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 15:01:17 -0400
This message is RESENT with changes (never revisit post, Henrik?).
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, LinoColor 6.0 and Kodak ProfileEditor
2.1. As can be seen by the data, ProfileEditor and LinoColor and ColorFlow
ALL interpret the ICC profile data pretty much 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
Kodak ColorFlow 2.1****
Cyan 58 -36 -52
Magenta 61 78 0
Yellow 95 -4 95
If you calculate the difference of colors in DeltaE*ab between Photoshop's
Lab and the other three'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).
**** KodakColorFlow's Lab readout were obtained by first opening as Input
the "cromalin ICC profile", then opening the file "TX2.9 CMYK.tiff" chart
and then read the Source PCS. (please correct me if I am wrong)
(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