24 Apr
2015
24 Apr
'15
8:13 a.m.
On 4/24/2015 10:03 AM, Johnny Billquist
wrote:
On 2015-04-24 17:00, js at cimmeri.com
wrote:
Again, TRY it. Unless you need to
magnify things 10-20x the original,
100-200 is more than sufficient *in
practice* for most purposes.
Despite the differences in opinion on
*perceived* DPI, the actual thrust of my
argument here is that it's far more
important to preserve the _grayscale_
quality of a document -- especially for
those that have photos pictures,
diagrams -- than any excessive DPI.
- J.
On 4/24/2015 9:46 AM, Paul Koning wrote:
Why don't you actually try it.
Also, I'm assuming reading on a screen
(where I read most of my vintage
manuals) vs. re-printing. My screen
resolution is 90dpi. Anything over
that is pure waste. Maybe you have
better eyes than I do, but I can't
discern image quality over 100-200dpi
for printing.
That seems like a weak argument. While
looking at documents on a screen, I
often magnify them to see details. So
a higher resolution of the source
material than what the screen offers
is very meaningful.
Johnny On Apr
24, 2015, at 10:40 AM,
js at cimmeri.com wrote:
On 4/24/2015 8:48 AM, Noel Chiappa
wrote:
> > From: shadoooo
>
> > I'm scanning at 600dpi
> grayscale, lossless compression.
>
> I've been scanning a few things
> too, and I found that 600dpi
> grayscale
> produced absolutely enormous files
> (many, many MB's per page, for
> prints), no
> matter what I tried to do,
> compression-wise.
>
> 600dpi black and white, followed
> by saving as TIFF's with CCITT
> Group 4
> compression, produced immensely
> smaller files (small 100's of KB's
> for the
> same pages), and they are quite
> readable (even the fine letter seems
> to be
> readable - b/6 is quite
> distinguishable, etc).
While smaller, I've always found 1
bit b/w scans to be nightmarish to
read (too much font detail is
sometimes lost), and forget about
grayscale pictures and diagrams
coming across intact. Grayscale is
best. The problem comes in
overdoing the DPI. Even 90 dpi is
good
enough. 150, more that
sufficient. 300 or 600, total
waste, but
they are (obviously) the most
accurate renderings.
I would not call 90 dpi ?good
enough?. The professional printing
rule
of thumb is that for an n grayscale
dots per inch halftone image you
need 2n DPI resolution. So 90 dpi
is, at best, low grade newspaper
resolution. A standard commercial
grade scan for good quality
printing is 260 dpi or so ? which
means 300 is certainly a fine
choice. 150 or below may well be
acceptable if that?s the best you
can get, but you?re definitely
compromising image quality if you do
that.