Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!lll-winken!uunet!jtsv16!kevin
From: kevin@jtsv16.UUCP (kevin)
Newsgroups: comp.graphics
Subject: Re: How big are scanned bitmaps and how small can they be made?
Summary: Group 4 won't do it
Keywords: bitmap, compression
Message-ID: <456@jtsv16.UUCP>
Date: 29 Mar 89 14:46:08 GMT
References: <3003@looking.UUCP> <3349@entire.UUCP>
Reply-To: kevin@apricot.jts.com (kevin brighton)
Followup-To: comp.graphics
Organization: JTS Computer Systems Ltd., Toronto
Lines: 28

In article <3349@entire.UUCP> elt@entire.UUCP (Edward L. Taychert) writes:
>In article <3003@looking.UUCP>, brad@looking.UUCP (Brad Templeton) writes:
> 
>> How small does a typical 8.5 by 11 page of stuff get when scanned at
>> 300 by 300 and compressed?  I would guess 40K, but I would like to
>> find something that can take it down to 10K 
>
>It all depends on the source, but fax group 4 format should get you
>down in your target numbers.
>

Lets see, 8.5 * 300 = 2550 pixels per scan line, 11 * 300 = 3300 scanlines.
Thats 1,051,875 bytes for the image.  Taking this down to 10k bytes
is about 105:1 compression.  Group 4 is not going to do it for you.
Ok, maybe if your page is entirely blank.  

I have done some playing with Group 3 and 4 compression and typical
business documents get somewhere between 10:1 and 20:1 compression,
depending on the content.  You will have to try something else to
get the kind of compression you want.  I read some
time ago that fractal techniques can be used to yield amazing 
compression factors, but I don't know anything else about it.


-- 
Kevin Brighton                          kevin@jtsv16.jts.com    
JTS Computer Systems Ltd.       { suncan | geac | uunet }!jtsv16!kevin
Toronto, Ontario, CANADA                   +1 416 665 8910