[argyllcms] Re: Gamma wrong for calibration curves?

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Thu, 07 Dec 2006 23:57:16 +1100

Roger Breton wrote:
Your figures show that you reached the gamma curves you intended to reach
with great precision. Now, have you considered what that does for gray
balance? I.e., to gave neutral RGB triplets yielding your desired calibrated
white point chromaticities? Like D50 x=0.3457 y=0.3585.

The grey balance tolerance depends on the display, the instrument,
and how long you are prepared to wait (ie. which -q flag you use).
If you use -u (update/retune and existing calibration)
you can even keep trying to improve things as long
as you like.
If you use the -e flag, it will do a final verify pass that
gives you a max/average delta E measure of the neutral
accuracy (just like it does for each pass using -v).

On a good CRT, you might expect a worst case of 3 delta E or better,
and an average of 1 delta E or better. On some LCD's it's
hard to adjust for neutral near the black, and the aim points
have to be compromised (-k parameter).

The next release will address Bill Wood's issues, without
changing the type of calibration curve used when a gamma
is selected as the target.

Graeme Gill.

Other related posts: