Bob wrote:
Using your 120 ppi 1" example at "D"
size scanned at 800 dpi
No. There are (at least) 120 dots of information (assuming
you could magically transform the actual typeface to a 5x7
rendition -- which seems to be the crudest representation
that people can readily recognize) in that 1" of the D size
original (which *I* don't have).
That was printed at B-size. So, those 120 dots of information
are now represented in a 0.5" physical span. Scanning this
"240 dpi" data (again, *assuming* you could magically transform
the original font to that crude of a representation) at 300dpi
is a bit "if-fy".
I am saying I would prefer to scan the *B* size drawing
(which is what I *have* -- I also don't have a scanner
that will handle anything larger than B size :> )
at 800dpi. This would correspond to scanning the
original D-size drawing (if it was available in that form)
at *400* dpi -- which I consider a reasonable resolution
for preserving content.
scaled dow to "B" size at .5 inch gives you
a effictive print size of 1600 dpi.
I don't see where you came up with 1600dpi. You *lose*
effective resolution, not gain it! (i.e. the image has
been reduced prior to scanning)
Scanning at 300dpi will give you a print resolution at
50% reduction of 600dpi
which is the pratical limit of my laser printer.
I'm advocating images scanned at ~400dpi IN THEIR ORIGINAL FORM.
I.e. I would need to print 8 (?) A-size sheets at 400dpi and paste
them together to get the original D-size drawing -- reproduced
at 400dpi.
The D-size original (with 120 "dots of information" per inch)
was originally *printed* in a form that represented those
120 dots in half that space (B-size) -- which is recognizable
(hmmm... do the Brits write "recognisable"?) on a *good*
300dpi printer (but quickly turns to crap when those sheets
are later photocopied).
I am not interested in *printing* D-size drawings. :>
Rather, I want to reproduce their content in fine enough
detail that I can *view* it on a screen and not see big black
"ink blots" (Hmmm... why do they all look like *bacon*? ;-)
where there should be *text*.
With that said, I have been known to scan some small
things at 1200 dpi and then print at 150 lpi and end up with
a 8x magnification while still retaining the 1x1 scan to print pixel relationship.
Are you starting with "D" or "B" and what is your destination size ?
I typically create drawings as D-size. I.e., I set whatever
CAD/EDA tool I am using for a "canvas" of that size. It's
just too hard to draw anything "substantial" on B size
originals (though C is sometimes acceptable).
From these, I usually "print" B-size versions as working copies
(because it is much cheaper to print B size than D size :> and,
because D-size drawings take up a metric crapload of benchspace!).
So, those "120 dots of information" per inch, get reproduced
on a 300 - 600 dpi printer. That's usually reasonably legible.
I usually end up keeping a set of *pristine* B-size drawings in my
files (originals go to client, etc.). I.e., I don't keep
photocopies (which are much crappier quality).
I would like to be able to scan *these* and have "nice" digital
copies of them. (I haven't always remembered to keep copies
of the drawings in their original "digital" form; nor do I
often have access to the *tools* with which I created those
files -- even if I did manage to save copies of the files!)
I can always tell the software that this is a D-size drawing
*after* it has been scanned (by tweaking the document dimensions
and letting the resolution adjust inversely).
If you are attempting to recover "D size"
information from a previous
"B size reduction" then the scan resoultion should be set to 1.5
(2 times max) the desired final print resolution for best results.
Note: you will never get past the loss of detail caused by the
origional reduction from D to B size.
Correct. The issue is not losing *more*. I.e. you can read
this text and realize it is reproduced at a greater "definition"
(trying to avoid the word "resolution", here) than a simple
5x7 typeface.
I have a D size plotter that has a native resolution
of 600 dpi and a 600 dpi laser printer.
When printing the same D size 1x1 drawing to both, the laser printer will reduce the
image to the point where I
have an equilivant image as if I had made a a 75 dpi scan of the full size 600lpi D size
plot printed 1x1.
If I am going to scan the smaller laser image to try to get back to a printable
"D" size image than 800 dpi sounds
about right to me.
I understand your desire to retain detail , but remind you the upper limit to usefull
resolution is about 1.5x the
destination print or display resolution, and it is hard to beat 1x1 for efficancy.