[Openicc] ProPhoto, ICCv4, was: meta data in test chart

[Graeme Gill]

Chris Murphy wrote:

> values are imaginary colors. But yes, I'm understanding what you're saying. While I
> still think it's correct to say one is rendering into ProPhoto RGB using any Raw
> processing application, what hinders this from being fully utilized is we're making
> these rendering choices based on a display that is distinctly not capable of showing us
> everything in ProPhoto RGB (or even much of it).

Nothing will ever be able to render the whole of ProPhoto, any more than the
whole of ICC L*a*b* or scRGB can be displayed. It has a blue primary
with an XYZ of 3.1339 0.0091 82.4895. Look at the Y :- that means it's black!

So given a calibrated/profiled wide gamut display, the author of an image
can choose whatever appearance they like within that gamut. In the past,
they would be forced to render it down to a small gamut such as sRGB, or
a printer gamut if they were going to deliver it as a print. But now,
as long as it is delivered electronically, and as long as they are using
a wide gamut encoding space, nothing is forcing them to deal with that.

But if they choose to create a very wide gamut image, somewhere down
the track it's going to be squeezed into smaller gamut output devices.
If they don't create versions of the image that they've hand crafted to
fit within those smaller gamuts, it will be done for them by the
technology, either crudely (ie. clipping), wrongly (gamut mapped
from the wrong/too large source gamut), or more cleverly (gamut mapped
to just fit that image in the destination).

Graeme Gill.