Graphics Programs Reference
In-Depth Information
Fig. 7-5
The UCA portion
of the Photoshop Classic
Engine illustrates the effect
on the CMY curve when a
value is inserted. I've gone
overboard with this setting
for illustration purposes
only. Five to 10% would
probably be the limit used
here when necessary.
Notice how the CMY inks
have been raised
compared to the same
curves in the heavy setting
in Fig. 7-3 in the darker
area of the tone scale.
and instead use CMYK profiles built with packages that used measured
data of the print conditions.
Sidebar
GCR Up Close:
Figure 7-6 shows two separations made with light GCR (top) and heavy GCR
(bottom), with the black channel to the left of each separation, and to the right, just the CMY
channels. In the center of each separation is the Photoshop GCR portion of the custom CMYK
dialog. This shows the curves for the GCR settings used. Let's examine the light GCR first. Notice
that the white to black steps in the black channel (outlined in red) shows only the last few
steps from pure black appearing on the black channel. Notice that the density behind the hands
with balls is quite light. This is because more CMY ink is being used on these channels (less
black) seen in the composite image to the right. Not much CMY is being replaced with K.
Now examine the two images separated using heavy GCR. The white to black steps (out-
lined in red) shows much more density is on this black channel. A heavy GCR setting replaces
more CMY with black so the black channel is heavier. The background behind the hands with
balls is quite dark due to the heavy GCR, as you would expect. This is the opposite of the com-
posite seen above using light GCR. Once again, in the center is the Photoshop GCR curve used
to make this separation. Notice the position of the red outline indicating where heavy GCR has
moved the CMY curves compared to the light setting. A red square shows where the black
begins within the tone curve seen under the curve itself. This is the Black Start, affected by the
choice of GCR. Also, notice the areas in the tone curve where both light GCR and heavy GCR
are most pronounced as the mix of inks starts to shift over to black.
Other Black Generation Options
Some of the more advanced profile building applications provide addi-
tional options to improve the black generation of CMYK profiles. For
example, in ProfileMaker Pro, an option known as the
Black Width
slider
controls the amount of black ink used in highly saturated portions of an
image. This is commonly used for building CMYK profiles for gravure
