Re: Conversion from CMYK to Wavelength (lambda)

From: Tom H. (tom_reader_at_att.nospam*.net)
Date: 02/14/05 

Date: Mon, 14 Feb 2005 20:51:39 GMT

I am more familiar with RGB and spectroradiometry than CMYK, but the same
arguments probably apply. Think about the CIE color chart (chromaticity
diagram). The CIE values are obtained by integrating the spectrum of the
source with the CIE color matching functions to give three values which are
normalized to add to one and hence be representable in a 2 dimensional
diagram. So, depending on how finely you collect the spectral data ( for
example every 5 nanometers or every 1 nanometer) you are compressing the
tens or hundreds of datapoints down to just 2 numbers (the CIE X and Y) or
for RGB that is 3 numbers. You can't really go back the other way, because
information is thrown away in the process of making a more manageable
representation of color. If you make assumptions about the shape of the
emission spectra that might make up the color, then you might be able to do
some back calculations. There may also be ways to establish the "dominant
wavelength", but you cannot really reproduce the actual spectrum.

Tom
"Martijn" <m.w.hendrikx@student.utwente.nl> wrote in message
news:cuquon$1uq$1@netlx020.civ.utwente.nl...
> Hi there,
>
> I am interested in the distribution of wavelenghts in an image, of which
> only the CMYK values are available for each pixel. To this end I am
> looking
> for some algorithm that tells me the wavelength lambda in nanometers for
> each particular combination of C,M,Y and K.
>
> Question:
> * Is there a mathematical prodecure that transforms cmyk-data into
> wavelengths?
>
> My attempt to find information on this field with google have failed, so I
> hope there is someone in this juicy newsgroup who can help.
> Thanks a lot!
>
> Kind regards,
> Martijn
>
>
> --
>
>
>
>
>

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