JP2007025558A - Exposure control method and device, and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To excellently control emitted flash light quantity even when flash light is emitted in a low-luminance state while preventing the shake of an imaging apparatus. <P>SOLUTION: When a subject gets dark, shutter speed is kept to the one higher than camera shake limit shutter speed, and sensitivity adjustment that photographing sensitivity is made high is performed. When the flash light is not emitted, the photographing sensitivity is made high to a maximum value in the adjustable range of the photographing sensitivity. On the other hand, when the flash light is emitted, the sensitivity is made high to a value which is smaller than the maximum value in the adjustable range thereof and which is a maximum value of the sensitivity at which the emitted flash light quantity can be properly adjusted. By restricting so that an upper limit value in the adjustable range of the photographing sensitivity may be low when the flash light is emitted, the emitted flash light quantity is controlled to prevent overexposure even when a subject exists at a short distance. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exposure control method and apparatus and an image pickup apparatus, and more particularly to a technique for controlling exposure by adjusting an aperture value and a shutter speed, and controlling exposure by adjusting photographing sensitivity and adjusting a flash emission amount.

  In recent years, there has been proposed a digital camera in which shooting sensitivity is increased so that a dark scene can be shot without flash emission (Patent Document 1).

  In this digital camera, when the aperture value is the minimum (open aperture) and the shutter speed is less than the camera shake limit value (for example, 1/60 second), the shooting sensitivity is increased by one step, and the shutter speed is increased. If the camera sensitivity reaches the upper limit and the shutter speed falls below the camera shake limit value, the shutter speed is maintained at the camera shake limit value and the flash fires. I have to.

In addition, digital cameras that automatically adjust the amount of light emitted from a flash by detecting reflected light from a subject using a light control sensor or an image sensor (CCD) have become widespread.
JP 2005-20341 A

  By the way, as shown in FIG. 10, the light emission characteristic of a flash emitted from a general flash light emitting device has a peak light emission amount immediately after the start of light emission, and the light emission amount gradually decreases from the peak as time passes.

  In FIG. 10, T1 is a light emission time range in which light control cannot be performed due to a circuit delay of the flash light control means or the like, and T2 indicates a light emission time range in which the flash light emission amount can be controlled. ing. T3 is a light emission time for giving an appropriate light emission amount to a subject at a short distance when photographing with ultra-high sensitivity (for example, ISO 1600).

  Therefore, when the subject is dark, the shooting sensitivity is increased to the upper limit value as in the exposure control method described in Patent Document 1, and then the flash is emitted when the shutter speed cannot maintain the camera shake limit value. Then, since the shooting sensitivity is the upper limit value during flash emission, it is not possible to shoot with an appropriate flash emission amount (for example, the flash emission amount at the emission time T3 in FIG. 10), and the subject is particularly close. In the case of, there is a problem that it is overexposed.

  The present invention has been made in view of such circumstances, and provides an exposure control method and apparatus, and an imaging apparatus capable of controlling the flash emission amount even when the flash light is emitted at low luminance while preventing camera shake. The purpose is to do.

  In order to achieve the above object, an exposure control method according to claim 1 controls exposure by adjusting an aperture value, shutter speed, and photographing sensitivity, and controls exposure by adjusting a flash emission amount during flash emission. In the control method, the upper limit value of the sensitivity when adjusting the shooting sensitivity is set to the maximum value within the adjustable range of the shooting sensitivity when the flash is not flashing, and is smaller than the maximum value when the flash is flashing and is appropriate. It is characterized by the maximum value of sensitivity that can adjust the flash emission level.

  In other words, when the subject becomes dark, sensitivity adjustment is performed to increase the shooting sensitivity, but when the flash is not flashing, the sensitivity can be increased to the maximum value within the adjustable range of shooting sensitivity, while it can be adjusted when the flash is flashing. The sensitivity can be increased to a maximum value of sensitivity that is smaller than the maximum value of the range and that can appropriately adjust the flash emission amount. As described above, when the flash is fired, the upper limit of the adjustable range of the shooting sensitivity is limited so that the flash light emission can be controlled so that the subject is not overexposed even when the subject is at a short distance. ing.

  As shown in claim 2, in the exposure control method according to claim 1, the maximum value of the adjustable range of the photographing sensitivity is ISO 1600, and the maximum value of the sensitivity capable of adjusting the appropriate flash light emission amount is It is characterized by being ISO800.

