Plural operating mode ambient light responsive television picture control
First Claim
1. In a video signal display system including a video signal processing channel;
- an image reproducing device for producing a picture display on a viewing screen in response to output video signals from said signal channel; and
manually adjustable picture contrast control means for manually controlling the gain of said signal channel;
automatic picture contrast control apparatus for automatically controlling the gain of said signal channel, comprising;
sensing means for providing output signals representative of the ambient light level striking said display screen, and representative of the average video signal level; and
threshold control means independently operative of the setting of said manual contrast control means and responsive to said representative signals for selectively providing to said video channel an automatic contrast control voltage for reducing picture contrast proportionally with reduced ambient light levels when a prescribed combination of ambient light level and average video signal level causes an operating threshold of said control means to be exceeded.
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Accused Products
Abstract
The contrast of an image reproduced by a television receiver is manually adjustable by means of a picture control potentiometer, and automatically adjustable by means of an ambient light responsive circuit. Automatic picture control is accomplished selectively, independent of the manual control setting, in accordance with a predetermined combination of ambient light and image brightness levels such that the contrast of bright images, rather than the contrast of all images, is automatically reduced in low ambient light. In a preferred embodiment such automatic picture control is accomplished by using the light responsive circuit to control the threshold operating level of an automatic kinescope beam current limiter of the receiver.
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Citations
9 Claims
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1. In a video signal display system including a video signal processing channel;
- an image reproducing device for producing a picture display on a viewing screen in response to output video signals from said signal channel; and
manually adjustable picture contrast control means for manually controlling the gain of said signal channel;
automatic picture contrast control apparatus for automatically controlling the gain of said signal channel, comprising;sensing means for providing output signals representative of the ambient light level striking said display screen, and representative of the average video signal level; and threshold control means independently operative of the setting of said manual contrast control means and responsive to said representative signals for selectively providing to said video channel an automatic contrast control voltage for reducing picture contrast proportionally with reduced ambient light levels when a prescribed combination of ambient light level and average video signal level causes an operating threshold of said control means to be exceeded. - View Dependent Claims (2, 3)
- an image reproducing device for producing a picture display on a viewing screen in response to output video signals from said signal channel; and
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4. In a video signal display system including a video signal processing channel;
- a kinescope for producing a picture display on a viewing screen associated therewith in response to video signals from said channel;
manually adjustable picture contrast control means for manually controlling the signal gain of said channel; and
an automatic kinescope beam current limiter network for monitoring the level of the picture brightness representative average current conducted by said kinescope and modifying the signal gain of said video channel in a direction to limit excessive kinescope beam current when beam current above a threshold level is sensed;
automatic picture contrast control apparatus comprising;light responsive variable conduction means positioned relative to said viewing screen such that proportional amounts of ambient light strike said light responsive means and said viewing screen; and means for coupling said light responsive means to said automatic kinescope beam current limiter network for varying the beam limiter threshold operating level in accordance with variations in the level of ambient light, independent of the setting of said manually adjustable gain control means, said threshold being varied in response to a low ambient light condition in a direction for increasing the sensitivity of the beam limiter to high average beam currents representative of high picture brightness. - View Dependent Claims (5, 6, 7, 8, 9)
- a kinescope for producing a picture display on a viewing screen associated therewith in response to video signals from said channel;
Specification