On Sat, Oct 11, 2014 at 1:18 AM, Elle Stone <ellestone@xxxxxxxxxxxxxxxxxxxx> wrote: > I really don't want to forget about LAB. The plan is that "sRGB as PCS" will > be used for "something". I'm trying to figure out what exactly "something" > covers. So I have two specific questions. The first question is about > converting to LAB. The second question (which I haven't asked yet) has to do > with Y. We will try to do what makes sense and helps us achieve what we need to achieve efficiently; while keeping what works well, working well. > "sRGB as PCS" is linear gamma unbounded sRGB. I think it's reasonable to ask > why a conversion to unbounded sRGB should be involved in a conversion from > User_RGB to LAB. For the same reason XYZ is involved (or not, depending on how the CMM does it) in an ICC workflow. >> Existing code written with assumptions of sRGB, whether in GIMP and >> GEGL that we control or in XPM, GTK, GDK, or elsewhere that has sRGB >> assumed will continue to work. We take the existing architecture which >> is following general guidelines of assuming sRGB where none is >> specified. > > Assigning sRGB to images with no embedded profile is done because you can't > display images in an ICC profile color-managed workflow until an ICC profile > is assigned. How images with no embedded profile are handled is irrelevant > to the question of why a conversion from User_RGB to LAB needs to involve > unbounded sRGB. This is not about how images with no embedded profile are handled. sRGB derived 8bit (and to a lesser degree 16bit) formats are used for many other things than images with no embedded profile. These pixel formats are crucical for integrating with existing file formats and libraries; and we want these conversions to be as fast as possible - even if it might have an impact on the conversion speed for CIE Lab, though that does not have to be the case either. Choosing any PCS *but* linear sRGB would tend to make these important conversions slower. > I can move on to my question about Y and unbounded sRGB. But I still don't > understand why unbounded sRGB should be involved in a conversion from > User_RGB to LAB. We will do what makes most sense and is neccesary when we get there, I suspect each RGB model with have an associated Y and YA model. Due to how the existing BablModels interact with components and vocabulary used to address them in babl; potential support for different TRCs is even vaguer; we'll know when we have more code. Maybe we have more code by the time of LGM, if not that would be an excellent place to elaborate; until then I prefer IRC. /pippin _______________________________________________ gegl-developer-list mailing list List address: gegl-developer-list@xxxxxxxxx List membership: https://mail.gnome.org/mailman/listinfo/gegl-developer-list
