Maximizing Compression of Apple II Hi-Res Images
5 days ago
- #Apple II
- #Retro Computing
- #Compression
- Apple II hi-res images are 8k uncompressed, with a unique memory layout due to interleaving and padding.
- Compression with ZX02 is effective, but de-interlacing first can save an additional ~100 bytes per image.
- The de-interlacing algorithm involves adding back memory holes and sorting lines, done in-place without extra buffer.
- De-interlacing adds 355 bytes to code size, making it a net win after 4 images, assuming existing lookup tables.
- Time overhead for de-interlacing is ~350ms, adding ~21 frames to decompression time.
- Potential applications include double-hires demos, lo-res/double-lores scenes, and space-constrained games.
- Modifying ZX02 to be Apple II hi-res aware is challenging due to pattern matching in compressed data.