JP2817820B2 - Exposure control device for video camera - 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 apparatus for a video camera, and more particularly to an exposure control apparatus for a video camera having a high brightness clip circuit.

[0002]

2. Description of the Related Art In this type of conventional exposure control apparatus for a video camera, a photometric value is obtained by inputting a luminance signal of a subject image through a high luminance clipping circuit, and the photometric value becomes a reference value. There is one that adjusts the opening of the iris. In recent years, in order to obtain an appropriate photometric value,
There has been proposed an exposure control apparatus for a video camera in which a plurality of high-brightness clip circuits having different clip levels are provided, and a luminance signal passed through a high-brightness clip circuit having a clip level corresponding to a shooting scene is used (particularly). JP-A-2-268080).

[0003]

However, in the above-described exposure control apparatus for a video camera, a clip circuit and an integrating circuit at the subsequent stage are required for the number of clip levels.
Also, in a video movie camera, when the clip level is switched, the exposure changes abruptly, resulting in a visually unnatural change in brightness as a continuous image.

Further, in a normal scene which is not a backlight scene, the whole image is photographed brightly due to clipping at a low clip level, and a bright portion tends to be saturated, which is not preferable. On the other hand, if a low clip level is set higher to avoid this effect, there is a problem that the main subject is likely to be blackened in a backlit scene or the like with a high contrast because the effect of the high luminance portion becomes large.

Furthermore, since the clip level is switched by comparing the brightness of a specific photometry area, it depends on a specific photometry pattern or photometry method. In addition, since the clip level is switched instantaneously according to the state of the subject at the time of photometry, if the main subject is photographed at the center of the screen with backlight, sufficient backlight compensation and high brightness clip However, if the main subject moves off the center of the screen for a moment due to the movement of the main subject, the clip level is instantly switched to a higher level immediately after the main subject deviates from the center. However, there is a problem that the image is taken dark due to insufficient exposure.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and a video camera exposure apparatus capable of visually changing the brightness when the clip level is changed and simplifying the circuit configuration. It is an object to provide a control device. It is another object of the present invention to provide an exposure control device for a video camera that can set an appropriate clip level according to a shooting scene and perform good exposure control.

Still another object of the present invention is to provide an exposure control for a video camera which does not depend on a specific light metering pattern or a light metering method and which can perform stable exposure control even if the scene slightly changes due to the operation of a main subject or the like. It is to provide a device.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention converts subject light incident on an image pickup device via a photographing lens and an iris into an electric signal by the image pickup device, and converts the electric signal to an amplifier. The video signal processing circuit outputs the luminance signal of the subject image to the video signal processing circuit through a video signal processing circuit to obtain a required video signal by performing appropriate signal processing. A high-brightness clipping unit for converting a luminance signal of a level or higher into the same luminance signal; Photometric means,
Determining means for determining the state of the photographic scene based on each photometric information from the divided photometric means; and gradually increasing the current clip level so that the current clip level becomes a clip target value corresponding to the determined photographic scene. And an iris control means for controlling the iris based on the respective photometric information from the divided photometric means.

Further, at least a first clip level for obtaining appropriate photometric information in a backlight scene and a second clip level for obtaining appropriate photometric information in a photographic scene other than a backlight scene are obtained. High-luminance clipping means for clipping a luminance signal; a luminance signal having passed through the high-luminance clipping means; divided photometric means for obtaining respective photometric information in a plurality of areas including a central area of the subject image; Determining means for determining the state of the shooting scene based on each photometric information from the photometric means,
If this determined shooting scene is a backlight scene, the first
An iris for controlling the iris based on the respective photometric information obtained from the divided photometric means for inputting the luminance signal clipped at the clip level of the second clip level in a case other than the backlight scene in a scene other than a backlight scene And control means.

Further, in an exposure control device for a video camera for controlling the amount of incident light from a photographic lens to an image sensor via an iris to be a reference value, a luminance signal indicating a subject image is clipped at a plurality of clip levels. High-brightness clipping means, means for determining an exposure correction amount based on a luminance signal passing through the high-brightness clipping means, and correcting the reference value according to the exposure correction amount; and a magnitude of the determined exposure correction amount. Means for switching the clip level to a clip level for obtaining an appropriate exposure correction amount in response to the clip level, and a clip level switching means for giving a predetermined time delay when the clip level is switched. .

[0011]

According to the present invention, the state of a photographic scene such as a backlight state or a spotlight illumination state is determined based on each photometric information from the divided photometric means. Then, a clip target value is set according to the shooting scene. That is, a low clip target value is set to reduce the influence of a bright background in a backlight state, and a high clip target value is set to capture bright luminance information of a main subject or the like in a spotlight illumination state. I do. Then, when changing from one clip target value to another clip target value, the change is gradually made in about 2 seconds. Thus, the change in brightness of the video when the clip level is changed can be made visually natural, and the single high-brightness clipping unit and the divided photometry unit can be used, so that the circuit configuration can be simplified.

