Adobe PHOTOSHOP 5.0, User Manual, Page: 347 / 400

339 ADOBE PHOTOSHOP 5.0
User Guide
Keep in mind that trapping is intended to correct
the misalignment of solid tints in CMYK images.
In general, you should not create trap for
continuous-tone images such as photographs.
Excessive trapping may generate a keyline effect
(or even cross-hair lines) in the C, M, and Y plates.
These problems may not be visible in the
composite channel and might show up only when
you output to film.
Trapping values determine how far overlapping
colors are spread outward (not choked) to
compensate for misregistration on the press.
Adobe Photoshop uses standard rules for
trapping:
•
All colors spread under black.
•
Lighter colors spread under darker colors.
•
Yellow spreads under cyan, magenta, and black.
•
Pure cyan and pure magenta spread under each
other equally.
To create trap:
1
Save a version of the file in RGB mode, in case
you want to reconvert the image later. Then choose
Image > Mode > CMYK Color to convert the
image to CMYK mode.
2
Choose Image > Trap.
3
For Width, enter the trapping value provided
by your print shop. Then select a unit of
measurement, and click OK. Consult your print
shop to determine how much misregistration to
expect.
Using monotones, duotones,
tritones, and quadtones
Photoshop lets you create monotones, duotones,
tritones, and quadtones. Monotones are grayscale
images printed with a single, nonblack ink.
Duotones, tritones, and quadtones are grayscale
images printed with two, three, and four inks. In
these types of images, colored inks are used to
reproduce tinted grays rather than different colors.
This section uses the term duotone to refer to
duotones, monotones, tritones, and quadtones.
About duotones
Duotones are used to increase the tonal range of a
grayscale image. Although a grayscale repro-
duction can display up to 256 levels of gray, a
printing press can reproduce only about 50 levels
of gray per ink. This means that a grayscale image
printed with only black ink can look significantly
coarser than the same image printed with two,
three, or four inks, each individual ink repro-
ducing up to 50 levels of gray.
Sometimes duotones are printed using a black ink
and a gray ink—the black for shadows and the gray
for midtones and highlights. More frequently,
duotones are printed using a colored ink for the
highlight color. This technique produces an image
with a slight tint to it and significantly increases
the image’s dynamic range. Duotones are ideal for
two-color print jobs with a spot color (such as a
PANTONE ink) used for accent.