Video brightness control circuit
First Claim
1. A control circuit for controlling the brightness of a video signal that fluctuates between a peak dark level and a peak bright level about an average brightness level comprising:
- brightness controlling means having a signal input to which the video signal is applied as an input video signal and a signal output from which an output video signal is provided, said brightness controlling means being operable by a control signal for controlling the brightness of the video signal so that respective portions of said output video signal corresponding to portions of the input video signal at said peak dark level and at said peak bright level are provided substantially at said peak dark and bright levels while the average picture level of said output video signal is provided at a predetermined optimum level;
average picture level detecting means for detecting the average brightness level of at least one of said input and output video signals and providing said control signal in response to the detected average brightness level; and
a variable gamma correction circuit included in said brightness controlling means and having an input-output characteristic such that for the input video signal having a level proportional to a value X, where X is in the range 0≦
X≦
1, said video signal is provided at a level proportional to a value X.sup.γ
; and
the value of γ
is automatically determined in response to the control signal from said average picture level detecting means.
1 Assignment
0 Petitions
Accused Products
Abstract
A control circuit for controlling the relative brightness of a video signal includes an average picture level (APL) detector to measure the average brightness of the video signal and a brightness control circuit responsive to the detected average brightness to provide an output video signal wherein the picture areas containing most of the picture information are corrected to give greater contrast. In the output signal, portions corresponding to the black and peak white levels of the incoming video signals are provided substantially at the black and peak white levels, respectively, while the average brightness level of the output video signal is provided at an optimum level, such as 50%. The brightness control circuit can include a variable gamma correction circuit in which the value of gamma is automatically determined by a control signal provided from the APL detector.
131 Citations
21 Claims
-
1. A control circuit for controlling the brightness of a video signal that fluctuates between a peak dark level and a peak bright level about an average brightness level comprising:
-
brightness controlling means having a signal input to which the video signal is applied as an input video signal and a signal output from which an output video signal is provided, said brightness controlling means being operable by a control signal for controlling the brightness of the video signal so that respective portions of said output video signal corresponding to portions of the input video signal at said peak dark level and at said peak bright level are provided substantially at said peak dark and bright levels while the average picture level of said output video signal is provided at a predetermined optimum level; average picture level detecting means for detecting the average brightness level of at least one of said input and output video signals and providing said control signal in response to the detected average brightness level; and a variable gamma correction circuit included in said brightness controlling means and having an input-output characteristic such that for the input video signal having a level proportional to a value X, where X is in the range 0≦
X≦
1, said video signal is provided at a level proportional to a value X.sup.γ
; and
the value of γ
is automatically determined in response to the control signal from said average picture level detecting means. - View Dependent Claims (2, 3, 4, 5)
-
-
6. A control circuit for controlling the brightness of a video signal that fluctuates between a peak dark level and a peak bright level about an average brightness level comprising:
-
brightness controlling means having a signal input to which the video signal is applied as an input video signal having a level proportional to a value X, where X is in the range 0≦
X≦
1, and a signal output from which an output video signal is provided, said brightness controlling means being operable by a control signal for controlling the brightness of the video signal so that respective portions of said output video signal corresponding to portions of the input video signal at said peak dark level and at said peak bright level are provided substantially at said peak dark and bright levels while the average picture level of said output video signal is provided at a predetermined optimum level;
said brightness controlling means including first correction circuit means having an input-output characteristic such that a first corrected video signal is provided at a level proportional to √
X, second correction circuit means having an input-output characteristic such that a second corrected video signal is provided at a level proportional to X2 and summing circuit means for combining said first and second corrected video signals in relative amounts depending upon said control signal so that the combined first and second corrected video signals are provided as said output video signal; andaverage picture level detecting means for detecting the average brightness level of said input video signal and providing said control signal in response to the detected average brightness level. - View Dependent Claims (7, 8, 9)
-
-
10. A control circuit for controlling the brightness of a video signal that fluctuates between a peak dark level and a peak bright level about an average brightness level comprising:
-
brightness controlling means having a signal input to which the video signal is applied as an input video signal and a signal output from which an output video signal is provided, said brightness controlling means being operable by a control signal for controlling the brightness of the video signal so that respective portions of said output video signal corresponding to portions of the input video signal at said peak dark level and at said peak bright level are provided substantially at said peak dark and bright levels while the average picture level of said output video signal is provided at a predetermined optimum level;
said brightness controlling means including correction circuit means having an input terminal to which said input video signal is applied and an output terminal at which a corrected video signal is obtained, the latter being substantially proportional to the square of the input video signal, polarity inverter means coupled to the output terminal of the correction circuit means for providing an inverted version of said corrected video signal, summing circuit means for combining said corrected video signal and the inverted version thereof in relative amounts depending upon said control signal to provide a resultant video signal and adder means for combining the input video signal with said resultant video signal to produce said output video signal; andaverage picture level detecting means for detecting the average brightness level of said input video signal and providing said control signal in response to the detected average brightness level. - View Dependent Claims (11)