According to another aspect of the present invention, at least a first clip level for obtaining appropriate photometric information in a backlight scene and a second clip for obtaining appropriate photometric information in a shooting scene other than a backlight scene. A high-brightness clipping means for clipping a luminance signal of a subject image input at each level is provided. Then, the respective photometric information in a plurality of areas including the central area of the subject image is fetched from the divided photometric means at the subsequent stage of the high-brightness clipping circuit, and each photographic scene such as a backlight scene is determined based on the respective photometric information. . A divided light metering means for inputting a luminance signal clipped at a first clip level when the determined photographic scene is a backlight scene, and a luminance signal clipped at a second clip level when the determined photographic scene is not a backlight scene The iris is controlled based on the respective photometric information obtained from.

According to still another aspect of the present invention, an exposure correction amount is obtained based on a luminance signal passed through the high luminance clipping means, and a clip level is set to an appropriate exposure correction amount in accordance with the magnitude of the exposure correction amount. Switch to the clip level to get That is, since the clip level is switched based on the exposure correction amount, the clip level can be switched independently of the light metering pattern and the light metering method. Further, a predetermined time delay is provided when the clip level is switched. Thus, stable exposure control can be realized even if the scene slightly changes due to the operation of the main subject or the like.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of an exposure control apparatus for a video camera according to the present invention will be described below in detail with reference to the accompanying drawings. [First Embodiment] FIG. 1 is a block diagram of a video camera including a first embodiment of an exposure control device for a video camera according to the present invention.

Referring to FIG.
Then, an image is formed on a light receiving surface of an image sensor (CCD) 14 via the iris 12. The CCD 14 accumulates the incident light,
The stored charge is read out in synchronization with a timing pulse applied from the timing generator 16. The electric signal read out from the CCD 14 in this way is amplified by the preamplifier 18 and then applied to the video signal processing circuit 20 and also to the LPF (low-pass filter) 24 as an iris detection signal.

The video signal processing circuit 20 includes a white balance circuit, a gamma correction circuit, a matrix circuit, an encoder circuit, and the like. After performing predetermined signal processing by these circuits, for example, an NTSC video signal is transmitted to the recording device 22. Output. The recording device 22 includes a recording circuit, which converts the video signal into a recording signal suitable for magnetic recording,
This recording signal is magnetically recorded on a recording medium such as a video tape via a magnetic head.

On the other hand, the signal that has passed through the LPF 24 is detected as a signal indicating a luminance signal, then converted into a digital signal by an A / D converter 26, and applied to a high luminance clip circuit 28 as luminance data. High brightness clip circuit 2
A high-brightness clip circuit 28 clips luminance data input from the A / D converter 26 at a clip level controlled by the clip level control signal. That is,
When luminance data higher than the clip level is input, luminance data is output with the clip level as an upper limit.

The luminance data that has passed through or clipped the high luminance clip circuit 28 is input to a divided photometry circuit 30. The other input of the divided photometry circuit 30 is a screen of one field from the window signal generation circuit 36, as shown in FIG.
As shown in the figure, a timing signal for dividing the region 1 to 5 into five is added.
Photometric data S _{1 to} S ₄ obtained by adding and averaging luminance data for _four
Is output to an MPU (microprocessor unit) 36. Since the region 5 is a region where the main subject is rarely located, it is excluded.

The MPU 36 controls the photometric data S _{1 to} S
₄ is processed based on a program stored in a ROM (read only memory) 40 and various numerical values, and outputs an iris control signal via a D / A converter 46 and also via a D / A converter 42 Outputs clip level control signal. That, MPU 36 inputs the photometric data S ₁ to S ₄ of each area, as shown in FIG. 3, the photometric data from the photometric data _{S 1 ~S 4 S ijk (i} , j, k =
1) to 4) are calculated. And these photometric data S ₁ to S ₄ as will be described later, based on the S _{ij k} performs determination of the photographic scene, photometric values C ₀ ~ select an arithmetic expression ♯0~6 corresponding to each shooting scene to calculate the C _6.

The above arithmetic expressions # 0 to # 6 are shown below. The values of the weights W ₁₁ , W ₁₂ , W ₂₁ , W ₃₁ , W ₃₂ , W ₄₁ , and W ₅₁ are, for example, W ₁₁ = 10, W ₁₂ = 1, and W ₂₁ = 1, respectively.
0, W ₃₁ = 10, W ₃₂ = 1, W ₄₁ = 10, and W ₅₁ = 10.

