Re: Spectro question
Re: Spectro question
- Subject: Re: Spectro question
- From: Marc Levine <email@hidden>
- Date: Tue, 03 Sep 2002 10:43:44 -0400
>
"James B. Reswick, Jr." wrote:
>
> 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? 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?
>
>
You are missing a major step. You can't make a CMYK1->CMYK2 device link
>
without _two_ device profiles. The steps you outline are the steps
>
to create a mapping between device independent colorspace and
>
a single device (PCS<->CMYK2). To create a CMYK1->CMYK2 mapping
>
you need to link two device profiles (CMYK1->PCS->CMYK2). The
>
choice of input profile (CMYK1->PCS) determines which color
>
space will be emulated by your actual output device (PCS->CYMK2).
In other words, every ICC transform needs 2 profiles, an input or source,
and an output or destination. What you feed into the transform is device
data - RGB or CMYK most likely. The input profile describes the relationship
of device data to some device independent color space (most likely Lab). In
other words, it assigns real color to the device data. Now the data will
preview correctly in ICC compliant applications like photoshop and can be
transformed accurately using an output profile.
When making the transform, the color information specified by the input
profile is then rewritten into new device data using the output profile. In
this way, we can transform color from one device to another. Keep in mind
that even when you have an untagged file loaded in photoshop, you are still
effectively assigning the workspace profile (from your color settings) as
the input.
The simplest way to think about it is this: all profiles (input, output,
display) are tables the describe the relationship of device data to real
color. For printers, you print a bunch of CMYK combinations, measure the
actual colors and build a table. For scanners, you get the measured data in
a file and the scanner makes the device data by scanning a target - a table
is then built using these 2 pieces of information. Try and forget that RGB
and CMYK have real color properties and that the foundation of a good ICC
workflow is properly associating the correct profiles with the correct
device data.
Hope this helps.
-Marc
--
Marc Levine
Monaco Systems
North American Accounts Manager
Technical Sales Engineer
www.monacosys.com
email@hidden
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