Neighbor based signaling of intra prediction modes

A device for decoding video data, the device comprising:

• a memory configured to store the video data;
• one or more processors implemented in circuitry and configured to:
• determine that a current block of video data is coded using an intra prediction mode;
• add an intra prediction mode of a first neighboring block of the current block to a most probable mode candidate list for the current block;
• add an intra prediction mode for a second neighboring block of the current block to the most probable mode candidate list for the current block, wherein the intra prediction mode of the first neighboring block of the current block is different than the intra prediction mode of the second neighboring block of the current block;
• add a first derived intra prediction mode to the most probable mode candidate list for the current block, wherein to add the first derived intra prediction mode to the most probable mode candidate list for the current block, the one or more processors are further configured to:
• determine whether the intra prediction mode of the first neighboring block belongs to a subset of modes that includes a planar mode and a DC mode, wherein the subset of modes includes fewer than all available intra prediction modes;
• and
• in response to determining that the intra prediction mode of the first neighboring block does not belong to the specified set of modes, add a first offset to a mode index of the first neighboring block to derive the first derived intra prediction mode;
• add a second derived intra prediction mode to the most probable mode candidate list for the current block, wherein to add the second derived intra prediction mode to the most probable mode candidate list for the current block, the one or more processors are further configured to determine the second derived intra prediction mode by adding a second offset to the mode index of the first neighboring block;
• determine an intra prediction mode using the most probable mode candidate list;
• and
• decode the current block of video data using the intra prediction mode.

A computer-readable storage medium storing instructions that when executed by one or more processors cause the one or more processor to:

• determine that a current block of video data is coded using an intra prediction mode;
• add an intra prediction mode of a first neighboring block of the current block to a most probable mode candidate list for the current block;
• add an intra prediction mode for a second neighboring block of the current block to the most probable mode candidate list for the current block, wherein the intra prediction mode of the first neighboring block of the current block is different than the intra prediction mode of the second neighboring block of the current block;
• add a first derived intra prediction mode to the most probable mode candidate list for the current block, wherein to add the first derived intra prediction mode to the most probable mode candidate list for the current block, the instructions cause the one or more processors to:
• determine whether the intra prediction mode of the first neighboring block belongs to a subset of modes that includes a planar mode and a DC mode, wherein the subset of modes includes fewer than all available intra prediction modes;
• and
• in response to determining that the intra prediction mode of the first neighboring block does not belong to the specified set of modes, add a first offset to a mode index of the first neighboring block to derive the first derived intra prediction mode;
• add a second derived intra prediction mode to the most probable mode candidate list for the current block, wherein to add the second derived intra prediction mode to the most probable mode candidate list for the current block, the one or more processors are further configured to determine the second derived intra prediction mode by adding a second offset to the mode index of the first neighboring block;
• determine an intra prediction mode using the most probable mode candidate list;
• and
• decode the current block of video data using the intra prediction mode.