Image encoding/decoding method and device using coefficients of adaptive interpolation filter

An image encoding method, the method comprising:

• calculating adaptive interpolation filter coefficients of a current frame;
• encoding the current frame by using an interpolated reference frame after interpolating the reference frame with a fractional pixel precision by using the adaptive interpolation filter coefficients of the current frame;
• determining whether to interpolate the reference frame by using adaptive interpolation filter coefficients of a previous frame, based on a comparison between the adaptive interpolation filter coefficients of the current frame and the adaptive interpolation filter coefficients of the previous frame;
• encoding a coefficient-inserted flag or a coefficient non-inserted flag as a filter flag into a bit stream, based on the result of the determining;
• and
• encoding the adaptive interpolation filter coefficients of the current frame into the bit stream when the filter flag is the coefficient-inserted flag,
• wherein the bit stream includes the encoded current frame, the encoded filter flag and the encoded adaptive interpolation filter coefficients of the current frame, when the filter flag is the coefficient-inserted flag, and
• wherein the bit stream includes the encoded current frame and the encoded filter flag but without the encoded adaptive interpolation filter coefficients of the current frame, when the filter flag is the coefficient non-inserted flag, wherein the coefficient non-inserted flag indicates that the adaptive interpolation filter coefficients of the previous frame are used as the adaptive interpolation filter coefficients of the current frame.

An image decoding apparatus, the apparatus comprising:

• a filter flag decoder configured to extract and decode an encoded filter flag of a current frame from a bit stream, to reconstruct a filter flag;
• a coefficient decoder configured to extract and decode, when the reconstructed filter flag is a coefficient-inserted flag, encoded adaptive interpolation filter coefficients of the current frame from the bit stream, to reconstruct the adaptive interpolation filter coefficients of the current frame;
• an image decoder configured to
• extract an encoded current frame from the bit stream,
• interpolate a reference frame with a fractional pixel precision by using either of (i) the reconstructed adaptive interpolation filter coefficient of the current frame when the filter flag is the coefficient-inserted flag and (ii) previously reconstructed adaptive interpolation filter coefficients of a previous frame when the filter flag is a coefficient non-inserted flag, wherein the coefficient non-inserted flag indicates that the previously reconstructed adaptive interpolation filter coefficients of the previous frame are used as the reconstructed adaptive interpolation filter coefficients of the current frame, and
• decode the encoded current frame by using the interpolated reference frame, to reconstruct the current frame.

An image decoding method, the method comprising:

• extracting and decoding an encoded filter flag of a current frame from a bit stream, to reconstruct a filter flag;
• extracting and decoding, when the reconstructed filter flag is a coefficient-inserted flag, extracting and decoding an encoded adaptive interpolation filter coefficients of the current frame from the bit stream, to reconstruct the adaptive interpolation filter coefficients of the current frame;
• extracting an encoded current frame from the bit stream
• interpolating a reference frame with a fractional pixel precision by using either of (i) the reconstructed adaptive interpolation filter coefficients of the current frame when the filter flag is the coefficient-inserted flag and (ii) previously reconstructed interpolation filter coefficients of a previous frame when the filter flag is a coefficient non-inserted flag, wherein the coefficient non-inserted flag indicates that the previously reconstructed adaptive interpolation filter coefficients of the previous frame are used as the reconstructed adaptive interpolation filter coefficients of the current frame;
• and
• decoding the encoded current frame by using the interpolated reference frame, to reconstruct the current frame.