Method and apparatus for image encoding with intra prediction mode

A method of encoding an intra prediction mode, the method comprising:

• determining an intra prediction mode of a current block among two non-directional intra prediction modes and a plurality of directional intra prediction modes;
• constructing a most probable mode (MPM) group including three intra prediction modes using presented intra prediction modes of left and top blocks of the current block;
• determining a prediction mode index specifying the intra prediction mode of the current block within the MPM group when the intra prediction mode of the current block belongs to the MPM group;
• and
• determining a prediction mode index specifying the intra prediction mode of the current block among intra prediction modes which are not included in the MPM group when the intra prediction mode of the current block does not belong to the MPM group,
• wherein the two non-directional intra prediction modes are a DC mode and a planar mode,
• wherein a mode number of the planar mode is lower than mode numbers of the plurality of directional intra prediction modes,
• wherein when the intra prediction mode of the left block is a DC mode and the intra prediction mode of the top blocks is the DC mode, the MPM group includes the DC mode, a planar mode and a vertical mode, and
• wherein lowest prediction mode indices are assigned to the two non-directional intra prediction modes when the intra prediction mode of the current block does not belong to the MPM group and the two non-directional intra prediction modes are not included in the MPM group.