Luminance and chrominance separation system
Provided are decoding methods and decoders for separating luminance and chrominance components of a video signal. In one aspect, a reference subcarrier of a first line of the video signal is used for subsequent lines by applying an appropriate rotation to the reference subcarrier of the first line for each subsequent line. In another aspect, comb filtering is adaptively controlled based on determining whether 90 or 180 degrees relationship is maintained from line to line. In a further aspect, both complimentary and non-complimentary comb filtering are implemented. In yet another aspect, SECAM bell filtering is achieved by rotating the video signal to obtain a baseband signal, low-pass filtering and modulating the baseband signal, and subtracting the modulated low-pass filtered baseband signal from the video signal to notch the chroma component from the luma component.
1. A method of controlling a comb filter for comb filtering a plurality of video signal lines to demodulate a chrominance portion of each of said plurality of video signal lines into U and V components, said method comprising:
determining a first reference subcarrier of a first video signal line of said plurality of video signal lines;
demodulating said chrominance portion of said first video signal line into first U and V components using said first reference subcarrier;
using said first U and V components to determine a number of degrees of rotation of said first reference subcarrier from a second reference subcarrier of a second video signal line previous to said first video signal line; and
disabling said comb filter if said number of degrees is different from a predetermined number of degrees.
2. The method of claim 1 , wherein said predetermined number of degrees is 90 degrees.
3. The method of claim 1 , wherein said predetermined number of degrees is 180 degrees.
4. The method of claim 1 further comprising: enabling said comb filter if said number of degrees is the same as said predetermined number of degrees.
5. A decoder comprising:
a comb filter configured to filter a plurality of video signal lines;
a subcarrier generator configured to determine a first reference subcarrier of a first video signal line of said plurality of video signal lines;
a demodulator configured to demodulate said chrominance portion of said first video signal line into first U and V components using said first reference subcarrier; and
wherein said decoder uses said first U and V components to determine a number of degrees of rotation of said first reference subcarrier from a second reference subcarrier of a second video signal line previous to said first video signal line, and said decoder disables said comb filter if said number of degrees is different from a predetermined number of degrees.
6. The decoder of claim 5 , wherein said predetermined number of degrees is 90 degrees.
7. The decoder of claim 5 , wherein said predetermined number of degrees is 180 degrees.
8. The decoder of claim 5 , wherein said decoder enables said comb filter if said number of degrees is the same as said predetermined number of degrees.