Digital video filter sequence for bandwidth constrained systems

Abstract

A video filter unit is described which is implemented as a three-stage filter comprising a vertical filter, a horizontal decimation filter, and a horizontal interpolation filter. The three stages of the filter unit preferably connect serially with the vertical filter comprising the input first stage, the horizontal decimation filter comprising the second stage and the horizontal interpolation filter comprising the third stage which provides the output filtered image from the filter unit. As such, the video data to be filtered is provided to the vertical filter which provides its output to the horizontal decimation filter. After horizontal decimation, which can be disabled if desired (i.e., no horizontal decimation), the video data is then horizontally interpolated. The horizontal interpolation filter stage can also be disabled if desired. The vertical filter can be configured to operate either as a decimation filter or an interpolation filter. The vertical filter is a four-tap filter and thus calculates weighted averages of four video values (e.g. luminance values) at a time. The horizontal decimation filter preferably is implemented as a two-tap filter and thus averages two video values at a time. Lastly, the horizontal interpolation filter comprises an eight-tap filter and, accordingly, calculates a weighted average of eight video values.