Method of coding and decoding image
A method of simplifying the arithmetic operation in a global motion compensation process approximates the motion vector field of the whole image without using many parameters. Motion vectors in the global motion compensation are found by the interpolation and/or extrapolation of the motion vectors of a plurality of representative points 602, 603 and 604 having particular features in the spatial distance thereof. Since the shift operation can be substituted for the division for synthesizing a predicted image of global motion compensation, the processing using a computer or a dedicated hardware is simplified.
1. A method for decoding images comprising:
a step for storing a reference image, which is a decoded image of a previously decoded frame;
a step for calculating a motion vector of each pixel in a predicted image of a current frame by using motion vectors or representative points having coordinates (i, j), (i+p, j), (i, j+q), where i and j are integers, and p and q are powers of integers of 2; and
a step for synthesizing said predicted image by using said motion vector of each pixel and said reference image, wherein:
the horizontal and vertical components of said motion vector of each pixel are integral multiples of 1/m;
the horizontal and vertical components of said motion vectors of representative points are integral multiples of 1/k; and
said motion vector of each pixel is calculated according to equations:
u ( x,y )=(( u 0 pq +( u 1− u 0)( x−i ) q +( u 2− u 0)( y−j ) p ) m )//( pqk ),
v ( x,y )(( v 0 pq +( v 1− v 0)( x−i ) q +( v 2− v 0)( y−j ) p ) m )//( pqk ),
where (u,(x, y), v(x, y)) is m times of a motion vector of a pixel having coordinates (x, y), (u0, v0), (ul, vl), and (u2, v2) are k times of said motion vectors of said representative points (i, j), (i+p, j), and (i, j+q) respectively, m and k are powers of integers of 2, “//” represents integer division that rounds the quotient of ordinary division into an adjacent integer when the quotient of ordinary division is not an integer, and its priority as an operator is the same as that of ordinary multiplication and division, and u(x,y), v(x,y), u0, v0, ul, v1, u2 and v2 are integers.
2. A method for decoding images according to claim 1 , wherein said “//” rounds a quotient of ordinary division of which the value is the sum of an integer and 1/2 toward 0 when the dividend is negative, and away from 0 when the dividend is positive.