Subsequently, the MPU 36 calculates a luminance difference between the respective areas.
calculate. First, target data REF of the luminance level of the screen
The video output is, for example, IRE60 (γ = 0.45 system)
Set so that The IRE is for NTSC video.
This indicates the luminance level of the image signal.
It is bright white. Then, the target data REF and the area
1, 2, 3 average photometric data S_{one two Three}Brightness difference D₀Is D₀= Log (S_{one two Three}/ REF) / log 2. Also, the photometric data S of the area 1₁And area 3 photometry
Data S_ThreeBrightness difference D ₁Is D₁= Log (S₁/ S_Three) / Log 2 Similarly, area 1 photometric data S₁And photometric data S of area 2
_TwoBrightness difference D_TwoIs D_Two= Log (S₁/ S_Two) / Log 2 Average photometric data S of areas 1 and 3₁₃And area 4 photometry
Data S_FourBrightness difference D _ThreeIs D_Three= Log (S₁₃/ S_Four) / Log 2.

The MPU 36 compares the threshold values Th _{0 to} Th ₃ stored in the ROM 40 in advance with the absolute values | D ₀ | to | D ₃ | of the luminance differences D _{0 to} D ₃ to determine the photographing scene. Then, the photometric values C _{0 to} C ₆ are calculated by selecting the above-described arithmetic expressions # ₀ to # ₆ according to the respective photographing scenes. In FIG. 3, first, | D ₀ | is compared with a threshold Th ₀ (for example, 3EV).

If | D ₀ | ≧ Th ₀ , it means that the current screen luminance is far from the target data REF. For example, immediately after the power is turned on to the video movie camera or from a dark room. For example, when panning suddenly into a bright outdoor. In such a case, if it is attempted to calculate the photometric value by determining the shooting scene, it takes time until the iris 12 is stabilized by feedback control. In order to shorten this time, it is considered that the main subject is located in the hatched portion in FIG. 4A, and ♯0 is selected as the arithmetic expression of the photometric value, and the photometric value C ₀ is calculated.

When | D ₀ | ≧ Th ₀ is not satisfied, | D ₁
Is compared with a threshold value Th ₁ (for example, 0.5 EV). |
If D ₁ | ≧ Th ₁ , it is considered that a main subject, for example, a face, is almost located in the area 1. In this case, | D ₂ | and the threshold Th ₂ (for example, 0.75 EV)
Compare with

When | D ₂ | ≧ Th ₂ , since there is a difference between the luminance of the face and the luminance of the clothes, the face is located as shown in FIG. An arithmetic expression # 1 for calculating the photometric value with emphasis on the wax region 1 is selected, and the photometric value C ₁ is selected.
Is calculated. When | D ₂ | ≧ Th ₂ is not satisfied,
Since there is almost no difference in luminance between the face of the subject and the clothes, as shown in FIG. 4C, an arithmetic expression for calculating the photometric value with emphasis on the average luminance value of the region 1 and the region 2 2
Select, calculates the photometric value C _2.

On the other hand, when | D ₁ | ≧ Th ₁ is not satisfied,
This is a state in which there is no luminance difference between the region 1 and the region 3. At this time, | D ₂ | is compared with threshold value Th ₂ . | D ₂ | ≧ T
If it is h ₂ has no luminance difference between the regions 1 and 3, and because it is a state where there is a luminance difference between the regions 1 and 2, further | D ₃ | and the threshold Th ₃ (e.g., 0. 5EV).

│D_Three| ≧ Th_ThreeIf, the area
Average photometric data S for 1,3₁₃And photometric data S of area 4_Four
Therefore, as shown in FIG.
Average photometric data S₁₃Select arithmetic expression # 3 with emphasis on
And the photometric value C_ThreeIs calculated. ｜ D_Three| ≧ Th_ThreeNot a place
In this case, as shown in FIG.
Data S₁₃And photometric data S of area 4_FourNo difference between
Therefore, the average photometric data S of the areas 1, 3, and 4₁₃₄To
Select the arithmetic expression # 4 with emphasis on _FourCalculate
You.

On the other hand, | D ₀ | ≧ Th ₀ and | D
₁ | ≧ Th ₁ and | D ₂ | ≧ Th ₂ , there is no luminance difference between the regions 1, 2, 3 and
Since the average photometric data S ₁₂₃ a few close to the target data REF, | it performs the whether ≧ Th ₃ determine | D _3.
When | D ₃ | ≧ Th ₃ , as shown in FIG. 4 (F), an arithmetic expression ♯5 which emphasizes the average photometric data S ₁₂₃ of the areas 1, 2, 3 is selected, and the photometric value C is selected. Calculate ₅ .

