[Openicc] Oyranos - proof of concept

[Chris Murphy]

Kai-Uwe Behrmann ku.b at gmx.de
Fri Apr 22 12:34:37 PDT 2005

> The smaller matrix profiles are prefered by current CMS's. They are 
> about
> 1-6kB. But I expect the CLUT become desireable for modern LCD's. Please
> can one of the profiling experts correct me if I am wrong here.

In theory, if we had well behaved flat panel displays, a matrix profile 
works just as well. My experience has been that table-based display 
profile cause profile-induced posterization that's noticeable in 
gradients.

However, displays that aren't so well behaved require more effort to 
calibrate in terms of gray balance and a reasonable white point which 
translates into a more aggressive curve in the video card DAC LUT. This 
can cause calibration-induced posterization.

If we had full system level display compensation, we could avoid 
video-card based calibration altogether and simply profile the display 
using table-based ICC profile rather than matrix, and compensate for 
its peculiarities with brute force. That's a little expensive until we 
can dump all of these conversions onto the video card (which I believe 
is on the way).

In the meantime, what I'm really enamored with are the Eizo flat panel 
displays that allow calibration to be done in their internal 10-bit to 
14-bit DAC LUT, which is in the display itself. The video card LUT 
remains linear, and the higher bit depth of the curve applied in the 
display itself translates into far smoother gradients. Thus far I'm 
finding I prefer matrix profiles for these displays, but they are quite 
well behaved once calibrated this way.

As the market is transitioning from CRT to LCD, I think we're in for a 
bumpy ride. We also have wide gamut displays on the way and HDR 
displays coming too. This could likely translate into wider disparity 
in behavior among displays out in the world compared to the CRT days, 
which means a greater dependence on DDC (or equivalent) to build 
profiles on-the-fly, and on display compensation. Sending existing 
internet images (as a simple example) to such a display will result in 
very apparent oversaturation; so we're going to need display 
compensation in even simple applications like web browsers. It will be 
interesting to see how all of this plays out—I expect on Windows and 
Mac OS to move to full display compensation powered by the video card, 
eventually.


Chris Murphy
Color Remedies (TM)
www.colorremedies.com/realworldcolor
---------------------------------------------------------
Co-author "Real World Color Management, 2nd Ed"
Published by PeachPit Press (ISBN 0-321-26722-2)
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