Capture One degrading in 8 Bit Conversions?

From: DMargulis@aol.com
Date: 8 October 2006 11:23:24 AM
To: colortheory@yahoogroups.com
Subject: Re: [colortheory] A case of clear 16 bit superiority
Reply-To: colortheory@yahoogroups.com

Ric writes,

>>This is the one point where I respectfully disagree. As I stated, I
reprocessed the Raw file into 16 bit mode so I could compare the 8
bit to 16 bit conversion with a true 16 bit file. In this particular
case I found the "16 bit all the way" file superior. >>

OK, I have re-read your initial post, and unfortunately I missed that point
on first reading. My apologies.

>>I have never doubted the quality of CaptureOne (the only Raw
processor choice for PhaseOne backs), however, it occurs to me that
the difference in appearance between the unedited files might be
showing a weakness in the programs internal 16 bit to 8 bit
conversion. Any thoughts?>>

This may well be the problem. In previous testing it became clear that
certain capture modules did a poor job of generating 8-bit. For this reason, I have
previously recommended to the list that they export into Photoshop in 16-bit
and then convert to 8-bit at their convenience. I have verified that Camera Raw
does not have this problem, but without checking my files, I seem to recall
that CaptureOne does. So, I think you need to try it again by starting with
16-bit in Photoshop, and converting immediately to 8-bit (for the mask, of
course, you'll need to go back to 16-bit for LAB).

That is, of course, just for curiosity--if you've opened in 16-bit RGB, and
you can see that you may be making a mask out of the B channel, it wouldn't
make much sense to go to 8-bit at all. But it would be nice to know.

I am a little vague on what procedure is involved here and where the mask
fits in. For sure, I expect that the mask will be better if you make it in
16-bit, but AFAIK it shouldn't make a difference whether you *start* in 16-bit RGB
or just convert into 16-bit LAB for the mask file.

My suggestion: if you are basing your comments on a Capture One-generated
8-bit file, redo the test by converting 16>8 in Photoshop. If you still think
that 16-bit all the way is significantly better, then for sure I want to see it,
but I think it would be easiest if you just e-mail me a 1 mb reproduction
offline together with a step-by-step of what you were doing to the file. It could
be that we're talking past one another.
.
Because of this issue with lousy 8-bit coming out of camera modules, I'm
including in the appendix to the forthcoming edition a relatively simple test,
requiring comparison of an 8-bit file generated by the module to a 16-bit file
converted to 8-bit in Photoshop. If anybody wants, I'll post the test here.

Dan Margulis



Ulf--is this true?

Des W