JPEG decoding via two-dimensional optimal separable filters

In a JPEG decoder, the quantized discrete cosine transform (DCT) coefficient blocks are usually processed using the inverse DCT to reconstruct an approximation of the original image. In the presence of quantization of the transform coefficients, the use of the inverse DCT in the decoder is not the best choice: We propose a procedure to design a family of separable 2D synthesis filters that minimize the reconstruction error power and these filters are used in the decoder instead of the inverse DCT. The appropriate reconstruction filters are selected on the basis of the standard quantization information provided in the JPEG bit stream. We show that the proposed decoding method gives some gain with respect to the standard decoder, making use of only the information provided by the JPEG bit stream