JPH02141731A - Automatic exposure controller - Google Patents

Abstract

PURPOSE:To perform appropriate exposure to various object patterns by deciding a luminance pattern at the time when the position of a detected area is changed on a screen, setting a photometric area at a position fitted for the luminance pattern and performing the control of exposure. CONSTITUTION:A signal level detection circuit 113 detects the mean value of signal levels on the inside and outside of detection frame 202 and the detected value is transmitted to a microcomputer 115, which detects a photometric mode and decides the position of a photometric frame based on the data. The detection frame 202 is subjected to wobbling up and down on the entire screen 201 based on a detection frame signal 110. The microcomputer 115 detects the luminance pattern and performs the decision of the photometric mode (to decide what position in the screen the photometric frame is set) and calculates appropriate exposure correction quantity from the signal levels on the inside/ outside of the detection frame. An exposure correction circuit 401 performs the control of exposure through an exposure correction signal 402 according to the calculated quantity. Thus, the appropriate control of exposure corresponding to the various object patterns is accomplished.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application of the Invention) The present invention relates to an improvement in an automatic exposure control device disposed in a video camera or the like.

(Background of the Invention) Photometry methods for video cameras mainly include weighted photometry using an average photometry one-screen specific section, peak photometry that makes the peak value of the signal level constant, and combinations thereof. Each method has its advantages and disadvantages, but experience has shown that in general live-action photography, the frame-weighted metering method, in which a specific part of the screen is designated by a frame and weighted metering is applied to that part, has a wide range of applications.

However, in the conventional frame-weighted metering method, the frame position is fixed at a predetermined position within the screen, so proper exposure can only be achieved when the subject or a part of the same brightness as the subject exists within the frame. Furthermore, when a high-brightness area such as the background was included in the frame, the subject was likely to have blackout.

For example, the example in FIG. 6 (1) models the case where the sky appears at the top of the screen in general outdoor live photography, where 301 is the entire screen, 302 is the metering frame for weighted metering,
303 is the sky (high brightness background).

304 is a subject portion.

If such a screen is assumed, by setting the metering frame 302 slightly below the center of the screen, the subject 304 can be captured within the metering frame 302 even if the camera is slightly tilted outward, and proper exposure can be achieved. is obtained.

However, as shown in FIG. 6(2), the subject portion 305
When the brightness area 306 is at the top of the screen and the high-brightness area 306 is at the bottom of the screen, the high-brightness area 306 tends to fit into the metering frame 302, and as a result, the subject area 305 tends to suffer from blackout. In such a shooting scene, This is a case in which the subject portion 305 is assumed to be a tree, and the high-brightness portion 306 is assumed to be a white tile or concrete snow surface.

Figure 6 (3) assumes a person wearing black clothes who is strongly illuminated in a dark room at a wedding, etc.
07 is the background, 308 is the body, and 3o9 is the face. In such a case, the photometry frame 302 enters the human eye area, so the face 30
9 tends to cause overexposure.

As mentioned above, in general live-action photography, brightness pattern changes in the vertical direction of the screen often occur, but the conventional fixed frame weighted metering method can only adapt to the negative part of the screen.
Appropriate exposure control was not possible.

(Object of the Invention) The object of the present invention is to solve the above-mentioned problems, and to solve the problems described above, such as shooting scenes where a subject has a large difference in brightness from the background, and a background having a brightness different from the subject occupies a larger proportion of the screen. ,
An object of the present invention is to provide an automatic exposure control device capable of giving appropriate exposure to various subject patterns.

(Features of the invention) In order to achieve the above object, the present invention according to claim 1 includes:
A variable means for changing the position of a detection area within a screen, and calculating difference information of luminance components in a video signal obtained inside and outside the detection area changed by the variable means, A determination means for determining a brightness pattern within the screen from the respective difference information in the position, and a photometry area position setting means for setting the position of the photometry area within the screen according to the determination result of the determination means, The present invention is characterized in that the brightness pattern at that time is determined by changing the position of the detection area within the screen, and the photometry area is set at a position suitable for the brightness pattern to perform exposure control.

The present invention as set forth in claim 2 also provides a variable means for changing the position of a detection area within the screen in an automatic exposure control device that performs exposure control based on a video signal obtained in a photometric area designated within the screen. Then, the difference information of the luminance components in the video signal obtained inside and outside the detection area changed by the variable means is calculated, and the luminance pattern in the screen is determined from the calculated difference information at different positions of the detection area. and an exposure correction means for correcting the video signal obtained in the photometric area according to the judgment result of the judgment means, thereby changing the position of the detection area within the screen. The present invention is characterized in that the brightness pattern at that time is determined, and the exposure correction amount is calculated according to the brightness pattern and the position of the photometric area within the screen to perform exposure control.

