[argyllcms] Re: Gamma wrong for calibration curves?

  • From: william.wood@xxxxxxx
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Mon, 4 Dec 2006 12:08:10 -0500


I took your advice and calculated the gamma from 3 readings taken with
"spotread" at 64, 127, and 191. The results are interesting and you can see
them in the link below:


The spreadsheet is sorted by the "Error" column, which is calculated as:
(2.2 - G at 64)^2 + (2.2 - G at 127)^2 + (2.2 - G at 191)^2

The gamma is calculated as a truncated ideal gamma curve (ignoring black

As expected, the difference between the measured gamma and gamma 2.2 is
lowest when the calibration curve and its corresponding profile is applied.
The next most accurate is the uncalibrated display (a Thinkpad T42p with
Flexview 1600x1200 screen).  Next most accurate is the calibration curve
from when dispcal is run with -g2.6, then when dispcal is run with -gs or
-g2.4, and lastly when dispcal is run with -g2.2.

Can you check my results and if they look ok, doesn't this indicate
significant error in the generation of the calibration curve for g2.2?

I can give you access to the original active spreadsheet (instead of the
static page above) if you want to look at it in more detail.  I'll need
your Google mail address to share it.

- Bill

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