Method and apparatus for encoding/decoding images using a motion vector
The present invention relates to image processing, and more particularly, to a video coding/decoding method using a clipped motion vector and an apparatus thereof. An embodiment of the present invention relates to a method of decoding an image. The method includes clipping a motion vector of a reference picture in a predetermined dynamic range to generate a clipped motion vector, storing the clipped motion vector in a buffer, deriving a motion vector of a coding treeblock using the motion vector stored in the buffer, and performing inter prediction decoding process using the motion vector of the coding treeblock. According to the exemplary embodiment of the present invention, a size of a memory required for storing motion vectors may be reduced.
1. An image decoding apparatus, characterized by comprising:
a reference picture buffer for storing a reference picture; and
a motion compensating unit for:
calculating a scaling factor based on a picture order count of the reference picture,
clipping the scaling factor in a first predetermined range,
scaling a motion vector of the reference picture based on the clipped scaling factor,
clipping the scaled motion vector of the reference picture in a second predetermined range, and
generating a prediction block using the reference picture and the clipped scaled motion vector of the reference picture;
wherein the scaled motion vector of the reference picture is clipped in the second predetermined range after the motion vector of the reference picture is scaled,
wherein the scaling of the motion vector of the reference picture is performed based on the picture order count of the reference picture,
wherein the motion vector of the reference picture is determined as a motion vector of a collocated block in the reference picture, and
wherein the collocated block is determined by performing the ordered steps of:
calculating a first position corresponding to a right-bottom position representing a position displaced from an upper-left position of a current block in a current picture by a height and a width of the current block;
determining a first block covering the calculated first position in the reference picture;
determining whether the first block is coded in an intra prediction mode,
calculating, when the first block is coded in an intra prediction mode, a second position corresponding to a central position of the current block in the current picture;
modifying the second position based on an arithmetic shift operation; and
determining a second block covering the modified second position in the reference picture,
wherein the clipped scaled motion vector for generating a prediction block is modified based on the motion vector resolution derived by first motion vector resolution information and second motion vector resolution information,
the first motion vector resolution information about a motion vector resolution for all blocks referring to a sequence parameter set is obtained from the sequence parameter set, and
the second motion vector resolution information specifying whether a motion vector resolution for all blocks in a current slice is an integer pixel unit is obtained from a slice header of the current slice.
2. The image decoding apparatus of claim 1 , wherein the motion vector of the collocated block is restored in a predetermined block unit.
3. The image decoding apparatus of claim 1 , wherein the second predetermined range is a fixed value range.
4. The image decoding apparatus of claim 3 , wherein the motion compensator is further configured to clip X and Y components of the scaled motion vector in the same fixed value range.
5. The image decoding apparatus of claim 1 , wherein the motion vector of the reference picture is a motion vector of a block decoded in an inter-prediction mode.
6. An image encoding apparatus, characterized by comprising:
a reference picture buffer for storing a reference picture; and
a motion compensating unit for:
calculating a scaling factor based on a picture order count of the reference picture,
clipping the scaling factor in a first predetermined range,
scaling a motion vector of the reference picture based on the clipped scaling factor,
clipping the scaled motion vector of the reference picture in a second predetermined range, and
encoding a motion vector of a current block based on the clipped scaled motion vector of the reference picture,
wherein the scaled motion vector of the reference picture is clipped in the second predetermined range after the motion vector of the reference picture is scaled,
wherein the scaling of the motion vector of the reference picture is performed based on the picture order count of the reference picture,
wherein the motion vector of the reference picture is determined as a motion vector of a collocated block in the reference picture, and
wherein the collocated block is determined by performing the ordered steps of:
calculating a first position corresponding to a right-bottom position representing a position displaced from an upper-left position of the current block in a current picture by a height and a width of the current block;
determining a first block covering the calculated first position in the reference picture;
determining whether the first block is coded in an intra prediction mode,
calculating, when the first block is coded in an intra prediction mode, a second position corresponding to a central position of the current block in the current picture;
modifying the second position based on an arithmetic shift operation; and
determining a second block covering the modified second position in the reference picture,
wherein the clipped scaled motion vector for generating a prediction block is modified based on the motion vector resolution derived by first motion vector resolution information and second motion vector resolution information,
the first motion vector resolution information about a motion vector resolution for all blocks referring to a sequence parameter set is obtained from the sequence parameter set, and
the second motion vector resolution information specifying whether a motion vector resolution for all blocks in a current slice is an integer pixel unit is obtained from a slice header of the current slice.
7. A bitstream transmitting method to transmit a bitstream comprising:
generating the bitstream by encoding an image based on an image encoding method; and
transmitting the bitstream, and
wherein the image encoding method comprises:
calculating a scaling factor based on a picture order count of a reference picture,
clipping the scaling factor in a first predetermined range,
scaling a motion vector of the reference picture based on the clipped scaling factor,
clipping the scaled motion vector of the reference picture in a second predetermined range, and
encoding a motion vector of a current block based on the clipped scaled motion vector of the reference picture,
wherein the scaled motion vector of the reference picture is clipped in the second predetermined range after the motion vector of the reference picture is scaled,
wherein the scaling of the motion vector of the reference picture is performed based on the picture order count of the reference picture,
wherein the motion vector of the reference picture is determined as a motion vector of a collocated block in the reference picture, and
wherein the collocated block is determined by performing the ordered steps of:
calculating a first position corresponding to a right-bottom position representing a position displaced from an upper-left position of the current block in a current picture by a height and a width of the current block;
determining a first block covering the calculated first position in the reference picture;
determining whether the first block is coded in an intra prediction mode,
calculating, when the first block is coded in an intra prediction mode, a second position corresponding to a central position of the current block in the current picture;
modifying the second position based on an arithmetic shift operation; and
determining a second block covering the modified second position in the reference picture,
wherein the clipped scaled motion vector for generating a prediction block is modified based on the motion vector resolution derived by first motion vector resolution information and second motion vector resolution information,
the first motion vector resolution information about a motion vector resolution for all blocks referring to a sequence parameter set is obtained from the sequence parameter set, and
the second motion vector resolution information specifying whether a motion vector resolution for all blocks in a current slice is an integer pixel unit is obtained from a slice header of the current slice.