Techniques for intra prediction for 360 image and video coding

A method of decoding a coded image or a coded picture in a coded video sequence, into a picture representing a projection on a planar surface of a non-planar surface, the method being performed by a decoder employing intra prediction, the method comprising:

• performing a reverse projection on a block of the picture, the block having a first aspect ratio;
• identifying a rectangle corresponding to a surface area on the non-planar surface of the block on which the reverse projection is performed, based on at least one property of the projection and a position of the block in the picture;
• and
• based on a second aspect ratio of the identified rectangle, performing either one or both of adding to and removing from at least one intra prediction direction available for decoding the block in accordance to the first aspect ratio and a video compression standard.

An apparatus for decoding a coded image or a coded picture in a coded video sequence, into a picture representing a projection on a planar surface of a non-planar surface, the apparatus being a decoder employing intra prediction, and the apparatus comprising:

• at least one memory configured to store computer program code;
• and
• at least one processor configured to access the at least one memory and operate according to the computer program code, the computer program code comprising:
• obtaining code configured to cause the at least one processor to obtain an intra prediction mode indicative of an intra prediction direction, for a block of the picture;
• determining code configured to cause the at least one processor to determine at least one non-straight curve representative of a straight line on the non-planar surface, based on the projection and the obtained intra prediction mode;
• creating code configured to cause the at least one processor to create, for the block, prediction samples along the determined at least one non-straight curve, from at least one boundary sample along the determined at least one non-straight curve;
• first, performing code configured to cause the at least one processor to perform a reverse projection on the block of the picture, the block having, a first aspect ratio,
• identifying code configured to cause the at least one processor to identify a rectangle corresponding to a surface area on the non-planar surface of the block on which the reverse projection is performed, based on at least one property of the projection and a position of the block in the picture;
• and
• second performing code configured to cause the at least one processor to, based on a second aspect ratio of the identified rectangle, perform either one or both of adding to and removing from at least one intra prediction direction available for decoding the block in accordance to the first aspect ratio and a video compression standard.