Re: Profile Internals
Re: Profile Internals
- Subject: Re: Profile Internals
- From: email@hidden
- Date: Thu, 27 Dec 2001 03:48:07 -0500
- Priority: normal
Daniel,
I think I can answer some of your questions, and also point you to
some useful websites.
>
Is there a whitepaper which doesn't go as deep as to enable
>
me to programm my own profile but still gives me an insight
>
about the structure.
The ICC Specification is available for download at
<
http://www.color.org>. You might also want to look at the
"Introduction to the ICC profile Format" and a paper that Dawn
Wallner wrote entitled "Building ICC Profiles: the Mechanics and
Engineering"
>
In postings I read about A1B1 (etc.) tables. I am sure those are
>
the in/out tables of the rendering intents but where can I read
>
which one is which ?
The Letter "A" represents the device's native color space (i.e.,
Monitor RGB, Printer CMYK) whatever it is, "A" is a generic symbol
for it.
The letter "B" represents the PCS "Profile Connection Space". Thus,
an "A2B" transform converts device color space to the PCS. A "B2A"
transform converts PCS values into a device space such as RGB.
The numbers 0, 1, and 2 represent the Perceptual, Colorimetric, and
Saturation rendering intents respectively. Thus, and "A2B0"
transform is a perceptual transform that converts Device colors to
PCS colors.
>
Since I only do one mesuring session all the vendors of profiling
>
software seem to brew their own soup. How do the in and out
>
tables of a profile differ after profiling? If there is only one set
>
of data why aren't they always symmetrical.
As far as a I know, everyone has their own method of producing input
/ output tables.
>
How do the tables differ between rendering intents. Again I only
>
have one set of data so what happens with the data in the tables ?
>
Obviously they all have to be different.
This is most likely covered on the ICC website somewhere, so I won't
go into it.
>
Does editing the whitepoint tag have any effect on the tables ?
>
Like .. if I edit the wp will there be an inconsistancy because
>
there are also white patches in the profile (tables) part?
All my friends tell me that editing the WP tag SHOULDN'T affect the
relative intents, but will affect the absolute colorimetric. But
people on this forum seem to have experienced otherwise.
>
Is the table for the colorimetric intent actually RelCol with the wp
>
to be added in AbsCol transformations (which would mean the wp was
>
subtracted first) or is it AbsCol with the wp to be subtracted for
>
RelCol.
Absolute colorimetry in this context means the colors are relative to
D50 as defined in the ICC spec. Relative colorimetry means
the colors are specified relative to the media WP (i.e., paper
white). This is used so that 0% dot will map to 0% dot in graphics
applications.
>
How is the wp tag generated .. since for example when measuring in
>
printopen the wp tag values differ from the value measured in the
>
white patches.
The media WP is simply measured and reduced to XYZ.
Hope this helps. You might also want to look at some of the docs on
the colorsync website as well as Don Hutcheson's website
<
http://www.hutchcolor.com>
Toshia
--------------------------------------------
Toshia McCabe
web:
http://www.belarc.com
voice: 978-461-1112
email: email@hidden