JP2003158673A - Image pickup device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain a scrupulous exposure in response to the feature of an object. SOLUTION: A digital still camera 1 produces a histogram denoting the frequency of pixels with respect to a luminance level from an object image picked up with an optional exposure control variable, and detects the feature of the object image on the basis of the histogram. Then the digital still camera 1 corrects the original exposure control variable in response to the feature to calculate a new exposure control variable and controls the exposure to be the new exposure control variable and picks up the object image.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a CCD (Charge C
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup device and an image pickup method for electronically picking up a still image or the like by using a photoelectric conversion element such as an image sensor or a C-MOS image sensor.

[0002]

2. Description of the Related Art An electronic image pickup device called a so-called digital still camera using a CCD image sensor or a C-MOS image sensor as a photoelectric conversion element is widely used.

Such a digital still camera is generally provided with an AE (automatic exposure) function for automatically adjusting the exposure amount. The exposure control of a digital still camera measures the amount of light in the field of view with a sensor and the like, and based on the result of the photometry, the aperture of the lens, the amount of electronic shutter, and the CCD.
This is performed by adjusting the gain of the electric signal output from the image sensor or the like.

[0004]

However, the CCD
A photoelectric conversion element such as an image sensor has a very narrow dynamic range in a photographable luminance region as compared with a silver halide photographic film. Therefore, when there is a large difference in brightness between the bright and dark areas included in the field of view, the range of the proper exposure becomes extremely narrow, and if exposure control was performed based on the photometric results from a simple sensor, optimal exposure control would be possible. It was difficult to do. For example, when the exposure is matched to the bright part, the dark part becomes an image that is underexposed, and when the exposure is matched to the dark part, the bright part becomes a white image. In addition, depending on the subject, there is a possibility that the entire image will be a dim image (so-called sleepy image).

In order to solve such a problem, in recent years, the amount of light is measured from an image obtained by actually taking an image, and the exposure at the time of shooting has been controlled. As the method to measure the light intensity from the actual image pickup screen, the total average photometry method that measures the average brightness of the entire screen, the center-weighted photometry method that intensively measures the brightness of the center part of the screen, and the split screen Then, there are a multi-divisional photometry system for measuring the average brightness in each area, a spot photometry system for measuring the brightness at an arbitrary position in the screen, and the like.

However, even if the method of measuring the light amount from the actual imaged image as described above is used, the average amount of luminance is simply calculated, or only partial luminance measurement is performed. Therefore, it was difficult to control the exposure in detail.

The present invention has been made in view of the above circumstances, and an image pickup apparatus capable of performing fine exposure control according to the characteristics of a subject without causing overexposure or underexposure. An object is to provide an image capturing method.

[0008]

In an image pickup apparatus according to the present invention, image pickup light from a subject is incident, the image pickup light is converted into an electric signal by an image pickup device, and the electric signal thus converted is converted into a pixel unit or a pixel block. A camera image capturing unit that captures a subject image by digitizing in units to generate an image capturing signal and a control unit that controls the camera image capturing unit are provided, and the control unit controls exposure of the camera image capturing unit to an arbitrary value. By controlling the exposure control amount, from the subject image captured with the arbitrary exposure control amount, a histogram showing the frequency of pixels with respect to the brightness level is generated, and the feature of the subject image is detected based on the histogram, Accordingly, the new exposure control amount is calculated by correcting the arbitrary exposure control amount, and the subject image is captured by controlling the exposure of the camera imaging unit to the new exposure control amount. Characterized in that it.

In this image pickup device, a histogram showing the frequency of pixels with respect to the brightness level is generated from the subject image picked up with an arbitrary exposure control amount, and the feature of the subject image is detected based on this histogram. Then, an arbitrary exposure control amount is corrected according to the characteristic to calculate a new exposure control amount, and the exposure is controlled to the new exposure control amount to capture a subject image.

