[adrianmonk]

I'd rather they had just done entropy coding. It's good at using a smaller number of bits per character to represent a subset of characters, which is what they're trying to do. But it's more general, so you wouldn't be limited to only those characters.

Huffman is probably simple enough. The typical approach is adaptive Huffman, which doesn't compress the initial data very well since it needs to adjust to actual character frequencies. So that wouldn't work well for QR codes since they're short.

But you can start adaptive Huffman with a pre-agreed initial tree (as static Huffman does), which would give good compression from the start. There could be several standard pre-agreed Huffman trees, and instead of using bits in the QR code to select a character set, those bits could select one of a few pre-agreed initial Huffman trees.