[Openicc] meta data in test chart

[Graeme Gill]

> The system above is actually not a bad design, but it would be even
> better provided the handoff space were ProfotoRGB (very wide gamut)
> or PRNG (all printable colors), and a 16 bit conversion were

I'm not sure that's a good idea with current workflows. The reason
is that few if any workflows have, or communicate the concept
of an image gamut. Unlike other smaller gamut color spaces, where
typically the image has been rendered to just fit into that space,
and therefore the colorspace gamut is a reasonable guide to the image gamut,
a very wide gamut space like ProPhoto or L*a*b* cannot be used
as a guide, because the images gamut will almost always be a great
deal smaller than the space it is encoded in.

The reason this is important is gamut mapping. If an image is to
be mapped well into the destination colorspace, the gamut it
occupies needs to be known or anticipated. If the encoding colorspace
no longer provides that information, where does it come from ?

Graeme Gill.