For example, in this image pickup apparatus, a new exposure control amount is calculated by calculating a correction amount based on the histogram and correcting the arbitrary exposure control amount based on the correction amount.

In the image pickup method according to the present invention, image pickup light from a subject is incident, the image pickup light is converted into an electric signal by an image pickup element, and the converted electric signal is digitized in pixel units or pixel block units. An image capturing method for capturing an image of a subject by generating an image pickup signal by capturing an image of the subject at an exposure according to an arbitrary exposure control amount, and from the image of the subject imaged at the above arbitrary exposure control amount. , Generating a histogram showing the frequency of the pixel with respect to the brightness level, detects the features of the subject image based on the histogram, calculates a new exposure control amount by correcting any exposure control amount according to the feature, It is characterized in that a subject image is captured by controlling the exposure to a new exposure control amount.

In this image capturing method, a histogram showing the frequency of pixels with respect to the brightness level is generated from the subject image captured with an arbitrary exposure control amount, and the feature of the subject image is detected based on this histogram. Then, the arbitrary exposure control amount is corrected in accordance with the feature to calculate a new exposure control amount, and the exposure is controlled to the new exposure control amount to capture a subject image.

For example, in this image capturing method, a new exposure control amount is calculated by calculating the correction amount based on the histogram and correcting the arbitrary exposure control amount based on the correction amount.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, as embodiments of the present invention,
An image pickup device (digital still camera) to which a still image is electronically applied according to the present invention will be described. Figure 1
FIG. 1 shows a configuration diagram of the digital still camera 1 according to the embodiment of the present invention.

As shown in FIG. 1, the digital still camera 1 includes a camera section 11, a CCD 12, a timing signal generating circuit (TG) 13, an S / H / GC (Sampling Hol).
d Gain Control) circuit 13, AD converter 15,
The digital signal processing circuit 16, the finder 17, the recording circuit 18, the detection circuit 19, the shutter release button 20, the shutter determination circuit 21, and the control unit 30 are provided.

The CCD 12 converts the image pickup light of the subject formed on the light receiving surface through the lens unit 11 into an electric signal for each pixel and outputs an image signal. The image signal accumulated by the CCD 12 has a predetermined timing (image update period),
It is supplied to the S / H / GC circuit 14.

The timing signal generating circuit 13 is a CCD 1
2 generates various drive pulses required for reading out an image signal for each screen, and an electronic shutter pulse for controlling an accumulation time of charges accumulated in the CCD 12. The various pulses generated from the timing signal generation circuit 13 are
It is supplied to the CCD 12 and is used as a timing signal for image signal image pickup processing and output processing. The timing signal generation circuit 13 also controls the shutter speed of the electronic shutter in accordance with a control command from the control unit 30.

The S / H / GC circuit 14 performs analog processing such as sampling processing and amplification processing on the image signal supplied from the CCD 12. The analog image signal output from the S / H / GC circuit 14 is the AD converter 1
5 is supplied. The amplification degree of the image signal supplied from the CCD 12 is controlled by the control unit 30.

The AD converter 15 samples the analog image signal supplied from the S / H / GC circuit 14 at a predetermined sampling rate and converts it into a digital image signal. The digital image signal output from the AD converter 15 is supplied to the digital signal processing circuit 16.

The digital signal processing circuit 16 generates a digital video signal in the NTSC format or a format required for a recording medium from the digital image signal supplied from the AD converter 15 and outputs it to the outside. The digital signal processing circuit 16 generates a display image signal from the digital image signal and supplies it to the finder 17 during framing. The digital signal processing circuit 16 is
When capturing a still image, one still image signal is generated from the digital image signal, and after being compressed, the recording circuit 18
Supply to.

The finder 17 is an electronic display device composed of, for example, a liquid crystal panel or the like. Finder 17
At the time of framing, a display image signal is input from the digital signal processing circuit 16 to display the image signal.

The recording circuit 18 outputs the still image signal output from the digital signal processing circuit 16 when the still image is picked up.
For example, it is recorded in a storage medium such as a memory card.

