[argyllcms] Re: Bad measurements & white point calibration with Argyll 0.7b7 and GretagMacbeth i1Display 2
- From: "Hal V. Engel" <hvengel@xxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Wed, 9 Jan 2008 19:18:28 -0800
On Wednesday 09 January 2008 18:07:48 Graeme Gill wrote:
> Craig Ringer wrote:
> > I'm having some severe issues getting decent results out of an i1Display
> > 2 using Argyll 0.7b7 . If I use dispcal to adjust the gains to target a
> > D65 white point I end up with a bright purplish-blue display.
>
> It's not clear where you see a problem. From your reference:
> > craig@wallace:~/build/argyll_0.7b7$ bin/dispcal -R -y l
> > Place instrument on test window.
> > Hit Esc, ^C or Q to give up, any other key to continue:
> > Uncalibrated response:
> > Black level = 0.19 cd/m^2
> > White level = 170.82 cd/m^2
> > Aprox. gamma = 1.72
> > Contrast ratio = 921:1
> > White chromaticity coordinates 0.3141, 0.3296
> > White Correlated Color Temperature = 6422K, DE to locus = 4.1
> > White Correlated Daylight Temperature = 6423K, DE to locus = 0.7
> > White Visual Color Temperature = 6282K, DE to locus = 3.9
> > White Visual Daylight Temperature = 6444K, DE to locus = 0.6
> > The instrument can be removed from the screen.
> >
> > The luminosity readings are fairly sane based on what i1Match has to say
> > about the display,
> >
> > but the colour information is amazingly out.
>
> In what way is it "out" ? You've asked for a D65 white point, and that's
> exactly what has been achieved (according to the instrument at least).
> You've got Daylight 6500K within 0.6 delta E. Pretty good.
I think the issue is that LProf and ArgyllCMS, although they basically agree
with each other, are giving significantly different results for white point
=D65 then the vendors software with the same devices (IE. meter and display).
It might be useful to measure the monitor in it's sRGB mode with ArgyllCMS and
the vendors software to see how much different the readings are. And Craig
did write that calibrating the white point using the i1 match software did
give a result that looked neutral to him where as ArgyllCMS and LProf gave
results that looked way too blue. If the result where that ArgyllCMS seemed
slightly too blue then I would be inclined to write off the difference. But
it appears that the difference is a very large one.
>
> Without calibration, the mid greys may not be aligned with D65
> though, depending on how the display actually creates the
> R/G/B "gain" controls.
> [It doesn't follow that the display "gain" controls work in such a
> fashion that the chromaticities of all the greys will track the
> white point. It really depends on how smart the people creating
> the "gain" control function for the LCD display are, and the
> characteristics of the display.]
>
> If other white references in your visual field are a warmer white
> (D50 or lower for incandescent illuminants), then D65 will look
> very "blue".
>
> In contrast the "native"/sRGB display is not close to any
> normal white point (delta E 9). A poor result for the display
> (or a faulty instrument).
>
> [And the usual caveats about trying to change the basic nature of an LCD
> apply. It probably won't work very well compared to a CRT, unless you've
> got a LED R/G/B backlight LCD display. In such a display the mid greys will
> tend to track better, simply because of the nature of the physics
> involved.]
>
> Graeme Gill.
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