Method and apparatus for decoding intra prediction mode

A method of decoding an intra prediction mode, comprising:

• reconstructing an intra prediction mode group indicator and a prediction mode index;
• constructing an MPM group including three intra prediction modes using valid intra prediction modes of left and top blocks of the current block;
• determining an intra prediction mode of the MPM group corresponding to the prediction mode index as the intra prediction mode of the current block when the intra prediction mode group indicator indicates that the intra prediction mode of the current block belongs to the MPM group;
• and
• determining the intra prediction mode of the current block using the prediction mode index and the three intra prediction modes of the MPM group when the intra prediction mode group indicator indicates that the intra prediction mode of the current block does not belong to the MPM group;
• wherein mode numbers of two non-directional intra prediction modes are lower than mode numbers of directional intra prediction modes, and
• wherein when the intra prediction modes of the left and top blocks are equal to each other and the intra prediction mode of the left block is one of the two non-directional intra prediction modes, the MPM group includes the two non-directional intra prediction modes and a vertical mode.