Graphics Programs Reference
In-Depth Information
devices, like my Fuji Pictography, which is linear and well behaved. Some
products support this prelinearization process and some do not. Products
that do support prelinearization usually ask the user if they wish to use
this option. If you know the printing is very nonlinear, it's worth testing.
On the accompanying CD is a TIFF file called
InkDensityTest.tif
, which
can be useful for visually evaluating if the output device is nonlinear. If
most of the steps block up in color and don't show good tonal separa-
tion, the printer is exhibiting this nonlinear behavior. You can try a
different driver setting if available. However, this can often alter the
resulting color gamut of the printer. Alternatively, you can try conduct-
ing a prelinearization process, but even this can't produce miracles. A
profile can do only so much to overcome the limitations of poor printer
behavior (see the sidebar, “Printer Drivers and Their Effect on Quality
and Color Gamut”).
Some packages also offer a postlinearization process. This can be quite
useful for devices that change their behavior. After an initial profile is
built, the user prints a special postlinearization target. This target is meas-
ured and the profile can be updated to account for some changes in
the output device. This postlinearization process can't work miracles
on output devices whose behavior has greatly shifted. In such a case,
building a new profile from a standard target is the only viable solution.
However, for some devices where the drift of a printer isn't large, this
postlinearization process is a useful feature. Some users running
commercial labs print out a postlinearization target every day and update
their existing profile to account for slight device drift.
Sidebar
Printer Drivers and Their Effect on Quality and Color Gamut:
The print driver sending the
data to the printer can play a profound role on the color quality and color gamut of the profile
targets and thus the resulting output profile. We have discussed the
sweet spot
for scanners
and digital cameras. Settings that produce the best data prior to profiling are necessary if we
are to create the best quality device profiles. This is true with many print drivers. Some print
drivers provide little or no options. However, some print drivers do provide numerous settings
for handling the data going to the output device; for example, the print drivers from Epson that
control their ink-jet printers. There is one option called
No Color Adjustment
, seen in Fig. 6-10.
This setting sends the data to the printer in its most unmodified form. When sending a profile
target through this setting, the result is the widest gamut the printer can produce. The canned
profiles supplied by Epson were made in this fashion. The downside is this behavior is very non-
linear so a great deal of ink gets laid down and blocks up a good deal of darker tonal areas. If
a user instead sends a target though the driver using the
Vivid
or
Photo Realistic
driver setting,
the resulting target is far more linear. Yet the final profile shows that the gamut of the printer
has been slightly reduced. Figure 6-11 shows two profiles from the Epson 2200 built using the
No Color Adjustment
setting versus the
Vivid
setting. What we have here is a compromise
between the best possible ink delivery and maximum color gamut.