When | D ₃ | ≧ Th ₃ is not satisfied,
Figure 4 select arithmetic expression ♯6 because a state where there is no difference in luminance region 1, 2, 3 and 4 as shown in (G), and calculates the photometric value C _5. In this manner, one of the arithmetic expressions # 0 to # 6 is selected to calculate the photometric value, and the iris 12 is controlled based on the calculated photometric value. That is, the calculated photometric value is compared with a reference value for iris control. If the photometric value is larger than the reference value, it is determined that the image is too bright, and the D / A converter 46 is used to close the iris 12. To output an iris control signal to the iris drive circuit 48, thereby driving the iris 12 in the closing direction. On the other hand, if the photometric value is smaller than the reference value, it is determined that the image is too dark, and the iris 12 is opened. An iris control signal is output to the iris drive circuit 44 via the D / A converter 46, thereby driving the iris 12 in the opening direction.

The MPU 36 is a high brightness clip circuit 2
8, a clip level control signal is output to the high-brightness clip circuit 28 via the D / A converter 42 in order to set the clip level for the next photometry, and the process returns to the start of the photometry flowchart as shown in FIG. . Next, a method of setting the clip level for the next photometry will be described with reference to the flowchart shown in FIG.

First, it is determined whether or not the arithmetic expression # 1 has been selected. When the arithmetic expression # 1 is selected, it is considered that the center of the screen is in a spotlight illumination state where the luminance is higher than its surroundings or the center of the screen is in a backlight state where the luminance is lower than its surroundings.
In this case, compared with the photometric data S ₃ of photometric data S ₁ and region 3 region 1, S ₁ <clip target value level 1 is regarded as in the case of S ₃ is a backlight state (e.g. I
RE100).

On the other hand, when the arithmetic expression # 1 is not selected or when S ₁ <S ₃ , the clip target value is set to level 2
(For example, IRE200). After the clip target value is determined in this way, the current clip level is compared with the clip target value. If “current clip level> clip target value”, the current clip level is reduced by 1 (IRE), and if “current clip level <clip target value”, the current clip level is reduced. If the current clip level is increased by 1 (IRE) and “current clip level = clip target value”, the current clip level matches the clip target value, and the clip level is not increased or decreased.

When the next clip level of the high-brightness clip circuit 28 is set in this way, the photometric calculation is performed again based on the brightness data clipped at the set clip level. That is, the clip level used for the (n + 1) -th photometry is set at the n-th photometry calculation that is periodically repeated. In the first photometry operation, for example, the clip level 2 is set in advance. The photometric calculation is performed in synchronization with a vertical synchronization signal input from the timing generator 16. Therefore, the clip level is changed from level 1 to level 2 or level 2
When changing from to level 1, it changes gradually by 1 (IRE) in synchronization with the vertical synchronization signal. Level 1
And level 2 have a difference of 100 IRE, so 100 inputs (approximately 1.7 times) of the vertical synchronizing signal (1/60 second cycle)
After a lapse of seconds), the level is changed from level 1 to level 2 or from level 2 to level 1.

Since the clip level is gradually changed as described above, the change in brightness when the clip level changes becomes visually natural. In the first embodiment, the clip level is also gradually changed when the level is changed from the level 2 to the level 1. However, in this case, it means that the shooting scene has changed to a backlight state.
The level may be immediately changed to level 1 so that the responsiveness of the exposure control is prioritized. [Second Embodiment] FIG. 6 is a block diagram of a video camera including a second embodiment of the exposure control device for a video camera according to the present invention. Note that the same reference numerals are given to portions common to the first embodiment shown in FIG. 1, and a detailed description thereof will be omitted.

In the second embodiment, two sets of high-brightness clip circuits 100 and 102 and divided photometric circuits 104 and 106 are provided. High brightness clip circuit 10
In 0, a low clip level (for example, IRE100) for obtaining proper photometric information in a backlight scene is set.
The high-brightness clip circuit 100 operates at this low clip level,
The luminance data input from the A / D converter 26 is clipped. That is, when luminance data equal to or higher than the low clip level is input, luminance data is output with the low clip level as an upper limit.

The high-brightness clipping circuit 102 is set with a high clip level (for example, IRE200) for obtaining appropriate photometric information in a shooting scene other than a backlight scene. Then, the luminance data input from the A / D converter 26 is clipped. These high brightness clip circuits 100 and 102
The luminance data that has passed through or has been clipped is input to the divided photometric circuits 104 and 106, respectively.

To the other inputs of the divided photometric circuits 104 and 106, a timing signal for dividing the screen of one field into five areas 1 to 5 as shown in FIG. And split photometry circuit 10
4 outputs to the MPU 108 photometric data SL1 to SL4 obtained by averaging the luminance data for each of the areas 1 to 4, and the divided photometric circuit 106 converts the photometric data SH1 to SH4 obtained by averaging the luminance data for each of the areas 1 to 4 to the MPU 108. Output to

The MPU 108 controls the photometric data SL1
To SL4 and SH1 to SH4 are processed based on the program and various numerical values stored in the ROM 40, and output an iris control signal through the D / A converter 46, and output the iris control signal through the D / A converters 42 and 44. To output a clip level control signal. That is, as shown in FIG. 7, the MPU 108 controls the photometric data SL1 to SL4 and SH1 of each area.
To SH4. Subsequently, the photometric data SH1 to SH
With substituted into S ₁ to S ₄ 4, respectively, S ₁ to S
_{From 4} , S _ijk (i, j, k = 1 to 4) is calculated. Then, as described above, the photometric data S _{1 to} S ₄ , S
_The photographing scene is determined based on _ijk, and arithmetic expressions # ₀ to # ₆ corresponding to each photographing scene are selected, and photometric values C0 to C6 are selected.
Is calculated. In FIG. 7, the description of the same parts as those in the flowchart shown in FIG. 3 is omitted.

