JPH07203287A - Automatic exposure controller - Google Patents

Abstract

PURPOSE:To provide the automatic exposure controller implementing proper exposure control with respect to an outdoor backlighted picture and an indoor excess forward light picture for a moving object. CONSTITUTION:A representative luminance calculation section 10 calculates a representative luminance of a screen based on full screen average luminance, a peak luminance, a weight applied to a full screen average luminance and a weight for a peak luminance. Then an aperture control section 11 controls an aperture 2 so that the obtained representative luminance and a prescribed object luminance are made coincident.

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.

[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-luminance portion 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, for example, a technique disclosed in Japanese Patent 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, an automatic exposure control apparatus according to the present invention comprises a full-screen average detection unit for calculating the full-screen average brightness and a peak brightness detection for detecting the peak brightness in the screen. Unit, a color temperature detection unit that detects the color temperature of the light source, a weight calculation unit that calculates a weight to be applied to the average brightness over the entire screen and a weight to be applied to the peak brightness from the color temperature,
Representative brightness calculation unit that calculates the representative brightness of the screen from the average brightness of the entire screen, the peak brightness, the weight that is applied to the average brightness of the entire screen, and the weight that is applied to the peak brightness, and the aperture opening to make the representative brightness follow the predetermined target brightness. A diaphragm control unit for determining is provided.

[0007]

According to the present invention, by providing the above means, the peak brightness in the screen is kept constant in a room where the color temperature of the light source is low.
In the outdoors where the color temperature is high, by making the average brightness of the entire screen constant, it is possible to obtain appropriate exposure even when the subject moves in the backlight and the over-illumination image in which the high brightness part exists in the screen.

[0008]

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 showing an embodiment of an automatic exposure control device according to the present invention. In FIG. 1, 1
Is a lens, 2 is a diaphragm 2, and a subject image is a lens 1 and a diaphragm 2.
An image is formed on the image pickup element 3 via the and is 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.

First, the average luminance of the entire screen is calculated by the all-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, the color temperature detecting section 8 detects the color temperature of the light source from the average color difference of the video signals over the entire screen.

A method of detecting the color temperature of the light source from the average color difference of the entire screen of the video signal will be described in detail with reference to FIG.

FIG. 2 shows a change in color difference of a video signal when a white subject is imaged and the color temperature of a light source is changed. It can be seen from FIG. 2 that the color temperature of the light source can be detected from the color difference of the white subject. Further, since the average color difference of the image signals on the entire screen is close to the color difference of the white subject, the color temperature can be detected from the average color difference of the image signals on the entire screen.

The weight calculation unit 9 calculates a weight to be applied to the average brightness of the entire screen and a weight to be applied to the peak brightness from the color temperature detected by the color temperature detection unit 8.

In the representative luminance value calculating section 10, the representative luminance value of the screen is calculated from the whole screen average luminance, the peak luminance value, the weight for multiplying the whole screen average luminance, and the weight for multiplying the peak luminance (Equation 1). calculate.

[0016]

[Equation 1]

In the aperture control unit 11, the representative brightness value calculation unit 1
The diaphragm is controlled so that the representative brightness value obtained from 0 and the predetermined target brightness match.

Here, the weight calculation method performed by the weight calculator 9 and its effect will be described in detail with reference to FIGS. 3, 4 and 5.

FIG. 3 shows a brightness distribution 32 when the ratio of the weights to be multiplied to the average brightness of the entire screen and the peak brightness is 1 to 0 for the backlight image, the over-forward light image and the normal light image, respectively, and the weight ratio is 1 to 2. A luminance distribution 33 when the weight is 1 and a luminance distribution 34 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 31.

From FIG. 3, when the weight ratio is 1 to 0 in the backlight image and when the weight ratio is 0 to 1 in the over-forward image, the brightness of the object is closest to the target brightness. In the 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 each of them do not change even when the subject moves, it is possible to obtain an appropriate exposure that does not change even when the subject moves.

By the way, the over-lighting condition in the room such as a wedding tends to cause the backlighting condition in front of the window or outdoors. Therefore, the color temperature is used to discriminate between indoors and outdoors / in front of the window, and a weight 41 is applied to the average brightness of all screens as shown in FIG.
By switching the weight 42 for multiplying the peak brightness, an appropriate exposure can be obtained even when the subject moves in the over-lighting condition generated indoors and the backlighting condition generated outdoors or in front of the window.

FIG. 5 shows the relationship between the color temperature and the weights to be applied to the average brightness of the entire screen and the peak brightness. As shown in FIG. 5, as the color temperature increases, the weight 51 applied to the average brightness over the entire screen is gradually increased, and conversely, the weight 52 applied to the peak brightness is gradually decreased, thereby changing the angle of view. When the color temperature changes, the exposure state can change smoothly.

As described above, appropriate exposure is obtained for an outdoor backlight image in which a subject moves or an indoor over-illumination image.

It is obvious that the same effect can be obtained by measuring the spectral distribution of the light source with the color temperature detecting section 8 and detecting the color temperature using the measurement result.

[0026]

As described above, according to the present invention, by providing the representative luminance calculation unit for calculating the representative luminance value which changes depending on the color temperature of the light source, the peak value can be kept constant indoors and outdoors and at the window. It is possible to provide an automatic exposure control device that performs appropriate exposure control for backlit and over-illuminated images in which the subject moves by making the average brightness of the entire screen constant in front of the window. If the present invention is applied to an image pickup device such as a video camera in which a bright backlight is generated around the screen during shooting, and a subject often moves, the practical effect is large.

[Brief description of drawings]

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

FIG. 2 is a characteristic diagram of a relationship between a color temperature of a light source and a color difference of a video signal of a white subject in the embodiment.

FIG. 3 is a characteristic diagram of a backlight, an over-forward light, a full-screen average brightness in a normal light, a change in weight applied to the peak brightness, and a change in subject brightness.

FIG. 4 is a characteristic diagram of a relationship between color temperature and average luminance of all screens and peak luminance in the example.

FIG. 5 is a characteristic diagram of a relationship between color temperature and average luminance of all screens and peak luminance in the same example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lens 2 Aperture 3 Image sensor 4 Signal processing circuit 5 Video signal output terminal 6 Full screen average detection unit 7 Peak brightness detection unit 8 Color temperature detection unit 9 Weight calculation unit 10 Representative brightness calculation unit 11 Aperture control unit

Claims (4)

[Claims] 1. A full-screen average detection unit for calculating the full-screen average brightness, a peak brightness detection unit for detecting the peak brightness in the screen, a color temperature detection unit for detecting the color temperature of the light source, and the color temperature from the color temperature. A weight calculation unit that calculates a weight to be applied to the full-screen average luminance and a weight to be applied to the peak luminance, a screen from the full-screen average luminance, the peak luminance, a weight to be given to the full-screen average luminance, and a weight to be given to the peak luminance. 2. An automatic exposure control apparatus comprising: a representative brightness calculation unit that calculates a representative brightness of 1. and an aperture control unit that determines an aperture opening so that the representative brightness follows a predetermined target brightness. 2. The color temperature detector detects the color temperature from the average color difference of the entire screen of the video signal.
The automatic exposure control device described. 3. The automatic exposure control apparatus according to claim 1, wherein the color temperature detection unit detects the color temperature from the spectral distribution of the light source. 4. The automatic weight calculating unit according to claim 1, wherein the weight calculating unit calculates the weight to be applied to the average brightness over the entire screen and the weight to be applied to the peak brightness so as to smoothly change with respect to a change in color temperature. Exposure control device.