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So to get this postage stamp printed in color, you would deliver to your
print shop four pieces of film or paper that look like Figure 27.5, right?
Wrong! As part of the process of making the metal plates that go
onto the press, the operators at your print shop dont want positive
images, they want negative ones, like the ones shown in Figure 27.6. They
want film negatives, so that is what youll be asked for when you
send the print files to your service bureau.
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| NOTE If you
are creating camera-ready artwork for small print jobs,
t-shirts, or other projects where laser-printed art is acceptable,
then you would send positive images.
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| NOTE DRAW offers
an option to create negative output (Invert) on the Prepress page
of its Print dialog, but most service bureaus would rather do it themselves.
So check with your service bureau first. Chances are that you will
be asked not to check the negative option, but instead give them a
positive print file.
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Unless you have a lot of experience studying film negatives, they are
difficult to use as proofs because they are quite different from the image
that you see on screen. Thats why its crucial to make proofs
and trial separations on your laser printer. Dont worry if you dont
own a color printer and cant proof in color. In some ways, its
better to proof in black and white, because thats how the film will
be made. At the proof stage, your job is to make sure there are no copy
errors (obviously) and that all the colors that you intend to use are
correctly represented on the separated printouts. Print Preview can do
this for you, as well.
FIGURE
27.6 Now were getting somewhere. These
negative images are just what your print shop wants as it prepares your
work for press.
Trap Your Colors Before
They Trap You
In the previous section, we discussed the importance of proofing your
color work before sending it off to your print shop. But one thing your
proofs wont show you is whether you need to apply trapping
to your work. This word typically strikes fear in the hearts of experienced,
well-intentioned designerswere even afraid of writing about
it. Color trapping defies a simple definition, so bear with us here.
Print shops do their best to make sure that a sheet of paper running
through a high-speed press will come out with all the layers of colored
ink placed in exactly the right places. The degree of accuracy in this
process is called registration, and one of the options when you
print in DRAW is to enable registration markslittle bulls-eyes
that print on every piece of film for a given project. Despite their best
efforts, print shops cant align the paper perfectly on the press
every time. Truth is, registration errors are common in color-printed
work, but the degree to which they harm your finished work depends upon
the nature of your drawing and the extent to which you can prepare for
these errors. This section is a qualitative introduction to color trappingwhy
you need it, how you can apply it, and in some cases, how you can best
avoid it.
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| NOTE Color trapping
is not required when printing to a desktop color printer, slide processor,
or other single-pass output device. Trapping is only required for
printing on a traditional printing press, where the various colors
will be applied to the paper in separate passes.
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Where Colors
Touch
Figure 27.7, also available on the Web site, is a rendition of a cube
along with a list of the colors used. If you were to print it in color,
the cube would require three distinct pieces of film and three individual
passes on the press (there is no black in this cube).
Understanding registration and trapping issues begins with an analysis
of the areas in a drawing where colors meet, because that is where registration
errors can hurt you. For instance, the top face of the cube is made up
of 20% magenta, and the left face is 100% yellow. Lets assume that
there is a registration error when printing the yellowit is not
lined up exactly where it is supposed to be. If this error causes the
yellow to be placed too high (and in terms of registration errors, were
talking about errors of less than 1 point), then the yellow will bang
into the magenta. By all accounts, this is a friendly error.
A tiny bit of yellow overlapping the magenta will probably be unnoticeable.
Even if you could see it, you wouldnt react negatively to it because
your eye is expecting to see both yellow and magenta in that vicinity.
There would be about a quarter-point of space where the magenta is a bit
redder than it should be, and thats okay.
But what if the registration error is such that the yellow is placed
too low, so that it doesnt actually reach the magenta? Again, were
talking about less than a quarter-point, but now instead of an overlap
of colors, there would be a small area without any color. Youd see
a streak of white (or whatever color the paper is) which, though tiny,
would be both noticeable and objectionable.
FIGURE
27.7 Can you find the places on this cube where
color trapping is required?
There is no way for you to know whether a registration error will be
a friendly one or not, so you have to trap against all possibilities.
(Hence the term trapping, and this is about as close as we can
get to definitionnobody seems completely sure where the term came
from.)
Trapping will also be needed for the big A that is inside the
yellow face. Here there is no possibility of a friendly registration error
because any error will result in a white streak somewhere. This becomes
clearer if you stop and think about how this cube is actually printed.
Figure 27.8 offers a depiction of the process. Notice how the yellow face
has a large A cut out of it, right where the magenta A is
to go. This is called a knockout, and it is necessary in process-color
printing. If the A werent knocked out of the yellow, then
the two ink colors would overlap to form red (remember, process-color
inks are transparent). The knocked-out area where the A is to fit
must not have any ink color at all, except for the magenta, the intended
color.
FIGURE
27.8 The outline of the A is knocked out
of the yellow face to accommodate the magenta A.
In Figure 27.8 we have tried to make it look like a jigsaw puzzle, which
seems a pretty good way to think of this knockout dynamic. You can see
why its so important for the registration to be accurate; the magenta
A needs to fit precisely into the hole in the yellow face. But again,
you cant always count on perfect accuracy, so you must take matters
into your own hands.
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