On Thursday 26 January 2006 05:51 am, Cory Papenfuss wrote:
snip
>
> Good to know that what I'm describing isn't just due to my
> ignorance of how the whole system works. Like I said, it's only been
> recently that I've been able to analyze the profiles enough to narrow it
> down to the localized convergence parameter. The built-in LPROF profile
> checker doesn't show any of the badness really... dE always looked good.
> Just for the record, the problem is worse as you say with RAW files and
> linear data... probably due to the reduced numerical contrast of linear
> data.
>
> As far as what I used to notice the problem... first it was the
> little graphical curve in UFRAW's input histogram plot. What nominally
> looks like a gamma curve ("fuzzy" due to the matrix) had large jumps in
> the curve in the brightest area of the histogram. The resulting RAW
> conversion had strange artifacts in the brightest areas of the image.
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.
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.
>
> 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.
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.
>
> -Cory
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