JP3134401B2 - Auto white balance circuit of television camera device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic white balance circuit for a television camera device, and more particularly to a circuit configuration for focusing at high speed and high accuracy.

[0002]

2. Description of the Related Art FIG. 3 shows a television camera device including a conventional automatic white balance circuit. In FIG. 3, a video signal input from each of the R / G / B image sensors 1 is gain-controlled by a gain control circuit 2. afterwards,
The data is color-encoded by an encoder circuit 5 via a process circuit 3 and a γ correction circuit 4 and output. In the conventional auto white balance circuit, the output of the gamma correction circuit 4 is used as an input of a comparison circuit 7 for selecting and comparing any two signals of R / G / B.

The R / G / B level difference output from the comparison circuit 4 is converted into a digital signal by an A / D converter 8, a microcomputer 9 calculates the amount of gain to be corrected, and controls the gain. The circuit 2 is controlled.

The above process is repeated several times, and if it can be confirmed that the difference between each level of R / G / B is within a certain range,
The auto white balance operation ends.

[0005]

In this conventional auto white balance circuit, since the gamma correction circuit 4 is a non-linear conversion, it is difficult to accurately determine the value of the gain to be corrected from the output value of the comparison circuit 7. Met. The reason is described below.

FIG. 4 shows an example of the input / output characteristics of the gamma correction circuit. As is clear from FIG. 4, the input / output characteristics of the gamma correction circuit are nonlinear characteristics. Now, assuming that two signals of R / G are selected as inputs of the comparison circuit 7,
The level difference between R and G at the output end of the γ correction circuit 4 alone gives
Some level differences between R and G at the input terminal of the correction circuit 4 are unknown. As an example, the slope of the curve in FIG. 4 is about 0.45 near the output of 100%, so if the level difference at the output terminal of the γ correction circuit 4 is 10%, the input terminal of the γ correction circuit 4 Is considered to have a level difference of about 22%. On the other hand, in the vicinity of the output of 70%, the slope of the curve becomes larger than 0.45 (about 0.55), so that the same level difference of 10%
However, at the input end of the gamma correction circuit 4, the level difference between R and G is smaller than 22% (about 18%). Therefore, in the conventional automatic white balance circuit, it is necessary to repeatedly output the value of the gain to be temporarily corrected from the output of the comparison circuit 7 to the gain control circuit 2 and measure the level difference again. As a result, the accuracy of the auto white balance circuit can be focused to a certain appropriate value, but the time required for focusing cannot be shortened.

As a means for solving the above-mentioned problem in the configuration of the conventional auto white balance circuit, not only the level difference at the output terminal of the comparison circuit 7 but also the R / G /
There is also a method of measuring the absolute value of each level of B. In this case, since it is possible to determine where the current signal level is located on the curve shown in FIG. 4, it is also possible to obtain the signal level difference at the input terminal of the γ correction circuit 4 by calculation. However, when the signal level difference is measured and when the absolute value is measured, the required dynamic range of the comparison circuit 7 and the A / D converter 8 greatly differs. Since the minimum resolution of the comparison circuit 7 and the A / D converter 8 is defined by the accuracy at which the white balance is focused, the bit number of the A / D converter 8 must be reduced in order to measure a higher level. Since it has to be increased, it becomes a problem in terms of cost and mounting technology.

An object of the present invention is to shorten the time required for focusing the accuracy of an auto white balance circuit to a certain appropriate value.

[0009]

In order to achieve the above-mentioned object, the present invention connects an output terminal of a gain control circuit to an input terminal of a process circuit, and connects an output terminal of the process circuit to an input terminal of a gamma correction circuit. The output terminal of the gamma correction circuit is connected to the input terminal of the encoder circuit and the second input terminal of the signal switch, and the output terminal of the signal switch is connected to the input terminal of the comparison circuit. And the output of the comparison circuit is connected to the input of the A / D converter, the output of the A / D converter is connected to the input of the microcomputer, and the output of the microcomputer is connected to the input of the gain control circuit. connected to second input terminal, so the input signal is applied to the first input terminal of the gain control circuit, said signal switching
First, the signal at the input terminal of the gamma correction circuit is
Select the input to the
Operation, and then the signal at the output terminal of the gamma correction circuit is
Switch to input to the comparison circuit
It is said to control the Nsu operations.

According to another aspect of the present invention, an output terminal of a gain control circuit is connected to an input terminal of a process circuit, and an output terminal of the process circuit is connected to an input terminal of a gamma correction circuit. The output terminal of the correction circuit is the input terminal of the encoder circuit,
Connect the input terminal of the inverse γ correction circuit and the second input terminal of the signal switch, connect the output terminal of the inverse γ correction circuit to the first input terminal of the signal switch, and compare the output terminals of the signal switch. The input terminal of the circuit is connected to the input terminal of the A / D converter, the output terminal of the A / D converter is connected to the input terminal of the microcomputer, and the output terminal of the microcomputer is connected to the input terminal of the microcomputer. The first input of the gain control circuit is connected to the second input terminal of the gain control circuit.
An input signal is applied to an input terminal, and the signal switch is first selected so that a signal at an output terminal of the inverse γ correction circuit is input to the comparison circuit to control a white balance operation. The white balance operation is controlled by switching so that the signal at the output terminal of the γ correction circuit is input to the comparison circuit.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a first embodiment of the present invention. FIG. 1 is different from FIG.
That is, a signal switch 6 is provided at the input terminal of the comparison circuit 7, and a function of measuring the R / G / B level difference at the input terminal of the gamma correction circuit 4 is added. With the addition of the signal switch 6, the automatic white balance operation is performed in the following process.

