Reduction of blocking effects in image coding with a lapped orthogonal transform

A new derivation for the lapped orthogonal transform (LOT) is presented. It has basis functions that overlap adjacent blocks and decay smoothly to zero, and so it can reduce the blocking effect to very low levels, without any data overhead. It is shown that a quasioptimal LOT can be computed with an algorithm based on the discrete cosine transform (DCT), with only 30% more computation than the DCT. Unlike earlier approaches to the reduction of blocking effects, there is no penalty in coding gain for the LOT, which actually increases the coding gain by 0.25 dB for a first-order Markov process with ρ=0.95