[argyllcms] Re: problems hitting white point (color temperature, RGB gain/contrast) while maintaining brightness: dE not stable

  • From: Nikolay Pokhilchenko <nikolay_po@xxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Fri, 11 Dec 2009 11:43:46 +0300

David Heinrich wrote

> Regarding lowering the target brightness, I presume I could just leave it
> the same but set one of the color gains to less than its maximum (90, 80?)
> and that wouldn't be any worse than changing the target as far as the
> accuracy of white and black points, right? But regarding this, I would think
> that the increments would be larger absolute values when channels are in
> their lower ranges rather than upper ranges; i.e., 99 is only 1% lower than
> 100, but 1 is 50% lower than 2?

Yes, You are right. But 100% value is "saturation". It's shows that the target 
or other condition should be changed.

> My final CRT settings are as such:
> =============
> Contrast 100
> Brightness 48
> R bright 98
> G bright 75
> B bright 100

"B bright 100" means that the overall brightness value must be changed down. 
For example Brightness=40, Rbright=90 Gbrigt=69 Bbright=93 - without any zeros 
or maximums.

> R contrast 100
> G contrast 60
> B contrast 58

"Contrast 100" and "R contrast 100" - it's bad. With saturated values You 
haven't the freedom to tune white point exactly. You should lover the target 
brightness value or change the temperature closer to display native (while 
contrasts R=G=B=100). Another way - to do the repair of Your display with 
hardware tuning of screen voltage or tube replacement.

> When adjusting my CRT, I can press the increase or decrease button and
> there seems to be some unmarked change in the values (i.e., I press up 1
> time, it might not change from 48 to 49..but if I press it twice, it goes
> from 48 to 49. I wonder if these "adjustments" that don't show a number
> change are actually doing anything?

It's OK. There may be or not to be a changes of real values by button clicks. 
Even the numbers are changing. The steps in display software can mismatch the 
hardware steps in hardware integrated circuits.

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