System and method for improved composite decoding
View Patent ↗A method of composite decoding in which the input signal is converted into the frequency domain, and the symmetry of frequency components with respect to the subcarrier frequency is compared. The comparison is varied in dependence upon the frequency being processed. In this way, the separation can be adapted to suit known characteristics of different portions on the input spectrum. This is particularly useful for processing NTSC signals. The allocation of a particular component to chrominance may be biased in dependence upon a measure of the luminance information of the composite signal at a corresponding spatial frequency.
1. A method of separating the chrominance and luminance of a composite color television signal comprising:
receiving in a processor a set of first frequency components of the signal, receiving a set of second frequency components of the signal, each second component having a frequency difference from the color subcarrier equal and opposite to the frequency difference from the color subcarrier of the associated first frequency component,
comparing in a processor each of said first frequency components with the respective second frequency component in a comparison process having inputs for the magnitude of the frequency component being processed, the magnitude of the corresponding component symmetrically disposed with respect to subcarrier and the frequency of the frequency component being processed, and
determining in a processor on the basis of said comparison process whether a particular component represents chrominance or luminance;
wherein the nature of the comparison depends upon the frequency of the frequency component being processed.
2. A method according to claim 1 , in which the nature of the comparison depends upon the horizontal spatial frequency of the frequency component being processed.
3. A method according to claim 1 , in which the nature of the comparison depends upon the vertical spatial frequency of the first frequency component being processed.
4. A method according to claim 1 , in which the nature of the comparison depends upon the temporal frequency of the first frequency component being processed.
5. A method according to claim 1 , in which the nature of the comparison depends upon horizontal, vertical or temporal differences of the composite television signal.
6. A method according to claim 1 , in which the comparisons differ in dependence upon horizontal, vertical or temporal differences derived from the chrominance demodulated output of the composite television signal.
7. A method according to claim 1 , wherein the comparison varies in dependence upon the magnitude of a third frequency component of the signal, said third component having a frequency which corresponds to the equivalent baseband chrominance frequency of the first frequency component.
8. A method according to claim 7 , wherein said third component has a frequency equal to the frequency difference between the frequency of the first frequency component and the color subcarrier frequency.
9. A method according to claim 7 , wherein said third frequency component contains no chrominance information.
10. A method according to claim 7 , in which the separation favours chrominance when the third frequency component has a magnitude which is greater than a threshold value.
11. A method according to claim 7 , in which the separation favours chrominance when the third frequency component has an amplitude which is not substantially less than the amplitude of said first signal component.
12. A method of processing a television signal according to claim 1 wherein the signal is sampled at an integer multiple of the line frequency.