[argyllcms] Re: DE to locus = 17.3

On Thu, Jan 8, 2009 at 9:58 AM, Graeme Gill <graeme@xxxxxxxxxxxxx> wrote:
>
> You get a White point error of zero if you've asked for the native
> white of the display, rather than a specific color temperature or
> chromaticity coordinate. The native white point (in your case)
> is 17 CIEDE2000 units away from the black body locus (ie.
> it is not very "white").
>
>> When I afterwards profile my monitor I noticed that the profile have a
>> whitepoint about the same as the calibrated monitor. Is this
>> whitepoint still of the locus by DE 17? Anyway, images I have created
>> whit this calibration and profile looks excellent on print, so I don't
>> think this there is any problem in my daily use.
>
> Typically one adapts to the white of a monitor, although setting the
> target temperature to the Visual Color or Daylight temperature
> may be a better choice.
>
> Graeme Gill.
>
>
>

Graeme, sorry I send an email in wrong name.


Thank you again.
From now on I will always check my calibration.

I have played a lot with this now.
My monitor have a uncalibrated responds like this:

 dispcal -v -c1 -R -yl
Setting up the instrument
 Instrument Type:  DTP94
 Serial Number:    053399
 Boot version:     D929
 Software version: DB06
Place instrument on test window.
Hit Esc, ^C or Q to give up, any other key to continue:
patch 3 of 3
Measuring VideoLUT table entry precision.
patch 6 of 6
patch 6 of 6
patch 6 of 6
Uncalibrated response:
Black level = 0.26 cd/m^2
White level = 126.80 cd/m^2
Aprox. gamma = 2.38
Contrast ratio = 488:1
White chromaticity coordinates 0.3484, 0.3877
White    Correlated Color Temperature = 4999K, DE to locus = 16.5
White Correlated Daylight Temperature = 5010K, DE to locus = 14.4
White        Visual Color Temperature = 4570K, DE to locus = 16.1
White     Visual Daylight Temperature = 4673K, DE to locus = 14.0
Effective LUT entry depth seems to be 8 bits
The instrument can be removed from the screen.


So instead of using native white point I have this concluded that at
5000K would be a naturally choice. I have the brightness at my monitor
at 100, the rest of the settings are at factory default. I have tried
with the daylight locus and the planckian locus:
Heres the result:

D50?
dispcal -v -c1 -yl -m  -t 5002.78 d50

........
Brightness error = -0.166590 cd/m^2
White point error = 0.225363 deltaE
Maximum neutral error (@ 0.321539) = 0.920143 deltaE
Average neutral error = 0.457058 deltaE
Number of measurements taken = 133
The instrument can be removed from the screen.
Written calibration file 'd50.cal'

$ dispwin d50.cal
$ dispcal -yl -c1 -r

Place instrument on test window.
Hit Esc, ^C or Q to give up, any other key to continue:
Current calibration response:
Black level = 0.26 cd/m^2
White level = 98.88 cd/m^2
Aprox. gamma = 2.38
Contrast ratio = 380:1
White chromaticity coordinates 0.3451, 0.3592
White    Correlated Color Temperature = 5025K, DE to locus =  5.5
White Correlated Daylight Temperature = 5026K, DE to locus =  1.0
White        Visual Color Temperature = 4909K, DE to locus =  5.3
White     Visual Daylight Temperature = 5009K, DE to locus =  0.9
The instrument can be removed from the screen.




And here with planckian locus:
dispcal -v -m  -yl -c1 -T 5000 T5000
......
Computing update to calibration curves...
Doing iteration 3 with 64 sample points and repeat threshold of 0.600000 DE
patch 64 of 64
Brightness error = -0.424535 cd/m^2
White point error = 0.244245 deltaE
Maximum neutral error (@ 0.900364) = 0.668959 deltaE
Average neutral error = 0.374921 deltaE
Number of measurements taken = 122
The instrument can be removed from the screen.
Written calibration file 'T5000.cal'

dispwin T5000.cal
dispcal -v -yl -c1 -r
Setting up the instrument
 Instrument Type:  DTP94
 Serial Number:    053399
 Boot version:     D929
 Software version: DB06
Place instrument on test window.
Hit Esc, ^C or Q to give up, any other key to continue:
patch 3 of 3
Current calibration response:
Black level = 0.27 cd/m^2
White level = 92.01 cd/m^2
Aprox. gamma = 2.36
Contrast ratio = 341:1
White chromaticity coordinates 0.3447, 0.3513
White    Correlated Color Temperature = 5013K, DE to locus =  0.0
White Correlated Daylight Temperature = 5011K, DE to locus =  4.8
White        Visual Color Temperature = 5014K, DE to locus =  0.0
White     Visual Daylight Temperature = 5114K, DE to locus =  4.6
The instrument can be removed from the screen.


-----------------------


At lest the error is much better than with native white point. But I
think there is some more banding and maybe some color cast compared to
native white point. I also really wonder why the native white point is
so far away from locus?

I have also tried higher temperatures but I don't think my monitor
have enough brightness to do that. Another nice feature of my monitor
are, If I do a recheck after some time the white point may be off with
0.5 DE or even more to locus. :-(

And here is an image of my kids taken in my living room straight
before a Christmas party. They are edited in a DE 17 calibration :-)
http://mulebakken.net/div/mykids.jpg

Regards
Lars Tore Gustavsen

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