JP3477936B2 - Automatic exposure control 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 exposure control device effective for use in a video camera or the like.

[0002]

2. Description of the Related Art As a conventional automatic exposure control apparatus, a method of detecting the average brightness level of an image pickup screen, a level such as a peak value, and controlling a diaphragm and a gain for a video signal based on these is often used. There is. However, this method has a problem in that a high-intensity part such as a light source exists in the screen, or conversely, when the background is dark, the main subject is not properly exposed due to the influence of the surroundings.

In order to solve this problem, a technique disclosed in, for example, Japanese Patent Application Laid-Open No. 62-110369 is disclosed. This utilizes the tendency that the main subject is likely to be located in the center of the screen, and the imaging screen is divided into the central part of the screen and the peripheral part other than that, and the brightness level of each part is obtained, and both of these are obtained. The exposure is controlled based on the ratio to obtain an appropriate exposure of the main subject at the center of the screen.

[0004]

However, in the above method, for example, when the main subject moves to the left or right in a backlight or over-illumination image in which a high-intensity part exists in the screen, the brightness level ratio between the center and the peripheral part of the screen is increased. However, there is a problem that the exposure of the main subject fluctuates due to the change of

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide an automatic exposure control device in which the exposure does not fluctuate even when the subject moves in a backlit or over-forward light image in which a high-luminance portion exists in the screen.

[0006]

In order to solve the above-mentioned problems, the automatic exposure control apparatus according to the present invention has a large area of a high brightness area in an over-forward light image and, conversely, a high brightness in a back light image. Focusing on the tendency that there are many scenes with a small area area, the area of the high-brightness area in the screen is detected, and when the area of the high-brightness area is large, the bright part of the screen has an appropriate brightness. As described above, and when the area of the high-brightness region is small, the diaphragm is controlled so that the dark part in the screen becomes bright.

To this end, the automatic exposure control apparatus according to the present invention comprises a full-screen average detection unit for calculating the full-screen average brightness,
A peak luminance detection unit that detects the peak luminance in the screen, a peak luminance region area detection unit that detects the area of the region of the peak luminance from the peak luminance and the video signal, and an average of the entire screen from the area of the peak luminance region. A weight calculation unit that calculates a weight to be applied to the brightness and a weight to be applied to the peak brightness;
A representative luminance calculation unit that calculates a representative luminance of the screen from the full-screen average luminance, the peak luminance, a weight to be multiplied to the full-screen average luminance, and a weight to be multiplied to the peak luminance, and the representative luminance is made to follow a predetermined target luminance. A diaphragm control unit that determines the diaphragm opening is provided.

[0008]

According to the present invention, by providing the above means, the peak luminance in the screen is made constant when the area of the high luminance area is large, and the average luminance of the entire screen is made constant when the area of the high luminance area is small. Appropriate exposure is obtained even when the subject moves in a backlit image in which a high-intensity part exists in the screen and an over-forward light image.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of an automatic exposure control apparatus according to the present invention. In FIG. 1, 1 is a lens, 2 is a diaphragm, 3 is an image pickup device for forming an image of a signal of a subject that has passed through the lens 1 and the diaphragm 2, and converting it into an electric signal, 4 is an electric signal converted by the image pickup device 3. A signal processing circuit for performing γ processing, 5 is a video signal output terminal, 6 is a full-screen average detection unit that calculates the average brightness of the entire screen, 7 is a peak brightness detection unit that calculates the peak brightness in the screen, and 8 is a peak A peak luminance region area detecting unit that detects the area of the peak luminance region from the peak luminance value calculated by the luminance detecting unit 7 and the video signal;
Is a weight calculation unit, 10 is a representative brightness calculation unit that calculates a representative brightness based on the calculation results from the full screen average detection unit 6, the peak brightness detection unit 7, and the weight calculation unit 9, and 11 is a representative brightness calculation unit 10.
The aperture control unit controls the aperture 2 according to the calculation result of

The operation of the automatic exposure control apparatus of the present embodiment having the above-described structure will be described below.

