Digital BW, The Print

Daniel & Tyler,

Here are some spectral plots (eye-one measurements) for a 50% gray 
patch printed with an Epson 2200 (UC inks) using the Epson driver and 
neutral, carbon, and sepia QTR profiles.  The spectral distribution of 
the QTR pure carbon 50% gray (K + LK) is smooth and the added LM + LC 
in the neutral QTR 50% gray and LM + Y in the QTR sepia 50% gray 
introduces some variations in the spectra, but not enough to cause 
visible metamerism.  In contrast, the Epson driver gray is highly 
metameric and the spectrum exhibits sharp fluctuations in spectral 
intensity.  The x axis in the plot should read wavelength in nm and not 
epson driver.

http://homepage.mac.com/scho/spectra.jpg


On Friday, September 17, 2004, at 09:53  PM, Daniel Staver wrote:

> Carl,
>
> If you print a picture with a deep blue sky using UC inks you'll easily
> see a shift from purplish blue to cyan if you move from fluorescent to
> daylight. This is consistent with the shift you would see with a
> "neutral" print printed with the Epson driver. This could indicate that
> either the cyan or the magenta inks (or both) are the cause of
> metamerism, not yellow.
>
> --
> Daniel Staver
> http://daniel.staver.no
>
>> I agree that the "yellow ink causes metamerism" hypothesis is
>> unverified and probably false, but it would be difficult to test.
>> Metamerism is most apparent in neutral prints so if one created a
>> series of neutral profiles with increasing amounts of yellow added it
>> would be necessary to also add increasing amounts of cyan and magenta
>> to maintain neutrality.  At some point the neutral grays would become
>> metameric, but does the metamerism occur because of the additional
>> yellow ink or the CM?  I suspect it is the latter but I'm not sure how
>> to set up a test to confirm this.  Sepia prints I've made with 
>> profiles
>> that use only K,LK, LM, and Y do not appear to be metameric but they
>> are of course also far from neutral.
>
>
>
>
>
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