Pedestal control circuit

Claim 2

A pedestal control circuit comprising: pedestal mixing means for mixing a reference pedestal signal with an input video signal which has not been gamma-corrected, and for producing a mixed video signal; gamma correcting means for gamma correcting the mixed video signal in accordance with a predetermined variable gamma correction characteristic, and for producing a gamma-corrected output video signal; pedestal detecting means for detecting from the gamma-corrected output video signal a component corresponding to the reference pedestal signal, and for producing a pedestal detection signal; and pedestal feedback means, responsive to the pedestal detection signal and a predetermined pedestal control signal, for feeding the reference pedestal signal, having a magnitude corresponding to the pedestal detection signal, back to said pedestal mixing means so that the pedestal detection signal converges to a value corresponding to the predetermined pedestal control signal; wherein said gamma correcting means includes: a first clamp circuit for performing DC clamping of the mixed video signal from said pedestal mixing means in accordance with a predetermined clamping control signal, and for producing a first DC restored signal; a gamma correction circuit for performing gamma correction of the first DC restored signal in accordance with the predetermined variable gamma correction characteristic, and for producing a gamma-corrected signal; and a second clamp circuit for performing DC clamping of the gamma-corrected signal from said gamma correction circuit in accordance with the predetermined clamping control signal, and for producing a second DC restored signal corresponding to the gamma-corrected output video signal.

Claim 3

A pedestal control circuit according to claim 1, wherein said pedestal detecting means includes: a sample/hold circuit for sampling and holding a DC level of the output video signal, or sampling and holding a DC level of a signal corresponding the output video signal, in accordance with a sampling pulse which is generated after the predetermined clamping control signal disappears in a vertical blanking period of the input video signal, and for producing the pedestal detection signal.

Claim 4

A pedestal control circuit according to claim 2, wherein said pedestal feedback means includes: comparing means for comparing the pedestal detection signal with the pedestal control signal, and for producing a comparison output signal corresponding to a difference between the magnitudes of these signals; and switching means for performing, in accordance with a switching pulse having a predetermined period, signal switching between the level of the comparison output signal and a predetermined level, and for producing a reference pedestal signal having an amplitude corresponding to the level of the comparison output signal and a period corresponding to the period of the switching pulse, said switching pulse being generated in a period wherein the clamping control signal and the sampling pulse disappear.

Claim 5

A pedestal control circuit according to claim 1, wherein said pedestal detecting means includes: a first sample/hold circuit for sampling and holding a DC level of the output video signal, or sampling and holding a DC level of a signal corresponding the output video signal, in accordance with a sampling pulse generated after the predetermined clamping control signal disappears in a vertical blanking period of the input video signal, and for producing the pedestal detection signal; and a second sample/hold circuit for sampling and holding the DC level of the output video signal, or sampling and holding a DC level of a signal corresponding the output video signal, in accordance with the clamping control signal, and for producing a reference level which corresponds to the converged value of the pedestal detection signal obtained by the feedback of said pedestal feedback means.

Claim 6

A pedestal control circuit according to claim 4, wherein said pedestal feedback means includes: comparing means for comparing the pedestal detection signal with the pedestal control signal, and for producing a comparison output signal corresponding to a difference between the magnitude of these signals; and switching means for performing, in accordance with a switching pulse having a predetermined period, signal switching between the level of the comparison output signal and a predetermined level, and for producing a reference pedestal signal having an amplitude corresponding to the level of the comparison output signal and a period corresponding to the period of the switching pulse, said switching pulse being generated in a period wherein the clamping control signal and the sampling pulse disappear.

Claim 7

A pedestal control circuit comprising: pedestal mixing means for mixing a reference pedestal signal with an input video signal which has not been gamma-corrected, and for producing a mixed video signal; gamma correcting means for gamma correcting the mixed video signal in accordance with a predetermined variable gamma correction characteristic, and for producing a gamma-corrected output video signal; pedestal detecting means for detecting from the gamma-corrected output video signal a component corresponding to the reference pedestal signal, and for producing a pedestal detection signal; and pedestal feedback means, responsive to the pedestal detection signal and a predetermined pedestal control signal, for feeding the reference pedestal signal, having a magnitude corresponding to the pedestal detection signal, back to said pedestal mixing means so that the pedestal detection signal converges to a value corresponding to the predetermined pedestal control signal; wherein said gamma correcting means includes: a first clamp circuit for performing DC clamping of the input video signal in accordance with a predetermined clamping control signal, producing a first DC restored signal, and supplying the first DC restored signal to said pedestal mixing means; a gamma correction circuit for performing gamma correction of a mixed video signal from said pedestal mixing means, in accordance with the predetermined variable gamma correction characteristic, and for producing a gamma-corrected signal, said mixed video signal corresponding to the first DC restored signal; and a second clamp circuit for performing DC clamping of the gamma-corrected signal from said gamma correction circuit in accordance with the predetermined clamping control signal, and for producing a second DC restored signal corresponding to the output video signal.

