Patent ID: 7724969

Claim:
A method of decoding images comprising the steps of: extracting motion vector information, quantized DCT coefficients, and rounding method information from input information to be decoded, the rounding method information specifying a rounding method used in bilinear interpolation; synthesizing a prediction image by performing motion compensation using the motion vector information and a reference image which is a previously decoded image; and synthesizing a currently decoded image by adding the prediction image to an error image obtained by applying dequantization and inverse DCT conversion to the quantized DCT coefficients; wherein the motion compensation is performed with half-pixel accuracy and uses bilinear interpolation to calculate intensity values of chrominance or luminance at points where no pixels actually exist in the reference image, the bilinear interpolation being performable using a positive rounding method and a negative rounding method; wherein the bilinear interpolation is performed using the rounding method specified by the rounding method information; wherein the rounding method information is included in coded information of the currently decoded image; wherein the rounding method information is included in a header section of the coded information of the currently decoded image; wherein the rounding method information specifies one of two values; and wherein one of the two values specifies a positive rounding method, and another one of the two values specifies a negative rounding method.