JPH06311423A - Automatic exposure controller - Google Patents

Abstract

PURPOSE:To enable a proper exposure control by performing the decision of backlight and excess forward light by using an upper and lower luminance difference and continuously switching the control by a peak value and the control by an average value. CONSTITUTION:The difference (p) of the average luminance of a first area and a second area is calculated from the signal of an image pickup element 3 in a first/ second area luminance comparison part 12. In a correction amount calculation part 16, if the average luminance is higher in the first area including the upper part area of a screen than that in the second area including the central area of the lower part of the screen, it is decided as backlight and if the average luminance is lower conversely, it is decided as excess forward light, the luminance difference (p) is converted into gain (g) to be used when correction amount is calculated, and correction amount (z) is calculated. In a target luminance calculation part 9, the target value of the average luminance of the whole screen is calculated every vertical scanning (frame or field) by adding the correction amount (z) to prescribed target luminance. In a weight calculation part 18, the weight Wp of the peak value is calculated from the luminance difference (p). In a weighted average error calculation part 17, a weighted average error (e) is calculated, and in a diaphragm control part 8, diaphragm is controlled so as to keep the weighted average error zero.

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 for 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. However, in this method, for example, when the main subject moves to the left or right in a backlight image in which a high-intensity part exists in the screen, the exposure of the main subject fluctuates because the brightness level ratio between the center of the screen and the peripheral part changes. was there.

In order to solve this problem, the technique disclosed in the prior application (request number H04-2039) is disclosed. This is because the histogram of the brightness level does not change even when the subject moves, the contrast of the entire screen is obtained from the histogram of the brightness level, the magnitude of the exposure correction amount is calculated from the contrast, and Backlit when the top is bright and conversely when the top of the screen is dark, there is a high probability that it will be over-lit. The exposure is controlled according to the size of the amount to obtain an appropriate exposure of the main subject.

This method will be described in detail with reference to FIG. The subject image is passed through the lens 1 and the diaphragm 2, and the image pickup device 3
It forms an image on the top and is converted into an electrical signal. The converted signal is amplified by the amplifier 4, passes through the signal processing circuit 5 that performs γ processing and the like, and is sent to the video signal output terminal 6. 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 7 from the signal of the image sensor 3. The diaphragm control unit 8 controls the average brightness of the entire screen to be the target brightness by operating the diaphragm opening in the direction in which the target brightness obtained from the target brightness calculation unit 9 and the average brightness of the entire screen match. .

Next, the screen is divided into a large number of small areas by the small area average detection unit 10 from the signal of the image pickup device 3 and the average brightness is calculated for each small area to obtain a brightness level histogram.

The degree calculating section 11 calculates the average luminance of the low-luminance portion from the histogram, performs non-linear conversion on the average luminance of the low-luminance portion by fuzzy reasoning, etc., and represents the degree of backlighting of the captured image. Calculate ur. Further, the average brightness of the high brightness part of the histogram is subjected to non-linear conversion by fuzzy reasoning or the like as before, and the degree wr of over-forward light is calculated.

On the other hand, from the signal of the image sensor 3,
The area brightness comparison unit 12 divides the entire screen into a lower center area 21, an upper area 22, a left area 23, and a right area 24 as shown in FIG. 2, and calculates the average brightness of each area. further,
The average brightness of the left area 23 and the right area 24 is compared, and the area having the higher average brightness and the upper area 22 is set as the first area, and the area having the lower average brightness and the lower central area 21 are set as the first area. The combined area is defined as the second area, and the difference p in average luminance between the first area and the second area is calculated. The degree of backlight / over-forward light and the average brightness difference p are sent to the correction amount calculator 16. The correction amount calculation unit 16 determines whether the brightness difference p is backlight or over-forward light, and converts the brightness difference p into a gain g used when calculating the correction amount as shown in FIG. Then, a correction amount z is calculated by the following equation from the back light intensity ur, the over-forward light intensity wr, the gain g, and the back-light / over-forward light determination result.

If p ≤ 0, over-forward light z = g * ur p> 0, then backlight z = g * wr In the target luminance calculation unit 9, the correction amount obtained by the correction amount calculation unit 16
By adding z to the predetermined target brightness, the target value of the average brightness of the entire screen is calculated for each vertical scan (frame or field). The aperture control unit 8 controls the aperture so that the average brightness of all screens is kept at the target value.

As described above, in a backlit image in which the subject moves left and right, the average brightness in the upper and lower regions does not change, and therefore, an erroneous determination is not made, which is suitable for a backlit image in which the subject moves left and right. Exposure control is performed. Furthermore, in a hyper-forward light image in which the subject moves up and down, some dark areas in the lower area are added to the upper area, and the dark areas are excluded from the lower area. By suppressing an increase in brightness and suppressing a decrease in average brightness in the second area, an erroneous determination as to the movement of the subject is eliminated, so that appropriate exposure control is performed on the over-light image in which the subject moves up and down.

