Variable block rate and blockwise spectral adaptation in cosine transform image coding

A block discrete-cosine transform coding scheme is implemented with a different rate assignment to each block for the purpose of maintaining a constant distortion per block. A spectral estimate is calculated for every block. Overhead rate and computation for adaptation are kept to a reasonable level through characterization of the block´s estimated spectrum by a one-dimensional autoregressive model. Simulations with natural and multimodality medical images provide reconstructions with nearly uniform block distortion and very high visual and measurable quality at low rates