Video encoding method and video decoding method
Provided is a video encoding/decoding technique for improving the compression efficiency by reducing the motion vector code amount. In a video decoding process, the prediction vector calculation method is switched from one to another in accordance with a difference between predetermined motion vectors among a plurality of motion vectors of a peripheral block of a block to be decoded and already decoded. The calculated prediction vector is added to a difference vector decoded from an encoded stream so as to calculate a motion vector. By using the calculated motion vector, the inter-image prediction process is executed.
1. A video decoding method comprising the steps of:
selecting a prediction mode to be performed among a plurality of prediction modes including an intra-prediction mode and an inter-prediction mode;
calculating a predictive motion vector, in case that the inter-prediction mode is selected as the prediction mode to be performed;
calculating a motion vector by summing the predictive motion vector calculated in the predictive motion vector calculating step and a differential motion vector decoded from a coded stream, in case that the inter-prediction mode is selected as the prediction mode to be performed; and
performing an inter-prediction process of the selected prediction mode using the motion vector calculated in the motion vector calculating step, in case that the inter-prediction mode is selected as the prediction mode to be performed,
wherein the predictive motion vector calculating step includes:
a first process to select a plurality of candidate blocks among blocks decoded prior to a block to be decoded, the candidate blocks are selected from five or more blocks, the five or more blocks including peripheral blocks in the same frame as the block to be decoded and a block in a different frame from the block to be decoded,
a second process to use any one of a first value and a second value when a difference between the first value and the second value in motion vector values of the plurality of candidate blocks is within a predetermined threshold,
a third process to make a motion vector list listing a plurality of motion vector values including the motion vector value of the first value or the second value selected in the second process and a motion vector value other than the first value and the second value in the motion vector values of the plurality of candidate blocks selected in the first process,
a fourth process to retrieve selection information from the coded stream, and
a fifth process to select one motion vector value among the plurality of motion vector values listed in the motion vector list,
wherein the one motion vector value selected from the plurality of motion vector values listed in the motion vector list is determined based on the selection information regardless of the differential motion vector,
wherein the number of the plurality of motion vector values listed in the motion vector list is smaller than five, and
wherein the block in a different frame from the block to be decoded, referred to in the first process is a block located at the same position as the block to be decoded in the different frame from the block to be decoded.
2. A method comprising:
selecting a prediction mode to be performed among a plurality of prediction modes including an intra-prediction mode and an inter-prediction mode;
calculating a predictive motion vector in case the inter-prediction mode is selected as the prediction mode to be performed;
calculating a motion vector by summing the calculated predictive motion vector and a differential motion vector decoded from a coded stream, in case the inter-prediction mode is selected as the prediction mode to be performed; and
performing an inter-prediction process of the selected prediction mode using the calculated motion vector in case the inter-prediction mode is selected as the prediction mode to be performed,
wherein the calculating the predictive motion vector includes:
selecting a plurality of candidate blocks among blocks decoded prior to a block to be decoded, the candidate blocks being selected from five or more blocks, the five or more blocks including peripheral blocks in the same frame as the block to be decoded and a block in a different frame from the block to be decoded,
using one of a first value or a second value when a difference between the first value and the second value in motion vector values of the plurality of candidate blocks is within a predetermined threshold,
generating a motion vector list listing a plurality of motion vector values including the motion vector value of the first value or the second value, and a motion vector value other than the first value and the second value in the motion vector values of the plurality of candidate blocks,
retrieving selection information from the coded stream, and
selecting one motion vector value among the plurality of motion vector values listed in the motion vector list,
wherein the one motion vector value selected from the plurality of motion vector values listed in the motion vector list is determined based on the selection information regardless of the differential motion vector,
wherein the number of the plurality of motion vector values listed in the motion vector list is smaller than five, and
wherein the block in a different frame from the block to be decoded, referred to in the selecting a plurality of candidate blocks, is a block located at the same position as the block to be decoded in the different frame from the block to be decoded.