[argyllcms] Re: Question about colprof and black point

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Thu, 18 Nov 2010 08:47:19 +1100

Vittorio Villani wrote:
Creating rspl..
Fine tuning white and black point mapping
White is [...]
Black is 9,994558 0.850210 1.285811, should be 10.012171 0.988195 1.630301

What are the numbers of the balck about? 9,99 is the L* value or what?

They are Jab values (CICAM02).

My black point is (.ti2 file):
"Q3" 0.0000 0.0000 0.0000 1.0000 1.0000 1.000
The reading of this patch with the ColorMunki software gives me this result in 
L*a*b* values:
Using profcheck I get this result for the Q3 patch:
[0.219403] 5: 0.000000 0.000000 0.000000 ->  4.715842 1.202572 1.658739 should 
be 4.812903 1.350490 1.624429

So I can't understand what is that black point about.

See above. There is an appearance conversion between D50 L*a*b* values and
the CIECAM02 Jab values, hence the difference. If you use xicclu -pj with the
appropriate viewing conditions set, you should get matching numbers.

Graeme Gill.

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