Hi Alastair,

I'm no colourspace expert (far from it), but there were a couple of things which
I spotted in this which prompted questions.

Quoting "Alastair M. Robinson" <[EMAIL PROTECTED]>:
> In the first method, is what I believe is what PhotoShop uses (and what
> I think Sven proposed):  When an image is loaded, scanned or whatever,
> it is converted from its source colour space into a "working" colour
> space (sRGB, AdobeRGB, etc.).  Of course, the source colour-space and
> working colour-space can be the same.  The advantage of this method is
> that the working data is always "normalised", so plugins and the like
> have perceptually identical results, whatever the image's "native"
> colour space.
> The workflow for an sRGB Image might be:
> Image (AdobeRGB) -> Working data (convert to sRGB) -> Editing -> Save
> (convert back to AdobeRGB)

Yes, this is what was discussed at the conference, with one important
difference. We don't convert back to AdobeRGB or whatever at save time, we
simply save the working image data, with the sRGB color profile.

> Personally, I don't think this method is appropriate for the GIMP until
> such time as we  have support for 16-bit or float pixels, because if we
> convert from the source space to a working space with only 8 bits per
> sample we're going to lose some information through quantization errors.

I see your point. Perhaps there could be some kind of pre-loading where we apply
the color profile in floating-point, and quantise afterwards? Just thinking out
loud, this may be completely unfeasible.

> The second method, which I think we should use for the time being, is
> just to keep track of the "source" profile for each image (and have a
> user-selectable default profile - sRGB, AdobeRGB or whatever).  


> The equivalent workflow would be:
> Image (tagged with AdobeRGB) -> Working data (8-bit RGB, unmodified) ->
> Editing -> Save (AdobeRGB)

How does this fit in with display calibration? If we work on the unmodified
image data as we read it in, then on what data should the monitor's calibration
profile work during projection? Should it work on the raw RGB data, or should we
apply the input profile at projection time? Would a color profile be a per-layer

I think these are the kinds of issues that Sven thought about before, and they
make adding color management considerably more complicated. I think that the
simplicity of applying a color profile on imput and not having to worry about it
in the rendering code outweighs the down side of any quantisation that occurs. 

> In short, though, if we use this method, we don't need to agree on what
> to call our working space, because it will simply be whatever is
> appropriate for the image being edited!

I think this is probably a very bad idea.


Dave Neary
Lyon, France
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