Improvements and modifications introduced in H.264 compared to the legacy standards using hybrid coding with intra-frame prediction and motion compensation are shown below. 1. Variable block size for motion compensation. Motion can be compensated not only in relation to the whole macro-blocks but also their parts. They are assigned individual motion vectors. The smaller block includes (4x4) luminance points. It produces smaller prediction errors that may be expressed with less bits. 2. Motion prediction with accuracy up to 1/4 of the image sampling interval. High motion vector accuracy allows high precision prediction with motion compensation. 3. Using multiple reference images - using a long -term memory for prediction of revealed areas. 4. Inter-frame directional prediction for the inter-frame coded macro-blocks. 5. De-blocking filter removes the block effects occurring in the predicted images at high compression. 6. The cosine transform operates at small blocks - (4x4) for luminance samples and (2x2) for chrominance samples for improved adjustment to local image properties. 7. Adaptive entropy coding: CAVLC (Context-Adaptive Variable Length Coding) – with variable word length and CABAC (Context-Based Binary Arithmetic Coding) – more complex adaptive arithmetic coding for better compression ratio.
|