Very nice! I wasn't aware of this algorithm at all, but it seems to be an early application of the lifting scheme to the DCT filter, 8 years before this method

Very nice! I wasn't aware of this algorithm at all, but it seems to be an early application of the lifting scheme to the DCT filter, 8 years before this method was introduced in the more general context of perfect reconstruction filters. There's a great expository paper about these kinds of filter implementations by Daubechies and Sweldens in the general case: https://9p.io/who/wim/papers/factor/factor.pdf https://9p.io/who/wim/papers/factor/factor.pdf Interestingly enough, Sweldens does not seem to cite Loeffler's paper, so it's likely that they came up with the same method independently of one another.