Martine already handle sprite and compression on sprite using -z option :
-z int
Compression algorithm :
1: rle (default)
2: rle 16bits
3: Lz4 Classic
4: Lz4 Raw
and pixel position in sprite like option -zigzag (same as imgcpc)
For the sprite hard (only for Amstrad CPC plus), nothing is already done. And if you wanted to apply those options on sprite hard tell me.
Sid