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Illustrations to be printed; was: Re: Viso/Office guru?
Subject:Illustrations to be printed; was: Re: Viso/Office guru? From:David Neeley <dbneeley -at- gmail -dot- com> To:techwr-l -at- lists -dot- techwr-l -dot- com Date:Mon, 7 Sep 2009 09:25:33 +0300
<Subject: Re: Visio/Office guru?
<If there is any intent to deliver printed documents, no resolution
under 600 dpi should be used. <For offset-printed books, 1200 dpi
minimum.
<Gene Kim-Eng
With all due respect to Gene, that is not my experience. (I suppose I
should add that over the years I have been a consultant for both
offset printers and companies using them, dealing with this sort of
issue. I also helped convert the entire production workchain at the El
Segundo Xerox facility's graphics production department when they
first were going to a digital workflow--feeding various kinds of
computers to an Agfa SelectSet digital typesetter. That involved, at
the time, Xerox proprietary workstations, Sun Sparcstations, and both
PC and Mac clients. Of course, all that is rather ancient history
these days!)
That said, please do keep in mind that I have been out of this game
for several years now. The march of technology may have made at least
some of the following partly or, perhaps, wholly outmoded. I do stand
to be corrected by those currently in the offset printing business or
who may have followed the current practice.
There are laser printers which print in high resolution mode at 1200
dpi, and raster graphics should at least match the resolution of the
printer for best quality. A high resolution laser printer has a
built-in RIP that is much less sophisticated than those of a large
commercial typesetter. If it is fed a graphic which is smaller in
resolution than its output image, it repeats lines to multiply the
apparent size of the image--but obviously without being able to add
information that is not in the original. Close examination of fine
diagonal lines, for example, will begin to show this. By matching its
output resolution with the image resolution, though, the RIP is
perfectly happy simply to lay the image into memory without
alteration.
(For reference, a "RIP" is a "raster image processor" that composes
the digital image for the output device or for screened original
printing plates, obviously including any raster images such as .png,
.tif, or .jpg files included.)
More commonly, though, laser printer output is 600 dpi in fact. Most
which claim 1200 dpi resolution are often automatically interpolating
for an "effective" 1200 dpi. They may not be able to use the detail of
a 1200 dpi original, so 600 is probably as good as you're going to get
anyway...while you save 3/4 of the file size compared to 1200 dpi.
For offset printing, the situation is a bit different. There is a
range of screen resolutions used, ranging from 100 or slightly less
for some web presses (mainly used for newspapers and things like
supermarket flyers, so not applicable here) through a minimum of 120
to 150 lines per inch for standard non-coated stock up through and
including resolutions as high as 300 lpi (mostly for very high quality
color, such as the lavish "coffee table" display volumes.
(As an aside, to the human eye, color depth substitutes readily for
resolution--which is why a full-color piece does not have to be as
high resolution as an equivalent black and white image for visual
similarity).
It also depends upon the RIP being used to process the file, to some extent.
However, if you know the printing resolution to be used for your book,
graphics should ideally be an even multiple of the output screen
resolution--usually at least twice the output. (While "dots per inch"
in computer terms is not precisely equivalent to "lines per inch" in
screen resolution, for practical purposes you can consider them to be
the same).
If, say, your output resolution for the screen will be 150 lines per
inch (a not uncommon resolution for a black and white technical book),
making your raster graphics at 300 dpi will give perfectly acceptable
results, while not consuming too much RIP time and resources. Giving
it a larger original image than that can only help marginally, if at
all.
Where it gets more problematical is where the graphic resolution is
not an even multiple, causing the RIP to have to do some more involved
calculation and interpolation that is not always the best
solution--plus it takes much more time to run. Sometimes, if the file
involved is too large, such an image may "choke" the RIP, which may
run out of memory resources for the calculation. Fortunately, today,
that is increasingly rare--but is not unknown.
So, for optimal results that will make your offset printer happy as
well, find out what their intended screen resolution will be and make
your raster graphics a multiple of that. (It does not necessarily have
to be a whole number multiple--2.5, for example, would work well also,
but 3 would be better).
A twelve hundred dpi raster graphics setting merely inflates the size
of the file without giving much, if any, advantage in the finished
product.
You might be well advised for such documents to be offset to consult
with the prepress operator you will be using--either at the printing
company or a specialized prepress house. They can often be extremely
helpful in determining with you what the settings should be for the
best results.
Obviously, computer screen resolutions are still a more difficult
proposition with raster images...but that is another story.
So endeth this lesson in increasingly antiquated and arcane subjects
such as "printed" manuals!
David
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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