FW: [Premium-Rx] 8640 - Manual for Options 2 and 5

[mikea]

On Wed, Mar 19, 2003 at 04:14:35PM -0500, Carcia, Frank A.           HS wrote:
> Anybody have any suggestions for George?
> 
> -----Original Message-----
> From: George Georgevits [mailto:georgg at bigpond.net.au]
> Sent: Wednesday, March 19, 2003 4:08 PM
> To: Carcia, Frank A. HS
> Subject: RE: [Premium-Rx] 8640 - Manual for Options 2 and 5
> 
> 
> Frank,
> 
> No problem with looking for it - I will see what I can do. Thanks for the
> advice about file size. I am relatively new to scanning. This is the first
> time I have done something where the zipped file size has become an issue. I
> have found that using the .bmp format, the zipped file for each page becomes
> quite small ~25kB whereas for other formats it is much larger. Anyone have
> any ideas on this subject?

Well, the Compuserve .gif format is pretty well compressed as it comes
out of the encoder, and .jpg is pretty compressed, too. In a .bmp,
the native file is just the unencoded color values, with a header and
possibly a trailer, and so those runs get compressed out by zip.

Keep in mind that compression really just takes repetitions of some
bit pattern and represents them unambiguously in some shorter bit
pattern somehow. Since scans of B&W pages generally will be done in
256 or fewer colors, one can expect to see large runs of the same
color value, which will be compressed out in the image encoding method
(gif/jpg) or by zip (bmp).

On the other hand, if the zipped file is so small for the bmp, what's
the original filesize? And how does it compare with zipped and 
original filesizes for jpg and gif formats? Are the scan resolutions 
identical for all three formats?

-- 
Mike Andrews
mikea at mikea.ath.cx
Tired old sysadmin since 1964