JPH03250978A - Video signal level controller - Google Patents

Abstract

PURPOSE:To always obtain a video signal of a proper level by varying a control signal of level control of a video signal based on a mixture ratio between a peak detection value and a mean detection value of the input video signal required for the level control of the video signal. CONSTITUTION:A level of a video signal output VOUT from a video signal output circuit 12 is detected by a video signal level detection circuit 13. A detection value based on a peak value and a detection value based on a mean value are added in the circuit 13 at a predetermined mixture ratio and the result is outputted as a mixture level VMIX. The output level VMIX and the mixture ratio RMIX are outputted respectively from the detection circuit 13 and given to a control signal output circuit 14. The control signal output circuit 14 multiplies a constant depending on the ratio RMIX with the inputted level VMIX to generate a control signal output VCT1 and it is fed to the video signal level control circuit 11. Thus, a video signal level close to an object level is always obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a video signal level control device, and particularly to a video signal level control device suitable for application to an automatic aperture control device of a video camera or an automatic gain control device of a video circuit. Regarding a control device.

(Prior Art) Conventionally, in a video signal level control device, a peak value and an average value of a video signal level are detected, these are added at an appropriate mixing ratio, and the resulting signal is set as a target level to control the video signal level. It was implemented to control the signal level.

However, the optimum mixing ratio between the detected value of the peak value and the detected value of the average value of the video signal level differs depending on the image expressed by the video signal. A P L of the video signal, (Av
The closer the APL, which represents the duty ratio between the white part and the black part of the video signal, is to a value close to 100%, the more the signal has a uniform level. Therefore, the difference between the peak value detection value and the average value detection value is small, and therefore the variation in the detection signal due to a change in the mixing ratio of the two, that is, the variation in the video signal level controlled based thereon, is also small. On the other hand, in the case of a screen with a small APL, the difference between the peak value and the average value is large. For this reason, fluctuations in the detection signal due to changes in the mixing ratio of both, that is, fluctuations in the video signal level controlled based thereon, also increase.

Generally, the video signal level settings are
It is often set to always be at a constant level at L (approximately 40 to 50 percent).

(Problem to be Solved by the Invention) A conventional video signal level control device is constructed based on the above concept. However, the mixing ratio between the peak value detection value and the average value detection value is not constant depending on the subject. For this purpose, it is common to make adjustments by changing the settings of a variable resistor or computer. However, in the case of a typical AFL image of about 50 percent, changing the mixing ratio significantly changes the video signal level that is controlled based on this. For this reason, it becomes necessary to adjust the control level at the same time. However,
Not only does adjusting the control level require a measuring device, but there is also a strong demand for wide outdoor use of dynamic images, making it impossible to actually adjust the control level. .

The present invention has been made in view of the above, and is a method for controlling the level of a video signal based on the mixing ratio of the peak value detection value and the average value detection value of the input video signal necessary for level control of the video signal. It is an object of the present invention to provide a video signal level control device that makes it possible to always obtain a video signal at an optimum level by changing the signal.

(Means for Solving the Problems) A video signal level control device of the present invention includes a peak value detection circuit that detects a peak value of an input video signal, and an average value detection circuit that detects an average value of the input video signal. and a calculation means for adding the peak value detected by the peak value detection circuit and the average value detected by the average value detection circuit at a predetermined mixing ratio and extracting the result as a level detection signal; and the calculation means a control signal output circuit that outputs a control signal for controlling the level of the input video signal based on the mixing ratio set to the mixing ratio and the level detection signal obtained from the calculation means; and a level control circuit that controls the level of the input video signal based on the control signal from the circuit.

(Function) The peak value detection circuit detects the peak value of the input video signal, and the average value detection circuit detects the average value of the input video signal. Then, the calculation means adds the detection values of the peak value detection means and the average value detection means at a predetermined mixing ratio to generate a level detection signal.

The control signal output circuit calculates and generates a control signal for controlling the level of the input video signal based on the mixing ratio set in the calculation means and the level detection signal obtained from the calculation means. This control signal is applied to a level control circuit to control the level of the input video signal.

(Example) Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of a video signal level control device according to an embodiment of the present invention. In the figure, a video signal level control circuit 11 receives a control signal output vct
It has the function of controlling the level of the video signal manually. The output of the video signal level control device 11 is sent out through the video signal output circuit 12 as a video signal output VoUT. The video signal output circuit 2 includes various video signal processing circuits such as a pedestal clamp, nonlinear amplification, etc., and is a circuit for obtaining a video signal of a required level and waveform. Video signal output V from the video signal output circuit 12. U
The signal level of T is detected by the video signal level detection circuit 13. In this circuit 13, the detected value based on the peak value and the detected value based on the average value are added at a predetermined constant mixing ratio and output as a mixing level vMlx.

