Commit Graph

5 Commits

Author SHA1 Message Date
f3d03a1b87 Update comments and fix some bugs
- use MASKED_DOTS since it does not have a simple relationship to the
- try disabling transposition distances for Damerau-Levenshtein, this
  may give better quality

- introduce separate notion of MASKED_DOTS which is the number of
  (coloured) pixels we can extract from MASKED_BITS.  For HGR this is
  not the same.
- fix bug in _fix_array_neighbours that was not fixing headers for HGR
- don't cache everything in byte_pair_differences, it's effectively
  unbounded.  Using 1M for LRU size seems to work just as well in
  practise, without leaking memory.
- fix bug in _diff_weights when comparing content, we want to evaluate
  the effect of storing content byte in each offset separately, not
- add a consistency check function (not currently wired up) to assert
  that headers/footers are in sync across columns
- HGR should have 16 body bits, this was causing headers not to
  propagate correctly to/from neighbouring column
- add test case for this bug

- Use 8 random bits consistently, using 16 in some places may have
  introduced bias
- ignore palette bit when comparing 0x00 and 0x7f in sanity check
2019-07-11 23:40:00 +01:00
666272a8fc Checkpoint WIP for easier comparison to dhgr branch:
- naive version of NTSC artifacting, it uses a sliding 4-bit window to
  assign a nominal (D)HGR colour to each dot position.  A more
  sophisticated/correct implementation would model the YIQ signal

- Switch DHGRBitmap implementation to use a 34-bit representation of
  the 4-byte tuple, comprised of a 3-bit header and footer, plus
  4*7=28-bit body.  The headers/footers account for the influence on
  neighbouring tuples from the 4-bit NTSC window.

- With this model each screen byte influences 13 pixels, so we need to
  precompute 2^26 edit distances for all possible (source, target)
  13-bit sequences.

- Checkpointing not-yet-working HGR implementation.

- Add new unit tests but not yet all passing due to refactoring
2019-07-02 22:40:50 +01:00
ca817999f6 Parametrize the RGB palette to encode with, and support both NTSC and
IIGS palettes.

Move the palette diff_matrix generation into since
that is the only place it is used.

Demand-load the edit distance matrices when transcoding.
2019-06-15 21:02:00 +01:00
a172214f16 Fix warnings 2019-06-13 23:41:28 +01:00
9f950739f9 Map DHGR colours to RGB values (for now using the BMP2DHR default
NTSC palette), and compute the matrix of pairwise perceptual
differences between these colours, using CIE2000 delta values.
2019-06-12 22:14:11 +01:00