gegl-developer-list mailing list List address: gegl-developer-list@xxxxxxxxx List membership: https://mail.gnome.org/mailman/listinfo/gegl-developer-list