In FIG. 7, when | D ₁ | ≧ Th ₁ , there is a luminance difference between the area 1 and the area 3, and it is considered that the face of the main subject, for example, a face is almost located in the area 1. , A backlight scene or a spotlight scene. In this case, it is determined whether D ₁ <0. If D ₁ <0, the luminance of the area 1 is lower than the luminance of the area 3 and the scene is regarded as a backlight scene, and the photometric data SL1 of each area measured based on the luminance data clipped at a low clip level.
~SL4 respectively substituted into S ₁ to S _4. On the other hand, D ₁
If not <0, the brightness of the area 1 is higher than the brightness of the area 3, so it is regarded as a spot light scene, and the photometric data SH1
SH4 is used as it is.

In this manner, one of the arithmetic expressions # 0 to # 6 is selected to calculate the photometric value, and the iris 12 is controlled based on the calculated photometric value. In addition, MP
U108 is a high-brightness clip circuit 1 based on a clip level control signal output via the D / A converters 42 and 44.
The clip level to be set to 00 or 102 can be reduced as the contrast strength between the main subject and other parts increases in a backlight scene, and increased as the contrast strength between the main subject and other parts increases in a spotlight scene. it can. Third Embodiment FIG. 8 is a block diagram of a video camera including a third embodiment of the exposure control device for a video camera according to the present invention. Parts common to those in the second embodiment shown in FIG. 6 are denoted by the same reference numerals, and detailed description thereof will be omitted.

The third embodiment shown in FIG. 8 mainly has three high-brightness clip circuits 200, 202 and 204 and divided photometric circuits 206, 208 and 210, and is similar to the second embodiment shown in FIG. Different from the example. A low clip level (for example, IRE100) for obtaining appropriate photometric information in a backlight scene is set in the high-brightness clip circuit 202 as in the high-brightness clip circuit 100 in FIG. A medium clip level (for example, IRE200) for obtaining appropriate photometric information in a normal shooting scene other than the backlight scene and the spotlight scene is set.
The high-brightness clip circuit 204 has a high clip level (for example, IR) for obtaining appropriate photometric information in a spotlight scene.
E300) is set. The luminance data that has passed through or clipped the high-luminance clip circuits 200, 202, and 204 are respectively divided into photometric circuits 206,
208 and 210.

To the other inputs of the divided photometric circuits 206, 208, and 210, a timing signal for dividing the screen of one field into five regions 1 to 5 as shown in FIG. The divided photometric circuit 206 outputs photometric data SL1 to SL4 obtained by averaging luminance data for each of the areas 1 to 4 to the MPU 212,
The divided photometric circuit 208 outputs photometric data SM1 to SM4 obtained by averaging luminance data for each of the regions 1 to 4 to the MPU 212, and the divided photometric circuit 210 performs photometric data SH1 to SH4 obtained by averaging luminance data for each of the regions 1 to 4. MPU
Output to 212.

The MPU 212 controls the photometric data SL1
To SL4, SM1 to SM4 and SH1 to SH4
Processing is performed based on the program and various numerical values stored in 40, and an iris control signal is output via the D / A converter 46. That is, the MPU 212 inputs the photometric data SL1 to SL4, SM1 to SM4, and SH1 to SH4 of each area as shown in FIG. Subsequently, the photometric data SM1
With substituted into S ₁ to S ₄ respectively ~SM4, S
S _ijk (i, j, k = 1 to 4) is calculated from _{1 to} S ₄ . Then, in the same manner as in the flow chart of FIG. 7, the photographing scene is determined based on the photometric data S _{1 to} S ₄ and S _ijk.
The photometric values C0 to C6 are calculated by selecting ₀ to ₆ .

