This is a very brief note on usage of enc.c and dec.c and on raw image
files.

FILE TYPE:

First, the input file to enc must be raw bytes which are not
references into a color lookup table. The image size must
be a multiple of 4. A typical calling sequence for a 256x256 image is:

enc -t 10 infile.raw outfile.trn



THE TOLERANCE FLAG:

A range of 4-20 is reasonable for the -t flag, with small values
giving good fidelity at poor compression and vice versa. 



INPUT IMAGE SIZE:

The -M flag controls the size of the smallest image pieces that are
compared for self similarity. The following table gives the value
that should be used:

Smallest Input Image Dimension                  -M value
--------------------------------------------------------
   128                                            5
   256                                            6 (default)
   512                                            7 
etc.

Using too large a -M will cause the program to warn you that it 
doesn't make sense to do that (the resulting compression will
be poor); using too small a -M flag will cause the resulting fidelity
to be poor (often, but not always). 

For (say) 512x512 images the calling sequence is:

enc -t 10 -M 7 -w 512 infile.raw outfile.trn

The -M flags should probably be automatic; oh well. 

DECODING: 

The decoding call is:

dec outfile.trn outfile.out

which creates a raw byte image outfile.out. 

The outputfile can be scaled with the -f flag. 

dec -f 2 outfile.trn outfile.out 

will result in an outputfile that is twice as big as the 
input. 


VIEWING THE IMAGE:

The file Images/r2s.c will create sunraster header. It can be prepended
to the raw data files to convert them to sunraster format. To use
r2s.c, compile it (cc -o r2s.c r2s), and then type 
r2s 256 256 > head
cat head imagefile.raw > imagefile.ras 
which will create a head file for a 256x256 sunraster file and prepend
it to the raw image file.... 

All of this should be automated; maybe it will be some day....

CREATING RAW FILES: 
ras2raw.c is a C program to convert just some types of sunraster images 
(no run length encoding, sorry) to raw byte files. It is in the Images
directory with the raw images. 

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Good luck; thanks for your interest. 
Yuval Fisher
yfisher@ucsd.edu