# [argyllcms] Re: How do I create a linear luminance LUT?

• From: Geoff Ghose <geoff@xxxxxxxxxxxx>
• To: argyllcms@xxxxxxxxxxxxx
• Date: Thu, 7 Jul 2011 11:24:30 -0500

```Hi Graeme,

I just don't get that behavior unfortunately.

Here's an exact transcript of what happens:

robin1:robin geoff\$ /mnt/pooh/Mac/usr/local/Argyll_V1.3.3/bin/dispcal -v -g
1 -yl -d 2 test
Setting up the instrument
Place instrument on test window.
Hit Esc or Q to give up, any other key to continue:
Display type is LCD
Target white = native white point
Target white brightness = native brightness
Target black brightness = native brightness

Press 1 .. 7
1) Black level (CRT: Offset/Brightness)
2) White point (Color temperature, R,G,B, Gain/Contrast)
3) White level (CRT: Gain/Contrast, LCD: Brightness/Backlight)
4) Black point (R,G,B, Offset/Brightness)
5) Check all
6) Measure and set ambient for viewing condition adjustment
7) Continue on to calibration
8) Exit
Commencing device calibration
patch 6 of 6
Black = XYZ   0.50   0.51   0.84
Red   = XYZ 102.89  53.72   4.48
Green = XYZ  61.26 126.60  21.26
Blue  = XYZ  29.90  12.43 159.21
White = XYZ 198.24 196.63 188.02
patch 64 of 64
Initial native brightness target = 196.629329 cd/m^2
Target white value is XYZ 198.235527 196.629329 188.021633
Adjusted target black XYZ 0.50 0.49 0.84, Lab 2.24 0.15 -3.12
Target black after min adjust: XYZ 0.499 0.488 0.843, Lab 2.240 0.148 -3.119
Gamma curve input offset = 0.000000, output offset = 0.002480, power =
1.003591
Total Iteration 3, Final Samples = 64 Final Repeat threshold = 0.600000
Creating initial calibration curves...
Doing iteration 1 with 16 sample points and repeat threshold of 1.200000 DE
patch 16 of 16
Brightness error = 0.000000 cd/m^2 (is 196.434849, should be 196.434849)
White point error = 0.000000 deltaE
Maximum neutral error (@ 0.895486) = 1.166039 deltaE
Average neutral error = 0.813299 deltaE
Number of measurements taken = 36
Computing update to calibration curves...
Doing iteration 2 with 32 sample points and repeat threshold of 0.848528 DE
patch 32 of 32
Brightness error = 0.000000 cd/m^2 (is 196.358199, should be 196.358199)
White point error = 0.000000 deltaE
Maximum neutral error (@ 0.419042) = 0.838664 deltaE
Average neutral error = 0.537847 deltaE
Number of measurements taken = 101
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 = 0.000000 cd/m^2 (is 196.459265, should be 196.459265)
White point error = 0.000000 deltaE
Maximum neutral error (@ 0.023233) = 1.504637 deltaE
Average neutral error = 0.490073 deltaE
Failed to meet target 0.600000 delta E, got worst case 1.272785
Number of measurements taken = 385
The instrument can be removed from the screen.
Written calibration file 'test.cal'

robin1:robin geoff\$ /mnt/pooh/Mac/usr/local/Argyll_V1.3.3/bin/dispwin -d 2
test.cal

robin1:robin geoff\$ /mnt/pooh/Mac/usr/local/Argyll_V1.3.3/bin/dispcal -d 2
-yl -r
Place instrument on test window.
Hit Esc or Q to give up, any other key to continue:
Current calibration response:
Black level = 0.48 cd/m^2
White level = 196.73 cd/m^2
Aprox. gamma = 2.30
Contrast ratio = 414:1
White chromaticity coordinates 0.3401, 0.3372
White    Correlated Color Temperature = 5160K, DE 2K to locus =  7.3
White Correlated Daylight Temperature = 5155K, DE 2K to locus = 10.8
White        Visual Color Temperature = 5354K, DE 2K to locus =  7.0
White     Visual Daylight Temperature = 5473K, DE 2K to locus = 10.3
The instrument can be removed from the screen.

Gamma of 2.2 verified with spotread:

White Yxy: 196.703246 0.340368 0.337594

Black Yxy: 0.829925 0.307911 0.290062

Gray Yxy: 47.263913 0.348618 0.335558

On Wed, Jul 6, 2011 at 9:51 PM, Graeme Gill <graeme@xxxxxxxxxxxxx> wrote:

> Geoff Ghose wrote:
>
>> Yes, it's OS X. After creating the calibration, I install it.
>>
>
> I don't seem to be able to reproduce such a problem using
> the Huey on the MacBook running 10.4:
>
>        dispcal -v -g 1 -yl test
>        dispwin test.cal
>        dispcal -yl -r
>                Approximate gamma 1.01
>
>
>                White Y = 179.1
>                50%   Y = 89.05
>                Black Y = 1.69
>
>        so the expected 50% value would be (179.1 + 1.69)/2 = 90.4,
>        which is reasonably close.
>
> You'll need to try and figure out why it isn't working
> on your machine. I note that the display visibly brightens when
> the calibration is installed. Do you see that too ?
>
> Graeme Gill.
>
>
```