In the flowchart shown in FIG.
The point different from the flowchart of FIG. 5 is the processing when | D ₀ | ≧ Th ₀ and not | D ₁ | ≧ Th ₁ and D ₁ <0. In this case, the brightness of the area 1 is
The deemed high for spot light scene than the brightness, the (photometric data SM1~SM4 of each region photometry based on clipped luminance data at medium clip level) of the contents photometric data S ₁ to S _4, respectively high Based on the luminance data clipped at the clip level, the photometry data SH1 to SH4 of each area is rewritten. As a result, the luminance signal of the subject image input at each of the high clip level (IRE300) is clipped, so that appropriate photometric data can be obtained in a spotlight scene. [Fourth Embodiment] FIG. 10 is a block diagram of a video camera including a fourth embodiment of an exposure control device for a video camera according to the present invention. The same parts as those in the first embodiment shown in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In the fourth embodiment shown in FIG. 10, a detection circuit 21 for inputting an electric signal from the preamplifier 18 detects an input signal and outputs it to an integration circuit 23. The integration circuit 23 converts the input signal into one field. The integral is obtained, and the integrated value is output to the iris drive circuit 48 as an average photometric value. A reference value for iris is set in the iris drive circuit 48 in advance, and the iris drive circuit 48 compares the iris reference value with the average photometric value. If the average photometric value is larger than the iris reference value, Determines that the iris 12 is too bright, and drives the iris 12 in the closing direction. On the other hand, if the average photometric value is smaller than the iris reference value, the iris 12 is determined to be too dark, and the iris 12 is driven in the opening direction. An exposure correction signal is added to the iris drive circuit 48, and the iris reference value is corrected by the exposure correction signal. The details will be described later.

A low clip level (for example, IRE100) for obtaining proper photometric information in a backlight scene is set in the high luminance clip circuit 300. The luminance data input from the D converter 26 is clipped. That is,
When luminance data at or above the low clip level is input, luminance data is output with the low clip level as an upper limit.

A high clip level (for example, IRE200) for obtaining appropriate photometric information in a shooting scene other than a backlight scene is set in the high luminance clip circuit 302. Then, the luminance data input from the A / D converter 26 is clipped. These high brightness clip circuits 300 and 302
Are passed through or clipped, and are input to the divided photometric circuits 304 and 306, respectively. The other inputs of the divided photometric circuits 304 and 306 are supplied with a timing signal for dividing the screen of one field from the window signal generating circuit 36 into a plurality of regions including, for example, a central region of the screen. The photometry circuit 304 outputs photometry data obtained by averaging luminance data for each area to the MPU 3
08, and the divided photometry circuit 306 similarly outputs photometry data obtained by averaging luminance data for each region to the MPU 308.

The MPU 308 includes the divided photometric circuits 104 and 1
06, one of the photometric data added from step 06 is selected as described later, and the selected photometric data is stored in the ROM.
Processing is performed based on the program and various numerical values stored in 40, and an exposure control signal is output via a D / A converter 46. In other words, as the selected photometric data, for example, if the photometric data at the center of the screen is I ₁ and the photometric data of the entire screen is I ₂ , the MPU 308 first determines the logarithm of the ratio of the photometric data I ₁ and the photometric data to I ₂ . D = log (I ₁ / I ₂ ) is obtained.

[0049] Then, the absolute value | D | if exceeds the threshold Th _D is a so that the center-weighted metering (exposure control mode that emphasizes the central section of the screen), and calculates the exposure correction amount, the exposure correction amount Is output to the iris drive circuit 48 via the D / A converter 46. Thus, when the luminance distribution in the subject screen is in a backlight or spotlight illumination state, the exposure correction is performed so that the center of the screen is appropriate. Incidentally, | D | average becomes metering in the case of a ≦ Th _D, exposure correction signal becomes a standard value.

The MPU 308 sets the clip level as shown in the flowchart of FIG. That is,
It is determined which one of the two sets of photometric data of the divided photometric circuits 304 and 306 for inputting the luminance data clipped at the low clip level and the high clip level respectively. First, it is determined whether or not the current clip level is a low clip level (IRE100).
If the clip level is not low (that is, if the clip level is high), it is determined whether or not the above-described exposure correction amount is equal to or greater than _a threshold value Th _a (eg, 1 EV). "Exposure compensation amount ≥ threshold Th
If it is not "a", the clip level is not switched and the operation returns to the original state.

Meanwhile, in the case of "the exposure correction amount ≧ threshold value Th _a" returns to the original after setting the current clip level to the low clip level. By setting this low clip level, an appropriate exposure correction amount can be obtained in a backlight scene. The setting of the low clip level is equivalent to employing the photometric data input from the divided photometric circuit 304 for calculating the exposure correction amount.

[0052] When current clip level is low clip level, the exposure correction amount being currently calculated is determined whether or not less than the threshold value Th _b (threshold Th _a following predetermined value). If “exposure correction amount <threshold Th _b ”, it is further determined whether or not the change in brightness is larger than 2 EV.
Note that “brightness change> 2EV” is usually obtained when the shooting scene is switched.

If "change in brightness> 2 EV" is not satisfied, the timer is stopped (time is reset to 0 to stop). That is, in this case, the low clip level is continuously set. On the other hand, if “exposure correction amount <threshold value Th _b ” or “brightness change> 2 EV”, it is determined whether or not the timer is operating, and if the timer is stopped, the timer is started.

