1. An image processing apparatus comprising: setting means for setting, as a decoded region, a region that is adjacent to a target block of a decoding target image, which is a target to be decoded, and that is decoded earlier than the target block, and for setting, as the reference region, a region whose positional relationship with a reference block of a reference image is the same as a positional relationship of the decoded region; calculating means for calculating a filter coefficient of a filter that converts pixel values of the reference region set by the setting means into pixel values of the decoded region set by the setting means; interpolating means for interpolating pixel values of the reference block by using an adjustment filter having the filter coefficient calculated by the calculating means; and generating means for generating a prediction image corresponding to the decoding target image by motion-compensating the reference block having the pixel values interpolated by the interpolating means for the target block.