[Openicc] meta data in test chart

[Chris Murphy]

On Jan 25, 2011, at 4:00 AM, Graeme Gill wrote:

> Chris Murphy wrote:
> 
>> Use of the PRMG would be useful here, in theory, because the idea is that the image is
>> rendered scene-referred to output-referred once in something like ProPhoto RGB. The
>> problem is that Adobe RGB and ProPhoto RGB do not come in v4 versions that make use of
>> the PRMG. And then also there are no widely available v4 + PRMG output device profiles.
>> So as far as I'm concerned ICC v4 and the PRMG are in a coma for mainstream users.
> 
> Hmm. I'm don't think that the PRMG helps in any way. You still need to identify
> the source gamut. If your source profile is ProPhoto, what gamut is mapped
> to the PRMG in the A2B table ?

In the grand v4 + PRMG scheme, it is the source profile's job to map the image to PRMG, and the destination profile's job to map from the PRMG.

But we don't have a v4 ProPhoto RGB, let alone one that describes how ProPhoto RGB images should be mapped to the PRMG. However I've been told this would be almost trivial because ProPhoto RGB is an output medium metric (hence its former name), but the work simply hasn't been done. It's probably Kodak's job to do it but AFAIK there's no interest.


> If you map the ProPhoto gamut, most images
> encoded in that space will end up looking very dull when linked with
> (say) a printer profile that then maps from the PRMG to the printer gamut.

Yes, if you use the existing v2 ProPhoto profile, which is why most people end up using RelCol+BPC, rather than bump up saturation in the perceptual intent at the time they build the profile.


Chris