I have stayed away from using the matrix in UFRAW as I don't think this gives
good results in a color managed workflow. This was not based on any
objective data but more on how I subjectively felt about the results when I
tested with the matrix turned on. I found this to be true even when I used
another profiler (ProfilePrism). So this in not LPROF specific. This may
also explain why you are seeing artifacts in the bright areas and I am not
with local convergence turned on. I should document this in the LPROF help
file UFRAW section.
Ooops. I guess I wasn't clear. The matrix I was referring to is
the LUT in the profile, not the "use color matrix" checkbox from within
UFRAW. I think I finally (and recently) figured out what that's supposed
to do. It enables the RGB->RGB transform matrix from dcraw (who got it
from Adobe) *before* it does any of the color management stuff. In other
words, it's only really useful if you're going to do a default sRGB
non-color-managed conversion. For any real profiles (like the ones I've
been playing with generated by LPROF), the checkbox should be off.
I should add that profiles generated by LPROF (without local convergence) and
ProfilePrism give results that are only very slightly different.
Subjectively the PP profiles are very slightly more saturated and that is
only difference that I can detect. Overall tonality, white balance, shadow
detail, highlight detail ... are almost identical. Of course it would be a
simple matter for a UFRAW user to make adjustments in how much saturation (or
contrast, shadow detail, brightness) the profile will add to the final result
when profiling with LPROF by adjusting the saturation level in UFRAW in the
opposite direction when converting the IT8 target. So with a slight
adjustment I could make the LPROF and PP profiles give subjectively identical
results.
I don't trust myself to do much subjective adjustments. :) The
profile I got with LPROF without local convergence yields a very similar
result to that which I ripped out of a BibblePro install. That's what
I'd been using so far.
Yesterday, I figured out how to load up multiple profiles in
iccexamin (0.38) and compare the gamuts. You can see the discontinuities
there, but only if you turn on the Spektral line and show the 3D surface
in color (not gray). If you do that, there is a projection onto the Lab
plane that shows discontinuities.
This helped and I now know what I am looking at. The differences between a
non-local convergence profile and a local convergence profile are very clear
when viewed this way.
... in particular the much larger gamut (at least in my case).
Without local convergence, the 3D space is more or less contained within
the Lab space. With local convergence on, the gamut is significantly
larger (and more broken).
snip
All of the curves (TRC, shaper, etc) have always looked good...
nominally linear or gamma as appropriate. Just FYI, I am using a Pentax
*ist-DS DSLR, so the sensor likely has the larger gamut than the IT8.7 can
adequately profile. I've even found the spectral response curves for the
Sony sensor inside... :)
The curves have always looked good and that is one of the reasons that I have
not looked into this in more detail. That is I did not have a good way to
visualize what was happening so it would have been difficult to tell if
changes to the code had the desired affect. I am going to dig into the code
to see if I might be able to get this fixed as part of the 1.11 series. This
might take a while since I have not looked that this part of the code in
detail and I suspect that the changes will not be trivial.
My D70 uses the same sensor as do most, if not all, of the 6 mega pixel DSLRs
with the exception of the Canon DSLRs.
The matrix view (NOT gamut view) is the most telling. Pretty
funky on the broken profiles, but very smooth on the non-local convergence
ones.
-Cory
--
*************************************************************************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
*************************************************************************
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