The detection circuit 19 is a digital signal processing circuit 1.
From the video signal supplied from No. 6, auto focus (A
F), various detection signals required for automatic exposure (AE), etc. are generated. The various detection signals are, for example, 1
It is read for each frame. The control unit 30 controls the lens unit 11 and the like based on the read various detection signals so that an appropriate image can be captured. Specifically, the detection signal detected by the detection circuit 19 includes, for example, a detection signal regarding autofocus, a detection signal regarding automatic exposure control, and the like. The detection circuit 19 detects an edge component of luminance in an AF detection area set at a predetermined position on a captured image as a detection signal for autofocus, and outputs a contrast value obtained by integrating the edge component. . Further, the detection circuit 19 generates a histogram indicating the frequency of pixels with respect to the brightness level from the captured image as a detection signal related to automatic exposure control, detects the characteristics of the subject image based on this histogram, and calculates according to the characteristics. The exposure control amount is output. The details of the detection signal relating to this exposure control will be described later.

The shutter release button 20 is a momentary type push switch operated by the user.
The shutter release button 20 distinguishes three states: a state in which the switch is not pressed (OFF), a state in which the switch is pressed fully (fully pressed), and a state in which the switch is pressed halfway (half pressed). A switching function is provided. This shutter release button 20 3
One of the pressed states (OFF, half-pressed, full-pressed) is discriminated by the shutter discriminating circuit 20, and the discriminating information is used as the discrimination information.
Supplied to zero.

The lens unit 11 includes a zoom lens 22, a focus lens 23, diaphragm blades 24, and diaphragm blades 24.
And a diaphragm blade drive unit 25 for driving the. Also,
In addition to these components, the lens unit 11 includes, for example, an infrared cut filter that cuts infrared rays of incident light, an optical system such as a shutter blade that blocks incident light, a zoom lens driving unit that drives the zoom lens 22, and a focus lens. It also includes a focus lens drive unit that drives the shutter, a shutter drive unit that drives the shutter blades, and the like.

The zoom lens 22 in the lens unit 11 is provided at a position where its optical axis coincides with a vertical line extending from the approximate center of the light receiving surface of the CCD 12. Zoom lens 2
Reference numeral 2 is provided so as to be linearly movable back and forth on the optical axis, and the imaging magnification of the image formed on the light receiving surface of the CCD 12 is changed according to the moving position. The movement position of the zoom lens 22 is
It is controlled by the control unit 30 via the zoom lens driving unit.

Focus lens 23 in lens unit 11
Is provided at a position where its optical axis coincides with a vertical line extending from the approximate center of the light receiving surface of the CCD 12. The focus lens 23 is provided so as to be linearly movable back and forth on the optical axis, and changes the focus position of the image formed on the light receiving surface on the CCD 12 according to the moving position. The focus lens 23 is
The moving position is set to the control unit 3 via the diaphragm blade drive unit 25.
Controlled by 0.

The diaphragm blades 24 adjust the amount of imaging light imaged on the light receiving surface of the CCD 12. The diaphragm blades 24 are
A hole centered on the optical axis of the optical system of the lens unit 11 is formed,
The amount of light is controlled by changing the hole diameter.
That is, this diaphragm blade 24 is used for the aperture value (F
Value). The aperture diameter of the aperture blade 24 is controlled by the control unit 30 via the aperture drive unit 25.

The control section 30 controls each section of the digital still camera 1. For example, shutter release button 2
Based on the pressed state of 0, framing process control (OFF), autofocus process control (half press), and still image recording control (full press) are performed.

