Directional intra frame interpolation for HEVC compressed video

Image interpolation is one of the most elementary imaging research topics. A number of image interpolation methods have been developed and tested on uncompressed images in the literature. However, a lot of videos have already been stored or have to be transmitted in compressed format due to the storage limitation or the bandwidth limitation. The existed image interpolation methods may not be efficient when directly applied to compressed images or videos. Inspired by the success of the intra prediction in HEVC and the edge-directed image interpolation methods, a directional intra frame interpolation for HEVC compressed video is proposed. The main idea is to use the directional prediction information in compressed low-resolution video bitstreams to estimate the associated high-resolution video. For intra frames, the prediction direction information is taken into account as context in the directional interpolation. When a pixel is decompressed with a small prediction residual, the interpolation is performed along its block direction. The interpolation weight for each block direction is off-line trained by the Wiener filter based on the representative video sequences. For each pixel with a large prediction residual, a piecewise autoregressive model is used as a regularization term into the interpolation function. Extensive experiments demonstrate that the proposed method achieves better performance than the traditional methods such as Bicubic, KR, LAZA, NEDI and SAI.