der Mouse wrote:
>>> I think TIFF is a mistake; I'd use JPEG, at about 5K to 10K per
>>> square inch for color, or about 1/3 that for monochrome.
>> Umm, ten thousand dpi!?
>
> Ten thousand pixels per *square* inch is only 100 per *linear* inch.
I read that as "ten thousand BYTES" per sq
in. :>
Color/gray scale depth will have the most effect on compression and the resulting loss.
There is a huge storage differance between the compressibility of a 1bpp image and an
eight bit grayscale
of the same image. at 1bbp that is only 1250 bytes or at 4bpp that is 10,000 nibbles or 5k
bytes :-)
I find scanning at 150dpi 8 bit makes a nice general scan, a modest boost in contrast aids
greatily in improving
compression while at the same time darkening fine lines. Fine artwork sometimes require
300 or 600 dpi
depending on how it was printed and how much magnification I require.
Don previously stated:
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 ?
To keep this all in perspective, my 21.5" Viewsonic is a 100 lpi or
1600x1400x24bits.
Items scaned at 100 dpi can displayed on screen at 1"=1".
I like to use 150dpi as giving me a 50% enlargement when viewing actual pixels and 150dpi
translates 1x1 to
printing 150 Lins per inch on a 600 dpi laser printer. That makes works out to be 4
printed toner points per
scaned pixel which makes a nice visually acceptable reproduction.
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.
That about 3 cents worth, YMMV :-)
Bob Bradlee