Method and device for processing video signal by means of affine prediction

An apparatus for processing a video signal comprising a current block using an affine prediction mode, the apparatus comprising:

• a memory;
• and
• an inter prediction unit configured to generate a candidate list of motion vector pairs using a motion vector of a pixel or block neighboring at least two control points of the current block, determine a final candidate list of a predetermined number of motion vector pairs based on a divergence value of the motion vector pair, determine a control point motion vector of the current block based on a rate-distortion cost from the final candidate list, and generate a motion vector predictor of the current block based on the control point motion vector,
• wherein the control point comprises at least two of a top left corner pixel, a top right corner pixel, a bottom left corner pixel or a bottom right corner pixel of the current block,
• wherein the motion vector pair indicates motion vectors of the top left corner pixel and the top right corner pixel or the top left corner pixel, the top right corner pixel and the bottom left corner pixel of the current block,
• wherein the candidate list is configured with motion vectors of pixels or blocks neighboring the top left corner pixel, the top right corner pixel, and the bottom left corner pixel, and
• wherein the final candidate list is determined in order of smaller divergence value, and the divergence value is calculated based on a difference of x component between the motion vectors, a difference of y component between the motion vectors, and height and width of the current block and becomes smaller when the motion vectors have similar directions.