On the other hand, if the timer is operating,
It is determined whether or not seconds have elapsed. "Timer> 2
If it is not “second”, the clip level is returned to the original without switching, and if “timer> 2 seconds”, the current clip level is set to the high clip level (IRE200) and then the timer is stopped. . The setting of the high clip level is equivalent to employing the photometric data input from the divided photometric circuit 306 for calculating the exposure correction amount.

As described above, switching from the low clip level to the high clip level requires that the condition for switching to the high clip level (“exposure correction amount <threshold Th _b ” or “brightness change> 2 EV”) be two. The requirement is that it lasts for more than a second. This makes it possible to perform stable exposure control even when the scene slightly changes due to the operation of the main subject in a backlight scene. Switching from the high clip level to the low clip level is performed immediately when the condition for switching to the low clip level is satisfied. This is because it is preferable that the exposure control responds immediately when the shooting scene becomes a backlight scene.

The exposure control device for a video camera according to the present invention can be applied not only to a video movie camera but also to an electronic still video camera.

[0057]

As described above, according to the exposure control apparatus for a video camera according to the present invention, the clip level for clipping the luminance signal for photometry is changed from one clip target value to another clip target value. When the clip level is changed, the change in the brightness of the image when the clip level is changed can be made visually natural, and a single high-brightness clip circuit and a divided photometry circuit can be used. Therefore, there is an advantage that the circuit configuration can be simplified.

As clip levels for clipping a luminance signal for photometry, at least a clip level for obtaining appropriate photometric information in a backlight scene and a clip level for obtaining appropriate photometric information in a shooting scene other than a backlight scene. Since the clip level is prepared and the clip level is switched to a clip level for obtaining appropriate photometric information according to the shooting scene, good exposure control can be performed.

Further, since the clip level is switched to a clip level for obtaining an appropriate exposure correction amount according to the magnitude of the exposure correction amount, the clip level can be switched independently of the photometric pattern and the photometric method. In addition, since a predetermined time delay is provided when the clip level is switched, stable exposure control can be realized even if the scene slightly changes due to the operation of the main subject or the like.

[Brief description of the drawings]

FIG. 1 is a block diagram of a video camera including a first embodiment of a video camera exposure control apparatus according to the present invention.

FIG. 2 is a schematic diagram used to explain each area to be subjected to split photometry.

FIG. 3 is a flowchart used to explain the processing contents of the MPU in FIG. 1;

FIGS. 4A to 4G are schematic diagrams showing a photometric area selected by discrimination of a shooting scene.

FIG. 5 is a flowchart used to explain a method of setting a clip level for the next photometry.

FIG. 6 is a block diagram of a video camera including a second embodiment of the video camera exposure control device according to the present invention.

FIG. 7 is a flowchart used to explain the processing contents of the MPU in FIG. 6;

FIG. 8 is a block diagram of a video camera including a third embodiment of the exposure control device for a video camera according to the present invention.

FIG. 9 is a flowchart used to explain the processing contents of the MPU in FIG. 8;

FIG. 10 is a block diagram of a video camera including a fourth embodiment of the exposure control device for a video camera according to the present invention.

FIG. 11 is a flowchart used to explain a clip level setting method.

[Explanation of symbols]

REFERENCE SIGNS LIST 10 photographing lens 12 iris 14 image pickup device (CCD) 16 timing generator 20 video signal processing circuit 21 detection circuit 23 integration circuit 24 LPF 28, 100, 102, 200, 202, 204, 30
0, 302... High brightness clip circuit 30, 104, 106, 206, 208, 210, 30
4, 306: divided photometric circuit 36, 108, 212, 308: MPU 40: ROM 48: iris drive circuit

Continuation of front page (56) References JP-A-2-268080 (JP, A) JP-A-3-179879 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H04N 5 / 235-5/243

Claims (5)

