Non-causal encoding of predictively coded samples

We study the INTRA-prediction operation employed in hybrid video coders where sample values to be compressed are predicted using previously-decoded context values and the prediction errors are transform coded. Given the context values this procedure can be argued to be rate-distortion optimal for Gaussian signals. Yet natural images and video contain many structures that do not readily fit into Gaussian signal assumptions. Targeting such structures we propose a technique that predicts each sample using the context values and samples that are jointly transform coded with the predicted sample. We show that this joint, non-causal encoding can be represented with a nonorthogonal transform whose form and parameters we derive. We augment the HEVC standard with our work and show significant compression improvements on images/video that contain directional structures.