JP3002298B2 - Exposure control method for imaging 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 exposure control method for an image pickup apparatus, and more particularly to an overexposure method in which a signal of a target object is saturated due to a contrast between a background and the target object, and a sufficient exposure of the target object. The present invention relates to an exposure control system provided with a means for suppressing black sun sinking.

[0002]

2. Description of the Related Art Exposure control means of a conventional image pickup apparatus is disclosed in, for example, Japanese Patent Application Laid-Open No. 56-19274, and has a structure as schematically shown in FIG. In the figure, 101 is a lens, 102 is an aperture, 103 is an image sensor, 104 is a signal processing circuit, 105 is a detection circuit, 106
Is a comparator, 107 is a reference voltage source, 108 is an aperture motor,
Reference numeral 109 denotes an output terminal. In the configuration shown in FIG. 8, light that has entered the image sensor 103 via the lens 101 and the aperture 102 is converted into an electric signal by the image sensor 103, and the output of the image sensor 103 is sent to the signal processing circuit 104, where the signal is output. A video signal is generated by the processing circuit 104 and output from the output terminal 109. Here, the luminance signal is branched and input from the signal processing circuit 104 to the detection circuit 105, and the exposure control signal voltage 110 output from the detection circuit 105 and the reference voltage Vref of the reference voltage source 107 are supplied to the comparator 106. The exposure control signal voltage 1
The aperture motor 108 is driven so that 10 and the reference voltage Vref coincide with each other, and the amplitude of the output signal of the imaging device is maintained at an appropriate value.

Here, the detection circuit will be described with reference to FIG. FIG. 9 shows a general diode detection circuit, which includes a detection transistor 111, a resistor (R1) 112, and a resistor (R).
2) 113, and a capacitor (C1) 114. In this diode detection circuit, the resistance (R
1) If the value of 112 is made sufficiently large, the voltage held in the capacitor (C1) 114 becomes a value indicating the maximum value of the luminance signal, and the maximum value is detected. If the value of the resistor (R1) 112 is sufficiently small, the voltage held in the capacitor (C1) 114 becomes a value indicating the average value of the luminance signal, and the average value detection is performed. Therefore,
By setting the three constants of the resistor (R1) 112, the resistor (R2) 113, and the capacitor (C1) 114, the exposure control signal voltage emphasizes the maximum value P of the luminance signal and the average value Av. Can also be set to a value.

It is to be noted that a general image pickup apparatus is usually designed so that, when an image of a single white object is picked up, the image is reproduced with a brightness of about 60% to 80% with respect to 100% of saturation. , With full maximum detection, it will be played back to 100%
Since the signal is reproduced to 50% in the complete average detection, an intermediate detection characteristic can be obtained by setting the above-described constants of the resistor (R1) 112, the resistor (R2) 113, and the capacitor (C1) 114. .

[0005]

In the above-mentioned general diode detection circuit, the exposure control signal can be set so that either the maximum value or the average value of the luminance signal is emphasized, but the average value is emphasized. When the setting is made, the person who is the main subject flies white in over-direct lighting with the background being very dark with respect to the main subject as shown in FIG. On the other hand, when setting is made with emphasis on the peak value, FIG.
At the time of backlight, as shown in (b), where the background is very bright with respect to the main subject, the subject person sinks black.
That is, the suppression of the overexposure and the suppression of the black sun are in conflict with each other, and it has been difficult to simultaneously achieve the suppression of the overexposure and the suppression of the black sun.

Accordingly, a technical problem to be solved by the present invention is to solve the above-mentioned problems of the prior art.
The purpose is to control the exposure of an image pickup device that can obtain an appropriate exposure for a target subject and suppress as much as possible overexposure and undersaturation, regardless of the brightness distribution in the screen. It is to provide a method.

[0007]

In order to achieve the above object, an exposure control method for an image pickup apparatus according to the present invention is provided with means for detecting a luminance distribution in a screen, and generates an exposure control signal in accordance with the detection result. The weighting of the average value Av and the weighting of the maximum value P of the luminance signal are changed, and the weight of the average value Av is changed.
Weighting from X1 to X2, weighting of maximum value P is Y1
When transitioning from Y1 to Y2, X1 <X3 <X2, Y1 <
Continuous transition via values X3 and Y3 where Y3 <Y2
Let Further, the exposure control method of the image pickup apparatus according to the present invention is described above.
In order to achieve the purpose, the imaging screen is divided into multiple areas.
Or set multiple areas at different positions on the screen.
Means for determining the average value Av of the luminance signal in each region,
Detecting means for detecting the maximum value P of the luminance signal;
And an exposure control signal is generated according to the detection result of the maximum value P.
Means for detecting the detection value Av or P
From the difference or ratio of each area,
The contrast between the subject and background is determined, and the target
When the object part is brighter than the background part, the weight of the maximum value P
The target subject part compared to the background part
When dark, the weight of the average value Av is increased.

