Method of generating quantized block
Provided is a method that derives an intra prediction mode of a prediction unit, selects an inverse scan pattern of a current transform unit among a diagonal scan, a vertical scan and a horizontal scan based on the intra prediction mode and a size of the transform unit, and generates a quantized block by inversely scanning significant flags, coefficients signs and coefficient levels according to the selected inverse scan pattern. If the transform unit is larger than a predetermined size, multiple subsets are generated and inversely scanned. Therefore, the amount of coding bits of the residual block is reduced by determining the scan pattern based on the size of the transform unit and the intra prediction mode, and by applying the scan pattern to each subset. Also, the signaling bits decreases by generating MPM group adaptively according to the neighboring intra prediction modes.
1. A method of generating a quantized block, comprising:
deriving an intra prediction mode of a current prediction unit using an MPM group including three intra prediction modes which are determined according to left and above intra prediction modes of the current prediction unit;
selecting an inverse scan pattern based on the intra prediction mode and a size of a transform unit; and
generating the quantized block by inversely scanning significant flags, coefficient signs and coefficient levels according to the selected inverse scan pattern,
wherein the inverse scan pattern is one of a diagonal scan, a vertical scan and a horizontal scan,
wherein when the left intra prediction mode and the above intra prediction mode are the same with each other and the left intra prediction mode is one of two non-directional intra prediction modes, the MPM group includes the two non-directional intra prediction modes and a vertical mode, and
wherein when both of the left intra prediction mode and the above intra prediction mode are unavailable, the MPM group includes the two non-directional intra prediction modes and the vertical mode.
2. The method of claim 1 , wherein if the size of the transform unit is equal or smaller than 8×8, the inverse scan pattern is determined by the intra prediction mode.
3. The method of claim 2 , wherein the horizontal scan is applied for the vertical mode and a predetermined number of neighboring intra prediction modes of the vertical mode, the vertical scan is applied for a horizontal mode and the predetermined number of neighboring intra prediction modes of the horizontal mode, and the diagonal scan is applied for all other intra prediction modes.
4. The method of claim 3 , wherein if the size of the transform unit is 8×8, the predetermined number is 8.
5. The method of claim 1 , wherein if the size of the transform unit is larger than 8×8, the diagonal scan is applied for all intra prediction modes.
6. The method of claim 1 , wherein if the size of the transform unit is 8×8, the significant flags, the coefficient signs and the coefficient levels are inversely scanned in a unit of a subset to generate a plurality of subsets and the quantized block is generated by inversely scanning the plurality of subsets according to the inverse scan pattern which is determined by the intra prediction mode.
7. The method of claim 6 , wherein a number of encoded subsets is determined using a last non-zero coefficient position and the selected inverse scan pattern.
8. The method of claim 6 , wherein the plurality of subsets to be generated are determined using a plurality of non-zero subset flags, and the plurality of subsets are generated by applying the inverse scan pattern to the significant flags, the coefficient signs and the coefficients levels.
9. The method of claim 1 , wherein when the left intra prediction mode is a DC mode and the above intra prediction mode is the DC mode, the MPM group includes the DC mode, a planar mode and the vertical mode.
10. The method of claim 1 , wherein when the left intra prediction mode is a planar mode and the above intra prediction mode is the planar mode, the MPM group includes a DC mode, the planar mode and the vertical mode.