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