Greetings!
This is the second
installment of Paper to Pixel to Paper Again, a series that explains
(in an overly thorough manner) the how-to's of preparing line art
(and later in the series, color art!) for print.
Last
week we started this series by throwing out some caveats, stating
some goals, and peeping at my work space and equipment. This week
we'll be laying down the basic knowledge you need on order to know
the behind
some of the things we'll be discussing and doing.
f you're impatient to actually, you know, get to it, then sit on your
hands for a week and skip this installment!
The past one and a half centuries have
seen tremendous changes in the ways images are created, and the ways
those same images are reproduced. Since the late 1800s, almost all
technical innovation in printing has involved improving the
reproduction of what are (misleadingly) called
continuous tone
images: that is, images that,
when viewed in the right circumstances, appear to have smooth
gradations of tone and value. If you're viewing a postcard with a
reproduced photograph, or looking at a color diagram in a text book,
in most viewing distances, these images appear to be smoothly
changing values of color. But in reality these images are made up of
tiny cells, distributed in an array, that through some miraculous
flaw in human vision, work together to create those gradated
illusions.
Above: a scanned detail of a Dave Sim commission. Below — an extreme closeup of the resulting print. Notice the array of dots that create the image.
But
there are limits to this illusion. Certain people (myself included)
have close vision that's significantly sharper than the mean, and are
able to see individual printing dots when they're anything other than the finest pitches. More significantly, the sharpness of human vision increases
with a corresponding increase in contrast, meaning that extremely
high contrast images (say, black on white) represent much sharper
visual acuity than a field of color. Additionally, we see another
corresponding increase when we're presented with edges. Lastly, fine
information that is near or beyond the fine-ness of the screen
itself, or oriented in direction in a way that is not perfectly
aligned with the screen, can cause all kinds of unintentional visual
oddities.
This
is why you will never see a professional publication that has a large
chunk of text that is screened and intended to be read. And this is
why you should NEVER, NEVER SCREEN LINE ART.
I'm
going to belabor this point (who, me?) because it seems to have been
forgotten or ignored as screening methods have improved, or as
expertise (and money!) have drained from the print fields. Unless
you're reproducing in color and intending to show the artist's
process as the intent of the print (a la IDW's Artist Series, the
Cerebus Archive portfolio
series, etc), LINE ART SHOULD NOT BE SCREENED FOR REPRODUCTION.
Above: scans of page 225 of the aborted February 2013 printing of High Society, which, as you can see, was half-toned, as it was supplied to the printer as 8-bit grayscale files. Below is an image from the restored files, produced from the exact same scans as the above images, but treated much differently in the prepress stage. Notice that the dots in the Cerebus image above are strange, gradually changing shapes, moire that is a result of the original halftone screen that makes up his fur passing through a second screening process at the printer.
Imagine,
if you will, the simplest of print methods, something along the lines
of a stamp. A chunk of potato in which you've carved out an object in
relief, maybe your name, carving back the potato from the sections of
the images that you wish to remain uninked, and then pressing it
against a flat surface slightly moist with ink, and then finally
transferring that ink with light pressure onto another surface.
Your
resulting print, any unevenness in the ink aside, is a binary. Either
a particular area of the paper is inked, or it is not. On, or off, no
in-between. And, really, how would you represent in between? You
examine your print some more, consider that you really would like to
have a “gray” area of, say, 30 percent to augment your totally
black and totally white portions of your image. So you cut some
parallel hatching lines into a previously fully inked area of your
potato, and you print again.
This
is line art in microcosm, line art at the beginning, just beyond
scraping lines in the sand with a stick, just beyond taking an old
torch and dipping it in bison blood and dragging it along the surface
of your cave. Primal, black marks on white, any “gray” an
illusion created by finer marks of black on white.
—
Okay,
let's skip ahead at least a millennium, where we arrive at the
present day.
No
longer satisfied with the speed of your potato print, you're now
interested in taking your paper line drawings and reproduce them with
all the bells of modern technology. A terrifyingly fast, abominably
loud web press, running off a thousand copies of your masterpiece in
an hour. Between you and that copy are a good dozen technicians and a
veritable space-shuttle level of switches and knobs and little blinky
lights. How do you ensure your drawing survives the process? How can
you signal to these strange, unknowably distant beings what it is you
want out of your print?
(And
please don't tell me that your desktop laser printer, or the, ahem,
helpful staff at your local copy center, are any more knowable or
accessible :) )
You
need to know how to prepare your files. You need to know what to ask
for. And you need to know about resolution.
RESOLUTION
In
order to actually, you know, get to the part of this series where we
actually DO something, I'm going to need you to take for granted a
few facts. Rest assured I'll come back to them in future
installments, and rest assured, I'll be happy to argue with you about
them in the comments.
When
you're preparing color or grayscale images for print, that is, images
intended to be reproduced as (not actually) continuous-tone images,
the limit of your effective resolution is the screen that these
images will pass through. The
fineness of a screen is measured in LPI — lines per inch. A printer
printing on an extremely coarse surface — a cardboard box,
newsprint, some kind of screenprinting application etc — will use a
really coarse screen, sometimes as coarse as 40 LPI. Printing on a
sheetfed offset press on coated paper, or on a very good one-off
digital press on coated paper, the LPI might be as high as 300 LPI.
A
good rule of thumb for supplying files that WILL be half-toned is,
the maximum effective resolution is twice the line screen resolution.
So, if your printer will be screening your final image at 200 LPI,
400 pixels per inch is the highest effective resolution you can
supply. Anything above that is pointless, as it's lost in the screen. (This is not the case if you're suppling some elements separately, a in a PDF, where you can have images with different resolutions and color spaces coexisting in the same document. More on this later!)
Conversely, when you're printing WITHOUT a screen — whether that's in black, or using a spot color — your only resolution limit is your vision, and the resolution of the output device, whether that's a laser printer or a plate setter at the printer.
Without
further ado, here are the resolutions you should be aiming for for
suppling files to your printer —
Color
or Grayscale--
as
low as 100 PPI in some extreme circumstances, as
high as 600 PPI on coated stock with good printing should
be dependent on the destination LPI. Remember, it's easier to
downscale than upscale! I always scan any color art that's going to
leave me permanently (go to a client, etc) at-size at 600 ppi, as a
safety.
Line
art/bitmap--
1200
ppi for laser printers and other digital printers (600 PPI might be
acceptable on rough paper if there are no very fine lines or
repeating tones present)
1200
or 2400 for web or sheetfed offset with fine lines and tones.
But,
fortunately, since we're dealing with line art, just because you're SUPPLYING line art files at that
resolution, doesn't mean you need to
scan at that resolution!
… and
that's all we have time for next week. Next week — we finally (for
real!) get to it!Thoughts?
Questions? Quibbles? Hit me up in the comments!
Sean Michael Robinson is a writer, artist, and musician. See more at LivingtheLine.com.
