Patent ID: 7856053

Claim:
An image coding control method for controlling a quantization parameter by using a prediction mode selected from plural prediction modes every any coding unit, comprising: calculating an undetermined multiplier serving as a parameter used for a cost function from a given reference quantization parameter; selecting a set of secondary number of coded bits-coding distortion pairs from a set of primary number of coded bits-coding distortion pairs that correspond to plural combinations of the prediction mode and the quantization parameter every coding unit; selecting number of coded bits-coding distortion pairs providing the minimum cost function as the optimal number of coded bits-coding distortion pairs from the set of the secondary number of coded bits-coding distortion pairs by using the undetermined multiplier thus calculated every coding unit; and determining a prediction mode and a quantization parameter used for the coding from the optimal number of coded bits-coding distortion pairs, wherein when the set of the secondary number of coded bits-coding distortion pairs is selected every coding unit, (1) a convex hull comprising the set of the primary number of coded bits-coding distortion pairs is formed on a two-dimensional orthogonal coordinate system in which the number of coded bits is set as one axis and the coding distortion is set as the other axis, (2) a set on the convex hull that connect the position of a number of bits-coding distortion pair providing the minimum number of coded bits and the position of a number of coded bits-coding distortion pair providing the minimum coding distortion is determined, and (3) a set of number of coded bits-coding distortion pairs that is on the convex hull and exists at a nearer side to the origin of the two-dimensional orthogonal coordinate system is selected as a set of the secondary number of coded bits-coding distortion pairs.