[0012]

However, in the above method, the area of the high-intensity part of the main subject is small in an over-illuminated image such as when the subject is spotlighted indoors such as a wedding. When the area is smaller than the area, a sufficient correction effect cannot be obtained, and there is a problem that the brightness of the main subject is saturated and white. Further, when the main subject moves at this time, there is a problem that the exposure of the main subject slightly changes because the correction amount differs depending on whether the main subject is completely included in one small area or when the main subject extends over two small areas. there were.

In view of such a point, the present invention obtains appropriate exposure even when the area of the main subject is smaller than the area of the small area of the screen division in the over-illuminated image, and also with respect to the movement of the main subject. Another object of the present invention is to provide an automatic exposure control device in which the exposure does not change.

[0014]

In order to solve the above problems, the automatic exposure control apparatus according to the present invention may be backlit when the upper part of the screen is bright and may be over-forwarded when the upper part of the screen is dark. By utilizing the tendency that the value is high, over-forward light and back light are discriminated, and the control by the average value and the control by the peak value are continuously switched based on the discrimination result.

To this end, the automatic exposure control apparatus according to the present invention obtains from the full-screen average detecting section for calculating the average brightness of the full-screen, the peak value detecting section for obtaining the maximum brightness in the full-screen, and the full-screen average detecting section. An average value error calculation unit that calculates an error between the obtained average brightness and a predetermined target brightness, and a peak value error calculation unit that calculates an error between the peak brightness obtained from the peak value detection unit and a predetermined target value, Includes a weighted average error calculation unit that calculates a weighted average of the average value error and the peak value error obtained from the two parties, an aperture control unit that determines the aperture opening so that the weighted average error follows 0, and an upper screen portion. From the comparison results of the first and second area brightness comparison sections that compare the average brightness of the first area and the average brightness of the second area including the screen center, the average value and the peak value Weights to calculate the appropriate weighted average weights It is intended to include a detecting section.

[0016]

According to the present invention, by providing the above means, the above-mentioned problems can be solved by controlling the peak value for an over-forward light image without affecting the operation for a backlight image, and an appropriate exposure can be achieved. To get

[0017]

EXAMPLES An example of the present invention will be described below.

FIG. 1 shows a first embodiment of an automatic exposure control device according to the present invention. The same components as those of the conventional automatic exposure control apparatus are designated by the same reference numerals and perform the same operation.

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 amplified by the amplifier 4, passes through the signal processing circuit 5 that performs γ processing and the like, and is sent to the video signal output terminal 6. 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 full-screen average detection unit 7 and the peak value in the entire screen is calculated by the peak value detection unit 13 from the signal of the image pickup device 3. In the aperture control unit 8,
The weighted average error of the peak value error 14 and the average value error 15 is 0.
The throttle opening is controlled to operate in the direction.

Next, from the signal of the image pickup device 3, the small area average detection unit 10 divides the screen into a large number and calculates the average brightness for each small area to obtain a brightness level histogram.

The degree calculating unit 11 calculates the average luminance of the low-luminance portion from the histogram, performs a non-linear conversion such as fuzzy inference on the average luminance of the low-luminance portion, and calculates the degree of backlighting of the captured image. Calculate ur. Further, the average brightness of the high brightness part of the histogram is subjected to non-linear conversion by fuzzy reasoning or the like as before, and the degree wr of over-forward light is calculated.

On the other hand, from the signal of the image pickup device 3, the first and second signals are obtained.
The area brightness comparison unit 12 divides the entire screen into a lower center area 21, an upper area 22, a left area 23, and a right area 24 as shown in FIG. 2, and calculates the average brightness of each area. further,
The average brightness of the left area 23 and the right area 24 is compared, and the area having the higher average brightness and the upper area 22 is set as the first area, and the area having the lower average brightness and the lower central area 21 are set as the first area. The combined area is defined as the second area, and the difference p in average luminance between the first area and the second area is calculated.

The above average brightness difference p and the degree of backlight / over-forward light are sent to the correction amount calculator. The correction amount calculation unit 16 utilizes the tendency of being backlit when the upper part of the screen is brighter than the lower part and being over-forward when the upper part of the screen is dark, so that the first region including the upper part of the screen is more than the second region including the central part of the screen. If the average brightness is high, the backlight is determined, and if the average brightness is low, it is determined that the backlight is excessive and the brightness difference p is used to calculate the correction amount as shown in FIG.
Convert to g. Then, a correction amount z is calculated by the following equation from the back light intensity ur, the over light intensity wr, the gain g, and the back light / over light determination result.

When p ≦ 0, over-forward light z = g * ur p> 0, when backlight z = g * wr In the target brightness calculation unit 9, the correction amount z obtained by the correction amount calculation unit 16 as described above Is added to the predetermined target brightness to calculate the target value of the average brightness of the entire screen for each vertical scan (frame or field).

The weight calculator 18 calculates the weight w _{p of the} peak value from the brightness difference p as shown in FIG. The weight w _{a of the} average value is calculated by the following equation.