[0008]

[Function] Weighting of average value Av according to luminance distribution in screen
From X1 to X2, and the maximum value P from Y1 to Y
X1 <X3 <X2, Y1 <Y3
<Continuous transition via values X3 and Y3 as Y2
Aperture operation due to sudden change in exposure correction amount
Can be prevented from being transiently unstable. Each area in the screen
The weighting of the average value Av and the weighting of the maximum value P of the luminance signal when the exposure control signal is generated are changed according to the average value Av and the maximum value P of the luminance signal of the area, so that the target subject portion is compared with the background portion. When bright, the weight of the maximum value P is increased, and when the target subject portion is darker than the background portion, the weight of the average value Av is increased. In this way, even when the contrast between the target subject and the background is significantly different, an appropriate exposure can be obtained for the target subject.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the illustrated embodiments. First, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a configuration diagram of an imaging device according to the present embodiment, and FIG. 2 is an explanatory diagram illustrating an example of screen division for determining a luminance distribution of a captured image. FIG. 3 is an explanatory diagram showing an example of imaging in a state of excessive forward light, normal time, and backlight.

In FIG. 1, 1 is a lens, 2 is an aperture, 3
Is an image sensor, 4 is an A / D converter, 5 is a signal processing circuit, 6
Is a D / A converter, 7 is an output terminal, 8 is a comparator, 9 is an aperture motor, 10 is a reference voltage source, and 11 is a microcomputer. Here, the microcomputer 11 actually includes various I / O interfaces, a ROM in which a main control program and fixed data are stored, a RAM in which various data and flags are read and written, and a CPU which controls the entire system. The D / A converter 111 and the first coefficient circuit 1 are configured and execute various control processes according to predetermined various programs.
12, a second coefficient circuit 113, a first comparison circuit 114,
A peak reference value setting circuit 115, a correction amount calculating circuit (K-fold circuit) 116, an adding circuit 117, a second comparing circuit 118,
The following description will be made assuming that the third comparison circuit 119 and the luminance distribution determination circuit 120 are provided.

In the configuration shown in FIG. 1, light incident on the image pickup device 3 through the lens 1 and the aperture 2 is converted into an electric signal, then converted into a digital signal by an A / D converter 4 and transmitted to a signal processing circuit 5. Is entered. In the signal processing circuit 5, for example, the average values Av ₁ and Av ₂ of the luminance information Yi in the respective regions S1 and S2 of the imaging screen shown in FIG. The maximum values P ₁ and P ₂ of the luminance information expressed by the formulas in FIG. 7 are obtained by the maximum value calculation circuit 52 and output to the microcomputer 11. In the microcomputer 11, the first coefficient circuit 112 uses the above-described areas S1,
The average values Av ₁ and Av ₂ of the luminance information Yi in S2 are given a coefficient, and Av ₀ shown in the equation of FIG. 7 is output. In the second coefficient circuit 113, each region S1, S2
The maximum values P ₁ and P ₂ of the luminance information Yi at
P ₀ represented by the equation in FIG. 7 is output.

Such a coefficient assignment is shown in FIG.
As shown in (b) and (c), a main subject (a person in the figure) is often arranged at the center of the screen, so that exposure control is performed largely depending on luminance information of the main subject. . Here, for example, Av ₀ is directly output as the exposure control signal Vd from the D / A converter 111, and further, an image of a single-color subject is taken, and an output signal of 50% with respect to 100% of saturation is output from the imaging device output terminal 7. Is set so as to obtain, exposure control by complete average detection is performed as described in the related art. The value of Vr at this time is set to Vr ₁ in this embodiment. In addition, if the reference voltage Vr of the reference voltage source 10 is set so that P ₀ is output as it is as the exposure control signal Vd from the D / A converter 111 and the output signal at the time of imaging a single-color subject becomes 100%, the maximum value is obtained. Exposure control based on value (peak value) detection is performed. Here, as described above, it is often the case that an exposure control characteristic intermediate between the two can provide natural exposure control for various subjects in many cases. , The correction by the maximum value detection is performed based on the first comparison circuit 11.
4. Peak reference value setting circuit 115, correction amount calculation circuit (K
(Multiplication circuit) 116 and an addition circuit 117 are used.

