Proofing Halftone Patterns
A client of mine recently decided
to go back to requesting bluelines instead of digital ink-jet
proofs for checking her work. She had scanned a map (previously
printed and therefore including a traditional halftone pattern),
descreened it, then finally sharpened the photo. The image
looked bad but acceptable on the color ink-jet proof and
horrible on the final, printed piece. The moire pattern
created by descreening, then sharpening, then rescreening
the map caused the problem, but it was far less offensive
in the ink-jet proof than in the printed piece. So in this
case the ink-jet did not function as an adequate proof.
Why? What could my client have done
to avoid this? First, understand that the ink-jet proof
does not display a traditional, offset printing halftone
pattern. An ink-jet proof is composed of tiny dots. This
"dithering" process differs from traditional halftoning
in the following way: Although tones are composed of patterns
of miniscule dots of color, side by side, to create the
appearance of all colors, the dots do not conform to an
equal-spaced grid and do not vary in size based on the amount
of color, in the manner of a traditional halftone.
So what? If you need to see a halftone
pattern (to catch possible moire patterns, which are the
result of one set of equally-spaced halftone dots conflicting
with another set of halftone dots), you need to see a blueline
as well as a color inkjet proof. Or, you can ask for a "velox"
or "white-print." This process, like the blueline
process, shows the traditional, printer's halftone screen
pattern. Of course, since a four-color image is just four
superimposed halftones set with their dot patterns at specific
angles to one another to minimize moire patterns, you might
ask for either a matchprint, a cromalin, or a Kodak Approval
when proofing a four-color project. The last option is one
of the few digital proofs that will actually show the dot
patterns (called rosettes in four-color work).
I also reassured my client that a blueline
should cost no more than a color ink-jet proof if the job
is not a direct-to-plate job. In both cases film must be
produced. However, whereas an author’s alteration to
a color ink-jet will cost very little (since no film has
been run yet), authors’ alterations after a blueline
or color laminate proof (matchprint, etc.) has been run
will be very expensive. In the former case, proofing and
correction are done prior to film output, but in the latter
case film is run to make the proof. Therefore, any corrections
require running all film a second time. This can be very
expensive in a multi-color job.
Folding
Unlike offset printing, folding--an
aspect of production under the general term finishing--is
one of the least precise of the machine processes in the
graphic arts. Each step is one of diminished accuracy. If
the first fold is slightly off, the second will be worse.
Inaccuracy cannot be remedied in the following folds. Industry
tolerance is 1/16" either way or 1/8" total. This
can wreak havoc with crossovers (especially if they involve
type crossing the gutter). This is useful to know while
you are designing your printed piece and before it goes
to press.
What can you do to avoid problems?
- Put crossovers on center
spreads of signatures to avoid the need for precise alignment.
- Keep type 3/8" from
the trim. In this way you can avoid type being cut through
or falling too close to the edge of the paper.
- In producing saddle-stitched
books, discuss "creep" with your printer. In
multi-page saddle-stitched publications, type in the centermost
pages of the nested signatures will be much closer to
the face trim than will type in the same position either
to the front or back of the book. This is called "creep"
or "shingling," and your printer can help you
adjust for it.
- Set up your files to allow
for slightly shorter interior panels when creating a barrel-fold
brochure. (Discuss specifics with your printer.)
- When possible, keep folds
"balanced" (with edges touching, not with one
shorter and one longer).
- Avoid designing a printed
piece with more than five folds.
- To ensure that all pages
lie flat, and to avoid cracks and wrinkles, make sure
the paper grain lies parallel to the binding edge or spine.
- When in doubt, discuss your folding
needs with your printer--early in the process.
[Steven Waxman is a printing consultant. He teaches corporations how to save money buying printing, brokers printing services, and teaches prepress techniques. Steven has been in the printing industry for thirty-three years working as a writer, editor, print buyer, photographer, graphic designer, art director, and production manager.]