[argyllcms] Re: How do I force dispcal to always map R0 B0 G0 -> R0 B0 G0 on the calibrated video LUT?
- From: Alexander <adfirestone@xxxxxxxxx>
- To: argyllcms <argyllcms@xxxxxxxxxxxxx>
- Date: Mon, 21 Dec 2009 06:41:09 -0800
>
> I believe this may come back to the Eye-One Pro's weakness with
>> differentiating between very close together dark measurements. Along with
>> the issue of the Eye-One Pro detecting 0.00cdm2 as 0.05cmd2 randomly on my
>> CRT. The Eye-One is probably telling Argyll there is a dead zone, even
>> though I can see with my eyes that there is not. When I am in a dark room
>> that is obviously inaccurate since the screen is bright grey instead of
>> black.
>>
>
> I think you are asking a lot of any instrument worth less than $10000,
> to expect a good reading below 0.05 cm/d^2. Adaptive mode may improve
> things at low levels with the i1pro, although because it then switches
> integration time and gain, it may introduce discontinuities.
>
>
> If would be nice if you could add some sort of override for heuristic,
>> since
>> it does sounds like it would prove useful for my situation.
>>
>
> dispcal and printcal -V in the next release.
>
> Graeme Gill.
>
>
>
Well if I take the specifications of the Eye-One Pro literally (*Measurement
range:* 0.2 ... 300 cd/m2) then I shouldn't be expecting accurate readings
below 0.20 cd/m2. In practice it may be a bit better then 0.20cd/m2 (maybe
0.15cd/m2) but the Eye-One Pro does seem utterly unreliable below 0.10cd/m2,
at least on a CRT. If I do multiple measurement of the same pitch black
screen, Argyll reports values seemingly at random jumping around between
0.00cd/m2 and 0.08cd/m2. Because of this it also appears, for example, to
sometimes think a measurement of a R5-G5-B5 patch may have a luminance
reading of 0.08cd/m2, while it measured a R10-G10-B10 patch as 0.01cd/m2,
and a R0-G0-B0 patch as 0.05cd/m2 which must cause a bit of chaos, and may
explain why Argyll overcompensates by brightening up the black-point
significantly.
That said, thinking about this a bit more, would it not make sense to add
some sort of 'accurate measurement range' parameter to Argyll?
So for example, if I set the minimum accurate measurement range to 0.15
cd/m2, once Argyll reads a patch with a luminance of 0.15 cd/m2, it then
records it as the lowest valid reading. It would skip all patch measurments
between 0.00-0.15 cd/m2 and in just evenly space any remaining luminance
measurements below 0.15cd/m2 (since Argyll appears to calculate the native
gamma of the the display, it should be able to make a reasonably accurate
guess of where those low luminance values would likely fall on the gamma
curve) while using the same R:B:G ratio that was found when measured at
0.15cd/m2.
From the looks of it BasICColor already does something similar to the above,
since it consistently reads very dark black values all as 0.00-0.01cd/m2,
and then always maps R0 B0 G0 -> R0 B0 G0 on its calibrated video LUT curve.
The only problem with BasICColor is it appears to sacrifice accuracy for
speed by using the fewest calibration/adjustment points possible when
generating it's video lut and ICC profiles.
Now before getting too far astray, can you say a little more about how that
-V parameter will work?
Will the -V parameter have a number value after it? If not, then I assume it
just tells Argyll to disable heuristics?
When heuristic mode is disabled, how will Argyll behave differently
internally? What should it do instead when it runs into a problem like the
one I have been trying to describe? Would there be any other situations,
other then the one I describe, that disabling heuristic mode may be useful?
@andrzej duda I'll try testing those parameters at some point today and
see if it helps at all. Not particularly hopeful, but it's worth a shot.
Other related posts:
