an hdtv down conversion system including apparatus for forming a set of low resolution down - sampled pixel values corresponding to a current frame of a video signal from a set of low resolution pixel values corresponding to a residual image of a current frame of the video signal and from a set of down - sampled low resolution pixel values corresponding to reference frames of the video signal . the apparatus includes a memory for storing the set of down - sampled low resolution pixel values . an up - sampling processor receives from the memory and uses lagrangian interpolation to convert the set of down - sampled low resolution pixel values corresponding to the reference frame of the video signal into a set of up - sampled low resolution pixel values corresponding to the reference frame of the video signal . a summing processor adds the set of low resolution pixel values corresponding to the residual image of the current frame of the video signal to the set of up - sampled low resolution pixel values corresponding to the reference frame of the video signal to form a set of low resolution pixel values corresponding to the current frame of the video signal . a decimating processor deletes selected ones of the set of low resolution pixel values corresponding to the current frame to generate the set of low resolution down - sampled pixel values corresponding to the current frame of the video signal .