The framing process is a process of displaying an image picked up by the CCD 12 on the finder 17 so that the user can confirm the position of the subject in the screen and the composition of the screen before photographing. During this framing process, the CCD 12 performs an image-capturing process for one screen at a constant image update cycle (for example, every 1/30 seconds), and an image signal obtained by imaging is output. Therefore, the image displayed on the viewfinder 17 is also displayed at regular intervals (for example, 1/3).
Updated every 0 seconds), the user can check the captured image displayed on the finder 17 as a moving image. This framing process is performed when the digital still camera 1 itself is in a state capable of photographing and the shutter release button 20 is off, that is, when the user does not press the shutter release button 20.

The autofocus process is a process for automatically setting the focus of a subject image which is an object for capturing a still image. That is, the autofocus process is a process of automatically adjusting the moving position of the focus lens 23 to adjust the focus of the captured image. When the shutter release button 20 is pressed halfway while performing the framing process, the digital still camera 1 starts the autofocus process for detecting the in-focus position based on the captured image. Specifically, during the autofocus process, the control unit 30 acquires the contrast value at each position from the detection circuit 19 while moving the focus lens 23, and determines whether the contrast value for each moving position of the focus lens 23 is increased or decreased. . Then, the control unit 30 determines the degree of focusing of the image with respect to the moving position of the focus lens 23 based on the increase / decrease of the contrast value, and moves the focus lens 23 to the position having the highest degree of focusing.

Further, in this digital still camera 1,
During this autofocus process, the aperture of the diaphragm blade during recording of a still image, the speed of the electronic shutter, and the like, that is, the F value and the shutter speed can also be set. However, when setting a special F value, shutter speed, or the like during autofocus, the F value and shutter speed during still image recording are reset after the autofocus processing.

The still image photographing process is a process of picking up one screen of a subject image and recording the one screen of subject image on the medium. In the digital still camera 1, when the shutter release button 20 is fully pressed after completing the autofocus process, the moving position of the focus lens 23, the aperture of the diaphragm blades, the electronic shutter time, and the S / H / GC 14 are set. The gain is set and the still image for one screen is captured by the CCD 12. The captured still image is subjected to processing such as compression by the digital signal processing circuit 16 and the like, and then stored in the medium.

Next, the automatic exposure control process will be described.

In the automatic exposure control processing, the aperture of the diaphragm blades 24 is adjusted so that the photographed subject image has the optimum exposure during the framing processing and the autofocus processing.
Electronic shutter speed of CCD12 and S / H / G
The amplification degree of the C circuit 14 is set.

Each of these settings is performed according to the exposure control parameter stored in the internal memory of the control unit 30. Exposure control based on the exposure control parameter, for example,
This is performed by using a table showing the opening degree of the diaphragm blades 24, the electronic shutter speed amount, the amplification degree of the image signal, etc. for each value of the exposure control parameter, and an arithmetic expression for calculating these data from the exposure control parameter.

The control unit 30 controls the exposure so that the image becomes brighter when the value of the exposure control parameter becomes larger, and controls the exposure so that the image becomes darker when the value of the exposure control parameter becomes smaller. That is, if the exposure control parameter increases, the control unit 30 increases the aperture of the diaphragm blade 24 (opens the diaphragm blade 34), slows the electronic shutter speed (extends the exposure time of the CCD 12), and C
Control is performed in the direction of increasing the amplification degree of the image signal output from the CD 12 (increasing the gain of the S / H / GC circuit 14). On the contrary, if the exposure control parameter becomes smaller, the control unit 30 reduces the aperture of the diaphragm blade 24 (closes the diaphragm blade 34), increases the electronic shutter speed (shortens the exposure time of the CCD 12), and C
Control is performed in a direction such that the amplification degree of the image signal output from the CD 12 is reduced (the gain of the S / H / GC circuit 14 is reduced).

The exposure control parameters stored in the internal memory of the control unit 30 are sequentially corrected, for example, frame by frame, based on the brightness level detected from the actually picked-up image and the brightness level histogram. To go. The automatic exposure control processing described below corrects the exposure control parameter based on the histogram of the brightness level.

