[Openicc] Questions about color pickers and graphics libraries under LINUX

[Bob Friesenhahn]

On Mon, 11 Feb 2008, Chris Murphy wrote:
>
> Umm well if users are having a problem that an OS could solve, seems
> like it's something the OS should solve rather than being a bump on a
> log. Why do we have operating systems anyway?

If the display was capable of resolving the required colors, then the 
OS could certainly help.  The interface to LCD panels is still only 8 
bit.  Assuming that the internal LCD panel drivers are capable of 
sufficient resolution (it seems that most/all are still 8 bits or 
less), it makes the most sense to load a LUT directly into the display 
device which correctly translates from the computer provided levels 
(e.g. "sRGB") to the LCD stimulus levels.

LCD panel native white point is often 9500K and primarily depends on 
how bright the CCFL backlight is (apparently brighter every year). 
This does not really translate well via LCD control to 6500K.

LCD is a linear optical device which results in problems (non-uniform 
use of panel levels) when linear intensity is desired.

There are a few things which could be done to help alleviate problems:

   * Increase the number of useful bits in the LCD panel drivers.

   * Increase the number of bits in the computer/display interface
     (e.g. DVI or HDMI).

   * Upload a LUT directly into the display panel.

   * Use something other than "sRGB" interface levels in order to
     improve the "impedance match" between the computer and the display
     so that every computer specified level has a better chance of
     resulting in a discrete panel level.

Note that all of these are attempting to address deficiencies in the 
LCD display device so it behaves better (is calibrated) rather than 
attempting to color manage the display.

I just ran across this interesting page http://www.techmind.org/lcd/ 
which talks about LCD panel drivers and provides test patterns so that 
you can see what type of panel refresh your LCD uses.  Mine seems to 
be of the "Line-paired RGB sub-pixel dot-inversion" type.

Bob
======================================
Bob Friesenhahn
bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/