Video and image coding with wide-angle intra prediction

A method, comprising:

• receiving a bitstream comprising encoded image data;
• forming from said bitstream in a computer memory a set of reference pixels having reference pixel values for intra-picture directional prediction;
• determining an intra-prediction mode for an image block;
• determining whether both a wide-angle prediction direction and a narrow-angle prediction direction are associated with said intra-prediction mode, said wide-angle prediction direction forming an obtuse angle with top-left direction;
• in case both the wide-angle prediction direction and the narrow-angle prediction direction are associated with said intra-prediction mode, determining from said bitstream a syntax element, and, based on a value of said syntax element, setting a prediction direction of said image block to be said wide-angle prediction direction;
• predicting a pixel value in a predicted image block by using intra-picture directional prediction and by using values of one or more selected reference pixels in forming a predicted pixel value, wherein the selected reference pixels are selected from said wide-angle prediction direction with respect to the predicted pixel value;
• and
• repeating the pixel prediction for a number of pixels to form a predicted image block;
• using said predicted image block in decoding an image block from said bitstream to obtain a decoded image block.

A method, comprising:

• receiving image data to be encoded;
• forming from said image data in a computer memory a set of reference pixels having reference pixel values for intra-picture directional prediction;
• determining an intra-prediction mode for an image block;
• determining whether both a wide-angle prediction direction and a narrow-angle prediction direction are associated with said intra-prediction mode, said wide-angle prediction direction forming an obtuse angle with top-left direction;
• in case both the wide-angle prediction direction and the narrow-angle prediction direction are associated with said intra-prediction mode, forming into said bitstream a syntax element indicating the prediction direction, and, based on a value of said syntax element, setting a prediction direction of said image block to be said wide-angle prediction direction;
• predicting a pixel value in a predicted image block by using intra-picture directional prediction and by using values of one or more selected reference pixels in forming a predicted pixel value, wherein the selected reference pixels are selected from a prediction direction with respect to the predicted pixel value;
• and
• repeating the pixel prediction for a number of pixels to form a predicted image block,
• using said predicted image block in encoding an image block into a bitstream.

An apparatus comprising at least one processor, memory including computer program code, the memory and the computer program code configured to, with the at least one processor, cause the apparatus to perform at least the following:

• receive a bitstream comprising encoded image data;
• form from said bitstream in a computer memory a set of reference pixels having reference pixel values for intra-picture directional prediction;
• determine an intra-prediction mode for an image block;
• determine whether both a wide-angle prediction direction and a narrow-angle prediction direction are associated with said intra-prediction mode, said wide-angle prediction direction forming an obtuse angle with top-left direction;
• in case both a wide-angle prediction direction and a narrow-angle prediction direction are associated with said intra-prediction mode, determine from said bitstream a syntax element, and, based on a value of said syntax element, set a prediction direction of said image block to be said wide-angle prediction direction;
• predict a pixel value in a predicted image block by using intra-picture directional prediction and by using values of one or more selected reference pixels in forming a predicted pixel value, wherein the selected reference pixels are selected from a prediction direction with respect to the predicted pixel, and said prediction direction being a wide-angle prediction direction that forms an obtuse angle with top-left direction of said predicted pixel;
• repeat the pixel prediction for a number of pixels to form a predicted image block;
• and
• use said predicted image block in decoding an image block from said bitstream to obtain a decoded image block.

An apparatus comprising at least one processor, memory including computer program code, the memory and the computer program code configured to, with the at least one processor, cause the apparatus to perform at least the following:

• receive image data to be encoded;
• form from said image data in a computer memory a set of reference pixels having reference pixel values for intra-picture directional prediction;
• determine an intra-prediction mode for an image block;
• determine whether both a wide-angle prediction direction and a narrow-angle prediction direction are associated with said intra-prediction mode, said wide-angle prediction direction forming an obtuse angle with top-left direction;
• in case both a wide-angle prediction direction and a narrow-angle prediction direction are associated with said intra-prediction mode, form a syntax element into said bitstream indicating the prediction direction, and, based on a value of said syntax element, set a prediction direction of said image block to be said wide-angle prediction direction;
• predict a pixel value in a predicted image block by using intra-picture directional prediction and by using values of one or more selected reference pixels in forming a predicted pixel value, wherein the selected reference pixels are selected from said wide-angle prediction direction with respect to the predicted pixel;
• repeat the pixel prediction for a number of pixels to form a predicted image block;
• and
• use said predicted image block in encoding an image block into a bitstream.

A bitstream signal embodied on a non-transitory computer-readable medium, the signal being arranged to, when decoded on a decoder, to cause the decoder to decode image data from said bitstream signal, the signal comprising a coded prediction error signal having been formed by using intra-picture directional prediction, wherein predicted pixel values have been formed in a predicted image block by using intra-picture directional prediction and by using values of one or more selected reference pixels in forming a predicted pixel value, wherein the selected reference pixels have been selected from a prediction direction with respect to the predicted pixel, and said prediction direction being a wide-angle prediction direction that forms an obtuse angle with top-left direction of said predicted pixel, the bitstream signal arranged to cause the decoder to select the prediction direction to be a wide-angle prediction direction for decoding of the bitstream by determining an intra-prediction mode for an image block, determining whether both a wide-angle prediction direction and a narrow-angle prediction direction are associated with said intra-prediction mode, said wide-angle prediction direction forming an obtuse angle with top-left direction, in case both a wide-angle prediction direction and a narrow-angle prediction direction are associated with said intra-prediction mode, determining based on a syntax element in said bitstream the prediction direction to be said wide-angle prediction direction.