Upsampling filter and half-pixel generator for an HDTV downconversion system

Upsampling filter circuitry for a digital video signal down conversion system which decodes a digitally encoded video signal representing a video image and decimates the decoded signal to produce a subsampled image signal that is stored for use as reference image data in decoding a subsequently received encoded image signal that is encoded as differential picture element (pixel) values relative to the earlier decoded image, the upsampling circuitry comprising:

• a programmable filter having a plurality of filter coefficient values;
• memory access circuitry which receives a motion vector, that defines the location of the desired segment with a resolution of one-half of one pixel position, from the encoded image signal, processes the received motion vector to locate a desired segment in the stored image, retrieves the desired segment from the stored subsampled image signal;
• a coefficient memory which holds a plurality of filter coefficient sets, each coefficient set corresponding to a distinct combination of subsampling phase and half-pixel position;
• and
• control circuitry which determines the subsampling phase of the desired segment from location information provided by the memory access circuitry and programs the programmable filter with the coefficient set that corresponds to the determined subsampling phase;
• wherein the programmable filter filters the retrieved desired segment to provide reference image data which corresponds to the decoded differential image data in image pixel position.

A method for upsampling data representative of a stored, subsampled digital image for use in a digital video signal down conversion system which decodes a digitally encoded video signal representing a video image and decimates the decoded signal to produce the stored subsampled image, wherein the subsampled image is stored for use as reference image data in decoding a subsequently received encoded image signal which is encoded as differential picture element (pixel) values relative to the earlier decoded image before the decoded image was subsampled, the upsampling method comprising the steps of:

• receiving a motion vector from the encoded image signal;
• processing the received motion vector to locate a desired segment in the stored image,
• retrieving the desired segment from the stored subsampled image signal;
• and
• determining, from the location of the desired segment, a subsampling phase of the desired segment;
• selecting, responsive to the determined subsampling phase of the desired segment, one set of coefficients from a plurality of coefficient sets, which one set of coefficients is to be used to filter the retrieved segment;
• and
• filtering the retrieved desired segment using the selected set of coefficients to produce reference image data which corresponds to the decoded differential image data in image pixel position.