Scanning formats

Bob caveguy at sbcglobal.net
Tue Aug 15 17:36:11 CDT 2006


Using your 120 ppi 1" example at "D" size scanned at 800 dpi
scaled dow to "B" size at .5 inch gives you a effictive print size of 1600 dpi.
Scanning at 300dpi will give you a print resolution at 50% reduction of 600dpi which is the pratical limit of my 
laser printer.

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 ?

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.

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.

later
Bob






On Tue, 15 Aug 2006 14:50:54 -0700, Don wrote:

>Bob wrote:
>> 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. 

>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.  :-(

>> 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. 






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