The histogram of the brightness level of the captured image is
It is calculated by the detection circuit 19. A concrete example of the histogram is shown in FIG. That is, the horizontal axis represents the luminance level of pixels, and the vertical axis represents the number of pixels in one captured image, that is, the frequency. Therefore, in the case of a captured image including many pixels with a high brightness level, the histogram has a peak in the high brightness level portion, as shown in FIG. In the case of a captured image that includes many pixels with low brightness levels,
As shown in (b), the histogram has a peak in the low luminance level portion.

The control unit 30 detects a histogram from the subject image in which the exposure is controlled by a certain arbitrary exposure control parameter. The control unit 30 detects the characteristics of the image captured with the arbitrary exposure control parameter from the histogram. Based on the characteristics, the control unit 30 determines how to correct the exposure to obtain the optimum exposure, and corrects the arbitrary exposure control parameter based on the result of the determination, thereby performing a new exposure control. Find the parameters. For example, if the characteristic of the captured image such that the number of pixels of the high-luminance component is very small is obtained from the histogram, the exposure control parameter is reduced and the exposure is controlled in the darkening direction. On the contrary, if a characteristic of the captured image that the number of pixels of the low luminance component is very small is obtained from the histogram, the exposure control parameter is increased to control the exposure to be bright.

Then, the control unit 30 controls the exposure with the new exposure control parameter to capture an image of the subject, and further detects a histogram from the image captured with the new exposure control parameter to determine the exposure control parameter. Follow up correction.

Therefore, in the present digital still camera 1,
The subject can always be imaged with the optimum exposure according to the characteristics of the subject.

Next, a specific processing example of the exposure control processing applied to the digital still camera 1 will be described with reference to FIG.
A description will be given using the flowchart shown in FIG.

In the digital still camera 1, when the power is turned on and the operation in the framing mode is started, the exposure control process is started from the following step S1.

First, the control unit 30 performs exposure control based on the exposure control parameters held in the internal memory,
A subject image is captured (step S1). At the start of this flow control, for example, the exposure control parameters calculated from the amount of reflected light of the subject detected based on normal photometry or the exposure control parameters preset in the memory or the like are stored in the internal memory. Is stored. Further, after the flow control is looped once or more, the new exposure control parameter obtained by the processing in step S11 in the previous loop is stored.

Subsequently, the detection circuit 30 obtains a histogram from the subject image whose exposure is controlled in step S1 (step S2).

Subsequently, the control unit 30 acquires the histogram obtained in step S2 from the detection circuit 30 (step S3).

Subsequently, the control unit 30 divides the brightness level of the obtained histogram into three levels, that is, a high brightness range, a medium term range, and a low brightness range, and calculates the number of pixels in each range (step). S4). Here, the number of pixels in the high luminance range is N _H , the number of pixels in the medium luminance range is N _M , and the number of pixels in the low luminance range is N _L. Further, the threshold for dividing the high brightness range, the middle brightness range, and the low brightness range is, for example, as shown in FIG. 4, 0 to 1/4 × Ymax is set as the low brightness range and 1
/ 4 × Ymax to 3/4 × Ymax is a medium luminance range, and 3/4 × Ymax to Ymax is a high luminance range. Note that Ymax is the maximum value of the brightness level. Further, it is desirable to consider the gamma correction process when dividing the brightness level. If a histogram is generated using luminance data before gamma correction, the threshold is calculated from the value corresponding to the luminance level after gamma correction, as shown in FIG. Further, here, the luminance level is divided into four, and the upper 1/4 is the high luminance range and the lower 1/4 is the low luminance range.
The upper 1 / N may be divided into the high luminance range and the lower 1 / N may be divided into the low luminance range. However, in this case, N must be an integer of 3 or more.

