Estimation of noise using burst gate response to video signal

For use with a machine that recovers a luminance signal and an accompanying color-under signal from a recording medium, a process for monitoring noise components of said color-under signal, said luminance signal including horizontal synchronizing pulses that recur at a horizontal line scan rate, there being a backporch interval after each horizontal synchronizing pulse during which at least at times said color-under signal includes a respective burst of a subcarrier signal, wherein the phase of said burst of subcarrier signal at points in each horizontal line scan of each field changes is in quadrature with the phase of said burst of subcarrier signal at corresponding points in each adjoining horizontal line scan in that field, said process comprising the steps of:

• delaying, by the period of two horizontal scan lines, said color-under signal as currently scanned;
• and
• performing a weighted summation in k:k ratio of corresponding pixels for said said color-under signal as currently scanned as currently scanned and as delayed by the period of two horizontal scan lines to generate an intermediate signal in which said bursts of subcarrier signal are suppressed by their combining out-of-phase;
• transmitting components of said intermediate signal during each of said backporch intervals, to provide a respective succession of noise samples, as selected from among other samples of said intermediate signal;
• and
• generating a representation of the noise level in the horizontal lines of color-under signal combined to generate each horizontal line of said intermediate signal, by accumulating the absolute values of the noise samples in said respective succession of noise samples, as selected from among other samples of said intermediate signal.

A circuit for monitoring noise components of a video signal, comprising:

• receiving means for receiving at least a first video signal for successive horizontal lines within the same field, said first video signal including horizontal synchronizing pulses that recur at a horizontal line scan rate, each said video signal having a respective backporch interval after each horizontal synchronizing pulse in said first video signal, one of said video signals having a respective burst of a subcarrier signal in each backporch interval thereof;
• means for generating an intermediate signal in which said bursts of subcarrier signal are suppressed, by additively combining pixels of a currently received horizontal line of said one of said video signals with corresponding pixels of at least one previously received horizontal line of said one of said video signals within the same field;
• means for selectively transmitting components of said intermediate signal during each backporch interval, to provide a respective plurality of noise samples;
• means responding to said noise samples for generating respective indications of their absolute values;
• and
• means for accumulating said respective indications of the absolute values of said plurality of noise samples during each backporch interval, thereby to generate a respective accumulation result.

For inclusion in a television receiver including:

• a video detector for supplying a composite video signal;
• a synchronizing signal separator for separating horizontal and vertical synchronizing pulses from said composite video signal;
• a burst gate generator responding to separated horizontal synchronizing pulses for generating a burst gate signal during burst gate intervals which occur soon after each horizontal synchronizing pulse and which each extend over a time corresponding to the time that the pedestal or back-porch period follows a horizontal synchronizing pulse in the composite video signal and includes the color burst, if any;
• a noise estimator responding to selected portions of said composite video signal for supplying a noise estimation signal having a magnitude directly related to the noisiness of a currently received television signal;
• and
• apparatus for altering the performance of the television receiver responsive to the noise estimation signal, the improvement wherein said noise estimator comprises:
• means for additively combining the burst gate intervals of a succession of horizontal scan lines having various-phase chroma burst components to generate a result-of-combination signal in which the various-phase chroma burst components of the combined components combine to substantially zero value while accompanying noise adds vectorially to non-zero value;
• means for supplying as its output signal a succession of unipolar indications of the energy in its input signal, connected to receive said result-of-combination signal as its input signal;
• and
• means for integrating the unipolar indications of the energy in said result-of-combination signal over each burst gate interval to provide a noise estimation sample.

For inclusion in a video tape recorder including:

• means for receiving a composite video signal to be recorded;
• a synchronizing signal separator for separating horizontal and vertical synchronizing pulses from said composite video signal;
• a burst gate generator responding to separated horizontal synchronizing pulses for generating a burst gate signal during burst gate intervals which occur soon after each horizontal synchronizing pulse and which each extend over a time corresponding to the time that the pedestal or back-porch period follows a horizontal synchronizing pulse in the composite video signal and includes the color burst, if any;
• a noise estimator responding to selected portions of said composite video signal for supplying a noise estimation signal having a magnitude directly related to the noisiness of a television signal currently received for recording;
• and
• apparatus for altering the performance of the video tape recorder responsive to the noise estimation signal, the improvement wherein said noise estimator comprises:
• means for additively combining the burst gate intervals of a succession of horizontal scan lines having various-phase chroma burst components to generate a result-of-combination signal in which the various-phase chroma burst components of the combined components combine substantially to zero value while accompanying noise adds vectorially to non-zero value;
• means for supplying as its output signal a succession of unipolar indications of the energy in its input signal, connected to receive said result-of-combination signal as its input signal;
• and
• means for integrating the unipolar indications of the energy in said result-of-combination signal over each burst gate interval to provide a noise estimation sample.

For inclusion in a video tape player including:

• means for recovering a frequency multiplexed signal from a recorded video tape, said frequency multiplexed signal including in an upper frequency band thereof sidebands of a frequency-modulated luma carrier encoding a luminance-descriptive signal including horizontal and vertical synchronizing pulses, said frequency multiplexed signal including in a lower frequency band thereof sidebands of an amplitude-modulated suppressed color-under carrier that includes a color-burst-descriptive signal segment each time the pedestal or back-porch period follows a horizontal synchronizing pulse in said luminance-descriptive signal;
• a filter for separating said lower and upper frequency bands of said frequency multiplexed signal;
• an upconverter for converting the amplitude-modulated suppressed color-under carrier in the separated lower frequency band of said frequency multiplexed signal up in frequency to regenerate chrominance sidebands of a suppressed color subcarrier;
• a frequency-modulation detector for recovering said luminance-descriptive signal from the separated upper frequency band of said frequency multiplexed signal;
• a synchronizing signal separator for separating the horizontal and vertical synchronizing pulses from said recovered luminance-descriptive signal;
• a burst gate generator responding to said separated horizontal synchronizing pulses for generating a burst gate signal during burst gate intervals which occur soon after each horizontal synchronizing pulse and which each extend over a time corresponding to the time that the pedestal or back-porch period follows a horizontal synchronizing pulse in said recovered luminance-descriptive signal;
• a noise estimator responding to selected portions of the separated lower frequency band of said frequency multiplexed signal for supplying a noise estimation signal descriptive of noise in said separated lower frequency band of said frequency multiplexed signal;
• and
• apparatus for altering the performance of the video tape player responsive to the noise estimation signal, the improvement wherein said noise estimator comprises:
• means for additively combining the burst gate intervals of a succession of horizontal scan lines of a signal at said upconverter, thereby to generate a result-of-combination signal in which the various-phase signals in the combined components that are descriptive of color subcarrier phasing combine substantially to zero value while accompanying noise adds vectorially to non-zero value;
• means for supplying as its output signal a succession of unipolar indications of the energy in its input signal, connected to receive said result-of-combination signal as its input signal;
• and
• means for integrating the unipolar indications of the energy in said result-of-combination signal over each burst gate interval to provide a noise estimation sample.