Video attenuator with output combined with signal from non-linear shunt branch to provide gamma correction and high frequency detail enhancement

Video signal processing apparatus for providing gamma correction and detail enhancement, comprising:

• a source for providing a video input signal to be processed;
• a summing circuit having an output for providing a processed video output signal:
• an attenuator having a series branch and a shunt branch, each said branch for coupling said video input signal to said summing circuit;
• said shunt branch including a non-linear element providing attenuation as a direct function of the level of said video input signal;
• and wherein;
• said shunt branch includes a circuit node coupled to an input of said attenuator via a first resistor and coupled to an output of said attenuator via a second resistor;
• a transistor having a conduction path coupled at a first end thereof to said circuit node and coupled at a second end thereof to a source of reference potential;
• and a bias circuit coupled to said circuit node and to said source of reference potential for producing turn-on bias for said transistor.

Apparatus, comprising:

• a bridged-T attenuator including an input node and an output node;
• first and second resistors coupled in series between said input and output nodes;
• a third resistor coupled between said nodes;
• a transistor having a control electrode coupled to a source of bias, having a conduction path coupled between a junction of said first and second resistors and a first end of a fourth resistor having a second end coupled to a source of reference potential;
• and
• means for applying a video input signal to said input node for producing at said output node a gamma corrected first video output signal and for producing across said fourth resistor a second video output signal having an amplitude proportional to a current conducted by said transistor.

Video signal processing apparatus, comprising:

• a source for providing a video signal to be processed;
• a first circuit for applying gamma correction to said video signal
• a second circuit for boosting high frequency detail of said video signal at relatively high signal levels;
• a summing circuit for summing said gamma corrected signal, said boosted detail signal and said video input signal to form a processed video output signal;
• said first circuit comprising a bridged-T attenuator having a series branch and having a shunt branch, said shunt branch including a non-linear element for causing said attenuator to provide increasing attenuation to said video input signal as said input signal increases to generate said gamma corrected signal;
• and
• said second circuit comprises (i) a current sensing circuit for sensing current conducted by said shunt branch and (ii) a high pass filter responsive to the sensed current for producing said boosted detail signal.

Video signal processing apparatus, comprising:

• a source for providing a video input signal to be processed;
• an attenuator having a non-linear shunt branch for attenuating said video input signal as a function of the level of said video input signal for producing a gamma corrected video output signal;
• a current sensing circuit coupled to said non-linear shunt:
• branch of said attenuator for providing a video signal which increases with the level of said video input signal;
• a high pass filter coupled to said current sensing circuit for providing a high frequency boosted detail signal;
• and
• output means for summing said video input signal, said gamma corrected video signal, said high frequency boosted detail signal for producing a processed video output signal.

A method for applying gamma correction and high frequency detail augmentation to a video input signal, comprising:

• attenuating said video input signal as a function of the level of said video input signal for producing a gamma corrected video output signal;
• sensing a parameter of said video input signal for generating a detail indicating video signal having an amplitude which increases as a non-linear function of the level of said video input signal;
• high pass filtering said detail indicating signal for providing a high frequency boosted detail signal;
• and
• summing said video input signal, said gamma corrected video signal and said high frequency boosted detail signal for producing a processed video output signal having gamma correction and high frequency boosted detail.

Apparatus for applying gamma correction and high frequency detail augmentation to a video input signal, comprising:

• means for attenuating said video input signal as a function of the level of said video input signal for producing a gamma corrected video output signal;
• means for sensing a parameter of said video input signal for generating a detail indicating video signal having an amplitude which increases as a non-linear function of the level of said video input signal;
• means for high pass filtering said detail indicating signal for providing a high frequency boosted detail signal;
• and
• means for summing said video input signal, said gamma corrected video signal and said high frequency boosted detail signal for producing a processed video output signal having gamma correction and high frequency boosted detail.

Apparatus, comprising:

• a bridged-T attenuator includes an active non-linear element in a shunt branch thereof for providing increasing attenuation to a video input signal applied to an input terminal of said attenuator to produce a gamma corrected video output signal;
• a current sensor in said shunt branch for generating an exponentially increasing detail signal for increases in said video input signal;
• a filter for high pass filtering said detail signal;
• and
• a combiner for combining the high pass filtered detail signal with said gamma corrected signal for providing a video output signal having gamma correction and high frequency detail augmentation.

Apparatus, comprising:

• a bridged-T attenuator having an input for receiving a video input signal and having an output for providing a variably attenuated video signal, said bridged-T attenuator having a shunt branch including a non-linear network for controlling said attenuation;
• said non-linear network having a voltage response selected for increasing the bridged-T attenuation as a function of the amplitude of the video input signal so as to provide gamma correction to said video output signal;
• said non-linear network including a current responsive sensor for providing a sensed video signal exponentially related to the amplitude of said video input signal;
• and
• circuit means for combining said said variably attenuated video signal and said sensed video signal to form a processed video output signal having gamma correction and high frequency detail enhancement.