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 for a current block in a current picture 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 which is defined as a predetermined fixed value range,
obtain first motion vector resolution information from a sequence parameter set within a bitstream, wherein the first motion vector resolution information in the sequence parameter set specifies a first motion vector resolution,
obtain second motion vector resolution information, from a slice header of a current slice within a bitstream, specifying whether a second motion vector resolution for all blocks in the current slice is an integer pixel unit,
modify the clipped scaled motion vector of the reference picture based on a motion vector resolution derived by the first motion vector resolution information and second motion vector resolution information,
generate a prediction block based on the reference picture and the modified motion vector of the reference picture, and
reconstruct the current block in the current picture by adding the prediction block and a residual block of the current block,
wherein the motion vector of the reference picture is determined as a motion vector of a collocated block in the reference picture, and
wherein determining the motion vector of the collocated block by the one or more processors comprises:
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,
calculating a second position corresponding to a central position of the current block in the current picture in case that the first block is coded in an intra prediction mode, and
determining a second block covering the second position in the reference picture.
2. The image decoding apparatus of claim 1 , wherein X and Y components of the scaled motion vector are clipped in a same fixed value range.
3. 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.
4. 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 which is defined as a predetermined fixed value range,
determine first motion vector resolution information to be encoded in a sequence parameter set, wherein the first motion vector resolution information in the sequence parameter set specifies a first motion vector resolution,
determine second motion vector resolution information specifying whether a second motion vector resolution for all blocks in a current slice is an integer pixel unit,
modify the clipped scaled motion vector of the reference picture based on a motion vector resolution derived by the first motion vector n ation information and second motion vector resolution information,
encode the motion vector of the current block based on the modified motion vector of the reference picture, and
encode a residual block of the current block generated by subtracting the prediction block from the current block,
wherein the motion vector of the reference picture is determined as a motion vector of a collocated block in the reference picture, and
wherein determining the motion vector of the collocated block by the one or more processors comprises:
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,
calculating a second position corresponding to a central position of the current block in the current picture in case that the first block is coded in an intra prediction mode, and
determining a second block covering the second position in the reference picture,
wherein the first motion vector resolution on is encoded in the sequence parameter set within a bitstream,
wherein the second motion vector resolution information is encoded in a slice header of the current slice within a bitstream.
5. 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 which is defined as a predetermined fixed value range,
determine first motion vector resolution information to be encoded in a sequence parameter set, wherein the first motion vector resolution information in the sequence parameter set specifies a first motion vecto or resolution,
determine second motion vector resolution information specifying whether a second motion vector resolution for all blocks in a current slice is an integer pixel unit,
modify the clipped scaled motion vector of the reference picture based on a motion vector resolution derived by the first motion vector resolution information and second motion vector resolution information,
encode the motion vector of the current block based on the modified motion vector of the reference picture, and
encode a residual block of the current block generated by subtracting the prediction block from the current block,
wherein the motion vector of the reference picture is determined as a motion vector of a collocated block in the reference picture, and
wherein determining the motion vector of the collocated block by the one or more processors comprises:
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,
calculating a second position corresponding to a central position of the current block in the current picture in case that the first block is coded in an intra prediction mode, and
determining a second block covering the second position in the reference picture,
wherein the first motion vector resolution information is encoded in the sequence parameter set within the bitstream,
wherein the second motion vector resolution information is included in a slice header of the current slice within the bitstream.
6. 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 for a current block in a current picture 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 which is defined as a predetermined fixed value range,
obtain first motion resolution information from a sequence parameter set within a bitstream, wherein the first motion vector resolution information in the sequence parameter set specifies a first motion vector resolution,
obtain second motion vector resolution information, from a slice header of a current slice within the bitstream, specifying whether a second motion vector resolution for all blocks in the current slice is an integer pixel unit,
modify the resolution of the clipped scaled motion vector of the reference picture based on a motion vector resolution derived by the first motion vector resolution information and second motion vector resolution information,
generate a prediction block based on the reference picture and the modified motion vector of the reference picture, and
reconstruct the current block in the current picture by adding the prediction block and a residual block of the current block,
wherein the motion vector of the reference picture is determined as a motion vector of a collocated block in the reference picture, and
wherein determining the motion vector of the collocated block by the one or more processors comprises:
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,
calculating a second position corresponding to a central position of the current block in the current picture in case that the first block is coded in an intra prediction mode, and
determining a second block covering the second position in the reference picture.
7. The image decoding apparatus of claim 1 , wherein the motion vector of the reference picture is a motion vector restored in a block unit having a predetermined size, the predetermined size being greater than 4x4.