Re: about negs and ROMM / Pro Photo RGB
Re: about negs and ROMM / Pro Photo RGB
- Subject: Re: about negs and ROMM / Pro Photo RGB
- From: Steve Upton <email@hidden>
- Date: Tue, 7 Aug 2001 01:45:32 -0700
At 10:48 AM +0000 8/4/01, neilB wrote:
This theory was reinforced by opening a few workingspaces in
Steve Upton's Colorthink [I love it].
Thanks...
There I noted that, for
example, both Adobe RGB and ProPhoto are set up to default to
Perceptual - [and to add to the confusion - apparently have no
rendering tags at all.]
Well, Matrix-based profiles do not, by their definition, have
rendering intents. They are simply a collection of gamma curves,
phosphor color coordinates and white point. The rendering is totally
up to the CMM.
I also noted that Ektachrome space has Percept AND Colorimetric
tags - however , as you pointed out, selecting either gives an
identical result after conversion.
There are several different versions of this space floating around,
some matrix and others LUT-based. When you have LUT-based profiles
then they need to follow different conventions and have more required
tags. The 3 intents need to be represented in the profile, in both
directions. This means that the profile will have 6 entries in the
tag table (table of contents). Each direction's 3 tags can point to
the same table however so even though you have 6 tags, you can have
as little as 2 tables. I suppose you could even get away with one but
I can't imagine a table that would work both ways except for strange
effects stuff.
Regards,
Steve Upton
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