Subsequently, the control unit 30 performs the following calculation,
The first correction ratio R ₁ is calculated (step S5). R ₁ = | N _H −N _L | / (N _H + N _M + N _L )

Subsequently, the control unit 30 performs the following calculation,
The second correction ratio R ₂ is calculated (step S6). R ₂ = N _M / (N _H + N _M + N _L )

Subsequently, the control unit 30 performs the following calculation,
The third correction ratio R ₃ is calculated (step S7). R ₃ = N _H / (N _H + N _M + N _L )

Subsequently, the control unit 30 performs the following calculation,
The fourth correction ratio R ₄ is calculated (step S8). R ₄ = N _L / (N _H + N _M + N _L )

Subsequently, the control unit 30 controls the first correction ratio R
₁ , the second correction ratio R ₂ , the third correction ratio R ₃ , and the fourth correction ratio R ₄ are multiplied to calculate the total correction ratio R (step S9).

Subsequently, the control unit 30 corrects the exposure control parameters stored in the internal memory based on the total correction ratio R to obtain new exposure control parameters (step S10). For example, the total correction ratio R and the coefficient k
A new exposure control parameter is calculated by multiplying by and subtracting this multiplication result from the exposure control parameter stored in the internal memory.

Subsequently, the control unit 30 stores the new exposure control parameter in the internal memory (step S1).
1).

Then, the control unit 30 performs the processing from step S1 to step S11 for each frame, for example, and when performing the processing for the next frame, restarts the processing from step S1.

The first correction ratio R ₁ , the second correction ratio R ₂ , the third correction ratio R ₃ , and the fourth correction ratio R ₄ obtained in steps S5 to S8 are the total correction ratio R
The following effects will be applied to each of the above.

First correction ratio R₁Is a pixel in the high brightness range
If there are many pixels in the low brightness range, or if there is a high brightness
Value when there are few pixels in the range and many pixels in the high brightness range
Grows larger. That is, the first correction ratio R₁Is the image
If the image is overexposed, or the image is crushed in black
In that case, the value becomes large. Therefore, the first correction ratio R ₁
Means, for example, that the subject image has a low brightness range or a high brightness range.
Being biased to one side, it is possible to widely utilize the CCD sensitive range width
If not, the effect is to increase the total correction ratio.
Can be given. Therefore, such a first supplement
Positive ratio R₁Correct the exposure control parameters based on
Depending on the image, whiteout, blackout, or dim images
If the image is too sleepy, give it to the exposure compensation parameter.
It is possible to increase the correction amount.

The second correction ratio R ₂ has a large value when the histogram has a large number of pixels in the medium luminance range, for example, a mountain shape, and a large value when the histogram has a small number of pixels in the medium luminance range, for example, a valley shape. Becomes smaller. That is, the second correction ratio R ₂
Is small when there are many pixels in the high-luminance range or low-luminance range and few pixels in the medium-luminance range, and it is unknown whether the subject is on the high-luminance side or the low-luminance side. Therefore, the second correction ratio R ₂ can be influenced so as to reduce the correction amount given to the exposure control parameter when there is a possibility of making an incorrect correction.

The third correction ratio R ₃ has a large value when there are many pixels in the high luminance range with respect to the total number of pixels. Therefore, the third correction ratio R ₃ can increase the correction amount given to the exposure control parameter, for example, when the face is overexposed when a person is photographed.

The fourth correction ratio R ₄ has a large value when the number of pixels in the low luminance range is large with respect to the total number of pixels. Therefore, the fourth correction ratio R ₄ is, for example, a correction amount given to the exposure control parameter for an image in which the gradation of the black portion disappears, which occurs when a black car or the like is photographed. It is possible to increase it.

In this example, the first to fourth correction ratios R
_The total correction ratio R is calculated by multiplying all of _{1 to} R ₄ , but the total correction ratio R may be calculated using only one of these correction ratios without using all the correction interest rates. Alternatively, a combination of these may be used.

As described above, in the digital still camera 1 according to the embodiment of the present invention, the feature of the subject image is detected based on the histogram obtained from the subject image imaged with an arbitrary exposure control parameter, and from the feature An arbitrary exposure control parameter is corrected, a new exposure control parameter is calculated, the exposure is controlled to a new exposure control amount, and a subject image is captured.

