Apparatus for correcting a black level of a video signal

An apparatus for correcting a black level of a video signal, comprising:

• a pedestal clamp circuit for clamping a pedestal level of an input luminance signal in response to a predetermined pedestal voltage, and converting the input luminance signal into a clamped luminance signal;
• a black-level expanding circuit for expanding a tone of a black portion of the clamped luminance signal, and converting the clamped luminance signal into a black-level expanded luminance signal;
• a color greatest detecting circuit for detecting a greatest of input color difference signals;
• a level limiting circuit for limiting a level of an output signal from the color greatest detecting circuit to within a predetermined range;
• a first gain control circuit for controlling an amplitude of an output signal from the level limiting circuit;
• an adding circuit for adding an output signal from the gain control circuit and the pedestal voltage;
• and
• a black-level comparing circuit, responsive to the black-level expanded luminance signal and an output signal from the adding circuit, for detecting a blackest portion of the black-level expanded luminance signal, comparing the detected blackest portion of the black-level expanded luminance signal with the output signal from the adding circuit, and controlling a degree of expanding the black tone by the black-level expanding circuit in response to a difference between the detected blackest portion of the black-level expanded luminance signal and the output signal from the adding circuit.

An apparatus for correcting a black level of a video signal, comprising:

• a pedestal clamp circuit for clamping a pedestal level of an input luminance signal in response to a predetermined pedestal voltage, and converting the input luminance signal into a clamped luminance signal;
• a black-level expanding circuit for expanding a tone of a black portion of the clamped luminance signal, and converting the clamped luminance signal into a black-level expanded luminance signal;
• an average luminance level detecting circuit for detecting an average luminance level of the black-level expanded luminance signal, and outputting an average luminance detection signal representative thereof;
• a gain control circuit for controlling an amplitude of the average luminance detection signal;
• an adding circuit for adding an output signal from the gain control circuit and the predetermined pedestal voltage;
• and
• a black-level comparing circuit, responsive to the black-level expanded luminance signal and an output signal from the adding circuit, for detecting a blackest portion of the black-level expanded luminance signal, comparing the detected blackest portion of the black-level expanded luminance signal with the output signal from the adding circuit, and controlling a degree of expanding the black tone by the black-level expanding circuit in response to a difference between the detected blackest portion of the black-level expanded luminance signal and the output signal from the adding circuit.