Combined intra-prediction mode for bitstream decoder

A method of decoding in a decoder a bitstream representing an image, where the bitstream comprises a plurality of blocks of residual samples, where a block of reconstructed image samples is obtained by adding a block of residual samples to a block of predictions, the predictions being formed by applying a selected prediction process to reference samples in the reconstructed image, the method comprising the steps of:

• receiving the bitstream;
• for each block, forming predictions and adding a respective prediction to each residual sample to form a reconstructed image sample;
• providing a reconstructed image from the reconstructed image samples;
• and
• outputting the reconstructed image;
• wherein the step of forming predictions for a block comprises:
• determining reference samples for said block;
• applying a first directional or non-directional prediction mode to the reference samples to form at least a first set of one or more predictions for said block;
• and
• applying one or more subsequent, different, directional or non-directional prediction modes to the reference samples to form at least one subsequent set of one or more predictions for said block, where any subsequent directional prediction mode differs from any first directional prediction mode in the spatial direction of prediction;
• wherein the predictions formed for said block include the first set of one or more predictions and the one or more subsequent sets of one or more predictions;
• and
• wherein at least one of the following prediction parameters is derived at the decoder for said block:
• a first non-directional prediction mode:
• a direction of a first directional prediction mode:
• a subsequent non-directional prediction mode:
• a direction of a subsequent directional prediction mode:
• the location in the block of the first set of predictions;
• and
• the location in the block of a subsequent set of predictions:
• wherein at least one of the prediction parameters is determined by interpolating between the first direction and/or prediction mode and a final direction and/or prediction mode and/or wherein at least one of the prediction parameters is determined by interpolating linearly between the first direction and/or prediction mode and a final direction and/or prediction mode.

A method of decoding in a decoder a bitstream representing an image, where the bitstream comprises a plurality of blocks of residual samples, where a block of reconstructed image samples is obtained by adding a block of residual samples to a block of predictions, the predictions being formed by applying a selected prediction process to reference samples in the reconstructed image, the method comprising the steps of:

• receiving the bitstream;
• for each block, forming predictions and adding a respective prediction to each residual sample to form a reconstructed image sample;
• providing a reconstructed image from the reconstructed image samples;
• and
• outputting the reconstructed image;
• wherein the step of forming predictions for a block comprises:
• determining reference samples for said block;
• applying a first directional or non-directional prediction mode to the reference samples to form at least a first set of one or more predictions for said block;
• and
• applying one or more subsequent, different, directional or non-directional prediction modes to the reference samples to form at least one subsequent set of one or more predictions for said block, where any subsequent directional prediction mode differs from any first directional prediction mode in the spatial direction of prediction;
• wherein the predictions formed for said block include the first set of one or more predictions and the one or more subsequent sets of one or more predictions;
• and
• wherein the bitstream defines a process to derive one or more subsequent directional or non-directional prediction modes given a different initial directional or non-directional prediction mode;
• wherein one or more of the subsequent prediction modes are derived at the decoder based on the process defined in the bitstream and the first prediction mode;
• wherein at least one of the prediction parameters is determined by obtaining a value from a look-up table;
• and
• wherein the look-up table comprises an indication of a function used for interpolating between at least one of:
• any first non-directional prediction mode and any subsequent non-directional prediction mode;
• and/or the direction of any first directional prediction mode and the direction of any subsequent directional prediction mode.