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

  • From: Kristian Jörg <krjg@xxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Wed, 21 Mar 2012 14:59:54 +0100

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 
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 
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".


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