Creating Color Traps; Printing Duotones - Adobe PHOTOSHOP 6.0 Manual

CHAPTER 14
384
Printing (Photoshop)

Creating color traps

After you have converted an image to CMYK,
you can adjust the color trap. Trap is the overlap
needed to ensure that a slight misalignment or
movement of the plates while printing does not
affect the final appearance of the print job. If any
distinctly different colors in your image touch,
you may need to overprint them slightly to prevent
tiny gaps from appearing when the image is
printed. This technique is known as trapping.
In most cases, your print shop will determine if
trapping is needed and tell you what values to
enter in the Trap dialog box.
Misregistration with no trap, and misregistration with trap.
Keep in mind that trapping is intended to correct
the misalignment of solid tints in CMYK images.
In general, don't create traps 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.
A B
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.

Printing duotones

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.