Claim 8

A pedestal control circuit comprising: pedestal mixing means for mixing a reference pedestal signal with an input video signal which has not been gamma-corrected, and for producing a mixed video signal; gamma correcting means for gamma correcting the mixed video signal in accordance with a predetermined variable gamma correction characteristic, and for producing a gamma-corrected output video signal; pedestal detecting means for detecting from the gamma-corrected output video signal a component corresponding to the reference pedestal signal, and for producing a pedestal detection signal; and pedestal feedback means, responsive to the pedestal detection signal and a predetermined pedestal control signal, for feeding the reference pedestal signal, having a magnitude corresponding to the pedestal detection signal, back to said pedestal mixing means so that the pedestal detection signal converges to a value corresponding to the predetermined pedestal control signal; wherein said gamma correcting means includes: a first clamp circuit for performing DC clamping of the input video signal in accordance with a predetermined clamping control signal, producing a first DC restored signal, and supplying the first DC restored signal to said pedestal mixing means; a gamma correction circuit for performing gamma correction of a mixed video signal from said pedestal mixing means, in accordance with the predetermined variable gamma correction characteristic, and for producing a gamma-corrected signal, said mixed video signal corresponding to the first DC restored signal; and a second clamp circuit for performing DC clamping of the gamma-corrected signal from said gamma correction circuit in accordance with the predetermined clamping control signal, and for producing a second DC restored signal corresponding to the output video signal.

Claim 9

A pedestal control circuit according to claim 6, wherein said pedestal detecting means includes: a sample/hold circuit for sampling and holding a DC level of the output video signal, or sampling ahd holding a DC level of a signal corresponding the output video signal, in accordance with a sampling pulse which is generated after the predetermined clamping control signal disappears in a vertical blanking period of the input video, and for producing the pedestal detection signal.

Claim 10

A pedestal control circuit according to claim 7, wherein said pedestal feedback means includes: comparing means for comparing the pedestal detection signal with the pedestal control signal, and for producing a comparison output signal corresponding to a difference between the magnitudes of these signals; and switching means for performing, in accordance with a switching pulse having a predetermined period, signal switching between the level of the comparison output signal and a predetermined level, and for producing a reference pedestal signal having an amplitude corresponding to the level of the comparison output signal and a period corresponding to the period of the switching pulse, said switching pulse being generated in a period wherein the clamping control signal and the sampling pulse disappear.

Claim 11

A pedestal control circuit according to claim 6, wherein said pedestal detecting means includes: a first sample/hold circuit for sampling and holding a DC level of the output video signal, or sampling and holding a DC level of a signal corresponding the output video signal, in accordance with a sampling pulse generated after the predetermined clamping control signal disappears in a vertical blanking period of the input video signal, and for producing fhe pedestal detection signal; and a second sample/hold circuit for sampling and holding the DC level of the output video signal (Sout), or sampling and holding a DC level of a signal corresponding the output video signal, in accordance with the clamping control signal, and for producing a reference level which corresponds to the converged value of the pedestal detection signal obtained by the feedback of said pedestal feedback means.

Claim 12

A pedestal control circuit according to claim 9, wherein said pedestal feedback means includes: comparing means for comparing the pedestal detection signal with the pedestal control signal, and for producing a comparison output signal corresponding to a difference between the magnitudes of these signals; and switching means for performing, in accordance with a switching pulse having a predetermined period, signal switching between the level of the comparison output signal and a predetermined level, and for producing a reference pedestal signal having an amplitude corresponding to the level of the comparison output signal and a period corresponding to the period of the switching pulse, said switching pulse being generated in a period wherein the clamping control signal and the sampling pulse disappear.

Claim 13

A pedestal control circuit comprising: pedestal mixing means for mixing a reference pedestal signal with an input video signal which has not been gamma-corrected, and for producing a mixed video signal; gamma correcting means for gamma correcting the mixed video signal in accordance with a predetermined variable gamma correction characteristic, and for producing a gamma-corrected output video signal; pedestal detecting means for detecting from the gamma-corrected output video signal a component corresponding to the reference pedestal signal, and for producing a pedestal detection signal; and pedestal feedback means, responsive to the pedestal detection signal and a predetermined pedestal control signal, for feeding the reference pedestal signal, having a magnitude corresponding to the pedestal detection signal, back to said pedestal mixing means so that the pedestal detection signal converges to a value corresponding to the predetermined pedestal control signal; wherein said pedestal feedback means includes: comparing means for comparing the pedestal detection signal with the pedestal control signal, and for producing a comparison output signal corresponding to a difference between the magnitude of these signals; and switching means for performing, in accordance with a switching pulse having a predetermined period, signal switching between the level of the comparison output signal and a predetermined level, and for producing a reference pedestal signal having an amplitude corresponding to the level of the comparison output signal and a period corresponding to the period of the switching pulse.

Claim 14

A pedestal control circuit comprising: pedestal mixing means for mixing a reference pedestal signal with an input video signal which has not been gamma-corrected, and for producing a mixed video signal; gamma correcting means for gamma correcting the mixed video signal in accordance with a predetermined variable gamma correction characteristic, and for producing a gamma-corrected output video signal; pedestal detecting means for detecting from the gamma-corrected output video signal a component corresponding to the reference pedestal signal, and for producing a pedestal detection signal; and pedestal feedback means, responsive to the pedestal detection signal and a predetermined pedestal control signal, for feeding the reference pedestal signal, having a magnitude corresponding to the pedestal detection signal, back to said pedestal mixing means so that the pedestal detection signal converges to a value corresponding to the predetermined pedestal control signal; wherein said pedestal feedback means includes: comparing means for comparing the pedestal detection signal with the pedestal control signal, and for producing a comparison output signal corresponding to a difference between the magnitude of these signals; and switching means for performing, in accordance with a switching pulse having a predetermined period, signal switching between the level of the comparison output signal and a predetermined level, and for producing a reference pedestal signal having an amplitude corresponding to the level of the comparison output signal and a period corresponding to the period of the switching pulse.