Re: Camera profiling with ICC et al
Re: Camera profiling with ICC et al
- Subject: Re: Camera profiling with ICC et al
- From: email@hidden
- Date: Mon, 15 Sep 2008 16:02:50 EDT
Graham,
Here is the reference in 6.2.1:
"In transforms for the media-relative and ICC-absolute colorimetric intents,
the PCS values may represent a colour rendering of the actual original
captured for input profiles. "
This is actually a reference from the v4 spec which was intended to clarify
then-current v2 practice and better define proper profile behavior. The
consensus of the ICC was that, in the absence of other data, the safe assumption was
that all ICC colorimetry is picture-referred (usually output-referred or
original-referred). It was a no-win situation what to assume. At the time, most
input profiles used only one RI. A scanner profile with one RI might well indeed
contain original-referred colorimetry. Unfortunately, In standards jargon,
original-referred is a form of picture-referred (since you are starting with
original flat art that is already a rendering of something else). A camera profile
with one RI might indeed produce output-referred colorimetry or it might
produce scene-referred colorimetry. And you are absolutely right, this attribute
of the ICC spec is poor. We wanted the CRI to be sacrosanct, but practice
proved otherwise. In the absense of the image state tag, in the general case, we
really don't know what's in the CRI, and whatever you assume, there is a good
chance you will be wrong. So now we have the image state tag to clue apps and
cmms whats really in the CRI.
Eric Walowit
Tahoe
In a message dated 9/15/08 12:04:18 PM,
email@hidden writes:
> I can't agree with you there. I don't recall any clear reference to
> colorimetric
> values being picture referred (do you have a reference in the V2.4 spec. ?),
> and in any case I think such an interpretation makes for a poor standard.
> The other intents are fair game for manipulating rendering for particular
> purposes, but colorimetric should be a sacrosanct, firm base for such
> renderings or re-renderings, and therefore needs to be instrument based
> (so that they can be verified), as is clearly, and unambiguously stated in
> V2.4 A.3,
> and reinforced in other areas (ie. V2.4, D.3 where measurements are clearly
> stated to be flare-less).
>
> Graeme Gill.
>
>
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