When executing the auto white balance operation,
First, the signal switch 6 is selected so that the signal at the input terminal of the γ correction circuit 4 is input to the comparison circuit 7. In this state, since the gain control circuit 2 to the comparison circuit 7 are all composed of linear circuits, the microcomputer 9 accurately calculates the value of the gain to be corrected from the output of the A / D converter. can do. Therefore, the balance operation at the input terminal of the γ correction circuit 4 is completed without repeating the loop of the level difference measurement and the control output many times.

Next, the signal switch 6 is switched so that the signal at the output terminal of the gamma correction circuit 4 is input to the comparison circuit 7. The subsequent operation is exactly the same as that of the auto white balance circuit having the configuration according to the related art,
Since the balance adjustment up to the input end of the γ correction circuit 4 has already been completed, the balance operation to be adjusted here is γ
It is only the error in R / G / B of the correction circuit 4. Therefore, the loop of the level difference measurement and the control output here can be completed in a sufficiently small number of times as compared with the configuration of the related art.

FIG. 2 is a diagram showing a second embodiment of the present invention. In FIG. 2, the auto white balance operation is represented by γ
A signal having an input / output characteristic opposite to that of the gamma correction circuit 4 is provided at the input terminal of the signal switch 6 without directly using the signal at the input terminal of the correction circuit 4.
Since the correction circuit 10 is inserted, since the gain control circuit 2 to the comparison circuit 7 are all composed of linear circuits, the microcomputer 9 determines the gain to be corrected from the output of the A / D converter 8. The value can be calculated accurately.

[0016]

As described above, the present invention provides an R / G
A / D comparing the level difference between any two signals
A signal switch for inputting two types of signals, a signal at the input terminal of the gamma correction circuit and a signal at the output terminal of the gamma correction circuit, is provided on the input circuit side of the converter, so that the auto white balance operation can be completed more quickly. The effect that it can be obtained is obtained.

Further, according to the present invention, γ is applied to the input terminal of the signal switch.
Since the reverse γ correction circuit having the input / output characteristics opposite to that of the correction circuit is provided, an effect that the auto white balance operation can be completed at higher speed can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a second embodiment of the present invention.

FIG. 3 is a diagram showing a conventional auto white balance circuit.

FIG. 4 is a diagram illustrating an example of input / output characteristics of a γ correction circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image sensor 2 Gain control circuit 3 Process circuit 4 γ correction circuit 5 Encoder circuit 6 Signal switch 7 Comparison circuit 8 A / D converter 9 Microcomputer 10 Reverse γ correction circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 9/73 H04N 9/04 H04N 9/69

Claims (2)

(57) [Claims] An output terminal of the gain control circuit is connected to an input terminal of the process circuit; an output terminal of the process circuit is connected to an input terminal of the gamma correction circuit and a first input terminal of the signal switch; The output terminal is connected to the input terminal of the encoder circuit and the second input terminal of the signal switch, the output terminal of the signal switch is connected to the input terminal of the comparison circuit, and the output terminal of the comparison circuit is connected to the input of the A / D converter. Terminal, the output terminal of the A / D converter is connected to the input terminal of the microcomputer, the output terminal of the microcomputer is connected to the second input terminal of the gain control circuit, and the output terminal of the A / D converter is connected to the first input terminal of the gain control circuit. An input signal is added, and the signal switch is first turned on at the input terminal of the gamma correction circuit.
Signal to be input to the comparison circuit
Controlling the balance operation, and then the output terminal of the gamma correction circuit.
Switch to input the signal of
An automatic white balance circuit for a television camera device, which controls a white balance operation. 2. An output terminal of the gain control circuit is connected to an input terminal of the process circuit, an output terminal of the process circuit is connected to an input terminal of the gamma correction circuit, and an output terminal of the gamma correction circuit is connected to an input terminal of the encoder circuit. Connect the input terminal of the inverse γ correction circuit and the second input terminal of the signal switch, connect the output terminal of the inverse γ correction circuit to the first input terminal of the signal switch, and compare the output terminals of the signal switch. The input terminal of the circuit is connected to the input terminal of the A / D converter, the output terminal of the A / D converter is connected to the input terminal of the microcomputer, and the output terminal of the microcomputer is connected to the input terminal of the microcomputer. connected to a second input terminal of the gain control circuit, so as to add an input signal to the first input terminal of the gain control circuit, said signal switching device, first, the signal of the output of the inverse γ correction circuit is the comparator circuit To control the white balance operation. Is switched so that the signal at the output terminal of the γ correction circuit is inputted to the comparison circuit,
An automatic white balance circuit for a television camera device, which controls a white balance operation.