[CREATE] Remaining issues for the color spec and future plan

[Cyrille Berger]

Hello,

For reference the draft is located at [2]

== Future plan

I think the spec should remained as a "draft" until the first application that 
use it is released, and at that time we would release version 1.0.

== Remaining issues
There are a few open points that needs to be addressed :

Blocking issues:
* channel and type. We haven't really decide between float and integers. Or 
more like should we allow integer. I can't see any usecase for allowing 
integer, but maybe someone has ?

* range of colors. There is also the problem of range. In case of float, 
should we allways limit to [0, 1.0] (for HDR see bellow) ?
There is also the case of LAB. It's usually ranged like this L in [0 ; 100], a 
nd b in [-125; 125], in case of integer should we use those range ? And in 
case of float should we use the [0, 1.0] range or L in [0, 1.0] and a and b 
in [-0.5 ; 0.5 ] ?

Not blocking issues:
* spot colors, there is nothing currently in the draft, and I have no idea of 
what is needed, seeing [1] it sounds like it's a matter of adding "Register" 
and "Spot" element, to either the color tag or the rgb, srgb, cmyk, ... 
elemets. Can someone with knowledge about spot colors comment on this ?
* extra information like alpha
* HDR support, that need to be discuss, but for the way Krita currently select 
colors in HDR (which is similar to [3]), colors are selected in LDR mode then 
the current "luminance" is applied to the color to compute the HDR color. 
That means that for the color spec, if we allow the color range to be [0.0 , 
infinity [ , there will be a problem for Krita to know if a color in the 
[0.0, 1.0] range is intented to be an HDR color to be use directly like this, 
or an LDR color.
There are two options for this :
 - add an attribute to the color that say the user wanted that color to be HDR
 - limit the range to [0.0, 1.0] and add a luminance element that can then be 
applied to the color
The main advantage of the second option is that the color has also a meaning 
for LDR images.

[1] http://documentation.scribus.net/index.php/Spot_Colors
[2] 
http://create.freedesktop.org/wiki/index.php/Swatches_-_colour_file_format/Draft
[3] http://graphics.cs.ucf.edu/HDRPaint/index.php
-- 
Cyrille Berger