[argyllcms] Re: Strange contrast clipping during calibration

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Mon, 03 Sep 2012 12:22:37 +1000

Gerhard Fuernkranz wrote:
> if you "search" the RGB cube anyway (i.e. adjust RGB, measure, adjust RGB, 
> measure, ... until
> optimum is found), what role does the model play then? For approximation of 
> the derivatives? (if
> the search/optimization is guided by gradients)

Hi,

I could do that, but I'm not sure how slow it would be. It's unclear how
rewarding this would be in general (ie. is it worth the effort ?).

> Btw, one could possibly also consider a 2D search here, i.e.
> 
>    * Keep R fixed at 1.0 and search the [R=1,G,B] plane in device RGB space 
> for an [1,G,B] triple
> closest to the desired chromaticity
>    * Do the same with fixed G=1.0, and then with fixed B=1.0
>    * Use the best of the three results

Yes, a 2D search would probably be desirable.

> If additivity is granted, then per channel curves should basically not 
> influence the CIELAB gamut
> hull. 

They will if they map 0 to !0 or 1.0 to !1.0, since they then shift the gamut 
boundaries !

Graeme.

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