I am currently playing with 10 bit/color capable hardwares (FirePro V5700
and Dell U2410).
My half-proven theory was that I can achieve significantly better results
when I skip the calibration (new VGAs, like my other one ---- a HD5850,
which is unable to send out 10 bit from the framebuffers (driver limit) ----
may offer 10-bit effective LUT precision, but this older professional AMD
card offers only 8 bit LUT precision, while it can send out 10 bit/color
from the framebuffers ---> It's funny, I think...).
So, I used ArgyllCMS 1.3.2 to create some fat cLUT profiles from numerous
spectral measurements, and I started to play with CMS supported softwares.
(I kept my linear VAG LUT and I left the R, G, B Gains at 255-255-255 in the
device's OSD -- to start with the highest available contrast ratio and less
hardware-processing.)
At the first time, I created a standard cLUT profile with usual colorprof
settings. But there were some problems:
- The Relative colorimetric and Preceptual intents won't correct my white
balance.
- The Absolute colorimetric intent is often buggy (absolutely broken in
MPC-HC, unavailable with Adobe ACE and strange with Microsoft ICM). And
black compensation is usually unavailable with this intent.
So, I searched for a solution which takes care about both white balance and
black offset. (Does everything I want to be done for an uncalibrated
display, at software level...)
I found the -u switch in the ArgyllCMS documentation. It creates an
"absolute" cLUT profile.
I am not really sure how it supposed to work or what it really does, but I
thought that "I found my holly grail" because it works like charm! (At least
in PhotoShop...)
The white point is always corrected with any intent modes (with both Adobe
ACE or Microsoft ICM engines) and it seems like my black point is also taken
into account, because I can't see any near-black banding. (Ok, I can see
some banding in 8 bit/color mode but it's really nice in 10 bit/color mode.
And it's a relatively low-contrast H-IPS panel, so I have serious black
crush with standard profiles and disabled black point compensation, while it
looks nice with absolute profiles. May be it's a little better than standard
profile + relative intent with black compensation.)
So, absolute profiles are real winners for me in PhotoShop. (But I have to
admit that I didn't really tested my results with instrument readings. I can
only tell that it looks great. The only thing I measured is the 100% white.
It was 6500K insted of the native white.)
But my main goal is to achieve the best quality for Rec709 movie playback,
and MPC-HC uses lcms2 for it's color management feature. (Current builds
fail to work in 10 bit/color mode. And the Absolute colorimetric intent
looks broken anyway... So, that's why I am testing with PhotoShop and this
is the other reason why I searceh for a "workaround" to get correct white
balance with relative colorimetric intent too. <- Without using the hardware
RGB Gains controls...)
After the success with PS, I was really excited about the results with
MPC-HC but the first test cleared off the smile from my face. Because
nothing changed here!
I still have a serious near-black banding (worse than an uncalibrated c-PVA
;; I thought that MPC-HC doesn't apply black compensation but it seemed to
be eliminated with absolute profiles) and the white point is untouched!
So, we finally arrived to my question:
---> What is the expected result when I use absolute cLUT profiles with
lcms2 based applications?
And: Is there a solution to achieve the result which I experienced in
PhotoShop?
Is it a bug in both Adobe ACE and Microsoft ICM (and is it a feature in
lcms2 then ; it sounds unlikely)? Or is it a missing feature in lcms2?
If it's a feature, then can it be easily turned off? If it's a missing
feature..., well... I would request it. :)
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