[DarkShikari]

JPEG2K is a terrible format that, in practice, often comes out worse than JPEG. This is partly because wavelets are terrible from a psychovisual standpoint, but also because the format is just badly designed; Snow, a similar wavelet format, trashes it completely even when using the exact same wavelet transform.

Also, wavelets are not at all "provably optimal." The only "provably optimal" transform is the KLT, and even that isn't really, since in practice overcomplete transforms tend to have better compression efficiency than complete ones, at the cost of turning compression from a simple O(nlog(n)) frequency transform into an NP-complete problem of matching pursuits.