Current video coding standards, including H.264/AVC, HEVC, and VVC, utilize discrete cosine transform (DCT), discrete sine transform (DST), to decorrelate the intra-prediction residuals. However, these transforms often face challenges in effectively decorrelating signals with complex, non-smooth, and non-periodic structures. Even in smooth areas, an abrupt transition (due to noise or prediction artifacts) can limit their effectiveness. This paper presents a novel block-adaptive separable path graph-based transform (GBT) that is particularly adept at handling such signals. This new method focuses on adaptively modifying the block size and learning GBT to enhance the performance. The GBT is learned in an online scenario using sequential K-means clustering, where each available block size has K clusters and K GBT kernels. This approach allows the GBT to be dynamically learned for the current block based on previously reconstructed areas with same block size and similar characteristics. Our evaluation, integrating this method with H.264/AVC intra-coding tools, shows significant improvement over the traditional H.264/AVC DCT in processing high-resolution natural images.
|