The weighted average error calculator 17 calculates the weighted average error e from the average value error e _a , the peak value error e _p , the average value weight w _a , and the peak value weight w _p by w _a = 1−w _p. calculate.

E = w _a * e _a + w _p * e _{p The} aperture control unit 8 controls the aperture so as to keep the weighted average error e at zero.

As described above, appropriate exposure is obtained by controlling the peak value for the over-illuminated image and controlling the corrected average value for the backlight image.

FIG. 5 shows a second embodiment of the automatic exposure control device according to the present invention. The same components as those of the conventional automatic exposure control apparatus are designated by the same reference numerals and perform the same operation.

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 amplified by the amplifier 4, passes through the signal processing circuit 5 that performs γ processing and the like, and is sent to the video signal output terminal 6. At this time, the diaphragm control is performed based on the signal obtained from the image sensor 3 as in the first embodiment.

This embodiment is different from the first embodiment in that the small area average detector 10, the degree calculator 11, and the correction amount calculator 1 are used.
6. Since the target brightness calculation unit 9 is not provided, the correction effect based on the screen division information cannot be obtained, but an appropriate exposure is performed by controlling the peak value for the over-light image and the average value for the backlight image. To get

[0033]

As described above, according to the present invention, the backlight and the over-forward light are determined by using the difference between the upper and lower luminances, and the peak value control and the average value control are continuously switched according to the determination result. Therefore, it is possible to provide an automatic exposure control device that performs appropriate exposure control, and if it is applied to an image pickup device such as a video camera in which outdoor shooting and indoor shooting such as weddings occur in normal shooting, its practical effect is great. .

[Brief description of drawings]

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

FIG. 2 is a diagram in which the screen is divided into an upper area, a left and right area, and a lower central area.

FIG. 3 is a conversion diagram of a brightness difference p between a first area and a second area and a correction amount calculation gain g.

FIG. 4 is a conversion diagram of a brightness difference p between a first area and a second area and a weight w _p of a peak value.

FIG. 5 is a configuration block diagram of an automatic exposure control device according to a second embodiment of the present invention.

[Explanation of symbols]

 1 Lens 2 Aperture 3 Image Sensor 4 Amplifier 5 Signal Processing Circuit 6 Video Signal Output Terminal 7 Full Screen Average Detection Section 8 Aperture Control Section 9 Target Luminance Calculation Section 10 Small Area Average Detection Section 11 Degree Calculation Section 12 1st / 2nd Luminance comparison unit 13 Peak value detection unit 14 Peak value error calculation unit 15 Average value error calculation unit 16 Correction amount calculation unit 17 Weighted average error calculation unit 18 Weight calculation unit 21 Lower central region 22 Upper region 23 Left region 24 Right region

Claims (2)

[Claims] 1. An all-screen average detecting section for calculating an average brightness of the entire screen, a peak value detecting section for obtaining maximum brightness in the entire screen, an average brightness obtained from the all-screen average detecting section and a predetermined target. An average value error calculation unit that calculates an error with the brightness, a peak value error calculation unit that calculates an error between the peak brightness obtained from the peak value detection unit and a predetermined target value, and the two values obtained from the two. A weighted average error calculation unit that calculates the weighted average of the average value error and the peak value error, an aperture control unit that determines the aperture opening so that the weighted average error follows 0, and the entire screen is divided into a number of small areas. Then, a small area average detection unit that calculates the average brightness of each small area, a degree calculation unit that calculates the backlight / over-forward light intensity from the average brightness of the small areas, and an average brightness of the first area including the upper part of the screen. First comparing the average brightness of the second area including the center of the screen -The second area brightness comparison unit and the first area
A correction amount calculation unit that calculates a correction amount from the comparison result of the average brightness of the region / second region and the degree of backlight / over-light, and a target brightness calculation unit that corrects the predetermined target brightness based on the correction amount. An automatic exposure control apparatus comprising: a weight calculation unit that calculates an appropriate weighted average weight of an average value and a peak value from the comparison result of the first and second area brightness comparison units. 2. A full-screen average detecting section for calculating the average brightness of the full-screen, a peak value detecting section for obtaining the maximum brightness in the full-screen, an average brightness obtained from the full-screen average detecting section and a predetermined target. An average value error calculation unit that calculates an error with the brightness, a peak value error calculation unit that calculates an error between the peak brightness obtained from the peak value detection unit and a predetermined target value, and the two values obtained from the two. A weighted average error calculation unit that calculates a weighted average of the average value error and the peak value error, an aperture control unit that determines the aperture opening so that the weighted average error follows 0, and an average of the first region including the upper portion of the screen. A first and second area luminance comparing section that compares the luminance and the average luminance of the second area including the screen center;
An automatic exposure control apparatus comprising: a weight calculation unit that calculates an appropriate weighted average weight of an average value and a peak value from the comparison result of the first and second area brightness comparison units.