Graphics Programs Reference
In-Depth Information
numbers 1 through 4 will toggle each color channel in the
order of the color channels: first cyan, then magenta, then
yellow, and last, black.
As we discussed in Chapter 7, the GCR settings alter the relationship
between CMY inks and black ink. If you examine each color channel,
especially the black channel in all the converted documents you just pro-
duced, you'll see how the lighter the GCR setting, the lighter the black
channel. Notice that in the conversion using the None GCR setting, the
black channel has no black ink at all. What is also interesting is that if
you examine the composite image (that is, view all four channels at once
and thus produce a full color image), the various GCR settings really do
not make a difference in the color appearance. Run the Eyedropper over
the images however and you'll see vastly different mixes of cyan/
magenta/yellow and black!
The 21-step wedge, as well as the solid colors, are good areas to inves-
tigate the mix of the four channels and resulting inks. You might have
noticed that in addition to the five black generation options, there is also
a Custom option that calls up a curves dialog and lets you plot any curve
you want. This isn't really a necessary area to investigate since the key
to this tutorial is to get you to become comfortable with how GCR affects
the relationship with the four-color process. You may want to open the
original Printer_Test_File.tif in ColorMatch RGB and try making a sep-
aration using the UCR setting in the Custom CMYK menu. The Black
Generation pop-up menu will gray out so there is only one option
to try.
Another item to consider is the role of the Total Ink Limit and Black
Ink Limit . Black Ink Limit is often referred to as Black Start in some
profile-building applications. You can pick a single GCR setting, enter dif-
ferent values in Black Ink Limit, make some conversions as you did
earlier, and visually see the effect on an image. Use the 21-step wedge to
view how this setting affects black with respect to the other three inks.
Note that different profiles built with different Total Ink Limits most likely
will not appear different on screen; however, if you use the Eyedropper,
you should see different values and if you set the Eyedropper to Total
Ink, you will certainly see the values specified in the black square of the
21-step wedge.
Be sure to set your color settings back to U.S. Prepress Defaults
( North America Prepress 2 in Photoshop CS2) when you finish this
tutorial.
Tutorial #15: Preserve Color Numbers and CMYK Files
The Preserve Color Numbers option in the Proof Setup is especially
useful when you are provided documents in CMYK but do not have
access to the original RGB data. In such a situation, there is no original
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