-
-
12. A color television camera providing a composite color video signal comprising a plurality of pickup tubes each responsive to light of a respective primary color to produce a corresponding primary-color signal that fluctuates between a peak dark level and a peak bright level about an average brightness level;
- average picture level detecting means for detecting the average brightness level of the composite color video signal and providing a control signal in response to such detected average brightness level;
a plurality of variable correction circuits each coupled to a respective pickup tube for processing a respective primary color signal, each such variable correction circuit being coupled to receive said control signal and having an input-output characteristic such that for the associated respective primary-color signal having a level proportional to a value X, where X is in range 0≦
X≦
1, said variable correction circuit provides an output signal substantially proportional to a value X.sup.γ
, where the value γ
is automatically determined in response to the control signal from the average picture level detecting means; and
encoding means coupled to receive the output signals from said variable correction circuits for providing said composite color video signal as a brightness-corrected composite color video signal. - View Dependent Claims (13)
- average picture level detecting means for detecting the average brightness level of the composite color video signal and providing a control signal in response to such detected average brightness level;
-
14. A control circuit for controlling the brightness of a video signal in a color television display apparatus having a color display tube providing a color video picture in response to a plurality of primary color signals, and in which a chrominance signal and a luminance signal that varies between a black level and a peak white level about an average brightness level are combined to form said plurality of primary color signals, comprising
average picture level detecting means coupled to receive the luminance signal for detecting the average brightness level of said luminance signal and providing a control signal in response to the detected average brightness level; - and a plurality of variable correction circuits each operative upon a respective primary color signal and disposed in advance of said color display tube, each such variable correction circuit being coupled to receive said control signal and having an input-output characteristic such that for the associated respective primary-color signal having a level proportional to a value X, where X is in the range 0≦
X≦
1, said variable correction circuit provides to the associated respective beam-generating device, an output signal that is substantially proportional to a value X.sup.γ
, where the value of γ
is automatically determined in response to said control signal.
- and a plurality of variable correction circuits each operative upon a respective primary color signal and disposed in advance of said color display tube, each such variable correction circuit being coupled to receive said control signal and having an input-output characteristic such that for the associated respective primary-color signal having a level proportional to a value X, where X is in the range 0≦
-
15. A correction circuit for controlling the brightness of a composite color video signal having a luminance component that fluctuates between a black level and a peak white level about an average luminance level, a chrominance component, and a synchronizing pulse with a pedestal portion, comprising clamping means for establishing the black level of said video signal as a function of said pedestal portion;
- means for providing said synchronizing pulse to said clamping means;
average picture level detecting means for providing a control signal in response to the average luminance level of said luminance component; and
brightness controlling means coupled to receive said control signal and having a signal input to which at least said luminance and chrominance components are applied and a signal output from which an output composite video signal is obtained, for controlling the brightness of the composite video signal so that respective portions of said output composite video signal corresponding to portions of the luminance component at said black level and at said peak white level are provided substantially at said black and peak white levels, while said output composite video signal has an average picture level that is provided at a predetermined optimum level. - View Dependent Claims (16, 17, 18)
- means for providing said synchronizing pulse to said clamping means;
-
19. A color video display apparatus to which is applied a composite color video signal including a chrominance component and a luminance component that fluctuates between a black level and a peak white level about an average brightness level comprising separating means for separating said luminance component and said chrominance component from said composite color video signal;
- average picture level detecting means having an input coupled to receive the separated luminance component for providing a control signal in response to the detected average brightness level;
variable luminance component controlling circuit means having an input to receive the separated luminance component, a signal output from which a corrected luminance component is provided, and a control input to receive said control signal, for controlling the brightness of the separated luminance component so that respective portions of the corrected luminance component corresponding to portions of the separated luminance component at said black and peak white levels are provided substantially at said black and peak white levels, while the average brightness level of said corrected luminance component is provided substantially at a predetermined optimum level;
variable chrominance component controlling circuit means having an input to receive the separated chrominance component, a signal output from which a corrected chrominance component is provided, and a control input to receive said control signal, for controlling the strength of the separated chrominance component, and having an input-output characteristic that varies as a function of said control signal;
processing circuit means to which said corrected luminance and chrominance components are applied for producing a plurality color signals; and
display means for producing a picture in response to said primary color signals. - View Dependent Claims (20, 21)
- average picture level detecting means having an input coupled to receive the separated luminance component for providing a control signal in response to the detected average brightness level;
Specification