[argyllcms] Re: Color errors on < 100% stimulus

  • From: János, Tóth F. <janos666@xxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Tue, 3 Apr 2012 19:53:32 +0200

Yes, HCFR supports multi-point primary/secundary color gradient
readings. I forgot about that.
I guess that's more likely for benchmark/validation purposes than
something you should base your calibration on. (But it could be a good
solution if it works for you.)

By the way, I am trying to find somebody who is intereated in HDTV
calibration and good in Java+HTML programming.
With some small changes, the profile validation feature of DispcalGUI
could serve as a great tool for that.
It's already usable for TVs with HSL color space and 2p grayscale
controls and you can also guess RGB color settings from the HSL errors
but it's hard to guess RGB settings for the 10/20p grayscale controls
from HSL errors (or is it...? May be it's only hard for me...). So a
few indicators (RGB balance graphs) could make the process easier,
more convenient and faster.

2012/4/2, Kristian Jörg <krjg@xxxxxxx>:
> János, Tóth F. skrev 2012-03-26 00:56:
>> I still don't understand the so-called „color decoding issue”.
>> My Pana G30E has relatively good and significantly better color
>> accuracy than my Samsung D550 had.
> According to avsforum threads there is an issue with at least the
> American versions of the GT and VT models. The issues are visible with a
> video sequence with a woman in purle dress that was decoded as blue - on
> a otherwise perfectly calibrated set.
> There has also been reports on lightness nonlinearities over different
> intensities/saturations - this is supposedly fixed by named patch.
> The problems I have myself is that if I calibrate my set to perfection
> with the tools and methods as usual, I end up with a set that measures
> perfectly with dE < 1.0 over the scale - but visibly has color errors
> with normal content! I just now calibrated my PC monitor (at last) and
> it shows no color casts whatever. Perfect calibration/profiling with
> Argyll. So it is not my meter that is malfunctioning... For the moment I
> have reverted to the stock THX mode which is fairly accurate. I'll try
> again to calibrate some day.
> How do you know that the 2012 models will not be improved with regard to
> CMS? They have hardly come out yet...
> Chromapure has options for calibrationg at 75% saturated patterns. These
> can be found on the AVSHD 709 disc under the HCFR header and the
> "Saturation" patterns. Use a 100% stimulus white pattern and then the
> 75% saturated.
> Actually, I haven't found any instructions on how to use the 75%
> intenity color patterns or when they are appropriate?
> /Kristian
>> 2012 won't be very different except the VT50.
>> 75% saturated pattern?
>> I never heard about such thing. On the other hand, 75% stimulus is
>> very common for HDTV calibration.
>> 2012/3/21, Kristian Jörg<krjg@xxxxxxx>:
>>> Graeme Gill skrev 2012-02-13 14:41:
>>>> Kristian Jörg wrote:
>>>>> Well, the reason I was a bit unimpressed is because this is supposed to
>>>>> be one of the very best TV
>>>>> sets to buy, and it includes full ISF controls for managing grayscale
>>>>> at
>>>>> 10% stimulus steps. Color
>>>>> however is only at 100% stimulus. So I can nail in the grayscale and
>>>>> gamma to mostly perfect result
>>>>> (according to the patterns used, i.e full windows cause lightness to
>>>>> drop
>>>>> a bit). Color however
>>>>> seems a bit more difficult. Now it is possible I have used the CP
>>>>> software wrongly at the 75% color
>>>>> intensity. It has a 75% Rec. 709 setting that I assumed should be used
>>>>> for the 75% W+ 75% RGB
>>>>> measurements. But maybe I should measure all those at 100% Rec. 709
>>>>> setting since i assume the Rec
>>>>> 709 standard is linear? When using 75% patterns all that happens is
>>>>> that
>>>>> luminocity falls a bit,
>>>>> but it is all realite to white which is measured as a baseline... ?
>>>> I'm afraid I have to smile a bit at all that. Rec 709 is an idealised
>>>> additive display.
>>>> Idealised displays have a perfect black, something no real display can
>>>> achieve.
>>>> So (as usual) you are faced with the issue of how do you deal with the
>>>> non-perfect black,
>>>> given that the transfer curve assumes that is is perfect. Non-LCD based
>>>> displays are not
>>>> so bad in this regard though. Then there are the viewing condition
>>>> assumptions inherent
>>>> in Rec 709.
>>>> The channel combination targets aren't too hard to compute - add the XYZ
>>>> of the individual channel
>>>> target or measurement values, since Rec 709 is additive.
>>>> Graeme Gill.
>>> Just a short follow up to this little thread that I started. It was all
>>> due to a misunderstanding of what patterns to use for the 75% Rec 709
>>> calibration settings in Chromapure. It should be 75% saturated, not 75%
>>> intensity. With correct patterns my results where correct. However if
>>> anybody tries this, there is a confirmed bug with it with at least
>>> version 2.0.10 (and probably 2.0.11) in CP, so wait for the next release
>>> before trying this.
>>> And there is also strong indication of color decoding issues in the 2011
>>> models of Panasonic plasmas. Something that should be fixed in the 2012
>>> models. Bummer. There will not be a fix to the 2011 models, or even any
>>> more firmaware updates at al,l according to those who "know".
>>> /Kristian

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