Re: Question about the RGB profiles...
Re: Question about the RGB profiles...
- Subject: Re: Question about the RGB profiles...
- From: Roger Breton <email@hidden>
- Date: Wed, 09 Jul 2003 08:20:15 -0400
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Could be a stupid question..., but how works profileMaker (or wathever) to
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create a RGB2lab Icc??? I mean.... It is easy to understand how works with the
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cmyk, you have your spectophtometer, and the aplication create a relation
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between the read values and the Theorical values of the printed chart...
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but... using a DCchecker??
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The camera capture a RGB values, How knows the aplication the Lab values of
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these colors???
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Using he monitor Icc???
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I dont know if the question is clear, but really I dont undestand how it
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works....
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Thanks in advance...
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>
Xabier Urien
There are no stupid questions on color -- not even my own (hmm). First, bear
in mind that there are no 'Theoretical values' in the case of a printed
chart : this is a myth. What the application creates is a relationship
between 'printed' CMYK values and measured tristimulus values (XYZ or Lab).
Second, in the case of DC camera, the Lab values comes either from custom
measurements you make with your spectrophotometer or values supplied on CD
that comes with the chart when you get it from your dealer. With this class
of device, the application builds a relationship between Lab values and
cameraRGB using statistics or other kinds of color modeling techniques.
Third, for monitors, a variety of technique can be used. The most popular is
based on the fact that the spectral concentration of phosphors is constant
as one raises the intensity (see Burns 'gog' model in CIE Publication 122).
So most application only need to measure gamma and color of primaries and
white to characterize a monitor. Then, to finish the job, they adjust gammas
in the videoLUT for each RGB ramp and tweak the maximum RGB to give you your
requested white point. That is called 'matrix/TRC' profile in the ICC specs.
Regards,
Roger Breton | Laval, Canada | email@hidden
http://pages.infinit.net/graxx
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