[argyllcms] Re: Correction for wide gamut screens and/or RGB-LED?

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Tue, 06 Apr 2010 10:17:19 +1000

Steffen wrote:
That's what I thought... unfortunatelly though, there is wide-held
believe that colorimeters – in some regards, surpass the accurary of
spectrophotometers when measuring emissive devices such as displays. I

That may be true for expensive colorimeters. Most people don't
use those though, they use cheap colorimeters.

just stumbled upon an example of that, where an i1 pro returned the
black level of a display to be around 0.8 cd/m^2, while a colorimeter
more accurately would measure 0.12cd/m^2. Seems to be that the accurary
of the spectrophotometer suffers greatly when luminosity approaches the
black level of most displays.

It depends on the driver you use. A better driver will use a longer
integration time for the i1, and will give better results for near black.

I do not know about how the i1 pro would behave using Argyll, as
measuring over a longer period of time might compensate for this
disadvantage (I think iColor Display was used in that particular case).

Exactly. Try the -V option of dispcal & dispread.

Also, some people argue 10nm resolution in the spectrum is not enough,
and 5nm resolution would improve on the accurary of results. Then again,
other people say there would not be much of a difference.

If the colorimeter had accurate filters, maybe this would be true. If
it's way off already, it's unlikely to be better than a 10 nm spectrometer
though. (You can always use the -H option with dispcal & dispread if this
concerns you.)

But everybody has an opinion, which is fine. There is just one problem
for the "regular user": there is currently no satisfactory option to
just "go and buy a device" as some have, or seem to have, disadvantages
in one area, whilst others perform "mediocre" elsewhere.

I think that's something that is best directed at the instrument manufacturers.
They are in a position to fix it. (Some will claim that their instruments
are perfect as they are though.)

I guess half of my brain was offline while composing that message. One
can be lucky if the colorimeter one buys does not stray to far from the
"reference" device for which the calibration was done. The DTP94 seems
to be very good in this regard, but still.

I think that the DTP94 is a better grade of instrument than it's competitors
(including the i1display) and is therefore more consistent instrument to
instrument, but it may not work well with some of the wide gamut
displays (there are some reports that it doesn't, or that it's hit or miss).

I do not expect you or anybody to come up with a solution (which just
might be impossible), but as there was no information available on this
topic regarding ArgyllCMS, I was simply curious.

It's certainly crossed my mind to add a facility to do this. The problem
is that only someone who has access to the display, the colorimeter and
a reference spectrometer can create a correction matrix. Even with a clearing
house for the result, I just wonder if it will be useful. If the list
of displays people use for serious color were small enough (20-40 displays)
it might (if those with access to the trio were feeling generous), but there
could still be big gaps (how many people own more than one colorimeter
and a spectrometer), and stuff that simply doesn't work (due to model
and instrument variation).

Graeme Gill.

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