[argyllcms] Re: Using BtoA1 table with rendering intent absolute

  • From: John Weissberg <jw@xxxxxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Fri, 07 Sep 2007 21:35:45 +0200

Can you supply details of which CAT we should use? Bradford? Von Kries? Another? 


Any reference to the actual formula would be appreciated?

Gerhard Fuernkranz wrote:

John Weissberg wrote:

Consider the following case: Converting from Lab -> CMYK using the
BtoA tables of an ICC profile with "Absolute Colorimetric" as a
rendering intent.

As I understand it, the ICC profile does not contain an Absolute
colorimetric BtoA table. Rather, it will use the relative colorimetric
BtoA table, along with whitepoint data, for any look-ups it makes.

Can anyone explain what algorithm is used for these conversions
between relative and absolute colorimetric?


This is a chromatic adaptation transformation.


Is it simply adding/subtracting the DeltaE between the whitepoint and
100,0,0 ?


No. Convert to XYZ, apply the CAT, and convert back to L*a*b*.

Regards,
Gerhard


Is delta value added for all points in the color space? Only for
points where L is above a certain limit?

Any information is appreciated.

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