Processing of N.T.S.C. color television signals

A method of encoding Y, I and Q signals into an N.T.S.C. colour television signal, comprising:

• spectrum folding the luminance signal Y with respect to a frequency twice the colour subcarrier frequency, the sampling phase being changed between each pair of lines by an amount equal to half the interval between samples;
• comb filtering the resultant luminance signal using a delay of an odd number of lines to provide a modulus sine response having peaks at integral multiples of f.sub.L /N, where f.sub.L is the television line frequency, and N is an odd integer;
• forming the I and Q signals into a composite chrominance signal C based on I and Q;
• modulating the chrominance signal C onto the phase perturbed colour subcarrier frequency;
• comb filtering the modulated chrominance signal with a modulus sine response having peaks at odd integral multiples of f.sub.L /2N;
• and
• combining the luminance and modulated chrominance signals.

A method of decoding an N.T.S.C. colour television signal into Y, I and Q signals, comprising:

• comb filtering the N.T.S.C. signal using a delay of an odd number of lines to provide a modulus sine response having peaks at integral multiples of f.sub.L /N, where f.sub.L is the television line frequency, and N is an odd integer;
• spectrum folding the said comb filtered signal with respect to a frequency twice the colour subcarrier frequency the sampling phase of which is changed between each pair of lines by an amount equal to half the interval between samples, to provide a luminance signal;
• comb filtering the N.T.S.C. signal with a modulus sine response having peaks at odd integral multiples of f.sub.L /2N;
• and
• multiplying the last-mentioned comb filtered signal by a signal of subcarrier frequency the sampling phase of which is likewise changed.

An N.T.S.C. coder for encoding Y, I and Q signals into an N.T.S.C. colour television signal, comprising:

• luminance processing circuitry adapted to cause spectrum folding of a luminance input signal Y with respect to a phase-perturbed frequency twice the colour subcarrier frequency but with its phase inverted between each pair of lines to produce alias components in the video band, and to comb filter the resultant luminance signal using a delay of an odd number of lines to provide a modulus sine response having peaks at integral multiples of f.sub.L /N, where f.sub.L is the television line frequency, and N is an odd integer;
• chrominance processing circuitry adapted to form the I and Q signals into a composite chrominance signal C based on I and Q, to modulate the chrominance signal C onto the phase perturbed colour subcarrier frequency, and to comb filter the modulated chrominance signal with a modulus sine response having peaks at odd integral multiples of f.sub.L /2N;
• and
• combining means for combining the luminance and modulated chrominance signals.