Video signal processing
View Patent ↗A method of generating an orthogonally sampled video signal based on a line phase measure. In a first aspect the input signal is sampled by a clock locked to the average line frequency of a video input and the resulting samples are time shifted, optionally with or without interpolation, to an orthogonal sampling grid. In a second aspect input samples are taken and shifted to an orthogonal sampling grid according to a line phase measure. The line phase measure can be derived from a number of measurements or interpolated. In one embodiment a delay is employed so that a measure of a later sample is used to shift an earlier sample.
1. A method of sampling an input video signal to produce an orthogonally sampled video signal comprising:
sampling the input video signal using a sampling clock;
taking a plurality of line phase measures of the video signal; and
shifting the resulting samples to an orthogonal sampling grid;
wherein the required sample shift is derived from more than one line phase measure.
2. A method according to claim 1 , wherein the line phase measures are filtered to produce interpolated phase measurements having an increased temporal resolution.
3. A method according to claim 2 , wherein said filtering is non-linear.
4. A method according to claim 1 , wherein the line phase measures are filtered to produce phase measurements having an increased numerical resolution.
5. A method according to claim 4 , wherein said filtering is non-linear.
6. A method according to claim 1 , wherein measures are made in integer sample interval units.
7. A method according to claim 1 , wherein measures are interpolated to a precision corresponding to a fraction of a sample interval.
8. A method according to claim 1 , wherein the samples are delayed prior to shifting so that a line phase measure corresponding to the phase of a later sample is used to calculate the required shift for an earlier sample.
9. A method of sampling an input video signal to produce an orthogonally sampled video signal comprising:
sampling the input video signal using a sampling clock locked to the average line frequency of the video signal; and
shifting the resulting samples to an orthogonal sampling grid.
10. A method according to claim 9 in which the samples are shifted without interpolation between samples when the instantaneous input line frequency is equal to the average input line frequency.
11. A method according to claim 9 where the samples are shifted by fractions of a sampling interval and no more than three input samples are used to interpolate an output sample.
12. A method according to claim 9 in which the required sample shift is derived from a line phase measure.
13. A method according to claim 12 , wherein the shift is derived from a plurality of line phase measures.
14. A method according to claim 12 , wherein measures are made in integer sample interval units.
15. A method according to claim 14 , wherein measurements are interpolated to a precision corresponding to a fraction of a sample interval.
16. A method according to claim 11 , in which the samples are delayed prior to shifting so that a measure of a later sample is used to calculate the required shift for an earlier sample.
17. A method according to claim 16 , wherein the measure is a line phase measure corresponding to the phase of the later sample.
18. A method of sampling an input video signal to produce an orthogonally sampled video signal comprising:
sampling the input video signal using a sampling clock;
delaying the sampled signal; and
shifting the delayed samples to an orthogonal sampling grid;
wherein the samples are delayed so that a line phase measure corresponding to the phase of a later sample is used to calculate the required shift for an earlier sample.
19. Apparatus for shifting samples of a sampled video signal comprising:
a sample shifter capable of shifting samples under the control of a shift control signal;
a line phase measurement unit operating on the sampled video signal to derive a measure of the input line phase;
a filter adapted to receive a plurality of line phase measures, and to output a shift control signal to the sample shifter based on said plurality of line phase measures; and wherein the sample shifter uses the shift control signal to output samples to an orthogonal sampling grid.
20. Apparatus according to claim 19 , wherein said filter produces interpolated shift values having a temporal resolution greater than the temporal resolution of the line phase measures.
21. Apparatus according to claim 19 , wherein said filter produces shift values having a numerical resolution greater than the numerical resolution of the line phase measures.
22. Apparatus according to claim 19 , wherein line phase measurements are made to integer input sample interval accuracy.
23. Apparatus according to claim 22 , wherein said filter produces shift values to a precision corresponding to a fraction of an input sample interval.
24. Apparatus according to claim 19 , further comprising a delay acting on the sample shifter input, such that a line phase measure corresponding to a later sample is used to calculate the shift for an earlier sample.
25. Apparatus according to claim 19 , wherein output samples are shifted without interpolation.
26. Apparatus for shifting samples of a sampled video signal comprising:
a sample shifter capable of shifting samples under the control of a shift control signal;
a line phase measurement unit operating on the sampled video signal to derive a measure of the input line phase and to output a shift control signal to the sample shifter based on a line phase measure;
a delay acting on the sample shifter input, such that a line phase measure corresponding to a later sample is used to calculate the shift for an earlier sample;
and wherein the sample shifter uses the shift control signal to output samples to an orthogonal sampling grid.