Re: [Lcms-user] Re: Convert a lot of Lab measurements to a different observer temperature?

[Marti M. <ma...@li...>]

Hi,

You may use lcms to do that programmatically:

hSrc =3D cmsCreateLabProfile(&D50);
hDest =3D cmsCreateLabProfile(&D65);

xform =3D cmsCreateTransform(hSrc, TYPE_Lab_DBL, hDest, TYPE_Lab_DBL, =
INTENT_ABSOLUTE_COLORIMETRIC, 0);
...

Or, if you are sure all your data is inside sRGB gamut, use following =
trick:

- Load Lab image in Photoshop, it is using D50=20
- Image-mode-convert to profile-sRGB USING ABSOLUTE COLORIMETRIC. You =
have now D50 data as seen by an D65 adapted observer (yellowish)
- Image-mode-convert to profile-Lab USING RELATIVE COLORIMETRIC intent.=20

Voila. But this will only work for values inside sRGB gamut.

Regards,
Marti.

  ----- Original Message -----=20
  From: Greg=20
  To: lcm...@li...=20
  Sent: Friday, January 30, 2004 12:44 PM
  Subject: [Lcms-user] Re: Convert a lot of Lab measurements to a =
different observer temperature?


  Um - typo - Photoshop only supports D50, of course.
    ----- Original Message -----=20
    From: Greg=20
    To: lcm...@li...=20
    Sent: Friday, January 30, 2004 10:41 PM
    Subject: Convert a lot of Lab measurements to a different observer =
temperature?


    Hi,
    I need to convert many D50 Lab measurements over to D65 illuminant.  =
I.e, I need the new measurements to be equivalent to
    the measurements I *would* have measured, had I set my colorimeter =
to D65.=20

    Any ideas how I could do this? Unfortunately, Photoshop only =
supports D65 Lab, otherwise I could have used it.
    (I can definitely bring the measurements into Photoshop, though, if =
you think there is a way to use Photoshop)

    Thanks,
    Greg.
    p.s I really don't want to take all the measurements again. ;^)