compression algorithm please...

compression algorithm please...

Post by Irene Y » Tue, 18 Apr 1995 04:00:00



A few friends and I are working on this electronic design project, and I
am hoping that somebody can lend me a hand.

We are trying to simulate a fax transmitter/receiver by:

1. scanning in an image via a video camera
2. encode the image using some algorithm
3. transmit the data serially (maybe via modem) to somewhere else
4. decode the image
5. display the image on some output device

and I am not sure what kind of encoding/decoding algorithm is available
and what I should be considering. I think fax machines use a Huffman
encoding? Also, I've heard about a CCITT encoding scheme for graphics.

I am wondering if anybody know where to find sources detailing these
algorithms and/or if anybody could recommend some other algorithm.
The image is most likely black and white (maybe grayscale)...

Thanks in advance!

Jack Fu
MIT '96

 
 
 

compression algorithm please...

Post by Menno Victor van der Sta » Fri, 21 Apr 1995 04:00:00



> A few friends and I are working on this electronic design project, and I
> am hoping that somebody can lend me a hand.

> We are trying to simulate a fax transmitter/receiver by:

> 1. scanning in an image via a video camera
> 2. encode the image using some algorithm
> 3. transmit the data serially (maybe via modem) to somewhere else
> 4. decode the image
> 5. display the image on some output device

> and I am not sure what kind of encoding/decoding algorithm is available
> and what I should be considering. I think fax machines use a Huffman
> encoding? Also, I've heard about a CCITT encoding scheme for graphics.

> I am wondering if anybody know where to find sources detailing these
> algorithms and/or if anybody could recommend some other algorithm.
> The image is most likely black and white (maybe grayscale)...

> Thanks in advance!

> Jack Fu
> MIT '96

A good compression algorithm for graphic data is the LZW algorithm
(used in the .GIF format). Maybe details and/or sources can be found
at x2ftp.oulu.fi  somewhere in directory pub/msdos/programming (I'm
not sure, you'll have to check yourself).

Hope this helps!

Delft, 20 april 1995


 
 
 

compression algorithm please...

Post by Wolfgang Schildba » Thu, 11 May 1995 04:00:00


[...]
: We are trying to simulate a fax transmitter/receiver by:
[...]
: and I am not sure what kind of encoding/decoding algorithm is available
: and what I should be considering. I think fax machines use a Huffman
: encoding? Also, I've heard about a CCITT encoding scheme for graphics.

Try the pbmtools package by Jeff Poskanzer. It has encoding / decoding code
for the g3-compression scheme employed by fax.

--

 W. Schildbach    University of Regensburg, Germany
                  Franz-Josef-Strauss-Allee 11, 93042 Regensburg

                snailmail: Weingartenstr. 10, 93053 Regensburg

 
 
 

compression algorithm please...

Post by HARI » Fri, 12 May 1995 04:00:00


I am trying to implement Polygon Fill based on Edge Table and Active Edge
Tables. But in this we have to sort the active edge list for every scan line.
We need to sort only at edge intersections (includes vertices). Can some one
suggest the best way to find the edge intersections of a polygon given all the
edges ?

--
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compression algorithm please...

Post by Andreas Schiffl » Sat, 20 May 1995 04:00:00



: [...]
: : We are trying to simulate a fax transmitter/receiver by:
: [...]
: : and I am not sure what kind of encoding/decoding algorithm is available
: : and what I should be considering. I think fax machines use a Huffman
: : encoding? Also, I've heard about a CCITT encoding scheme for graphics.

: Try the pbmtools package by Jeff Poskanzer. It has encoding / decoding code
: for the g3-compression scheme employed by fax.

If you have photorealistic images and you want good compression, the JPEG
format would be a good choice. Look around in comp.graphics for the JPEG FAQ
which explains what it does and where to get it.
The programs are usually called CJPEG and DJPEG.

If you want really good compression and time is not a problem, try Fractal
Compression (from Iterated Systems). It takes about a minute on a DX2-66 for
a 640x480 color image - but the final size is 20K-25 without any noticable
degradation.
Contact me for their address - I've got their package for windows.

Andreas

--
------------------------------------------------------------------------_
 Andreas Schiffler  Institute of Space and Atmospheric Studies (ISAS),
                    University of Saskatchewan, Saskatoon, Canada
------------------------------------------------------------------------_


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