Therefore, in the digital still camera 1 of the embodiment of the present invention, it is possible to perform fine exposure control according to the characteristics of the subject without causing overexposure or underexposure. For example, even when an image biased to the low luminance side as shown in FIG. 6A is captured, by performing the above exposure control and making corrections, as shown in FIG. 6B. It is possible to capture an image with a wide dynamic range that efficiently uses the sensitive range of the CCD from low brightness to high brightness.

[0065]

In the image pickup apparatus and the image pickup method according to the present invention, a histogram showing the frequency of pixels with respect to the brightness level is generated from the subject image picked up with an arbitrary exposure control amount, and the subject image is based on this histogram. Detect the features of. Then, the arbitrary exposure control amount is corrected according to the feature to calculate a new exposure control amount, and the exposure is controlled to the new exposure control amount to capture the subject image.

Therefore, according to the present invention, it is possible to perform fine exposure control according to the characteristics of the subject without causing overexposure or underexposure.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of a digital still camera according to an embodiment of the present invention.

FIG. 2 is a diagram showing a histogram of a subject image.

FIG. 3 is a flowchart showing a task of exposure control.

FIG. 4 is a diagram for explaining a division range of a brightness level of a histogram of a subject image.

FIG. 5 is a diagram for explaining a division threshold of a brightness level considering a gamma correction curve.

FIG. 6 is a diagram showing a histogram after exposure correction according to the present invention is performed.

[Explanation of symbols]

1 digital still camera, 11 camera section, 12 C
CD image sensor, 13 timing generator,
14 S / H / GC, 15 AD converter, 16 digital signal processing circuit, 17 finder, 18 recording circuit 19 detection circuit 20 shutter release button,
21 shutter determination circuit, 22 zoom lens, 23
Focus lens, 24 diaphragm blades, 25 diaphragm drive unit, 30 control unit

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H002 CC01 CC21 DB02 DB19 DB25                       DB26 DB29 HA04                 5C022 AA13 AB03 AB17 AB20 AB52                       AC42 AC52 AC69                 5C024 BX01 CX44 CX54 DX04 EX34                       HX18 HX29

Claims (18)

