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 comprising:
a reference picture buffer to store a reference picture; and
one or more processors to
calculate a scaling factor based on a picture order count of the reference picture, clip the scaling factor in a first predetermined range,
scale a motion vector of the reference picture based on the clipped scaling factor, clip the scaled motion vector of the reference picture in a second predetermined range,
generate a prediction block based on the reference picture and the clipped scaled motion vector of the reference picture, and
reconstruct a current block in a current picture based on the prediction block,
wherein the motion vector of the reference picture is determined as a motion vector of a collocated block in the reference picture,
wherein the motion vector of 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 the current picture by the current block's height and width,
determining a first block covering the 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, and
determining a second block covering the second position in the reference picture.
2. The image decoding apparatus of claim 1 , wherein the second predetermined range is a fixed value range.
3. The image decoding apparatus of claim 1 , wherein the motion vector of the reference picture is stored in a predetermined block unit, and
wherein the motion compensator is further configured to generate the prediction block using the motion vector of the reference picture stored in the predetermined block unit.
4. The image decoding apparatus of claim 2 , wherein the motion compensator is further configured to clip X and Y components of the scaled motion vector in a 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 comprising:
a reference picture buffer to store a reference picture;
one or more processors to generate a motion vector of a current block in a current picture and a prediction block of the current block based on the reference picture; and
an encoder configured to
calculate a scaling factor based on a picture order count of the reference picture,
clip the scaling factor in a first predetermined range,
scale a motion vector of the reference picture based on the clipped scaling factor,
clip the scaled motion vector of the reference picture in a second predetermined range,
encode the motion vector of the current block based on the clipped scaled motion vector of the reference picture, and
encode the current block based on the prediction block,
wherein the motion vector of the reference picture is determined as a motion vector of a collocated block in the reference picture,
wherein the motion vector of 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 the current picture by the current block's height and width,
determining a first block covering the 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, and
determining a second block covering the second position in the reference picture.
7. A non-transitory computer-readable storage medium storing a bitstream, wherein the bitstream is generated by an image encoding apparatus,
wherein the image encoding apparatus comprises
a reference picture buffer to store a reference picture;
a motion estimator to generate a motion vector of a current block in a current picture and a prediction block of the current block based on the reference picture; and
one or more processors to
calculate a scaling factor based on a picture order count of the reference picture,
clip the scaling factor in a first predetermined range,
scale a motion vector of the reference picture based on the clipped scaling factor,
clip the scaled motion vector of the reference picture in a second predetermined range,
encode the motion vector of the current block based on the clipped scaled motion vector of the reference picture, and
encode the current block based on the prediction block,
wherein the motion vector of the reference picture is determined as a motion vector of a collocated block in the reference picture,
wherein the motion vector of 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 the current picture by the current block's height and width,
determining a first block covering the 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, and
determining a second block covering the second position in the reference picture.
8. A non-transitory computer-readable storage medium storing a bitstream that is received and decoded by an image decoding apparatus to reconstruct a current block included in an image, the bitstream comprising:
prediction information of the current block,
wherein the image decoding apparatus comprises a reference picture buffer to store a reference picture, and one or more processors,
wherein, based on the prediction information, the one or more processors
calculate a scaling factor based on a picture order count of the reference picture,
clip the scaling factor in a first predetermined range,
scale a motion vector of the reference picture based on the clipped scaling factor,
clip the scaled motion vector of the reference picture in a second predetermined range,
generate a prediction block based on the reference picture and the clipped scaled motion vector of the reference picture, and
reconstruct a current block in a current picture based on the prediction block,
wherein the motion vector of the reference picture is determined as a motion vector of a collocated block in the reference picture,
wherein the motion vector of 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 the current picture by the current block's height and width,
determining a first block covering the 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, and
determining a second block covering the second position in the reference picture.