An adaptive circuit and method for separating luminance and chrominance
components from a composite video signal by deriving three input lines
from the composite video signal, determining whether any luminance
similarity exists among the three input lines, and then selectively
enabling a component filter based on any luminance similarity. If no
luminance similarity exists among all three of the input lines, then a
subtractive comb filter is enabled to maintain high vertical luminance
resolution. If luminance similarity exists among all three of the input
lines, then an additive comb filter is enabled. The additive comb filter
performs three-line averaging when a high degree of similarity exists
among all three consecutive input lines to minimize cross-chroma
artifacts on lines that are similar. Chrominance similarity among the
three input lines can also be determined by generating first and second
chrominance values using different pairs of the three input lines,
computing a difference of the first and second chrominance values, and
comparing the chroma difference to a threshold value. If no luminance
similarity exists between any of the three input lines or no chrominance
similarity exists (i.e., there is vertical chroma transition), then a
notch filter incorporated into the subtractive comb filter can be
enabled.