Re: Who's right?
Re: Who's right?
- Subject: Re: Who's right?
- From: Chris Murphy <email@hidden>
- Date: Mon, 7 Jun 2004 11:03:00 -0600
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?
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. 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.
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?
Note that there are many ways of remapping luminance ranges (it's a
sub set
of gamut mapping, so many approaches are possible). A simple approach
is to
linearly map the luminance range. Another might be to do it
non-linearly,
compressing highlights and shadows more than the middle range. It may
well be premature to standardize such a thing (at least as a "one and
only"
way of doing things).
It's not going to be standardized as far as I know it's just going to
be documented. Anyone who wants to do it the way Adobe does it can do
it. Linkolator from Left Dakota builds DeviceLink profiles using black
point compensation, but its their own method. There aren't that many
ways to do it, and for it to look right, and theirs very closely
approximates the results you'd get with Adobe's bpc.
Regardless, it is a necessary function for high quality results unless
you like stripped shadow detail.
I've personally never felt the need for "black point compensation",
simply because if
I'm interested in a quality result for a perceptual reproduction, I'll
make sure
that a proper gamut mapping from source to destination is used, rather
than trying
to use the (usually) wrong one in the B2A table of the ICC profile.
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.
Chris Murphy
Color Remedies (TM)
www.colorremedies.com/realworldcolor
---------------------------------------------------------
Co-author "Real World Color Management"
Published by PeachPit Press (ISBN 0-201-77340-6)
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