JPS62125782A - Agc circuit for camera - Google Patents

Abstract

PURPOSE:To apply an optimum AGC to a picture by inputting a camera output being picture information to a frame memory once, and arithmetically processing the data to obtain the control output of an AGC amplifier. CONSTITUTION:When the analog signal from an input terminal 10 is supplied to the AGC amplifier 11 and to an A/D converting circuit 12, converted into a digital signal and written in the frame memory 14 every frame as the picture information. The picture information written in the frame memory 14 is read after a prescribed time and supplied to an arithmetic part 15. In the arithmetic part 15, at first, the features such as rear light or high light are detected, then, the level (brightness) of the picture is detected in a system the most suitable for the feature of the picture, and finally, from the level of the detected picture, a required AGC gain is calculated and outputted in a required time response. In this manner, according to the feature of the picture, the most suitable AGC can be carried out automatically.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an AGC circuit for a camera suitable for use in, for example, a video camera.

[Summary of the invention]

In an AGC circuit for a camera, the present invention writes the camera output to a frame memory, calculates the contents of this frame memory, and controls the AGC circuit using the calculated output, thereby automatically selecting the optimal image according to the characteristics of the screen. AGC
It is designed so that it can be done.

[Conventional technology]

There is a conventional analog AGC circuit for cameras as shown in FIG. In the figure, an output signal from a camera (1) is supplied to an AGC amplifier (2), and its output is detected by a detection circuit (3). The detection circuit (3) has its time constant controlled by a control signal supplied from the terminal (4), and is switched to peak detection or average value detection depending on the characteristics of the screen.

The output of the detection circuit (3) is supplied to one input side of the error amplifier (5), and is compared with the reference voltage from the reference power supply (6) supplied to the other input side of the error amplifier (5). The comparison error signal is supplied as a control signal to the amplifier (2), its gain is controlled, and an output with a constant gain is obtained at the output side of the amplifier (2).

The output of the amplifier (2), whose gain is kept constant in this way, is supplied to the signal processing circuit (7), where the luminance signal Y and color difference signals R-Y, B-Y are formed. The signal is supplied to an encoder (8) and encoded, so that a standard television signal, for example of the NTSC format, is obtained at the output terminal (9).

[Problem that the invention seeks to solve]

However, the conventional circuit having the configuration as shown in FIG. 3 has the following drawbacks. First of all, the time constant of the detection circuit (3) is either fixed or switched externally according to the user's judgment, so there is no guarantee that it will always be the optimal time constant for the subject, and the time constant is determined internally by the camera. It is difficult to switch.

Second, since time-series signals are absorbed, the configuration of the detection circuit (3) becomes complicated because it satisfies both the requirements for a temporal AGC response and the requirements for how to obtain screen information such as peak detection and average value detection.
This is especially a problem when peak detection changes slowly over time.

Thirdly, when switching the time constant of the detection circuit (3) or detecting only part of the information on the screen, it is necessary to change the reference voltage supplied to the error amplifier (5).
This results in disadvantages such as a complicated circuit configuration and an increase in the number of adjustment steps.

This invention was made in view of this point, and has a simple circuit configuration that allows A, G, and C to be selected according to the characteristics of the screen.
A G CliJ for cameras that can automatically perform
It provides a road.

[Failure to solve the problem]

The camera AGC 1pl path according to the present invention derives the camera output via the AGC circuits (11) and (21), writes the camera output to the frame memory (14), and calculates the contents of this frame memory (15). ) to control the AGC circuit.

[Effect]

If the camera output is an analog signal, the A/D conversion circuit (
12), it is converted into a digital signal, and if it is a digital signal, it is written directly into the frame memory (14) via the write control circuit (13).

Then, the screen information written in the frame memory (14) is read out and supplied to the calculation unit (15), where it is processed and if the camera output is an analog signal, it is sent to the D/A.
After converting it into an analog signal in the conversion circuit (17), it is supplied to the AGC amplifier (11) to control its gain.On the other hand, if the camera output is a digital signal, the calculation result is directly sent to the LA.
It is supplied to a multiplier (21) as a GC amplifier to control its gain. Thereby, it is possible to automatically perform AGC that is optimal for the characteristics of the screen.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail based on FIGS. 1 and 2.

