Hola Paco,
CIE L*a*b is basically a relative way to measure
color. Its primary goal is on print, although people
keeps using Lab on other medium, like transmissive.
The L* measure is a correlate to perceived lightness
ranging from 0.0 for black to 100 for difusse white.
L* can sometimes exceed 100.0 for stimuly such as
specular highlights in images. L* predict lighness as
defined by Munsell. In fact, it does the prediction
even better than the fifth-order polynomial used
to define Munsell value.
L* of 0 is not feasible at all, since it implies and
XYZ of 0. The lowest L* I've ever seen is about 3,
and was in a prototype large format printer using
glossy media. But on perceptual intents, you can
get L*=1 or even 0. That is because the black
point compensation perceptual intent has and only
means that would be the black acomplished on
an ideal (infinite gamut) device. You are not going
to get such L* on a softproof, for example.
L* of 100 is easy: just unprinted paper since, as
said, Lab is a relative measure.
Hope this helps
Regards
Marti Maria
The littleCMS project
http://www.littlecms.com
----- Original Message -----
From: "Paco Rosso" <[EMAIL PROTECTED]>
To: <lcms-user@lists.sourceforge.net>
Sent: Thursday, March 30, 2006 12:55 PM
Subject: [Lcms-user] misunderstanding of what L* means
I have a problem with the concept of L* (You know, that of Lab)
I expect do not find L* lowers than 9 or greater than 96 in an "ideal scene"
(Ideal scene: scene with all lambertian reflectors, without fluorescense
and with a uniform illumination)
But my photoshop show me values so low as L 1 and so high as 99
¿Does photoshop make a particular interpretation of what L^* means or I am
wong with the concept?
2nd part of the question. In a print ¿What do you expect to find as L? ¿Are
L 100 the white of the paper or the white of the lambertian 100% reflection
reference? Because this cpould explain why Photoshop read L 99 and 1...
Paco Rosso
Luz-Color-Fotografía
http://pacorosso.blogspot.com
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