The video signal level detection circuit 13 outputs the mixing level V 1 and the mixing ratio RMIX, respectively, and applies them to the control signal output circuit 14 . The control signal output circuit 14 multiplies the input mixing level vM1x by a constant determined by the mixing ratio RMIx to output a control signal V.

11 and applies it to the video signal level control circuit 11.

In the above configuration, the operation thereof will be explained next.

Now, the video signal output V which is the output from the video signal output circuit 12. The peak value and average value of U are detected by the video signal level detection circuit 13. Then, these are mixed and added at a predetermined mixing ratio.

In the second case, the obtained detection value differs depending on the mixture ratio RMIx. The rate of this change varies depending on the APL of the screen represented by the video signal.

It is desirable to set the APL to a constant level of 40 to 50%. Therefore, in the video signal level detection circuit 13, when the mixing ratio of the detected value of the peak value and the average value is changed, the control signal is output so that the video signal output VOLIT becomes a constant level under the above conditions. Control signal output according to the mixing ratio RM1x in the circuit 14■
. , 1 are adjusted and applied to the video signal level control device 11. As a result, even when the mixing ratio between the peak value and the average value is changed in the video signal level detection circuit 13,
For screens with AFL of about 40 to 50 percent,
A video signal level close to the target is always obtained.

FIG. 2 illustrates an example of a combination of the video signal level detection circuit 13 and the control signal output circuit 14 shown in FIG. As shown in FIG.
is input in parallel to the peak value detection circuit 21 and the average value detection circuit 22 through the input amplifier 26. The peak value detection circuit 21 includes a diode D1, a capacitor C1, and a resistor R1.
It is composed of. This circuit 21 consists of a capacitor C
1 and resistor R1 to determine the discharge time constant, and further detect the peak value of the video signal VIN to obtain a peak value detection value V. ak' is output. On the other hand, the average value detection circuit 22 is an integrating circuit composed of a resistor R2 and a capacitor C2. This circuit 22 detects the average value of the video signal VIN and outputs the detected average value V 1 . The peak value detected value vpeak obtained from the peak value detection circuit 21 and the average value detected value V obtained from the average value detection circuit 22 are determined by a mixing ratio regulator composed of a variable resistor aνe resistor RA. Added to 23. And these two values v V are peak'
c Here, the mixing ratio RMIX based on the setting value of variable resistor RA
The mixed level vMIx is obtained by mixing and adding. This level VMIX is applied to the output amplifier 25. The setting value of the variable resistor RA in the mixing ratio regulator 23, that is, the mixing ratio RMIX, is determined by the variable resistor R that physically interlocks with this.
The reference level Vref' corresponding to the mixing ratio RMIX is sent to the output amplifier 25. The output amplifier 25 has a resistor R
3, the gain determined by the resistor R4, and the reference level based on the reference level Vrer, the mixed level vMIX is amplified and output as the control signal output Vct+.

According to the above configuration, if the mixing ratio RMIX in the mixing ratio adjuster 23 changes, this information is transmitted to the video signal level adjuster 24. As a result, the output amplifier 2
The reference level Vref added to 5 changes.

As a result, regardless of the mixing ratio RM1x of the peak value and the average value,
For a standard image in which the APL of the video signal VIN is approximately 40 to 5'0%, a video signal output VoUT of a constant level can always be obtained.

FIG. 3 shows a different example from FIG. 2.

In FIG. 3, the video signal output V is input via the input amplifier 26. UT is applied to the peak value detection section 3 to obtain the peak value detection value vpeak, and at the same time, it is also provided to the average value detection section 32 to obtain the average value detection value . The obtained peak value detection value ve Vpeak and average value detection value ■ave are
The signals are applied to the A/D converter 34 through the switching section 33 composed of WI, and are alternately converted into digital signals. The obtained digital signal is processed by a microprocessor (CP
U) is input to 35. Here, a mixing and addition operation is performed at the mixing ratio RMIX set in advance by the switch SW2.8W3 in the setter 40, and the control level is applied to the D/A converter 38 as a digital value. Here, the control signal output V is converted into an analog signal. 11. A display device f39 is connected to this microprocessor 35. This display device 39 displays control information such as "PEAK 73%" as illustrated in FIG. 5, for example. In addition, the CPU 35 includes a ROM 36 and an R
AM37 is connected.

These are the operations of the microprocessor 35.
This area is used as a storage and operation area for arithmetic procedures for executing a program flow as shown in the flowchart of FIG.

