Apparatus and method for video encoding or decoding
The present invention relates to efficient signaling of an intra prediction mode for predicting a current block in intra prediction coding. According to an aspect of the present invention, a video encoding apparatus divides dozens of intra modes into groups, selects a group to which an actual intra mode of the current block to be encoded belongs, and signals a value corresponding to the group. The video decoding apparatus acquires information on the group to which the actual intra mode of the current block belongs from a bit-stream and then evaluates intra modes belonging to the group to select a final intra mode.
1. An apparatus for encoding video data, the apparatus comprising:
an encoder configured to encode position information which indicates one reference line selected among a plurality of reference lines neighboring with a current block of the video data, and encode intra mode data which specifies an intra mode of the current block for predicting the current block; and
an intra predictor configured to predict the current block using the reference line indicated by the position information based on the intra mode of the current block,
wherein the encoding of intra mode data comprises:
encoding an most probable mode (MPM) flag indicating whether the intra mode of the current block is an MPM or not; and
when the MPM flag indicates that the intra mode of the current block is an most probable mode (MPM), further encoding one or more syntax elements which specify the intra mode of the current block among a plurality of most probable modes (MPMs),
wherein the plurality of MPM are classified into two MPM groups and include at least Planar mode and intra modes derived from reconstructed blocks neighboring with the current block, and
wherein the one or more syntax elements include at least one of:
a first syntax element indicating which MPM group of the two MPM groups the intra mode of the current block belongs to; and
a second syntax element indicating one of the MPMs belonging to the MPM group indicated by the first syntax element.
2. The apparatus according to claim 1 , wherein the encoding of intra mode data further comprises:
when the MPM flag indicates that the intra mode of the current block is not an MPM, further encoding one or more syntax elements which specify the intra mode of the current block among a plurality of non-MPMs.
3. The apparatus according to claim 1 , wherein the encoding of intra mode data further comprises:
when the MPM flag indicates that the intra mode of the current block is not an MPM, generating a list of non-MPMs by removing the MPMs from available intra modes;
sorting the non-MPMs in ascending order according to mode values of the intra modes;
dividing the intra modes sorted in the ascending order into a plurality of non-MPM groups; and
encoding a syntax element indicating a non-MPM group to which the intra mode of the current block belongs, without encoding data indicating an index of the same non-MPM as the intra of the current block within the non-MPM group indicated by the syntax element.
4. The apparatus according to claim 1 , wherein the encoding of intra mode data further comprises:
when the MPM flag indicates that the intra mode of the current block is not an MPM, generating a list of non-MPMs by removing the MPMs from available intra modes;
dividing the non-MPMs into a plurality of non-MPM groups, such that intra modes belonging to the same non-MPM group use the same scanning order in scanning transform coefficients of a residual block; and
encoding a syntax element indicating a non-MPM group to which the intra mode of the current block belongs, without encoding data indicating an index of the same non-MPM as the intra mode of the current block within the non-MPM group indicated by the syntax element.
5. The apparatus according to claim 1 , wherein the encoding of intra mode data further comprises:
when the MPM flag indicates that the intra mode of the current block is not an MPM, generating a list of non-MPMs by removing the MPMs from available intra modes;
dividing the non-MPMs into a plurality of non-MPM groups, wherein the plurality of non-MPM groups comprises a first group and a second group, and wherein the first group comprises intra modes determined based on statistics related to a possibility of coinciding with the intra mode of the current block, and the second group is divided into a plurality of subgroups;
encoding one or more syntax elements indicating a non-MPM group and/or a subgroup to which the intra mode of the current block belongs; and
encoding data specifying an intra mode coinciding with the intra mode of the current block within the non-MPM group and/or the subgroup to which the intra mode of the current block belongs.
6. An apparatus for decoding video data, the apparatus comprising:
a decoder configured to decode, from a bitstream, position information which indicates one reference line selected among a plurality of reference lines neighboring with a current block of the video data and decode, from the bitstream, intra mode data which specifies an intra mode of the current block for predicting the current block; and
an intra predictor configured to predict the current block using the reference line indicated by the position information based on the intra mode of the current block,
wherein the decoding of intra mode data comprises:
decoding, from the bitstream, an most probable mode (MPM) flag indicating whether the intra mode of the current block is an MPM or not; and
when the MPM flag indicates that the intra mode of the current block is an MPM, further decoding one or more syntax elements which specify the intra mode of the current block among a plurality of most probable modes (MPMs),
and wherein which the plurality of MPMs are classified into two MPM groups and include at least Planar mode and intra modes derived from reconstructed blocks neighboring with the current block,
and wherein the one or more syntax elements include at least one of:
a first syntax element indicating which MPM group of the two MPM groups the intra mode of the current block belongs to; and
a second syntax element indicating one of the MPMs belonging to the MPM group indicated by the first syntax element.
7. The apparatus according to claim 6 , wherein the decoding of intra mode data further comprises:
when the MPM flag indicates that the intra mode of the current block is not an MPM, decoding, from the bitstream, one or more syntax elements which specify the intra mode of the current block among a plurality of non-MPMs.
8. The apparatus according to claim 6 , wherein the decoding of intra mode data further comprises:
when the MPM flag indicates that the intra mode of the current block is not an MPM, generating a list of non-MPMs by removing the MPMs from available intra modes;
sorting the non-MPMs in ascending order according to mode values of the intra modes;
dividing the intra modes sorted in the ascending order into a plurality of non-MPM groups; and
decoding a syntax element indicating a non-MPM group to which the intra mode of the current block belongs,
and wherein the intra predictor is further configured to evaluate the non-MPMs belonging to the non-MPM group indicated the syntax element to determine the intra mode of the current block among the evaluated non-MPMs.
9. The apparatus according to claim 6 , wherein the decoding of intra mode data further comprises:
when the MPM flag indicates that the intra mode of the current block is not an MPM, generating a list of non-MPMs by removing the plurality of MPMs from available intra modes;
dividing the non-MPMs into a plurality of non-MPM groups, such that intra modes belonging to the same group use the same scanning order in scanning transform coefficients of a residual block; and
further decoding a syntax element indicating a non-MPM group to which the intra mode for predicting the current block belongs,
and wherein the intra predictor is further configured to evaluate the non-MPMs belonging to the non-MPM group indicated the syntax element to determine the intra mode of the current block among the evaluated non-MPMs.
10. The apparatus according to claim 6 , wherein decoding of intra mode data further comprises:
when the MPM flag indicates that the intra mode for predicting the current block is not an MPM, generating a list of non-MPMs by removing the MPMs from available intra modes;
dividing the non-MPMs into a plurality of non-MPM groups, wherein the plurality of non-MPM groups comprises a first group and a second group, the first group including intra modes determined based on statistics related to a possibility of coinciding with the intra mode of the current block, and the second group is further divided into a plurality of subgroups;
decoding, from the bitstream, one or more syntax elements indicating a non-MPM group and/or a subgroup to which the intra mode of the current block belongs; and
decoding, from the bitstream, data specifying an intra mode coinciding with the intra mode of the current block in the non-MPM group and/or the subgroup to which the intra mode of the current block.