Graphics Programs Reference
In-Depth Information
case, the profiles are all CMYK. One advantage of using CMYK output
profiles with a RIP is that specific ink conditions and black generation
can be built into the profile. As we will see in Chapter 7, CMYK provides
some control over how the mix of CMY and K ink are built into output
profiles. A user can load an RGB document into the ColorBurst RIP and
print beautiful images. However, this RIP expects the profiles to be built
using CMYK targets. If in doubt, try profiling the printer RIP combina-
tion using both an RGB and CMYK target and compare the results. By
and large, whenever you can send RGB data to a printer, the better, even
if the printer profiles are built from CMYK targets. RGB files are smaller
and the color gamut is usually larger. However this may not be the case
if the RIP specifically expects CMYK data and CMYK ICC profiles.
Metamerism and the Printer Profile
Metamerism (discussed briefly in Chapter 5) is a phenomenon whereby
two color samples of differing spectral properties can appear to match
when viewed in one light condition but appear different under a another
lighting condition. Metamerism is a common issue with many output
devices, but the effect can be so slight that no one notices. The opposite
can be true, whereby viewing a print made with what appears to be an
excellent output profile could show neutral grays in one lighting condi-
tion and appear to have a severe green colorcast when simply moved into
a different location with a different illuminant. There is no way to remove
this effect, but compensation can be a useful solution. In a perfect world,
all prints would be viewed under a single light source like D50. The
printer profile would aim for this viewing condition and account for
metamerism so that the color appearance would appear as expected.
Unfortunately, there are many kinds of light sources, and often mixed
lighting conditions. Most ICC profiles assume a viewing condition of D50.
Measuring the ultimate light under which a print will be viewed and
building that into an output profile is one way to produce an expected
color appearance using color management. Metamerism seems to be most
noticeable and objectionable in areas of a print with neutral grays. Our
eyes are more sensitive to small color shifts in neutral grays than in more
saturated hues. One of the most common issues photographers face is
producing neutral B&W prints on some ink-jet printers that exhibit
severe metamerism.
One solution that has been quite effective is to use a third-party RIP
that prints B&W using all the colored inks but one or two that are known
to be the cause of the metamerism. The ImagePrint RIP from ColorByte
software and the X-Photo RIP for ColorBurst are two examples of drivers
that print to an Epson in a B&W mode using all inks except yellow. The
yellow ink is the primary cause of the metamerism. In the case of the
ColorByte RIP, proprietary Grayscale ICC profiles, called Gray-profiles
are supplied. At this time, no software product allows the creation of such
