Like the author said this is completely unoptimized. The natural next step in optimization might be to profile and then SIMD optimize the slow bits in compression and decompression. This would likely produce a significant speedup and may even bridge the gap with lz4.
The algorithm is extremely resistant to SIMD optimizations.
Every pixel uses a different encoding, 95% of the encodings rely on the value of the previous pixel, or the accumulated state of all previously processed pixels. The number of bytes per pixel and pixels per byte swing wildly.
SIMD optimization would basically require redesigning it from scratch.
