Disclosed are techniques for coding coefficients of a video block having a non-square shape defined by a width and a height, comprising coding one or more of x- and y-coordinates that indicate a position of a last non-zero coefficient within the block according to an associated scanning order, including coding each coordinate by determining one or more contexts used to code the coordinate based on one of the width and the height that corresponds to the coordinate, and coding the coordinate by performing a context adaptive entropy coding process based on the contexts. Also disclosed are techniques for coding information that identifies positions of non-zero coefficients within the block, including determining one or more contexts used to code the information based on one or more of the width and the height, and coding the information by performing a context adaptive entropy coding process based on the contexts.

The present invention provides a method for decoding a video signal using a graph-based transform including receiving a generalized graph signal including a graph parameter set; obtaining a graph-based transform kernel of a transform unit based on the graph parameter set and a predetermined penalty function; and decoding the transform unit using the graph-based transform kernel.

An image encoding apparatus comprises a selector configured to select, from a set of candidate prediction operations each defining at least a prediction direction, a prediction operation for prediction of samples of a current region of a current image, the current region comprising an array of two or more rows and two or more columns of samples; an intra-image predictor configured to derive predicted samples of the current region with respect to one or more of a group of reference samples of the same image in dependence upon a prediction direction, defined by the selected prediction operation, between a current sample to be predicted and a reference position amongst the reference samples; in which, for at least some of the candidate prediction operations, the group of reference samples comprises two or more parallel linear arrays of reference samples disposed at different respective separations from the current region; a detector configured to detect whether samples corresponding to any of the two or more parallel linear arrays of reference samples are unavailable for use in prediction of samples of the current region and, if any of the two or more parallel linear arrays of reference samples are unavailable, to inhibit selection, by the selector, of a candidate prediction operation dependent upon the unavailable reference samples.

Methods, apparatus and systems for processing video blocks. The method including transforming, via a transform unit, the video residual data using a single one-dimensional transform to generate a first set of coefficients associated with the video block; quantizing, via a quantization unit, the first set of coefficients to generate a second set of quantized coefficients, wherein the method for processing the video residual data includes bit-shifting any of the first and second sets of coefficients; entropy coding the second set of quantized coefficients after the bit-shifting; and transmitting the entropy coded second set of quantized coefficients. In certain embodiments, the bit shifting may include integer and/or fractional bit shifting.

Coding efficiency is improved. A motion compensation filter unit acts on a motion vector applied image obtained by acting a motion vector on a reference image. The motion compensation filter unit causes filter coefficients mcFilter[i][k] designated by a phase i and a filter coefficient position k to act on the motion vector applied image. The filter coefficients mcFilter[i][k] includes filter coefficients calculated by using filter coefficients mcFilter[p][k] (p≠i) and filter coefficients mcFilter[q][k] (q≠i).

A method for encoding digital images or video streams, includes a receiving phase, wherein a portion of an image is received; a graph weights prediction phase, wherein the elements of a weights matrix associated to the graph related to the blocks of the image (predicted blocks) are predicted on the basis of reconstructed, de-quantized and inverse-transformed pixel values of at least one previously coded block (predictor block) of the image, the weights matrix being a matrix comprising elements denoting the level of similarity between a pair of pixels composing said image, a graph transform computation phase, wherein the graph Fourier transform of the blocks of the image is performed, obtaining for the blocks a set of coefficients determined on the basis of the predicted weights; a coefficients quantization phase, wherein the coefficients are quantized an output phase wherein a bitstream comprising the transformed and quantized coefficients is transmitted and/or stored.

Disclosed are methods and apparatuses for image data encoding/decoding. A method for decoding a 360-degree image includes the steps of: receiving a bitstream obtained by encoding a 360-degree image; generating a prediction image by making reference to syntax information obtained from the received bitstream; adding the generated prediction image to a residual image obtained by dequantizing and inverse-transforming the bitstream, so as to obtain a decoded image; and reconstructing the decoded image into a 360-degree image according to a projection format. Therefore, the performance of image data compression can be improved.

Techniques are described for optimizing memory used by a video decoder. A residual coefficient matrix including non-zero value residual coefficients of a larger parent matrix with both non-zero and zero value residual coefficients can be provided to the decoder. Residual coefficient matrix metadata can also be provided so that a modified and reduced inverse transform matrix can be selected and applied to the residual coefficient matrix.

An encoder which transforms a current block to be encoded in an image to encode the current block includes circuitry and memory. The circuitry, using the memory: determines a plurality of first transform basis candidates and transforms the current block using a transform basis included in the plurality of first transform basis candidates determined, when the current block has a first size; and determines one or more second transform basis candidates different from the plurality of first transform basis candidates and transforms the current block using a transform basis included in the one or more second transform basis candidates determined, when the current block has a second size larger than the first size.

An example device for decoding video data includes a video decoder configured to decode one or more syntax elements at a region-tree level of a region-tree of a tree data structure for a coding tree block (CTB) of video data, the region-tree having one or more region-tree nodes including region-tree leaf and non-leaf nodes, each of the region-tree non-leaf nodes having at least four child region-tree nodes, decode one or more syntax elements at a prediction-tree level for each of the region-tree leaf nodes of one or more prediction trees of the tree data structure for the CTB, the prediction trees each having one or more prediction-tree leaf and non-leaf nodes, each of the prediction-tree non-leaf nodes having at least two child prediction-tree nodes, each of the prediction leaf nodes defining respective coding units (CUs), and decode video data for each of the CUs.