Re: How do one generate profiling patches (The hen or the egg)
Re: How do one generate profiling patches (The hen or the egg)
- Subject: Re: How do one generate profiling patches (The hen or the egg)
- From: Steve Upton <email@hidden>
- Date: Wed, 23 Apr 2003 12:59:57 -0700
At 5:29 PM +0200 4/22/03, Thomas Holm / Pixl wrote:
>
I'm a firm advocate of ICC profiles but there is still one thing I can't get
>
into my head. If anyone would volunteer an explanation, I'd be grateful.
>
>
When one builds patches for profiling a printer, how do one obtain the
>
reference (LAB or XYZ) values used when comparing the actual spectral
>
readings of printed targets?
This is a color management myth - that there is a reference set of color when building profiles.
Myth:
- CMYK/RGB values (typically in a TIFF file) are sent to a printer.
- color patches are measured using an instrument yielding Lab or XYZ values
- measured Lab/XYZ values are compared to reference Lab/XYZ values to calculate profile
Actuality:
- CMYK/RGB values (typically in a TIFF file) are sent to a printer.
- color patches are measured using an instrument yielding Lab or XYZ values
- measured Lab/XYZ values are tabulated with original CMYK/RGB values
Profiles provide the lookup for RGB/CMYK -> Lab/XYZ and back again. There is no "judgement" about whether the printer was "correct" and how far "off" it was. Rather, the profile just records what colors (Lab/XYZ) correspond to the device values (RGB/CMYK,etc).
I have seen this myth propagated in seminars, books, discussion lists etc and it is simply not correct. Hope this clears things up...
Regards,
Steve
________________________________________________________________________
o Steve Upton CHROMiX www.chromix.com
o (hueman) 866.CHROMiX
o email@hidden 206.985.6837
o ColorGear ColorThink ColorValet ColorSmarts ProfileCentral
________________________________________________________________________
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