JPH07212790A - Automatic gamma balance adjustment method - Google Patents

Abstract

PURPOSE:To automatically adjust R, G, B signals by applying DC conversion to an output of three sets of gamma correction circuits to the R, G, B signals and applying a level difference between the signal G and the signals R, B to R, B gamma correction the use of a variable resistor. CONSTITUTION:At first a G gamma correction voltage 5 is adjusted so as to change the gamma correction linearly while signal levels of R, G, B inputs 1-3 are kept equal. An iris is adjusted to decrease a maximum level of a gray scale to an intermediate level. When automatic gamma adjustment is started, switches 21, 22 are switched to be closed. R, G output signals 11, 12 through gamma circuits 7, 8 and a signal processing circuit 10 are converted into a DC voltage equivalent to a white level by peak rectifier circuits 14, 15 and given to a differential amplifier 17. An error voltage resulting from the comparison of white levels of R, B channels at the amplifier 17 is received by the circuit 7 as an R gamma correction voltage and made stable when the white level of the R, G channels is matched with each other. The error voltage at this point of time is stored in a memory circuit 19 and the automatic gamma adjustment is finished. This is applied similarly as to the B signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an adjusting method in a gamma circuit of a color television camera.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional gamma adjustment circuit,
The operation will be described below. An image of a chart such as gray scale is taken for adjustment, and R, G, B inputs 1, 2,
In the state where the signal levels of 3 are equal, when the video waveform is G channel signal output 12, the level of the step wave changes linearly from the state of gamma correction off as shown in FIG. 3 to that of FIG. The G gamma adjustment volume 5 ′ is adjusted so that Next, in the VBS output 24, the R gamma adjustment volume 4'and the B gamma adjustment volume 6'are repeatedly adjusted so that the carrier leak near the intermediate level of the obtained video waveform is minimized.

[0003]

In the above-mentioned prior art,
Since three volumes are needed to adjust the gamma characteristics of the R, G, and B channels, and two more volumes are alternately and repeatedly adjusted to adjust the gamma balance, it takes time to adjust. However, the adjustment accuracy also varied depending on the adjuster. The present invention eliminates these drawbacks,
The purpose is to automate the adjustment of the gamma balance between R, G, and B.

[0004]

In order to achieve the above object, the present invention performs signal processing on the outputs of three sets of gamma correction circuits corresponding to R, G, and B, respectively, and then performs peak rectification on each output to obtain a direct current. Converted, the R signal with the G signal as a reference,
The difference in signal level from the B signal is detected, and the detected difference signal output is applied to the corresponding voltage control section of the gamma correction circuits of the R and B channels, and the maximum peak level of the output signal of each gamma correction circuit is detected. For the G channel, R,
The B channel is controlled so as to have the same value, these control values are stored in the corresponding memory circuits, and the gamma balance is automatically adjusted by these stored control values.

[0005]

As a result, it is possible to automatically adjust the gamma balance without adjusting the volume, which facilitates the setting in the camera adjustment process in the factory and improves the adjustment accuracy. It leads to improvement and cost reduction.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the gamma adjusting circuit according to the present invention will be described below with reference to FIG. 1, 2, 3 are R, G, B input signals, 4, 5, 6 are R, G, B gamma correction control voltages,
7, 8, 9 are R, G, B gamma circuits, 10 is a signal processing circuit for performing knee clip, contour correction, etc., 11, 12, 1
3 is R, G, B output signal, 14, 15, 16 are R, G,
B peak rectifier circuit, 17, 18 are differential amplifiers, 19, 2
Reference numeral 0 is a memory circuit, and reference numerals 21 and 22 are changeover switches. Next, regarding the operation, first, the R channel and the G channel will be described. For the purpose of adjustment, a chart such as a gray scale is imaged at a rated level, and when the signal levels of the R, G, B inputs 1, 2, 3 are equal, the video waveform is at the G channel signal output 12 as shown in FIG. As shown in FIG. 4, the G-gamma correction control voltage 5 is adjusted so that the level of the staircase wave changes linearly as shown in FIG.

Next, an iris (not shown) is adjusted to lower the maximum level (white level) of the grayscale image waveform to an intermediate level of 40 to 50% of the rated level. Here, when the automatic gamma adjustment operation is started, the switch 21,
22 is switched to the ON side. The R output signal 11 and the G output signal 12 that have passed through the signal processing circuit 10 are
At 4 and 15, a DC voltage corresponding to the white level of the video signal is formed and enters the differential amplifier 17, and an error voltage obtained by comparing the white levels of the R channel and the G channel is set as the R gamma correction control voltage 4 to the R channel. It becomes a loop by being applied to the gamma adjustment terminal of the gamma circuit 7 and becomes stable when the white level of the R channel matches the white level of the G channel. After the error voltage at this time is stored in the memory circuit 19, the switch 21 is switched to the off side and the automatic gamma adjustment operation ends. After that, the data of the memory circuit 19 is R
The gamma correction control voltage 4 is applied to the R channel. Regarding the operation of the B channel and the G channel, the same operation is performed by replacing the R channel with the B channel in the above operation.

If the color television camera has a built-in auto white circuit using a microcomputer, the R, G and B peak rectifying circuits 14, 15, 16 and the differential amplifiers 17, 18 and the memory circuit 19, Since 20 and the changeover switches 21 and 22 can be shared, they can be handled by software, and since the expansion of the memory circuits 19 and 20 can be accommodated in the original memory device, the interface circuit for R, G, and B gamma adjustment signals can be used. It can be realized only by expansion. If a voltage corresponding to the G gamma correction control voltage 5 is supplied from the memory of the microcomputer, a plurality of R, G, and B gamma data can be stored, so that, for example, the gamma data corresponding to the gain can be set. It is also possible to switch the value.

[0009]

According to the present invention, the gamma balance can be adjusted automatically without a volume adjustment, which facilitates the setting in the camera adjustment process in the factory and improves the adjustment accuracy. , Leading to quality improvement and cost reduction. The same applies to camera adjustment by the user.

[Brief description of drawings]

FIG. 1 is a block diagram showing the overall configuration of the present invention.

FIG. 2 is a block diagram showing an overall configuration of a conventional technique.

[Fig. 3] Output signal waveform diagram of gamma circuit (gamma correction: when off)

[Fig. 4] Output signal waveform diagram of the gamma circuit (gamma correction: when on)

[Explanation of symbols]

1, 2, 3: R, G, B input signals, 4, 5, 6: R,
G, B gamma correction control voltage, 7, 8, 9: R, G, B
Gamma circuit, 10: signal processing circuit, 11, 12, 13:
R, G, B output signals, 14, 15, 16: R, G, B peak rectification circuits, 17, 18: Differential amplifiers, 19, 20:
Memory circuits 21, 22: changeover switches.

Claims (1)

[Claims] 1. The G signal is obtained by subjecting the outputs of three sets of gamma correction circuits corresponding to at least R, G, and B whose gamma characteristics are variable by voltage control to signal processing, peak rectification, and DC conversion, respectively. The difference between the signal levels of the R and B signals is detected on the basis of the above, and the detected difference signal output is applied to the corresponding voltage control section of the gamma correction circuit of the R and B channels. The maximum peak level of the output signal is controlled so that the R channel and the B channel have the same value with respect to the G channel, these control values are stored in the corresponding memory circuits, and the gamma is controlled by these stored control values. An automatic gamma balance adjustment method characterized by automatically adjusting the balance.