Adaptive interpolation filters for video coding

An apparatus comprising:

• a processor;
• and
• memory including computer program code, the memory and the computer program configured to, with the processor, cause the apparatus at least to
• select a filter type for an interpolation filter based on symmetry properties of images in a digital video sequence for providing encoded data indicative of the video sequence wherein the interpolation filter is for use in motion compensated prediction for encoding the images in the encoded data indicative of the video sequence,
• calculate coefficient values for the interpolation filter based on the filter type, and
• provide information in the encoded data indicating the filter type, the calculated coefficient values, and a tap length of the interpolation filter, wherein the tap length of the interpolation filter is indicative of a number of the coefficient values of the interpolation filter.

A method for decoding encoded video data indicative of a digital video sequence comprising a sequence of video frames, each frame of the video sequence comprising a plurality of pixel values, said method comprising:

• retrieving from the encoded video data a filter type, a set of coefficient values of an interpolation filter and an indication of a tap length of said at least one interpolation filter, the tap length of the interpolation filter indicative of a number of coefficients of the interpolation filter;
• and
• constructing the interpolation filter based on the filter type, the set of coefficient values and the tap length, and
• reconstructing the pixel values in a frame of the video sequence based on the constructed interpolation filter and the encoded video data.

An apparatus comprising:

• a processor;
• and
• memory including computer program code, the memory and the computer program code configured to, with the processor, cause the apparatus at least to
• retrieve from encoded video data a filter type, a set of coefficient values of an interpolation filter and an indication of a tap length of the interpolation filter;
• and
• construct the interpolation filter based on the filter type, the set of coefficient values of the interpolation filter and the tap length, wherein the tap length of the interpolation filter is indicative of a number of coefficients of the interpolation filter, wherein the encoded video data is indicative of a digital video sequence comprising a sequence of video frames, each frame of the video sequence comprising a plurality of pixel values, and wherein the memory and the computer program are also configured to cause the apparatus to construct the pixel values in a frame of the video sequence based on the constructed interpolation filter and the encoded video data.

A video coding system comprising:

• an encoder for encoding images in a digital video sequence having a sequence of video frames for providing encoded video data indicative of the video sequence, and
• a decoder for decoding the encoded video data, wherein
• the encoder comprises:
• a selection module for selecting a filter type for an interpolation filter based on symmetry properties of images in the digital video sequence for providing the encoded video data indicative of the video sequence wherein the interpolation filter is for use in motion compensated prediction for encoding the images in the encoded data indicative of the video sequence, wherein said least one interpolation filter has a tap length, wherein the tap length of the interpolation filter is indicative of a number of coefficients of the interpolation filter, and wherein said apparatus is configured to provide information indicating the tap length in the encoded data, wherein the interpolation filter is representable by a plurality of coefficient values,
• a module for calculating the coefficient values based on the filter type, and
• a multiplexing module for providing information in the encoded data indicating the filter type, the calculated coefficients values, and the tap length in the encoded video data;
• and
• the decoder comprises:
• a demultiplexing module for retrieving from the encoded video data, the filter type, the set of coefficient values of the interpolation filter and the tap length of the interpolation filter, and
• a filter construction module for constructing the interpolation filter based on the filter type, the set of coefficient values and the tap length.