Re: LAB as working/interchange space
Re: LAB as working/interchange space
- Subject: Re: LAB as working/interchange space
- From: Roger Breton <email@hidden>
- Date: Sun, 27 May 2001 14:02:55 -0400
So there are "CIE" Lab and "ICC" Lab. Different encodings. OK. How about
Photoshop's own Lab? Which flavor of Lab is it exactly? Apart from the fact
that everyone knows that it is D50/2?
Below is an analysis of various interpretations of colors obtained from the
same ICC profile using three different pieces of software: Photoshop 6,
GretagMacbeth ProfileEditor 3.1.5 and LinoColor 6.0. As can be seen by the
data, ProfileEditor and LinoColor both interpret the ICC profile data the
same but not Photoshop. Why? Anyone?
Cromalin ICC Profile (can be downloaded at
http://www.thetascan.fr/imagerie/Documents/gretag/profil cromalin THETA%
20Scan.sea)
Photoshop 6* Lab LinoColor** Lab 6.0 ProfileEditor*** v3.1.5
L a b L a b L a b
Cyan 58 -39 -48 57.3 -36 -52 57.3 -35.77 -51.86
Magenta 51 72 -2 60.6 78 0 50.7 78.3 0.27
Yellow 94 -6 93 95.3 -4 95 95 -3.84 95.62
If you calculate the difference of colors in DeltaE*ab between Photoshop's
Lab and the other two's, you get 5.1 for the solid cyan, 6.7 for the solid
magenta and 3.5 for the solid yellow.
* Photoshop's Lab values were obtained by opening the file "TC2.9 CMYK.tiff"
in CMYK and assigning the "cromalin ICC profile" on open and then reading
the solid cyan, magenta and yellow in Lab in the Color Palette with the
color picker.
** LinoColor's Lab value were obtained by opening the same file as in
Photoshop, converting to Lab on open and reading the solid cyan, magenta and
yellow with LinoColor's color picker. (I take it that LinoColor is carrying
the conversion using the B2A1 tag).
*** ProfileEditor's Lab values were obtained by first opening the "cromalin
ICC profile", opening the file "TC2.9 CMYK.tiff" second and then read the
solid cyan, magenta and yellow values in Lch with ProfileEditor's color
picker. (values had to be converted from Lch to Lab for comparison).
(For those who do not have the file "TC2.9 CMYK.tiff", you can find it at
the above site for download).
Regards,
--
Roger Breton
Quibec Institute of Graphic Communications
Montrial (Quibec) Canada T. (514) 389-5061 F. (514) 389-5840
email@hidden