The operation of the configuration described above will now be explained according to the flowchart of FIG. 4.

First, in step SO, initial settings are performed, but here, the peak value mixture ratio RMIx (hereinafter referred to as AF
It is called L2. ) and a reference level vref.

Next, in step S1, switch S in the switching section 33
Switch WI to the peak value detection section 31 side. As a result, the peak value detecting section 31 is connected to the A/D converter 34, but in the next step S2, the peak value detected value Vpeak from the peak value detecting section 31 is A/D converted to the microprocessor 34.
Incorporate into 5. Next, in step S3, step SWI in the switching section 33 is switched to the average value detection section 32 side.

As a result, the average value detection unit 32 is connected to the A/D converter 34, and in the next step S4, the average value detection value V 1 from the average value detection unit 32 is A/D converted and taken into the microprocessor 35ve. In the next step S5, it is determined whether the switch SW2 of the setting device 40 is on or off, and if the switch SW2 is on, the process advances to step S7. On the other hand, if the switch SW2 is off, the process advances to step S6, where the switch SW2 is turned off.
3 is on or off. Here, if the switch SW3 is on, the process proceeds to step S8, and if the switch SW3 is off, the process proceeds to step $9. The ON setting of switch SW2 or SW3 in the setting device 40 is the peak value detection value■
Mixing ratio RMIxO value [hereinafter referred to as AP (%)]. ] is input to the microprocessor 35 as to whether to decrease or increase.

Now, in step S7, when the switch SW2 of the setter 40 is turned on, a calculation is performed to reduce the peak value mixture ratio AP (%). On the other hand, in step S8, when the switch SW3 of the setter 40 is turned on, the peak value mixture ratio A is
An operation is performed to increase P (%). Step S7. When the calculation in S8 is completed, the process moves to step S9, and calculation of the mixture level M1x of the detected peak value vpeak and the detected average value Vave is performed.

vMIX "'(Vpeak-■ave)xA"
00' +vave (1) When the calculation of equation (1) in step S9 is completed, the process proceeds to step SIO, where the control target value is changed.

■ref 2-■ver-2■erf・(100-AF
L2)X(APKI-AP)/(100+APL2)・
・・・・・・・・・・・・(2) However, APLI is the AFL (%) of the screen where the video signal level should be constant, regardless of the peak value mixing ratio AP (%).
corresponds to When vref2 giving a new control target value is obtained in step S10, the process moves to step S11, where a control signal output vctj is calculated.

V --K (V, e, 2-VM, x) --
----(3) ct+ However, K is a constant. When the calculation in step 311 is completed, the process moves to step S12, and the microprocessor 35
The control signal output V obtained digitally. tl is D/
The A converter 38 converts the signal into an analog signal.

In addition, in the above embodiment, the control signal output (■). Although the explanation has mainly been given to a configuration in which tl is used electrically to control the gain of the video signal IIT, it can also be used, for example, as an aperture adjustment signal (light amount control means) in a video camera.

〔Effect of the invention〕

As described above, according to the present invention, in a configuration in which a peak detected value and an average detected value of a video signal are mixed and used to adjust the level of an input video signal, each When changing the mixing ratio, it is possible to obtain a constant video signal level when the APL level of the video signal is in a predetermined pattern,
It becomes possible to realize optimal level adjustment according to the screen.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a video signal level control device according to an embodiment of the present invention, FIGS. 2 and 3 are different circuit diagrams showing a specific example of a part of FIG. 1, and FIG. Third
Flowchart for explaining the operation of the circuit shown in FIG.
The figure is an explanatory diagram showing a display example of the display device of FIG. 3. 11... Video signal level control circuit, 12 Video signal output circuit, 13... Video signal level detection circuit, 1
4... Control signal output circuit, 21... Peak value detection circuit, 22... Average value detection circuit, 23... Mixing ratio adjuster, 24... Video signal level adjuster, 25... - Output amplifier, 26... Input amplifier, 31... Peak value detection section, 32... Average value detection section, 33... Switching section, 34
...A/D converter, 35...Microprocessor, 36...ROM, 37...RAM. 38... D/A converter, 39... Display device, 4
0... Setting device.

Claims (1)

[Scope of Claims] A peak value detection circuit that detects a peak value of an input video signal; an average value detection circuit that detects an average value of the input video signal; and a peak value detected by the peak value detection circuit. and an average value detected by the average value detection circuit at a predetermined mixing ratio and extracting the result as a level detection signal; a control signal output circuit that outputs a control signal for controlling the level of the input video signal based on the level detection signal obtained; A video signal level control device comprising: a level control circuit that controls a signal level;