(57) [Claims] 1. An image pickup device converts object light incident on an image pickup device through a photographing lens and an iris into an electric signal by the image pickup device, and outputs the electric signal to a video signal processing circuit via an amplifier. A high-brightness clipping means for inputting a luminance signal of a subject image and converting a luminance signal equal to or higher than a preset clip level into the same luminance signal in a video camera in which a required video signal is obtained by appropriately performing signal processing in a circuit. And a luminance signal that has passed through the high luminance clipping means,
And dividing photometric means for determining the photometric information in a plurality of regions including a region of the central portion of the subject image, an object image on the basis of the photometry information from said divisional photometry means
Backlit scene, subject image where the center of the image is darker than the periphery
Spot light scene where the center of is brighter than the periphery, and
Determining means for determining two or more shooting scenes among other shooting scenes; and a first means for obtaining appropriate photometric information in a backlight scene.
The clip target value and the backlight scene and spotlight scene
Before obtaining proper photometric information in outside shooting scenes
A second clip target higher than the first clip target value
Obtain appropriate photometric information for the value and spotlight scene
A third clip higher than the second clip target value for
Has two or more of the clip target values,
When the change of the shooting scene is determined by the determination means,
Clip level changing means for gradually changing the current clip level so that the current clip level in the high-brightness clip means becomes a clip target value corresponding to the determined shooting scene; and each photometry from the divided photometry means Each shooting system is
Calculates the photometric value suitable for the pattern, and the photometric value becomes the reference value.
An exposure control device for a video camera , comprising: an iris control unit for controlling the iris as described above. 2. The video according to claim 1, wherein said clip level changing means gradually changes the current clip level from a certain clip target value to another clip target value over a period of about 2 seconds. Exposure control device for camera. 3. The image pickup device converts the subject light incident on the image pickup device through the photographing lens and the iris into an electric signal by the image pickup device, and outputs the electric signal to a video signal processing circuit via an amplifier. In a video camera that obtains a required video signal by appropriately performing signal processing by a circuit, at least a first clip level for obtaining appropriate photometric information in a backlight scene and proper photometric information in a shooting scene other than the backlight scene High-brightness clipping means for clipping a luminance signal of a subject image to be input at a second clip level for obtaining a luminance signal having passed through the high-brightness clipping means,
And dividing photometric means for determining the photometric information in a plurality of regions including a region of the central portion of the subject image, an object image on the basis of the photometry information from said divisional photometry means
Backlit scenes where the center of the image is darker than the
A determining means for determining a shooting scene other than the scene, and if the determined shooting scene is a backlight scene,
The greater the contrast strength of the backlight scene, the greater the first
Means for lowering a clip level, and a first means when the determined shooting scene is a backlight scene.
The luminance signal clipped at the clip level is suitable for each shooting scene based on the respective photometric information obtained from the divided photometric means for inputting the luminance signal clipped at the second clip level in a case other than a backlight scene . Calculate photometric value
And an iris control unit for controlling the iris so that the photometric value becomes a reference value . 4. An image pickup device converts object light incident on an image pickup device through a photographing lens and an iris into an electric signal, and outputs the electric signal to a video signal processing circuit via an amplifier. In a video camera in which a required video signal is obtained by performing appropriate signal processing by a circuit, the first clip level for obtaining appropriate photometric information in a backlight scene, and is suitable for a shooting scene other than a backlight scene and a spotlight scene. Brightness clipping means for clipping a brightness signal of a subject image to be input at a second clip level for obtaining accurate photometric information and a third clip level for obtaining appropriate photometric information in a spotlight scene; Input the luminance signal that has passed through the luminance clip means,
And dividing photometric means for determining the photometric information in a plurality of regions including a region of the central portion of the subject image, an object image on the basis of the photometry information from said divisional photometry means
Backlit or backlit scenes where the center of the image is darker than the periphery
Shooting scenes other than spotlight scenes and subject images
Discriminating means for discriminating a spotlight scene in which the central portion of the image is brighter than the peripheral portion ;
The greater the contrast strength of the backlight scene, the greater the first
Lower the clip level, and in the case of a spotlight scene,
The higher the contrast intensity of the spot light scene, the more
Means for increasing a third clip level, and a first means for increasing the clip level when the determined shooting scene is a backlight scene.
The luminance signal clipped at the clip level is clipped at the third clip level in the case of a spotlight scene, and the luminance signal clipped at the second clip level in a case other than a backlight scene and a spotlight scene. A photometric value suitable for each shooting scene is calculated based on each photometric information obtained from the divided
An exposure control device for a video camera , comprising: iris control means for controlling the iris so that a light value becomes a reference value . Wherein said as amount of incident light entering the imaging device from the imaging lens through the iris becomes the reference value Airi
In an exposure control device for a video camera that controls the exposure, a luminance signal indicating the subject image is appropriately compensated for exposure in a backlight scene.
First clip level and backlight scene to get positive amount
Second to obtain an appropriate exposure compensation amount for shooting scenes other than
High-brightness clipping means for clipping at a clip level of, and a luminance signal passed through the high-brightness clipping means ,
Average photometry value of the entire screen of the subject image and photometry at the center of the screen
A photometric means for determining the value and a luminance difference between the average photometric value and the photometric value at the center of the screen are large.
The brightness at the center of the subject image is appropriate
Means for obtaining such an exposure correction amount and correcting the reference value according to the exposure correction amount; and the magnitude of the obtained exposure correction amount becomes equal to or more than a first threshold value.
And switch to the first clip level, and then calculate
Exposure correction value is smaller than the first threshold value
When the state becomes smaller than the second threshold value or when the brightness of the subject changes.
A state that changes greatly to the extent that the shooting scene changes
Is the second clip when it continues for a predetermined time or more.
An exposure control device for a video camera, comprising: clip level switching means for switching to a level.