(Embodiments of the Invention) Hereinafter, the present invention will be described in detail based on illustrated embodiments.

FIG. 1 shows an embodiment of the present invention, in which a lens 1
01. The optical information passing through the aperture 102 is imaged on the CCD 103, where it is converted into an electrical signal, and then sent to the buffer 10.
4 to the AGC 105 and the aperture photometry circuit 107a. The output of the aperture photometry circuit 107a is sent to the aperture drive circuit 108 and used as a signal to control the aperture 102, while the output of the AGC 105 is sent to the signal processing circuit 1.
06 and the AGC photometry circuit 107b. The AGC photometry circuit 107b receiving the output has the function of controlling the gain of the AGC 105. Further, the signal processing circuit 106
The output is sent to a signal level detection circuit 113 and a subsequent signal processing circuit (not shown). the photometric circuit 107a,
Reference numeral 107b inputs the photometry frame signal 111 generated by the frame signal generation circuit 109 (details will be described later), and subjects that portion to weighted photometry.

The above is an example of the main configuration of the video signal level control system.

Next, brightness pattern detection and photometry circuit control will be described.

The frame signal generation circuit 109 manually generates the synchronization signal 112 and generates the detection frame signal 110. A photometric frame signal 111 is generated. The signal level detection circuit 113 detects the average value of signal levels inside and outside the detection frame 202. This detected value is the A/D converter 11
4, it is converted into a digital signal and sent to the microcomputer 115. Based on the data, the microcomputer 115 sets the photometry mode,
Determine the detection and photometry frame position.

The detection frame 202 is a second detection frame based on the detection frame signal 110.
As shown in Figures (1) and (2), the entire screen 201 is caused to wobble vertically, and the microcomputer 115 detects the signal level difference between the inside and outside of the frame as shown in Figures 6 (1) to (3) above. A brightness pattern example is estimated and the photometry mode is determined. Examples of the determination results are shown in FIGS. 3 (1) to (3), where 205 is a photometric frame. The determined position of the photometering frame 205 is determined by the photometering circuit 107a and the photometering frame signal 111.
107b, and weighted photometry is performed within this frame.

FIG. 3(1) is a brightness pattern similar to FIG. 6(1), and in this case, the photometry frame 205 is set at the bottom position of the screen.

FIG. 3(2) is the same brightness pattern as FIG. 6(3), and FIG. 3(3) is the same brightness pattern as FIG. 6(2), and in these cases, the photometry frame 205 is set at the upper position, In FIG. 3(2), overexposure of the head portion 207 can be prevented, and in FIG. 3(3), underexposure of the subject portion 209 can be prevented.

Detection of such a pattern can be done by setting the signal level difference between the inside and outside of the detection frame 202 to be below ΔS in FIG. 2 (1) and above ΔS in FIG. 2 (2), as shown in FIG. 3 (1). If 1ΔS lower 1>1
ΔS upper 1, in case of Fig. 3 (2) 1 ΔS lower 1 < 1 ΔS upper 1
, in the case of FIG. 3 (3), ΔS lower 1 × ΔS upper 1, and the one with the larger difference is determined to be the main subject. Whether it should be set at the top or bottom of the screen is clear by looking at the signs of ΔS above and ΔS below.

The position and shape of the photometry frame 205 described above do not necessarily have to match the detection frame 202.

In the example of FIGS. 2 and 3, the photometric frame 205 and the detection frame 202
is set based on another frame signal, and the detection frame 202 is constantly wobbling up and down. However, the photometry frame 205 and the detection frame 202 do not necessarily need to be separated. In that case, the photometric frame signal 111 is the detection signal 110
is the same as The movement of the frame when configured in this way will be explained.

The normal detection frame (=photometering frame) wobbles vertically as shown in Fig. 2 (1) and (2). When the pattern shown in FIG. 3(1) is detected, the frame is set to the lower position. Third
When detecting the patterns shown in FIGS. (2) and (3), the frame is set upward. However, if it remains set at this position, even if the screen changes and the setting position changes to a pattern that should be reversed, it will not be possible to determine this. Therefore, the frame is moved upside down from the set position once every few fields, and the brightness pattern is detected. This cycle may be a cycle that follows the brightness pattern change. For example, every 20 to 30 fields. At the moment of this frame movement, the frame leaves the subject, but if the cycle is of this order, there is no problem as long as the time constant of the photometry circuit is not extremely small.

In the embodiment described above, the photometric circuits 107a, 10.7b
Although the frame-weighted photometry method is used, another configuration example is shown in FIG. The same parts as in FIG. 1 are given the same reference numerals.

