BUGS:
-----
- Doesn't always give perfect reconstruction with binsize = 0 (a few pixels
  may be off by one graylevel value).


PROGRAM IMPROVEMENTS:
---------------------

- [DONE] Allow non-square images.  These are currently not accepted, because
  of collapse_pyr.

- [DONE, although it still is more effective for powers of 2]
  Allow arbitrary image sizes (the dimensions currently have to be divisible
  by 2^num_levels).  This is just a matter of augmenting the collapse_pyr code...

- [DONE, although requires re-compiling]
  Provide an option to use ORTHOGONAL wavelet filters, which produce
  slightly better (perceptually) compression results.

- include a im_stats utility for comparing images.

- Provide a silent (quiet) mode with -q flag.

- color images: provide rgb->yiq, yiq->rgb

- pipes: should be able to read from/write to stdin/stdout.

- allow PROGRESSIVE display (i.e., reconstruct low-res image, and
  then gradually add in detail).


CODER IMPROVEMENTS:
-------------------
- Choose quantization binsizes adaptively for each subband 
  [this usually gives a small improvement, and may not be worth it].

- Instead of sending Huffman trees, use a parameterized model for
  coefficient statistics to generate them automatically.

- Use an arithmetic coder, or a vector quantizer, instead of run-length 
  and/or huffman?  [problem: arithmetic is patented.]

- Use some sort of (nonlinear) prediction to guess the high-frequency
  subband coefficients given the low-frequency subbands.
