Method for improved intra prediction when reference samples are missing

Apparatus for compression of digital video images, each said digital video image including one or more prediction units, the apparatus comprising:

• a memory that stores a plurality of instructions;
• and
• a processor coupled to the memory and configured to perform said video image compression including an operation for intra frame prediction, said processor being configured to perform said intra frame prediction, for one of said prediction units, by:
• determining whether one or more reference samples are unavailable or missing on a line bordering one edge of said prediction unit or portion thereof given a particular directional mode;
• if it is determined that one or more reference samples are unavailable or missing, determining whether one or more reference samples are available on another line bordering another edge of the prediction unit and extending beyond said another edge along a direction of said another line, wherein said another line is at an opposite side of the prediction unit with respect to the particular directional mode;
• if it is determined that one or more reference samples are available at said another line, replacing the particular directional mode with a counterpart directional mode that is oppositely directed to the particular directional mode;
• and
• filling pixels of the prediction unit with the available reference samples of said another line using the counterpart directional mode, wherein said filling comprises:
• when the pixels of one contiguous region of the prediction unit have been filled with all the available reference samples of said another line using the counterpart directional mode, filling the pixels of the prediction unit in an unfilled region of the prediction unit excluding said one contiguous region with values based on said available reference samples.

A nontransitory computer readable medium having one or more executable instructions stored thereon, which when executed by a processor cause the processor to perform a method for compression of digital video images including an operation for intra frame prediction, each said digital video image including one or more prediction units, said intra frame prediction comprising, for one of said prediction units:

• determining whether one or more reference samples are unavailable or missing on a line bordering one edge of said prediction unit or portion thereof given a particular directional mode;
• if it is determined that one or more reference samples are unavailable or missing, determining whether one or more reference samples are available on another line bordering another edge of the prediction unit and extending beyond said another edge along a direction of said another line, wherein said another line is at an opposite side of the prediction unit with respect to the particular directional mode;
• if it is determined that one or more reference samples are available at said another line, replacing the particular directional mode with a counterpart directional mode that is oppositely directed to the particular directional mode;
• and
• filling pixels of the prediction unit with the available reference samples of said another line using the counterpart directional mode, wherein said filling comprises:
• when the pixels of one contiguous region of the prediction unit have been filled with all the available reference samples of said another line using the counterpart directional mode, filling the pixels of the prediction unit in an unfilled region of the prediction unit excluding said one contiguous region with values based on said available reference samples.