Adobe 13101332 - Photoshop - Mac User Manual page 124

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Adjusting the separation type and black generation
To make color separations, the three additive colors (red, green, and blue) are translated
into their subtractive counterparts (cyan, magenta, and yellow). In theory, equal parts of
cyan, magenta, and yellow combine to subtract all light reflected from the paper and
create black. Due to impurities present in all printing inks, however, a mix of these colors
instead yields a muddy brown. To compensate for this deficiency in the color separation
process, printers remove some cyan, magenta, and yellow in areas where the three colors
exist in equal amounts, and they add black ink.
A given color can be translated from RGB mode to CMYK mode in an endless number of
ways. But prepress operators typically use one of the following ways to generate black
in print:
In undercolor removal (UCR), black ink is used to replace cyan, magenta, and yellow ink
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in neutral areas only (that is, areas with equal amounts of cyan, magenta, and yellow).
This results in less ink and greater depth in shadows. Because it uses less ink, UCR is
used for newsprint and uncoated stock, which generally have greater dot gain than
coated stock.
In gray component replacement (GCR), black ink is used to replace portions of cyan,
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magenta, and yellow ink in colored areas as well as in neutral areas. GCR separations
tend to reproduce dark, saturated colors somewhat better than UCR separations do
and maintain gray balance better on press.
Choose the type of separation based on your paper stock and the requirements of your
print shop.
To adjust the separation type and black generation:
1 In the Custom CMYK dialog box, select a separation type.
The Separation Options area displays a graph based on current settings showing how
neutral colors in the image will separate. In the graph, sometimes called a gray ramp,
neutral colors have equal parts of cyan, magenta, and yellow. The horizontal axis repre-
sents the neutral color value, from 0% (white) to 100% (black). The vertical axis represents
the amount of each ink that will be generated for the given value. In most cases, the cyan
curve extends beyond the magenta and yellow curves, because a small extra amount of
cyan is required to produce a true neutral.
2 If you selected GCR as the separation type, choose an option for Black Generation:
None generates the color separation using no black plate.
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The Light and Heavy settings decrease and increase the effect of the Medium setting
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(the default). In most cases, Medium produces the best results.
Maximum maps the gray value directly to the black plate. This option is useful for
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images with a large amount of solid black against a light background, such as screen
shots from a computer.
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