The peak reference value setting circuit (memory) 115 rewritably stores data Pr corresponding to an amount of luminance that gives an almost 100% amplitude at the output terminal 7 of the imaging device. The data Pr of the peak reference value setting circuit 115 and the output P _{0 of} the second coefficient circuit 113 are compared by a first comparison circuit 114, and the comparison result Pd is used as a correction amount calculation circuit (K-times circuit). ) 116 to generate a correction signal K · Pd. And
The correction signal K · Pd and the output Av _{0 of} the first coefficient circuit 112 are added, and the D / A converter 111 outputs the exposure control signal voltage Vd shown in the equation of FIG. The reference voltage Vr of the reference voltage source 10 at this time is set to Vr ₁ described above.

In the case of picking up a white color image in such a configuration, since there is no prominent peak signal, P ₀ is a value of about 50% of the saturation amount, and as a result, K · Pd is a positive value. The aperture is wider than the position where a luminance signal amplitude of 50%, which is a stable point in the complete average detection, is obtained. Depending on the value of K, an appropriate value of the luminance signal amplitude of 70% to 80% is obtained. Conversely, if there is a large-amplitude signal that saturates the imaging device and protrudes at one or several places in the white-white subject, K · Pd becomes a negative value, and the aperture is slightly closed. The signal amplitude other than the protrusion is 30 to 40%
Becomes

[0015] With the above configuration alone, there is a case where a satisfactory reproduced image cannot always be obtained in an extreme photographing situation.
In order to improve those cases, in the present embodiment, Av ₁ , Av ₁ ,
Av ₂ and P ₁ , P ₂ are compared, and the luminance distribution determination circuit 12
At 0, the luminance distribution is determined from these results, and K or Pr is changed according to the results to change the correction amount by the maximum value (peak value). A specific example will be described with reference to FIG. FIG. 3A shows a case where the background is very dark with respect to the person's face, and FIG. 3C shows a case where the background is very bright with respect to the person's face. ,
FIG. 3B shows a normal case where the contrast between the face and the background is small. The most important thing to avoid in FIG. 3A is that the face is saturated and overexposed. Therefore, when such a luminance distribution is obtained in which the central portion of the screen is bright and the peripheral portion is very dark, exposure control is performed with emphasis on the maximum value P. For example, K of the correction amount calculation circuit 116 is increased by the signal from the luminance distribution determination circuit 120 to increase the correction amount by the maximum value (peak value). In this way, it is possible to prevent the face of the person from overexposing. FIG.
In the case of the backlight of (c), if the background is not narrowed down by the exposure control with emphasis on the maximum value, the face of the person becomes darker than necessary. The correction amount is reduced, and the average value Av is reduced.
Exposure control with an emphasis on is performed to prevent such adverse effects.

According to the present embodiment employing such a method, it is possible to provide an image pickup apparatus capable of obtaining an appropriate exposure for a target object in any luminance distribution.

Next, a second embodiment of the present invention will be described with reference to FIG. In the first embodiment, the method of dividing the imaging screen into a plurality of regions and determining the luminance distribution is used to change the weighting of the maximum value detection and the average value detection in the exposure control. , The main subject portion and the background portion are discriminated, and the weighting of the maximum value detection and the average value detection in the exposure control is changed from the difference or the ratio of the luminance signal amount of each portion. . The method of extracting the main subject by obtaining the contour information is discussed in, for example, MACHINE-PERCEPTION by R. Neuatia (Image recognition and image understanding, Minami Toshi Translate; Keigaku Shuppan 1986). The configuration of the imaging apparatus according to the present embodiment shown in FIG. 4 is basically the same as that shown in FIG.
, An outline is detected by an outline detection circuit 53, an area is divided into a main subject part and a background part by an area division circuit 54, and the average luminance value Av and the maximum luminance value P in each area are calculated by the average value calculation circuit 51 and The maximum value calculation circuit 52 calculates each of them and outputs them to the microcomputer 11. The processing in the microcomputer 11 is the same as the processing in the above embodiment, and when the background is dark relative to the main subject, the maximum value P
, And the exposure control signal is generated with an emphasis on the average value Av when the background is brighter than the main subject.

According to the present embodiment employing such a method, it is possible to provide an imaging apparatus capable of obtaining an appropriate exposure for a target object in any luminance distribution.

Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 5 is a configuration diagram of an image pickup apparatus according to the present embodiment, in which components equivalent to those in the first embodiment are denoted by the same reference numerals. This embodiment relates to a technique that is particularly effective when capturing a moving image. The configuration of the image pickup apparatus is almost the same as the configuration in the above two embodiments, but in this embodiment, a synchronization pulse FV is input from the synchronization circuit 12 to the microcomputer 11. A correction amount is determined according to a difference or a ratio of a luminance signal amount between the central region or the central subject region and the peripheral region or the background region determined by the second and third comparison circuits 118 and 119, and Determine the value of K. In the case where the light amount of a part of the screen suddenly changes in a state where the value of K is set to K1 and it becomes necessary to change the value of K for determining the correction amount to K2 accordingly, the present embodiment In FIG. 6, a transition speed control means 121 is added so that the actual value of K continuously changes as shown in FIG. This transition speed control means 1
For example, using the synchronizing signal FV input to the microcomputer 11 by the microcomputer 21, the data is output one bit at a time every one vertical blanking period.
The data may be incremented or decremented.
In this way, it is possible to prevent the aperture operation from being temporarily unstable due to a sudden change in the exposure correction amount due to the maximum value detection, and to obtain a stable reproduced image.