FIG. 1 shows the circuit configuration of a first embodiment of the present invention, in which the human input signal is an analog signal. In the figure, (10) is an input terminal to which an analog signal from an image sensor etc. is supplied, and this input terminal (10)
The analog signal from is supplied to the AGC amplifier (11) and is also supplied to the A/D conversion circuit (12), where the analog signal is converted into a digital signal and is controlled to be written as screen information. Times li! t(13
) is written to the frame memory (14) frame by frame.

The screen information written in the frame memory (14) is read out after a predetermined period of time and supplied to the arithmetic unit (15), where it is subjected to arithmetic processing according to the following procedure. In other words, the calculation unit (15) first detects screen characteristics such as backlight or highlights from the screen information, and then detects screen characteristics! Detects the screen level (brightness) using a comprehensive method, calculates the necessary AGC gain from the last detected screen level, and outputs it with the necessary time response. The above-described procedure in the arithmetic unit (15) can also be forcibly changed by an external control signal applied to the terminal (16).

The output signal from the calculation section (15) is sent to the D/A conversion circuit (17).
) converts the digital signal into an analog signal, which is supplied as a control signal to the amplifier (11) to control the AGC gain. and an AGC gain controlled amplifier (11
) is taken out to the output terminal (18).

Note that the calculation in the calculation unit (15) may take some time, but the AGC control does not require responsiveness to respond in real time, and the above calculation is performed for the entire screen. Since it is not necessary, screen information is stored in frame memory for each screen (1
4), sufficient performance can be obtained by writing part of the previous screen into the frame memory (14) and performing the above calculation to match the calculation speed. For this reason, a write control circuit (13) is provided before the frame memory (14).

As described above, in this embodiment, it is possible to automatically perform AGC that is most suitable for the characteristics of the screen.

FIG. 2 shows a second embodiment of the present invention, in which the human input signal is a digital signal. In this figure, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and detailed explanation thereof will be omitted.

(20) is an input terminal to which an analog signal from an image sensor, etc. is converted into a digital signal by an A/D conversion circuit (not shown) and supplied, and the digital signal from this input terminal (20) is sent to an AGC amplifier. The data is supplied to the hanger (21) as screen information, and is also written to the frame memory (14) via the write control circuit (13) as screen information for each frame in the frame memo IJ (14).

The screen information written in the frame memory (14) is read out after a predetermined time and supplied to the calculation section (15).
The arithmetic processing as described above is performed. Then, the calculation section (1
The output signal from 5) is supplied as a control signal to the multiplier (21), which controls the digital signal from the input terminal (20), and the multiplier (21) outputs the AGC according to the characteristics of the screen. is taken out and sent to the output terminal (22).

In this way, substantially the same effects as those of the above-mentioned embodiments can be obtained in this embodiment as well.

〔Effect of the invention〕

As described above, according to the present invention, part of the camera output, which is screen information, is stored in the frame memory and the data is processed to obtain the control output of the ζAGC amplifier, so that it is possible to know the nature of the screen. This allows you to select and switch the calculation method that corresponds to the analog detection time constant on your own, without receiving input from the outside (it is possible to apply the optimal AGC to the screen at any time, for example, automatically Backlight correction becomes possible.

Furthermore, the temporal response of AGC and the method of processing screen information can be separated, increasing the degree of freedom. Furthermore, even if only a part of the screen is extracted or the processing method is changed, the circuit configuration can remain the same and will not become complicated.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a block diagram showing another embodiment of the invention, and FIG. 3 is a block diagram showing an example of a conventional circuit. (11) is an AGC amplifier, (12) is an A/D conversion circuit,
(13) is a write control circuit, (14) is a frame memory, (15) is an arithmetic unit, (17) is a D/A conversion circuit, (
21) is B) Shuki.

Claims (1)

[Scope of Claims] A camera characterized in that a camera output is derived via an AGC circuit, the camera output is written into a frame memory, and the contents of the frame memory are calculated to control the AGC circuit. AGC circuit for.