[argyllcms] Re: Cctiff

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Sat, 01 Mar 2008 11:33:41 +1100

Alastair M. Robinson wrote:

Hmm. I don't pay any regard to this I'm afraid.

LOL - does anyone?  (Semi-serious question!)

If I was, Roger would be commenting that the Lab values
didn't match the measured ones, so in some ways it works
best to not worry about it. I could expand the coding options
to allow for CIELab D65 and CIELab D50, thereby at least
allowing someone to generate a TIFF file that meets the spec.!
(But it would leave the problem of how cctiff should interpret
a CIELab TIFF on input. Messy!)

The other aspect is what intent the data is assumed to have. If
the Lab data is assumed to represent relative colorimetric
intent, then encoding it so that 100,0,0 is white is the right
thing to do. If you are trying to encode absolute colorimetic
on the other hand, then it would be right to do a

   PCS D50 Lab -> XYZ -> D65 Lab

conversion on output.

Well, the post of Marti's that I linked to said PhotoShop 5 doesn't honour the D65 white point - I have no idea whether newer versions do.

Photoshop 5.5 doesn't understand ICCLab TIFF format either.

Graeme Gill.

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