Re: Do I want it?

[David Neeley <dbneeley -at- gmail -dot- com>]

Those doing full-color print advertising who use truly high-res images
commonly often use software that uses a low-res version of the image
to determine the various processing needed for the output, then when
the operater decides that things are correct, the program then
processes the actual high-res image.

You are correct that images "for publication" are often far less
detailed...and also that as a practical matter the original resolution
is retained in the image archive.

That said, if you have control over the input such as with a scanner,
there are choices to make and it is not always useful to try to do it
"as high res as possible". Inf act, the overwhelming majority of
scanners in use within offices list a much higher virtual resolution
than their physical resolution, using an interpolation routine to add
information between actual, measured pixels.

In that case, the maximum resolution I would suggest when scanning
would be at the highest *physical* resolution the device is capable
of; any interpolation that may be needed is much better done with
software later, so that the output resolution can be directly related
to the use of the image. Further modifying an image that was
interpolated to begin with can at times create problems that you can
bypass by doing any such operations with the best original image.

So again, doing image acquisition at "the highest resolution" is not
always the smartest way to proceed.

Fortunately, scanner standards have meant increased color depth
becoming the norm; 36-bit scanners are now commonplace where only a
few years ago the most common were 24-bit; the difference can be
pronounced in highlight and shadow detail, to give just one example.

Another point: the human eye interprets increased color depth in much
the same way it interprets physical resolution increasing. Thus, a
lower physical res but with a higher color depth can be just as
effective if not more so than the reverse.

I, too, have prepared many images "for publication"--but usually they
are for data sheets, catalogs, and the like but very rarely for large,
full-color printed images from anything produced for tech pubs.

Often, the images going into a catalog listing may be smaller than the
original; this means that the original resolution may translate to
higher res when reproduced at the smaller size. However, I still will
remain with my earlier statement as decent advice for offset printing:
going beyond double the output resolution is mostly wasted.  Although
a printer's lines per inch is not at all directly comparable to the
dpi readings for digital images, if you're going to be printing at 150
lpi, the detail inherent in a 300 dpi image with adequate color depth
should be quite adequate, and better than some other more arbitrary
resolution. This may also come into more relief to realize that many
offset books are done at 133 line screen; for these, I'd set the
original image resolution at 266 and generally have a faster and in
some cases more accurate job than making it 300...essentially because
of the RIP software that produces the plates from an imagesetter.
(FYI: RIP="raster image processor"...)

David

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