An adaptive spatio-temporal filter for use in video quality of service instruments
based on human vision system models has a pair of parallel, lowpass, spatio-temporal
filters receiving a common video input signal. The outputs from the pair of lowpass
spatio-temporal filters are differenced to produce the output of the adaptive spatio-temporal
filter, with the bandwidths of the pair being such as to produce an overall bandpass
response. A filter adaptation controller generates adaptive filter coefficients
for each pixel processed based on a perceptual parameter, such as the local average
luminance, contrast, etc., of either the input video signal or the output of one
of the pair of lowpass spatio-temporal filters. Each of the pair of lowpass spatio-temporal
filters has a temporal IIR filter in cascade with a 2-D spatial IIR filter, and
each individual filter is composed of a common building block,5 i.e., a first order,
unity DC gain, tunable lowpass filter having a topology suitable for IC implementation.
At least two of the building blocks make up each filter with the overall adaptive
spatio-temporal filter response having a linear portion and a non-linear portion,
the linear portion being dominant at low luminance levels and the non-linear portion
being consistent with enhanced perceived brightness as the luminance level increases.