[Claims] 1. Imaging light from a subject is incident, the imaging light is converted into an electric signal by an imaging device, and the converted electric signal is digitized in pixel units or pixel block units to generate an imaging signal, A camera image capturing unit that captures a subject image and a control unit that controls the camera image capturing unit are provided. The control unit controls the exposure of the camera image capturing unit to an arbitrary exposure control amount, and the arbitrary exposure control amount. A histogram showing the frequency of pixels with respect to the brightness level is generated from the subject image captured in, the feature of the subject image is detected based on the histogram, and the arbitrary exposure control amount is corrected according to the feature to newly generate the histogram. An image pickup apparatus, which calculates a different exposure control amount, controls the exposure of the camera image pickup unit to the new exposure control amount, and picks up a subject image. 2. The control unit controls the exposure by setting the aperture of the diaphragm, the shutter speed of the image pickup device and / or the gain of the electric signal output from the image pickup device. The image pickup device described. 3. The control unit calculates a correction amount based on the histogram, and corrects the arbitrary exposure control amount based on the correction amount to calculate the new exposure control amount. The image pickup device according to claim 1. 4. The control unit detects a histogram obtained by dividing the range of the brightness level of the subject image into at least three ranges, and compares the number of pixels in each range,
The image pickup device according to claim 1, wherein the correction amount is calculated. 5. The control unit sets a threshold value for dividing the range of the brightness level of the subject image according to the brightness level corrected by the gamma correction curve. The image pickup device described. 6. The control unit calculates the correction amount according to a relationship between a ratio of the number of pixels of a low brightness level to the total number of pixels and a ratio of a number of pixels of a high brightness level to the total number of pixels. The image pickup device according to claim 3, wherein 7. The image pickup device according to claim 3, wherein the control unit increases or decreases the correction amount according to a ratio of the number of pixels having an intermediate luminance level to the total number of pixels. 8. The image pickup apparatus according to claim 3, wherein the control unit calculates the correction value according to a ratio of the number of pixels of a high luminance level to the total number of pixels. 9. The control unit detects a histogram obtained by dividing a range of brightness levels of a subject image into three ranges of a high brightness range, a middle brightness range, and a low brightness range, and sets the number of pixels in the high brightness range to N _H. , Where N _{M is} the number of pixels in the medium luminance range and N _L is the number of pixels in the low luminance range, the first ratio, the second ratio, the third ratio and / or the fourth ratio are calculated based on the following equations. A ratio is obtained, a correction amount is calculated based on a total ratio obtained by multiplying each ratio, and the new exposure control amount is calculated by correcting the arbitrary exposure control amount based on the correction amount. The image pickup device according to item 1. First ratio _{= | N H -N L | /} (N H + N M + N L) second ratio _{= N M / (N H +} N M + N L) third ratio _{= N H / (N H +} N M + N _L ) Fourth ratio = N _L / (N _H + N _M + N _L ) 10. Imaging light from a subject is incident, the imaging light is converted into an electric signal by an imaging device, and the converted electric signal is digitized in pixel units or pixel block units to generate an imaging signal, In an image capturing method for capturing a subject image, a subject image is captured with an exposure according to an arbitrary exposure control amount, and a histogram showing the frequency of pixels with respect to a brightness level is captured from the subject image captured with the arbitrary exposure control amount. Generate, detect the feature of the subject image based on the histogram, correct the arbitrary exposure control amount according to the feature, calculate a new exposure control amount, and control the exposure to the new exposure control amount. An image pickup method comprising: taking a subject image. 11. The image according to claim 10, wherein the exposure is controlled by changing an aperture of a diaphragm, a shutter speed of an image sensor and / or a gain of an electric signal output from the image sensor. Imaging method. 12. The new exposure control amount is calculated by calculating a correction amount based on the histogram and correcting the arbitrary exposure control amount based on the correction amount. Image capturing method. 13. The correction amount is calculated by detecting a histogram obtained by dividing a range of brightness levels of a subject image into at least three ranges, and comparing the number of pixels in each range. 10. The image capturing method described in 10. 14. The image capturing method according to claim 12, wherein a threshold for dividing the range of the brightness level of the subject image is set according to the brightness level corrected by the gamma correction curve. . 15. The correction amount is calculated according to the relationship between the ratio of the number of pixels of the low luminance level to the total number of pixels and the ratio of the number of pixels of the high luminance level to the total number of pixels. The image capturing method according to claim 12. 16. The image capturing method according to claim 12, wherein the correction amount is increased or decreased according to a ratio of the number of pixels having an intermediate luminance level to the total number of pixels. 17. The image capturing method according to claim 12, wherein the correction value is calculated according to a ratio of the number of pixels of a high luminance level to the total number of pixels. 18. A histogram obtained by dividing a range of brightness levels of a subject image into three ranges of a high brightness range, a middle brightness range, and a low brightness range, and detecting the number of pixels in the high brightness range by N _H ,
The number of pixels in the medium luminance range is N _M , and the number of pixels in the low luminance range is N _L
Then, the first ratio, the second ratio, the third ratio and / or is calculated based on the following arithmetic expression, and the correction amount is calculated based on the total ratio obtained by multiplying each ratio, and based on the correction amount. The image capturing method according to claim 10, wherein the new exposure control amount is calculated by correcting the arbitrary exposure control amount. First ratio _{= | N H -N L | /} (N H + N M + N L) second ratio _{= N M / (N H +} N M + N L) third ratio _{= N H / (N H +} N M + N _L ) Fourth ratio = N _L / (N _H + N _M + N _L )