Re: Who's right?
Re: Who's right?
- Subject: Re: Who's right?
- From: Graeme Gill <email@hidden>
- Date: Tue, 08 Jun 2004 11:38:01 +1000
- Organization: Color Technology Solutions
Chris Murphy wrote:
On Jun 6, 2004, at 9:31 PM, Graeme Gill wrote:
I don't quite follow you. Black point compensation seems to be a
workaround for particular usage's and workflows using ICC profiles. In other
contexts it doesn't make any sense.
Other than proofing, such as?
No, other than Photoshops (and other similar) CMMs.
It's hard to tell exactly (because there
doesn't seem to a technical description available of what Adobe black
point compensation is), but from what I gather it's a partial workaround
>> for the problem ICC profiles have with embedding a perceptual/saturation
gamut mapping in the destination profile, and expecting that profiles will
normally be linked by simply concatenating them.
No. Black point compensation is a dynamic-dynamic range compression. The
compression you get depends on the source and destination black points.
Exactly. The gamut compression in the B2A table can't know what the source
black point is, which is why BPC can be viewed as a workaround for the
limitations of conventional ICC linking.
The only other way to salvage shadow end detail below the reproducible
black point is to scale the black up to the reproducible black point, is
to use perceptual rendering which is not dynamic. It's one size fits all.
We're not actually disagreeing here. I'm talking why it exists, and your
talking about how it works.
I would guess that black point compensation
enables a rescaling of the luminance range, to better map the
luminance dimension
of the source and destination gamuts.
Yes. So why would you not want to do that outside of a proofing context?
See above. I was referring to the context of Adobe Photoshop linking,
not the context of Proofing.
Regardless, it is a necessary function for high quality results unless
you like stripped shadow detail.
No it's not. It is (by your account) a necessary function for high quality
results if you're using a conventional ICC linking process.
The best results currently are achieved with relative colorimetric +
black point compensation for the vast majority of images. If you like
one size fits all, or you aren't using an Adobe product or DeviceLink
profiles, then the best option you have is perceptual rendering. But
it's not the ideal.
The best results I've achieved are to generate a specific gamut mapping for
the particular source and destination profile, and to invert the colorimetric
information in the destination A2B tables, rather than link the source A2B table
to the destination B2A table as in a conventional ICC linking process.
[ I was attempting to place BPC into the "big picture". ]
Graeme Gill.
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