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Subject:RE: tifs at 240 dpi worth redoing? From:David Neeley <dbneeley -at- gmail -dot- com> To:techwr-l -at- lists -dot- techwr-l -dot- com Date:Wed, 11 Nov 2009 10:25:51 +0200
Perhaps I can clear a few points up a bit.
First, Richard, your memory is faulty--120 lpi is *not* high res
offset printing. It is just a little better than most newspapers.
Novels and other text-containing books are often printed at 150 lpi,
partly because of the paper they use which may be difficult to get any
real detail from higher resolution.
When printing on plastic or other coated stock, very fine books
(including "presentation" or "coffee table" books) may be printed at
300 lpi or higher. The paper's coating allows the ink to sit on the
surface and dry without running or smudging--uncoated stock will
"feather" as the still wet ink runs a little along the paper fiber,
blurring the image.
Actually, best practice might be to produce two different .pdf files
of materials containing criticai, high-detail photographs--one with
images at about 100 dpi for viewing onscreen, one with images at 300
or 600 dpi for printing on modern laser or high-resolution inkjet
printers.
Do remember, though, that visually speaking image resolution is more
than simply how many elements per unit are there. The human eye also
finds color depth to be part of its resolution sense...so a color
image with lots of color depth will look higher res than any black and
white image of comparable spatial resolution.
Another factor which few take into account in critical photographic
work is the kind of color involved. Color on a paper substrate is
different than color on a screen. Thus, the color of paper itself is a
factor, as is the intensity of the color used for each situation.
These days, people are so often used to over-saturated color, though,
that they often lack an appreciation for visual subtlety of tone and
gradation thereof.
In offset printing, as in photography in general, the real
difficulties lie in having sufficient highlight and shadow detail.
Remember the bit about color depth--in the offset world, printing with
more base colors gives a richer tonal vocabulary, which in turn can
increase the image quality in many but often very subtle ways. Rather
than the typical "four color offset"--very critical pieces may be
printed with more colored ink--and often with such things as
ultra-violet coatings for special effects. One such system, for
instance, is hexachrome--which, as you would suspect, uses six primary
colors.
This is not the forum to get into other factors--such as the changing
paper dimensions depending upon the moisture of the paper--so running
the paper through a press multiple times to add additional colors can
be highly complicated, especially on very high-resolution jobs. The
small change of moisture, even from the ink itself, can cause
miniscule but crucial registration problems. (Where and for how long
paper is stored prior to use also enters into the calculation...)
The printing world is a fascinating one, but experience with it seems
to be a somewhat dying art...especially among tech writers. It's
mostly fossils like myself who have been down that road often enough
to have worn out the tee-shirt long ago...
> If you're thinking of halftone screens, that's lines per inch (lpi), a
> different animal. IIRC, 120 lpi is pretty high resolution printing.
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