In each of the embodiments described above, the aperture is used as the exposure control means, but it is obvious to those skilled in the art that this can be replaced with an electronic shutter.

[0021]

As described above, according to the present invention, the weighting of the average value and the weighting of the maximum value of the luminance signal when the exposure control signal is generated are continuously changed according to the detected luminance distribution of the screen. Therefore, it is possible to provide an imaging apparatus that can always obtain an appropriate exposure for a target subject, and the value of the imaging apparatus is enormous.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating an imaging device according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an example of dividing an imaging screen according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram illustrating an example of imaging at the time of excessive forward light, at the time of normal light, and at the time of backlight.

FIG. 4 is an explanatory diagram showing an imaging device according to a second embodiment of the present invention.

FIG. 5 is an explanatory diagram showing an imaging device according to a third embodiment of the present invention.

FIG. 6 is an explanatory diagram showing a state of transition of a correction coefficient K according to a third embodiment of the present invention.

FIG. 7 is an explanatory diagram showing mathematical expressions used in the embodiment of the present invention.

FIG. 8 is an explanatory diagram showing a conventional imaging device.

FIG. 9 is an explanatory diagram showing a detection circuit of a conventional imaging device.

FIG. 10 is an explanatory diagram showing an example of imaging at the time of overdirect light and at the time of backlight.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lens 2 Aperture 3 Image sensor 4 A / D converter 5 Signal processing circuit 6 D / A converter 7 Output terminal 8 Comparator 9 Aperture motor 10 Reference voltage source 11 Microcomputer 12 Synchronization circuit 51 Average value calculation circuit 52 Maximum Value calculation circuit 53 Outline detection circuit 54 Area division circuit 111 D / A converter 112 First coefficient circuit 113 Second coefficient circuit 114 First comparison circuit 115 Peak reference value setting circuit 116 Correction amount calculation circuit 117 Addition circuit 118 Second comparison circuit 119 Third comparison circuit 120 Luminance distribution determination circuit 121 Transition speed control means

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tomoyuki Kurashige 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside Hitachi Image Information Systems Co., Ltd. (56) References JP-A-4-222178 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04N 5/235-5/243 G03B 7 / 28

Claims (3)

(57) [Claims] A first detection means for detecting an average value Av and a maximum value P of a luminance signal; generating an exposure control signal in accordance with a detection result of the first detection means; In the imaging apparatus having an automatic exposure control function for driving an exposure control means such as an aperture and an electronic shutter to set an output signal amplitude of the imaging apparatus to an appropriate value, a second detection means for detecting a luminance distribution in a screen the provided, this in accordance with the detection result by changing the weighting of the mean value weighted and maximum value P of Av of the luminance signal in the generation of the exposure control signal of the second detecting means, weighting of the mean value Av X1 From X2 to the maximum
When shifting the weight of the value P from Y1 to Y2, X
1 <X3 <X2, Y1 <Y3 <Y2
An exposure control method for an image pickup apparatus , wherein the transition is performed continuously through the control unit. A first detecting means for detecting an average value Av and a maximum value P of the luminance signal; generating an exposure control signal according to a detection result of the first detecting means; In an imaging apparatus having an automatic exposure control function for driving exposure control means such as an aperture and an electronic shutter to set an output signal amplitude of the imaging apparatus to an appropriate value, the imaging screen is divided into a plurality of areas, means for setting a plurality of regions at different positions in the inner, second detecting means for detecting a maximum value P of the average value Av and luminance signal of the luminance signal in each region, and the average value Av said Means for generating the exposure control signal in accordance with the detection result of the maximum value P, wherein the detection value Av or P
The contrast between the target subject portion and the background portion in the imaged screen is determined from the difference or ratio of each region of the region, and when the target subject portion is brighter than the background portion, the maximum value P
Increasing the weighting, the exposure control method of the image pickup apparatus when the goal object portion is dark compared to the background portion, characterized in that to increase the weighting of the average value Av. 3. The average value Av according to claim 2 , wherein
Is changed from X1 to X2 and the weight of the maximum value P is changed from Y1 to Y2, X1 <X3 <X
2. An exposure control method for an image pickup apparatus, wherein the transition is made continuously via values X3 and Y3 satisfying Y1 <Y3 <Y2.