The difference is that an exposure correction circuit 401 is added and the exposure correction signal 402 is used instead of the photometry frame signal 111. The photometry circuits 107a and 107b receive an exposure correction signal 40.
Correct the exposure by the amount corresponding to 2. For example, as shown in FIG. 5, the photometry circuits 107a and 107b are configured as an average photometry circuit with a resistor 501 and a capacitor 502, and the exposure correction signal 402 is input through a resistor 503 to control the output of the photometry circuit. This can be achieved by

As described in the previous example, the microcomputer 115 detects the brightness pattern and determines the photometry mode (determines where on the screen the photometry frame should be set), and also determines the appropriate mode based on the signal levels inside and outside the detection frame. Calculate the exposure correction amount. The exposure correction circuit 401 performs exposure control via the exposure correction signal 402 accordingly.

As described above, it becomes possible to perform appropriate exposure control corresponding to various brightness patterns as shown in FIGS. 6(1) to (3), that is, subject patterns.

According to this embodiment, a detection frame is set within the screen, and the detection frame is wobbled up and down to detect a brightness pattern,
Since the metering mode is determined and the exposure is controlled by setting the position of a metering frame with a relatively large area based on the determination result or by performing exposure compensation, conventional fixed frame weighted metering cannot handle this. Appropriate exposure control is now possible for various subject patterns, such as subjects with a large difference in brightness from the background, and shooting scenes where the background has a brightness different from that of the subject and occupies a larger proportion of the screen. Become.

(Correspondence between the invention and the embodiments) In this embodiment, the frame signal generation circuit 109 is replaced by the signal lens detection circuit 11 as the variable means according to claim 1.2 of the present invention.
3. The A/D converter 114 and the microcomputer 115 are used as the determination means according to claims 1 and 2, the frame signal generation circuit 109 is used as the photometric area position setting means according to claim 1, and the exposure correction circuit 401 is used as the photometry area position setting means according to claim 2. Each corresponds to the exposure correction means described above.

(Effects of the Invention) As explained above, according to the present invention, there is provided a variable means for changing the position of a detection area within a screen, and a video signal obtained inside and outside the detection area changed by the variable means. a determination unit that calculates difference information of luminance components and determines a luminance pattern within the screen from the calculated difference information at different positions of the detection area; and a photometric area position setting means for setting the position of the detection area in the screen, thereby determining the brightness pattern at that time by changing the position of the detection area within the screen, and setting the photometric area at a position suitable for the brightness pattern. and an exposure correction means for correcting the video signal obtained in the photometric area according to the judgment result of the judgment means, thereby changing the position of the detection area within the screen. to determine the brightness pattern at that time,
Since the exposure control is performed by calculating the exposure correction amount according to the brightness pattern and the position of the photometric area within the screen, it is possible to provide appropriate exposure to various subject patterns.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG. 2 (
1) (2) are also diagrams explaining the operation of the frame for brightness pattern detection, and Figure 3 (1), (2), and (3) are diagrams explaining the photometry frame positions set corresponding to various brightness patterns. 4 is a block diagram of the main parts of another embodiment of the present invention, FIG. 5 is a circuit diagram showing an example of the internal configuration of the photometric circuit shown in FIG. 4, and FIG. 6 (1) (2) (3) ) is a diagram illustrating conventional photometry frame positions for various subject patterns. 107a, 107b...Photometering circuit, 109...
... Frame signal generation circuit, 113 ... Signal lens detection circuit, 114 ... A/D converter, 1
15... Microcomputer, 202... Detection frame, 205... Metering frame, 401... Exposure correction circuit.

Claims (2)

[Claims] (1) In an automatic exposure control device that performs exposure control based on a video signal obtained in a photometric area designated within a screen, a variable means for changing the position of a detection area within the screen, and a variable means for changing the position of a detection area within the screen; determining means for calculating difference information of brightness components in video signals obtained inside and outside the detected detection area, and determining a brightness pattern within the screen from the calculated difference information at different positions of the detection area;
An automatic exposure control device comprising: photometric area position setting means for setting the position of the photometric area within the screen according to the determination result of the determining means. (2) In an automatic exposure control device that performs exposure control based on a video signal obtained in a photometric area designated within the screen, a variable means for changing the position of the detection area within the screen; determining means for calculating difference information of brightness components in video signals obtained inside and outside the detected detection area, and determining a brightness pattern within the screen from the calculated difference information at different positions of the detection area;
An automatic exposure control device comprising: exposure correction means for correcting the video signal obtained in the photometric area according to the determination result of the determination means.