Digital BW, The Print

In a message dated 1/28/07 4:37:07 PM, pderocco@... writes:


> Printing BO avoids a lot of color problems--just try to get neutral prints
> from color inks!
> 
Actually, I see little or no visible difference in illuminant metamerism 
between black only, specialty B&W inksets, and OEM inks in the latest 'two grays' 
printers. They all fix this problem by minimizing color components.

>  Halogen bulbs tend to give the fewest problems with
> metamerism, since they are truly broadband light sources.
> 
Broadband, but not a very balanced broadband... I can't tell my teal shirt 
from my blue one under halogen, which doesn't bode well for the blues and 
purples in my images.

>  Some
> phosphor-based lights come close, but I've seen some stunning color shifts
> on fabrics under lights that claim to have a color rendering index north of
> 90, so I'll never trust phosphors.
> 
Fabrics sometimes use very localized dyes/pigments, which emit color only in 
a narrow band of the spectrum. Not so printing inks, which are designed to be 
very broadband, and generally emit across a third of the spectrum or more. So 
not using effective, low energy fluorescent proofing lights due to a problem 
that does not exist in our medium seens a bit extreme.
> 
> Solux makes inexpensive halogens that have reasonably accurate color
> temperature, and you can get pretty cheap fixtures for them at any lighting
> store.
> 
These lights are very low efficiency, very hot, and very shortlived; they 
change color temperature significantly in a few hundred hours, and must be tossed 
long before they burn out. Besides, they tend to start off below 5000k, and 
get even lower (yellower) over time, so they are never in the sweetspot for 
color balance, and get worse as they age. But some swear by them... others swear 
at them.

>  However, be aware that the cheap Chinese fixtures are designed for
> 125VAC, so if you use them in the US, they'll run a little cool, and the
> color temp will be a tad low. This isn't a huge problem,
> 
It is to me, since the better choice would be to run ABOVE 5000k, not below 
it...

>  but if you're
> really trying to dial in an exact color temp (measured with a spectro at
> table level), you can go to an elecetronics supply store and buy a variable
> transformer that can convert 115VAC into 0 to 130VAC, and run everything
> through that.
> 
Or you could get fluorescent tubes that run a bit above 5000k to begin with, 
and not use them to view textiles...

C. David Tobie
Product Technology Manager
ColorVision Business Unit
Datacolor Inc.
CDTobie@...
www.colorvision.com


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