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

  • From: David Heinrich <dh003i@xxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Thu, 10 Dec 2009 10:05:53 -0500

>
> > So even with the CRT in Standard Mode, doing fine-adjustments I still
> can't
> > get too great. The problem is still similar to what I quoted in the
> original
> > e-mail: when adjusting R, G, and B channel gains individually, the dE's
> > bounce around as does the recommendation of which values to change.
>
> David, did You try to lover Your target brightness by 2-3 cd/m^2? If one or
>
> more channel gain levers are at their maximums, it may help.
> This is a typical problem for some displays. There may be rather large
> steps of
> per-channel gain, so it's impossible to achieve the desired white point by
> hardware. With some displays I've got a best difference about 2.3dE or even
> a
> bit worse. The calibration can correct such deference.
>

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?

My final CRT settings are as such:

STANDARD MODE
=============
Contrast 100
Brightness 48
R bright 98
G bright 75
B bright 100
R contrast 100
G contrast 60
B contrast 58

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?

Now, it seems like the best my display can do is better than 2.3dE, around
0.2 or even = to sometimes 1.5 or 2. The problem is that my readings are
bouncing around as far as dE's go. When adjusting RGB gains, readings
fluctuate from 0.5-2 even when I'm not adjusting anything. So can the
calibration still correct this? Wouldn't it need steady readings?


>
> > Is there
> > a way to change how long the Spyder2 takes readings before updating? It
> > would seem that if there was a way to get the program to average the
> results
> > of 5-10 updates or 5-10 seconds (I'm not sure how this works: is argyll
> > getting a reading from spyder2 every several seconds, or is it averaging
> the
> > readings of spyder2 over several seconds?), it would smooth out this
> stuff
> > and allow for me to get a better idea as to what to do on my display.
>
> I'm just changing one channel by one step, waiting 5 seconds and looking is
> the
> difference less or more. Then I'm tuning the next channel. Repeat.
> Sometimes I didn't see at the dispcal recommendations at all.
>

I'll try this out. After getting the dE below 3-5, maybe this is the best
way, since what dispcal recommends bounces around so much.

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