[Ham-Computers] FW: Re How Do You Scan?

Tue May 3 17:38:04 EDT 2005

There are actually two different issues here that need to be handled
separately - how to scan the document (what settings to use), and, how
should it be saved (file format and compression).  For most scanning tasks,
one simple question can address both issues:

  "What is the final destination/purpose for this scan?" 

For example, is it going to be printed?  E-mail?  Archive? 

How to scan: 
------------ 

If the final destination is "print", then you should *always* scan at 300dpi
or higher...depends on content and especially if enlarging.  I've seen many
instructions that state 150dpi is fine for color photos, but every 150dpi
print I've seen looks like crap.

If the final destination is for archival purposes (e.g. preserving
documents), then scan at 300dpi or higher.  Some suggest at least 600dpi or
even 1200dpi and saving in TIF format (more on TIF below).

If the final destination is for viewing on a monitor (such as e-mail or a
screensaver/background image), then 72dpi or 96dpi will be just fine.  The
reason is that monitors are 72 or 96dpi devices.  Once you've scanned it,
re-size it to fit the screen -  800x600 is good for e-mails.  Prints at this
dpi will generally look like crap (unless you print them "thumbnail" sized)

One last thing...don't scan any higher than the true "optical" resolution of
your scanner.  Most scanners these days are 600 or 1200dpi optical, but are
marketed as 4800 or 9600dpi scanners - the scanner just "interpolates" (aka
"adds") the extra pixels.  Besides, most people will never need to scan past
600dpi.

How to save: 
------------ 

For typical use, JPG's at 4:1 compression is a good compromise between
filesize and quality.  4:1 is typically the "fine" mode on most digital
cameras and roughly equates to a "12" or "maximum quality" in Photoshop's
JPG save dialog.  This should also be equivalent to about 95% - 100%
"quality" or "minimum compression" in other graphics programs.  For example,
a 17MB "RAW" file reduced to a 2.5MB JPG using the "12" setting in
Photoshop.  The resulting print quality is virtually indistinguishable
except by enlarging or those with good eyes.  If the quality isn't that
critical (such as for e-mails), you can go down to 75% quality ("basic" mode
on many cameras) with good results and lower file sizes.  With very high dpi
scans (600+), you can even go down to 50% and not see much loss of detail as
you've increased the number of actual pixels scanned.

For critical or archival purposes, TIF is the universally accepted format.
If you use Photoshop, PSD is also good.  The resulting file is large as it's
uncompressed, but you won't lose any detail unlike "lossy" compression
formats like JPG.  Yes, there is LZW compression available in TIF, but it's
not quite standard and some programs won't recognize an LZW compressed TIF.

Remember that these file formats are "graphics" files and not editable
documents.  If you wish to scan a document and make it editable, you'll need
an Optical Character Recognition program like OmniPage Pro that takes the
content on the page and converts it back to an editable format (like
Microsoft Word).  Basic OCR programs only work with printed text...sorry,
won't work with handwriting.

So, Duane, if you're scanning "to print", try scanning at 300dpi and saving
as a 90% "quality" JPG (minimal compression).  If it's for e-mail, scan at
72 or 96 dpi and save as a 75% JPG.  Don't forget to re-size to 800x600 for
e-mail!

73, 

  - Aaron Hsu, NN6O (ex-KD6DAE) 
    {nn6o}@arrl.net 
    {athsu}@nbcuni.com 
    No-QRO Int'l #1,000,006 
    . -..- - .-. .-   ".... . .- ...- -.--" 

-----Original Message----- 
From: ham-computers-bounces at mailman.qth.net
[mailto:ham-computers-bounces at mailman.qth.net] On Behalf Of Duane B.
Fischer, W8DBF

Sent: Tuesday, May 03, 2005 11:40 AM 
To: ham-computers at mailman.qth.net 
Subject: [Ham-Computers] Re How Do You Scan? 

Hello All,                      

I have been told several different ways of scanning a document that contains

color photos that form the top and bottom borders with text between them.

There are three headings, in various fonts and in different colors.     

I am scanning it at the default resolution of 150 PI, in color, to an image
file. This results in a .bmp file. I then save it as a .jpg with 10%

compression.            

The results vary, none are acceptable. (from missing colr to missing text to
being off center to having the bottom edge missing.)  What is the 'correct'

method to scan a document such as I have described above?       

Thank you.      

Duane Fischer, W8DBF    
dfischer at usol.com   