Re: rendering intents (was: In search of a D50...)
Re: rendering intents (was: In search of a D50...)
- Subject: Re: rendering intents (was: In search of a D50...)
- From: Lars Borg <email@hidden>
- Date: Sat, 06 Sep 2014 01:03:10 +0000
- Thread-topic: rendering intents (was: In search of a D50...)
i must have missed something: i understood, there are cases in which some intents should be grayed.
I'd like to know at least one case that you want to disallow.
For a LUT profile, perceptual is required. It's also the default intent.
For a TRC profile, the TRC is relative colorimetric.
This can easily lead to cases where a pair of profiles have no intents in common:
Profile 1 TRC relative only -> profile 2 perceptual only.
This is a common conversion from display to print.
There is no common intent, so conversion should then not be allowed.
To prevent this, ICC has a fallback logic to these intents. See below.
Also to consider:
BPC is not colorimetric, so relative + BPC should be classified as perceptual.
And is saturation + BPC == perceptual?
If so, all intents become perceptual if BPC is on, so all combos are valid!
can anyone (who knows all intent relative tags) write down instructions to list the intents present? if so, it might be interesting to fork this thread on ColorSync-dev & add expert knowledge in the developer space.
Here is the precedence order.
You can ignore a).
AToB0Tag is for perceptual, so perceptual is a LUT profile's default intent.
From ICC 8.10.2:
For input, display, output, or colour space profile types, the precedence order of the tag usage for a designated rendering intent shall be the following.
a)
Use the BToD0Tag, BToD1Tag, BToD2Tag, BToD3Tag, DToB0Tag, DToB1Tag, DToB2Tag, or DToB3Tag designated for the rendering intent if the tag is present, except where this tag is not needed or supported by the CMM (if a particular processing element within the tag is not supported the tag is not supported).
b)
Use the BToA0Tag, BToA1Tag, BToA2Tag, AToB0Tag, AToB1Tag, or AToB2Tag designated for the rendering intent if present, when the tag in a) is not used.
c)
Use the BToA0Tag or AToB0Tag if present, when the tags in a) and b) are not used.
d)
Use TRCs (redTRCTag, greenTRCTag, blueTRCTag, or grayTRCTag) and colorants (redMatrixColumnTag, greenMatrixColumnTag, blueMatrixColumnTag) when tags in a), b), and c) are not used.
Lars
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