Patent ID: 7095452

Claim:
A clamp circuit comprising: a converter that converts an input analog video signal to a digital video signal; a separation unit that separates a chroma signal and a luminance signal from the digital video signal; a clamp control circuit that monitors the digital video signal and outputs a clamp control signal in response to a monitoring result of the digital video signal after a predetermined time for extracting a pedestal level inserted in a back porch included in a horizontal banking interval of the analog video signal has elapsed; and a clamp processing circuit that, while the clamp control circuit does not output the clamp control signal, extracts the pedestal level from a corrected luminance signal output from the clamp processing circuit, conducts computation processing to converge the extracted pedestal level to a digital signal processing reference level, and corrects the luminance signal input to said clamp processing circuit based on a result of the computation processing to output the corrected luminance signal, and once the clamp control circuit outputs the clamp control signal, holds a result of the computation processing at the time the clamp control circuit outputs the clamp control signal, and corrects the luminance signal input to said clamp processing circuit based on the held result to output the corrected luminance signal.