Re: Spectro question
Re: Spectro question
- Subject: Re: Spectro question
- From: Chris Murphy <email@hidden>
- Date: Mon, 2 Sep 2002 23:33:42 -0600
On Monday, September 2, 2002, at 11:00 PM, "James B. Reswick, Jr."
<email@hidden> writes:
My question is (finally): How can the profiling software know what
corrections to make when comparing only the CMYK text values
associated with
the target's patch and the measured Lab values for that patch, when the
information contained in the target's CMYK text values are relative
percentages?
It doesn't. The resulting profile is just a snapshot description of how
a given device behaves. A single output device profile contains
(simplistically) two pieces of information, what CMYK values output on
that device look like to a person, and what CMYK values to send to the
device to generate a specific color.
Wouldn't two device-independent coordinate descriptions for that
patch (one provided and one measured) have to be available for there
to be a
comparison? Wouldn't an additional text file with Lab coordinates
have to be
provided with the target?
Effectively you get this when two profiles are combined, which is a
requirement for a color space conversion to occur. For color management
to do anything, one profile is needed to define the source space and
another is needed for destination. The source profile effectively says
"these RGB values mean xxxx in LAB" then the CMS uses the destination
profile to lookup the LAB value and corresponding device values (CMYK
in this example) to produce that color.
The way to look at a single profile is merely as a record of how a
given device behaves. The profile doesn't say what corrections are
needed - that is up to the CMS and is determined once at least two
profiles have been specified (and a document to convert).
Chris Murphy
Color Remedies (tm)
Boulder, CO
303-415-9932
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