The subject image is formed on the image pickup device 3 through the lens 1 and the diaphragm 2 and converted into an electric signal. The converted signal is sent to the video signal output terminal 5 through the signal processing circuit 4 that performs γ processing and the like. At this time, diaphragm control is performed as follows based on the signal obtained from the image sensor 3. The average luminance of the entire screen is calculated by the entire screen average detection unit 6 from the signal of the image sensor 3. In addition, the peak luminance detection unit 7 calculates the peak luminance value in the screen.

On the other hand, in the peak luminance region area detecting section 8,
The area of the peak luminance region is detected from the peak luminance value calculated by the peak luminance detecting unit 7 and the video signal.

A method of detecting the area of the peak luminance region from the peak luminance and the video signal will be described in detail with reference to FIG.

FIG. 2 shows a low-pass filter (hereinafter, LPF).
Is a characteristic diagram showing the relationship between the cutoff frequency and the area of the region for calculating the average luminance value. In FIG. 2, the output levels of LPFs with different cutoff frequencies are compared to detect the maximum luminance value and the cutoff frequency of the LPF that outputs the maximum luminance value. It can be seen from FIG. 2 that the area of the region for calculating the average luminance value can be detected from the cutoff frequency of the LPF.

FIG. 3 shows the relationship between the difference between the peak luminance value and the maximum luminance value and the area of the peak luminance region. From FIG. 3, it is possible to improve the area detection accuracy by comparing the peak luminance value and the maximum luminance value.

The output of the peak luminance region area detection unit 8 is input to the weight calculation unit 9, and in the weight calculation unit 9, from the area of the peak luminance region detected by the peak luminance region area detection unit 8,
A weight to be applied to the average brightness of the entire screen and a weight to be applied to the peak brightness are calculated. The calculation result of the weight calculation unit 9 is input to the representative luminance calculation unit 10.

In the representative brightness calculation unit 10, the average brightness of all screens calculated by the average detection unit 6 of all screens and the peak brightness detection unit 7 are calculated.
The representative brightness value of the screen is calculated from the peak brightness value calculated in step (3), the weight applied to the average brightness of all screens calculated by the weight calculator 9, and the weight applied to the peak brightness (Equation 1).

[0019]

[Equation 1]

In the aperture control unit 11, the representative brightness calculation unit 10
The aperture is controlled so that the representative luminance value obtained from the above and the predetermined target luminance match.

Here, the weight calculation method performed by the weight calculator 9 and its effect will be described in detail with reference to FIGS. 4, 5 and 6.

FIG. 4 shows a brightness distribution 42 when the ratio of the weights to be multiplied to the average brightness of the entire screen and the peak brightness is 1: 0, and the ratio of the weights is 1 for the backlight image, the over-forward image and the forward-light image. A brightness distribution 43 when the weight ratio is 1 and a brightness distribution 44 when the weight ratio is 0 to 1 are shown. The aperture control here is
The representative luminance value Y obtained in (Equation 1) is controlled so as to match the predetermined target luminance 41.

From FIG. 4, when the weight ratio is 1 to 0 in the backlight image, and conversely when the weight ratio is 0 to 1 in the over-forward light image, the brightness of the subject is the closest to the target brightness. ,
In a normal-light image, the ratio of the weights does not change at any value. From this, it is possible to obtain appropriate exposure by increasing the weight to be applied to the average luminance of all screens in the case of backlight, and to increase the weight to be applied to the peak luminance in the case of excessive light.

Further, since the average brightness over the entire screen, the peak brightness, and the weights applied to the respective objects do not change even if the object moves, it is possible to obtain an appropriate exposure that does not change even if the object moves.

By the way, since the subject is bright in the over-illumination state, the area of the high-luminance region is large, and conversely, in the backlight state, there is a high-luminance region in the background, so that the area tends to be small. Therefore, the backlight and the over-forward light are discriminated by the area of the peak luminance region, and as shown in FIG. 5, by switching the weight 51 for multiplying the average brightness over the entire screen and the weight 52 for multiplying the peak luminance, the over-forward light state generated indoors, Even when the subject moves, it is possible to obtain an appropriate exposure in a backlit state that occurs outdoors or in front of a window.

