Method and apparatus for encoding/decoding images using a motion vector

An image encoding method comprising:

• calculating a scaling factor for a current block in a current picture 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 which is defined as a predetermined fixed value range,
• determining first motion vector resolution information to be encoded in a sequence parameter set, wherein the first motion vector resolution information is about motion vector resolutions for all blocks referring to the sequence parameter set,
• determining second motion vector resolution information specifying whether motion vector resolutions used for all blocks in the current picture are only integer pixel resolutions,
• modifying the clipped scaled motion vector of the reference picture based on a motion vector resolution derived by the first motion vector resolution information and the second motion vector resolution information,
• generating a prediction block based on the modified motion vector of the reference picture,
• encoding the motion vector of the current block based on the modified motion vector of the reference picture, and
• encoding 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 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 a bitstream,
• wherein the second motion vector resolution information is encoded in a picture header of the current picture within the bitstream.

A method of transmitting a bitstream generated by an image encoding method, the method comprising:

• encoding an image based on the image encoding method;
• and
• transmitting a bitstream including the encoded image,
• wherein the image encoding method comprises:
• calculating a scaling factor for a current block in a current picture 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 which is defined as a predetermined fixed value range,
• determining first motion vector resolution information to be encoded in a sequence parameter set, wherein the first motion vector resolution information is about motion vector resolutions for all blocks referring to the sequence parameter set,
• determining second motion vector resolution information specifying whether motion vector resolutions used for all blocks in the current picture are only integer pixel resolutions,
• modifying the clipped scaled motion vector of the reference picture based on a motion vector resolution derived by the first motion vector resolution information and the second motion vector resolution information,
• generating a prediction block based on the modified motion vector of the reference picture,
• encoding the motion vector of the current block based on the modified motion vector of the reference picture, and
• encoding 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 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 picture header of the current picture within the bitstream.