Method and apparatus for PCM-encoding NTSC color television at sub-Nyquist rate

Apparatus for digitally encoding an NTSC color television signal having a color subcarrier frequency F.sub.sc and a line scan frequency F.sub.h, comprising, in combination:

• means for generating a sampling sigal having a frequency 2F.sub.sc and the sampling phase of which shifts by 180.degree. every alternate time sequential television line;
• means for sampling the television signal in response to said sampling signal;
• and
• means for converting the sampled television signal into digital form.

Apparatus for deriving from a pulse code modulated NTSC color television signal having a color subcarrier frequency F.sub.sc, a line scan frequency F.sub.h, a maximum baseband frequency F.sub.v, and sampled at a sub-Nyquist sampling frequency of 2F.sub.sc, a pulse code modulated color television signal having a sampling frequency of 4F.sub.sc, said apparatus comprising:

• means for delaying said 2F.sub.sc sampled signal by two television lines,
• means for high-pass filtering said delayed 2F.sub.sc sampled signal to pass frequencies in the band above (2F.sub.sc -F.sub.v),
• means for low-pass filtering said 2F.sub.sc sampled signal to pass frequencies in the band from D.C. to (2F.sub.sc -F.sub.v),
• means for interpolating said low-pass filtered 2F.sub.sc sampled signal to generate video samples that are time-coincident with video samples of said 2F.sub.sc sampled signal delayed by two television lines,
• means for adding said high-pass filtered delayed sampled signal to said interpolated low-pass fitered sampled signal, and
• means for alternately switching the output signal from said adding means and said 2F.sub.sc sampled signal to an apparatus output terminal at a switching rate of 4F.sub.sc.

A system for encoding a composite NTSC color television signal including luminance and chrominance components wherein the chrominance component is formed by modulating a subcarrier wave having a frequency F.sub.sc with chrominance information, the frequency F.sub.sc having m/2 of the line scan frequency F.sub.h of said television signal, where m is an odd number, the phase of said subcarrier wave shifting by 180.degree. between two adjacent lines, said encoding system comprising:

• means for producing sampling pulses having a repetition frequency 2F.sub.sc ;
• means for sampling and encoding said television signal in response to said sampling pulses;
• and
• means for controlling said sampling pulses to cause samples of said television signal to be taken at points about 180.degree. of said subcarrier wave away from each other in each scanning line and also about 90.degree. of said subcarrier wave away from the samples taken in alternate time sequential scanning lines.