Patent ID: 8396125

Claim:
A picture coding apparatus which codes a current picture to be coded using at least bi-directional prediction for two fields making up an inputted frame, the picture coding apparatus comprising: a correlation degree calculating unit configured to calculate (i) a first correlation degree indicating a correlation between a first field of an inputted first frame and a second field of the first frame, and (ii) a second correlation degree indicating a correlation between the first field and a field of a coded frame adjacent to the first frame; a picture type determining unit configured to limit pictures that are referred to when a picture is coded using bi-directional prediction, by determining one of (i) a first bi-directional prediction picture type whose picture is coded using bi-directional prediction and is not a reference picture of another picture, and (ii) a second bi-directional prediction picture type whose picture is coded using bi-directional prediction and is a reference picture of another picture, as a picture type of the first field or the second field, based on the first correlation degree and the second correlation degree, in the case of performing bi-directional prediction for the first frame; and a coding unit configured to code the first field or the second field according to the determined picture type; wherein the correlation degree calculating unit is configured to calculate the first correlation degree and the second correlation degree based on a luminance value of the first field, a luminance value of the second field, and a luminance value of the field of the coded frame adjacent to the first frame.