[argyllcms] Re: Profile input white not mapping to output white

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Tue, 27 Nov 2012 18:14:06 +1100

Ben Goren wrote:
>
> Graeme, I think the new extrapolation code needs a bit of work. It didn't 
> always render
> input white as output white, and there were times when it seemed like there 
> might have
> been some inversion going on in the highlights. It did do quite swimmingly 
> when fed a
> profile with an added D50 patch. Oh -- and you hinted at this, but there 
> doesn't seem
> to be any difference between profiles with and without -u.

Hi,
        well, all input profiles are meant to render the chart white patch as
D50 using relative colorimetric. With the current code there will be a 
difference
between -u and non -u if the estimated device 1,1,1 has a higher Y than the 
white point
patch. I'm now wondering if that is good enough - it should really be whatever
color within the device gamut has the largest Y value, but given the 
extrapolated
nature of it, is not correct to search the whole cLUT - just the Y headroom
in the "white" direction would seem relevant.

I'm not sure I can do much more without a specific example in regard
to the extrapolation code - ie. a .ti3 and some indication of what you
think is wrong with it. (ie. I spent some time tuning the extrapolation code,
and I'm currently at a loss to know in what way it is lacking, given the
dubious nature of extrapolation in the first place.)

Graeme Gill.

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