Color killer circuit
View Patent ↗There is provided a color killer circuit comprising a burst amplitude detection unit that detects an amplitude of a color burst; a delay unit that stores, delays, by a predetermined period of time, and outputs the detected amplitude; a subtractor that calculates a difference between an output from the burst amplitude detection unit and an output from the delay unit; a first comparator that compares the output from the burst amplitude detection unit with a first threshold value to determine whether or not the output from the burst amplitude detection unit is less than the first threshold value; and a second comparator that compares an output from the subtractor with a second threshold value to determine whether or not the output from the subtractor is greater than the second threshold value, wherein the color killer circuit masks the color component of the composite video signal when the first comparator determines that the output from the burst amplitude detection unit is less than the first threshold value, or when the second comparator determines that the output from the subtractor is greater than the second threshold value.
1. A color killer circuit, comprising:
an analog-to-digital converter configured to convert an input video signal to a digital signal, which is input to a burst amplitude detection unit;
the burst amplitude detection unit that detects an amplitude of a color burst included in a composite video signal including signals for a color component and a luminance component;
a delay unit that stores, delays, by a predetermined period of time, and outputs the amplitude of the color burst detected by the burst amplitude detection unit;
a subtractor that calculates a difference between an output from the burst amplitude detection unit and an output from the delay unit;
a first comparator that compares the output from the burst amplitude detection unit with a first threshold value to determine whether or not the output from the burst amplitude detection unit is less than the first threshold value; and
a second comparator that compares an output from the subtractor with a second threshold value to determine whether or not the output from the subtractor is greater than the second threshold value, wherein
the color killer circuit masks the color component of the composite video signal when the first comparator determines that the output from the burst amplitude detection unit is less than the first threshold value, or when the second comparator determines that the output from the subtractor is greater than the second threshold value.
2. The color killer circuit according to claim 1 , further comprising:
a burst averaging unit that averages amplitudes of color bursts output from the burst amplitude detection unit for a plurality of horizontal lines included in the composite video signal, wherein
the first comparator compares, instead of the output from the burst amplitude detection unit, an output from the burst averaging unit with the first threshold value to determine whether or not the output from the burst averaging unit is less than the first threshold value, and
the color killer circuit masks the color component of the composite video signal when the first comparator determines that the output from the burst averaging unit is less than the first threshold value, or when the second comparator determines that the output from the subtractor is greater than the second threshold value.
3. The color killer circuit according to claim 1 , further comprising:
a noise averaging unit that averages outputs from the subtractor for a plurality of horizontal lines included in the composite video signal, wherein
the second comparator compares, instead of the output from the subtractor, an output from the noise averaging unit with the second threshold value to determine whether or not the output from the noise averaging unit is greater than the second threshold value, wherein
the color killer circuit masks the color component of the composite video signal when the first comparator determines that the output from the burst amplitude detection unit is less than the first threshold value, or when the second comparator determines that the output from the noise averaging unit is greater than the second threshold value.
4. The color killer circuit according to claim 1 , wherein
the first comparator sets the first threshold value to a smaller value when the first comparator determines that the output from the burst amplitude detection unit is less than the first threshold value, and
the first comparator sets the first threshold value to a larger value when the first comparator determines that the output from the burst amplitude detection unit is equal to or greater than the first threshold value.
5. The color killer circuit according to claim 2 , wherein
the first comparator sets the first threshold value to a smaller value when the first comparator determines that the output from the burst amplitude detection unit or the output from the burst averaging unit is less than the first threshold value, and
the first comparator sets the first threshold value to a larger value when the first comparator determines that the output from the burst amplitude detection unit or the output from the burst averaging unit is equal to or greater than the first threshold value.
6. The color killer circuit according to claim 3 , wherein
the first comparator sets the first threshold value to a smaller value when the first comparator determines that the output from the burst amplitude detection unit or the output from the noise averaging unit is less than the first threshold value, and
the first comparator sets the first threshold value to a larger value when the first comparator determines that the output from the burst amplitude detection unit or the output from the noise averaging unit is equal to or greater than the first threshold value.
7. The color killer circuit according to claim 1 , wherein
the second comparator sets the second threshold value to a larger value when the second comparator determines that the output from the subtractor is greater than the second threshold value, and
the second comparator sets the second threshold value to a smaller value when the second comparator determines that the output from the subtractor is equal to or less than the second threshold value.
8. The color killer circuit according to claim 2 , wherein
the second comparator sets the second threshold value to a larger value when the second comparator determines that the output from the subtractor or the output from the burst averaging unit is greater than the second threshold value, and
the second comparator sets the second threshold value to a smaller value when the second comparator determines that the output from the subtractor or the output from the burst averaging unit is equal to or less than the second threshold value.
9. The color killer circuit according to claim 3 , wherein
the second comparator sets the second threshold value to a larger value when the second comparator determines that the output from the subtractor or the output from the noise averaging unit is greater than the second threshold value, and
the second comparator sets the second threshold value to a smaller value when the second comparator determines that the output from the subtractor or the output from the noise averaging unit is equal to or less than the second threshold value.
10. The color killer circuit according to claim 4 , wherein
the second comparator sets the second threshold value to a larger value when the second comparator determines that the output from the subtractor is greater than the second threshold value, and
the second comparator sets the second threshold value to a smaller value when the second comparator determines that the output from the subtractor is equal to or less than the second threshold value.