15 Aug
2006
15 Aug
'06
2:50 p.m.
Bob wrote:
Don previously stated:
Right. *But*, if you take something that was *created* for a large
format (e.g., D size) and *print* it at a much smaller format
(e.g., B size), then the printing software scales the image down
before sending it to the printer (and, ultimately, the marking
engine therein). Lines/features get *finer* (of necessity).
For example, one of the signals on the drawing I was just now
examining is "AddressTerminalCount". 20 characters. It occupies
1 inch (width) on the *original* drawing. Reproduced on B-size
media, that's 0.5".
Even if you assume a really crappy typeface design (e.g., 5x7),
that's 120 "print elements" wide (i.e., 20 * (5+1)). Of course,
the actual typeface is much nicer/finer than that but I don't
have the time to figure out what exactly how fine-grained it is.
:>
So, you have to resolve 120 dots in 0.5". That's already
pushing the limits of a 300dpi scan if you don't want to
end up with just a hieroglyphic blur! :>
So, scan at 400dpi or better (in this example) and/or
expect the text to look AS IF it was rendered as a 5x7
typeface would have been. :-(
The size of the *original* document is important
as it has been
scaled down to print on a page 1/4 it's original size. I.e.
you start to approach the resolution of the marking engine
(e.g., 1 pixel wide lines) which, mathematically, looks like
a very high frequency component.
From a grayscale point of view a single pixel can have weight or intensity and can
represent a thin or thick line.
Just because my printer thinks it can print 2400dpi does not change the fact a 150 dpi
image is quite
acceptable built from those little dots using the printers built in dithering. My question is are we trying to make high grade
reproductions of artwork
or trying to preserve the information in the format of a small
readable scans ?
In my case, I want to be able to unambiguously resolve the original
document's content AFTER scanning. Without having to scratch my
head and wonder: "Is that an 'O' or a '0'?"
I'd rather scan at 800dpi, e.g., and rely on a compression technology
to make that "affordable" than have to live with a "cheaper"
scan and some potential ambiguity (which I will undoubtedly
only discover MUCH LATER -- after the originals have been
discarded!)
As for enlargement or in the origional case
reductions, they are best done at scan time by changing the DPI
setting on the scan and not attempting it in software later.