FIG. 6 shows the relationship between the area of the peak luminance area, the average luminance of the entire screen, and the weight to be applied to each of the peak luminances. As shown in FIG. 6, as the area of the peak brightness decreases, the weight 61 applied to the average brightness over the entire screen gradually increases, and conversely, the weight 62 applied to the peak brightness decreases gradually, thereby changing the angle of view. As a result, when the area of the peak luminance region changes, the exposure state can change smoothly.

By the above-mentioned method, an appropriate exposure is obtained for a backlight or an over-forward light image in which a subject moves.

It is obvious that the same effect can be obtained by dividing the screen into a plurality of small areas by the peak luminance area area detecting unit 8 and detecting the area of the peak luminance area from the peak luminance value of the small areas. Is.

[0029]

As described above, according to the present invention, by providing the representative luminance calculation unit that calculates the representative luminance value that changes depending on the area of the peak luminance region, the peak can be reduced when the area of the high luminance region is large. Constant value, by keeping the average brightness of the entire screen constant when the area of the high-brightness area is small, it is possible to provide an automatic exposure control device that performs appropriate exposure control for the backlight, which is the subject moving, and the over-forward light image. When applied to an image pickup apparatus such as a video camera in which a backlit or overlit state is likely to occur in normal shooting and a subject often moves, the practical effect is large.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of an automatic exposure control apparatus according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram of the relationship between the cutoff frequency of the LPF and the area of the region for calculating the average luminance value in the same example.

FIG. 3 is a characteristic diagram of the relationship between the difference between the peak luminance value and the maximum luminance value and the area of the peak luminance region in the example.

FIG. 4 is an explanatory view of backlight, over-forward light, average brightness of all screens in forward light, change in weight applied to peak brightness, and change in subject brightness.

FIG. 5 is an explanatory diagram of a relationship between color temperature, average luminance of all screens, and peak luminance in the same embodiment.

FIG. 6 is an explanatory diagram of a relationship between a color temperature, an average brightness of all screens, and a peak brightness in the example.

[Explanation of symbols]

1 lens 2 aperture 3 image sensor 4 Signal processing circuit 5 Video signal output terminal 6 Full screen average detector 7 Peak brightness detector 8 Peak luminance area area detection unit 9 Weight calculator 10 Representative brightness calculation unit 11 Aperture controller

Claims (4)

(57) [Claims] 1. A full-screen average detection unit for calculating the full-screen average brightness, a peak brightness detection unit for detecting peak brightness in the screen, and the peak from the peak brightness and the video signal detected by the peak brightness detection unit. A peak luminance region area detection unit that detects the area of the luminance region, and a weight to be applied to the full screen average luminance and a weight to be applied to the peak luminance from the area of the peak luminance region detected by the peak luminance region area detection unit are calculated. A weight calculation unit, a representative luminance calculation unit that calculates a representative luminance of the screen from the full-screen average luminance, the peak luminance, a weight to be multiplied to the full-screen average luminance, and a weight to be multiplied to the peak luminance; An automatic exposure control apparatus comprising: an aperture control unit that determines an aperture opening so as to follow a target brightness. 2. The automatic exposure control apparatus according to claim 1, wherein the peak luminance region area detection unit detects the area of the peak luminance region from outputs of a plurality of low-pass filters having different peak luminance and spatial frequency characteristics. . 3. The peak luminance area detection unit detects the area of the peak luminance area from the peak luminance and the average luminance of each small area obtained by dividing the entire screen into a large number of small areas. Automatic exposure control device. 4. The weight calculation unit calculates the weight to be applied to the average brightness of all screens and the weight to be applied to the peak brightness so that the weight changes smoothly with respect to the change in the area of the peak brightness region. The automatic exposure control device described.