EP0145966A2
Expired / Lapsed
EP
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Brightness control system for CRT video display
Assignee: General Electric Co
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Filing: 1984-11-15
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Granted: —
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Expires: 2004-11-15
Abstract
Abstract A video brightness control system for high performance CRT displays including a buffer amplifier for receiving high speed video information and applying it to a gain control variable resistor serving as a contrast control. An ambient light sensor drives a nonlinear amplifier to provide an ambient light signal which is in proportion to the logarithm of the ambient light level over a wide range. A manual brightness control potentiometer is adjustable to provide a constant brightness signal. The video information signal, the ambient light signal, and the manual brightness control signal are added together by a summing device, with the resultant signal approximating a logarithmic characteristic. The output of the summing device is applied to a gamma correction amplifier which drives a video driver amplifier, the video amplifier, in turn, drives the CRT. The gamma correction amplifier and video driver in combination with the video transfer function of the CRT approximates an exponential transfer function, thereby creating CRT screen brightness which is an antilogarithmic function of the total video signal appearing at the gamma correction amplifier input. This results in automatic brightness control as a function of ambient light level, minimum interaction between brightness and contrast controls, and a gamma characteristic which provides a reasonable approximation to the variation of brightness difference threshold of the eye.
Inventors
- 👤 John Snow Prince
- 👤 Harold Lee Herz
- 👤 Edward Paul Coleman, Jr.
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-01 07:53
CPC Classifications
H; H04; H04N; H04N5/00; H04N5/44; H04N5/57; H04N5/58
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
270 words
A brightness control system for a cathode ray tube video display, comprising: video information signal receiving means for receiving a video information signal including contrast control means for controlling the gain of said video information signal; ambient light signal generating means including an ambient light sensor means for providing a signal representation of the amount of ambient light in a viewed scene, and a nonlinear amplifier connected to the output of said ambient light sensor means to provide an amplified ambient light signal which is in proportion to the logarithm of the ambient light level; manual brightness control signal means for providing a manually adjusted brightness control signal; a summing means connected to receive the outputs of said video information signal receiving means, said ambient light signal generating means and said manual brightness control signal means, thereby providing a summation of the signals therefrom which corresponds to a logarithmic addition of said signals; nonlinear gamma correction amplifier means connected to the output of said summing means; video driver amplifier means connected to the output of said nonlinear gamma correction amplifier means; and cathode ray tube means connected to said video driver amplifier means; said gamma correction amplifier means, said video driver amplifier means and said cathode ray tube means in combination having an exponential transfer function which is an antilogarithmic function of the total video signal appearing at the input to said nonlinear gamma correction amplifier means, whereby the eye perceives a screen image on said cathode ray tube means having the brightness and contrast that is associated with a linear signal being fed into said gamma correction amplifier means.
Claim 2
Dependent Claim
270 words
A brightness control system for a cathode ray tube video display, comprising: video information signal receiving means for receiving a video information signal including contrast control means for controlling the gain of said video information signal; ambient light signal generating means including an ambient light sensor means for providing a signal representation of the amount of ambient light in a viewed scene, and a nonlinear amplifier connected to the output of said ambient light sensor means to provide an amplified ambient light signal which is in proportion to the logarithm of the ambient light level; manual brightness control signal means for providing a manually adjusted brightness control signal; a summing means connected to receive the outputs of said video information signal receiving means, said ambient light signal generating means and said manual brightness control signal means, thereby providing a summation of the signals therefrom which corresponds to a logarithmic addition of said signals; nonlinear gamma correction amplifier means connected to the output of said summing means; video driver amplifier means connected to the output of said nonlinear gamma correction amplifier means; and cathode ray tube means connected to said video driver amplifier means; said gamma correction amplifier means, said video driver amplifier means and said cathode ray tube means in combination having an exponential transfer function which is an antilogarithmic function of the total video signal appearing at the input to said nonlinear gamma correction amplifier means, whereby the eye perceives a screen image on said cathode ray tube means having the brightness and contrast that is associated with a linear signal being fed into said gamma correction amplifier means.
Claim 3
Dependent Claim
33 words
A brightness control system as recited in claim 1 wherein said contrast control means in said video information signal receiving means includes a buffer amplifier for receiving and amplifying said video information signal.
Claim 4
Dependent Claim
34 words
A brightness control system as recited in claim 2 wherein said buffer amplifier of said video information signal receiving means comprises a high speed monolithic operational amplifier connected as a balanced differential video buffer.
Claim 5
Dependent Claim
36 words
A brightness control system as recited in claim 2 wherein said contrast control means in said video information signal receiving means further includes a gain control variable resistor connected to the output of said buffer amplifer.
Claim 6
Dependent Claim
21 words
A brightness control system as recited in claim 1 wherein said ambient light sensor means comprises a cadmium sulfide photosensitive resistor.
Claim 7
Dependent Claim
54 words
A brightness control system as recited in claim 1 wherein said nonlinear amplifier of said ambient light signal generating means comprises an operational amplifier having a nonlinear feedback network which provides an amplifier output signal which is in proportion to the logarithm of the ambient light level over a range which exceeds two decades.
Claim 8
Dependent Claim
36 words
A brightness control system as recited in claim 1 wherein said manual brightness control signal means includes a potentiometer for providing a constant brightness control signal which can be adjusted for a comfortable viewing brightness level.
Claim 9
Dependent Claim
62 words
A brightness control system as recited in claim 1 wherein said gamma correction amplifier means comprises a high speed monolithic operational amplifier including a nonlinear feedback network, said network having piecewise linear feedback adjusted to provide a total transfer function from the output of said summing means to said cathode ray tube means which is exponential over several decades of screen brightness.
Claim 10
Dependent Claim
191 words
A brightness control system for a cathode ray tube video display, comprising: video information signal means for receiving a video information signal; manual brightness control signal means including means for manually adjusting the amplitude of a brightness control signal; summing means connected to receive outputs of said video information signal means and said manual brightness control signal means to thereby provide a summation of the signals therefrom which corresponds to a logarithmic addition of said signals; nonlinear gamma correction amplifier means connected to the output of said summing means; video driver amplifier means connected to the output of said nonlinear gamma correction amplifier means; and cathode ray tube means connected to said video driver amplifier means; said gamma correction amplifier means, said video driver amplifier means and said cathode ray tube means in combination having an exponential transfer function which is an antilogarithmic function of the total video signal appearing at the input to said nonlinear gamma correction amplifier means, whereby the eye perceives a screen image on said cathode ray tube means having the brightness that is associated with a linear signal being fed into said gamma correction amplifier means.
Claim 11
Dependent Claim
191 words
A brightness control system for a cathode ray tube video display, comprising: video information signal means for receiving a video information signal; manual brightness control signal means including means for manually adjusting the amplitude of a brightness control signal; summing means connected to receive outputs of said video information signal means and said manual brightness control signal means to thereby provide a summation of the signals therefrom which corresponds to a logarithmic addition of said signals; nonlinear gamma correction amplifier means connected to the output of said summing means; video driver amplifier means connected to the output of said nonlinear gamma correction amplifier means; and cathode ray tube means connected to said video driver amplifier means; said gamma correction amplifier means, said video driver amplifier means and said cathode ray tube means in combination having an exponential transfer function which is an antilogarithmic function of the total video signal appearing at the input to said nonlinear gamma correction amplifier means, whereby the eye perceives a screen image on said cathode ray tube means having the brightness that is associated with a linear signal being fed into said gamma correction amplifier means.
References Cited (Backward Citations)
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