  According to a third aspect of the present invention, in the exposure control method according to the first aspect, it is determined whether or not the flash light emission amount reaches a maximum during the flash light emission, and when the flash light emission amount reaches the maximum, The image signal acquired at the time of flash emission is amplified by a predetermined amplification amount.

  When the flash emission reaches the maximum, the flash light may not reach the subject and may be underexposed. Therefore, in this case, the image signal acquired at the time of flash emission is amplified by a predetermined amplification amount to prevent underexposure.

  4. The exposure control method according to claim 3, wherein the predetermined amplification amount is calculated from a preset target integrated value and an integrated value obtained by integrating the image signal acquired at the time of flash emission. It is characterized by.

  5. The exposure control method according to claim 3 or 4, wherein the amplification of the image signal by the predetermined amplification amount is performed together with white balance correction by a white balance correction means for performing white balance correction. It is said. That is, underexposure can be corrected using existing white balance correction means.

  6. The exposure control method according to claim 3, wherein the amplification of the image signal by the predetermined amplification amount is performed together with the gradation conversion by the gradation converting means for performing the predetermined gradation conversion. It is characterized by. That is, underexposure can be corrected using existing tone conversion means such as gamma correction means.

  The exposure control apparatus according to claim 7 is a flash light emitting means, a light adjusting means for adjusting a flash light emission amount emitted from the flash light emitting means, a photometric means for measuring the brightness of a subject, and a photometric measurement by the photometric means. Calculating means for calculating an exposure value based on the brightness of the subject, and controlling the exposure by adjusting the aperture value, shutter speed and photographing sensitivity based on the calculated exposure value, and adjusting the exposure value during flash emission. Exposure control means for controlling the exposure by adjusting the amount of flash emission through the light means, and the exposure control means flashes the upper limit value of the sensitivity when adjusting the photographing sensitivity from the flash light emission means. Is set to the maximum value within the adjustable range of the shooting sensitivity, and when the flash is not emitted from the flash emission means, the maximum is set. A value smaller than, is characterized in that the maximum value of the sensitivity can be adjusted appropriate flash intensity by the light control means.

  The exposure control device according to claim 7, wherein the exposure control means determines the aperture value, the shutter speed, and the photographing sensitivity based on the calculated exposure value, and a camera shake limit shutter. A shutter speed that is a predetermined speed higher than the speed is defined as a lower limit shutter speed, an aperture value, a shutter speed, and a photographing sensitivity are set so that the shutter speed is equal to or higher than the lower limit shutter speed, and the aperture value reaches a minimum value, and When the photographing sensitivity reaches the maximum value, the shutter speed can be set slower than the lower limit shutter speed.

  Normally, the shutter speed is specified as a lower limit shutter speed that is a predetermined speed faster than the camera shake limit shutter speed, so the shooting sensitivity is improved, but the shutter speed is fast even for relatively dark subjects. Accordingly, it is possible to prevent photographing errors due to camera shake and subject blur.

  9. The exposure control apparatus according to claim 8, wherein the exposure control means performs flash from the flash light emitting means when the shutter speed reaches a camera shake limit shutter speed in the low brightness flash light emission mode. It is characterized by emitting light.

  An imaging apparatus according to a tenth aspect is obtained by the exposure control apparatus according to any one of the seventh to ninth aspects, an imaging unit that acquires an image signal in a state in which exposure is controlled by the exposure control apparatus, and the imaging unit. A signal processing unit that performs signal processing on the image signal, a determination unit that determines whether or not the flash emission amount reaches a maximum when the flash is emitted from the flash emission unit, and the flash emission amount is maximum. When the signal processing means is determined to have reached, the signal processing means comprises control means for amplifying the image signal acquired at the time of flash emission by a predetermined amplification amount.

  The imaging device according to claim 9, further comprising integrated value calculation means for calculating an integrated value by integrating image signals acquired at the time of flash emission, wherein the control means is set in advance. The predetermined amplification amount is determined from a target integrated value and an integrated value calculated by the integrated value calculating means.

  12. The imaging apparatus according to claim 10, wherein the signal processing unit includes a white balance correction unit, and the control unit sets the predetermined white balance correction value in the white balance correction unit to the predetermined value. It is characterized by adding an amplification amount.

  The imaging apparatus according to claim 10 or 11, wherein the signal processing means includes a gradation converting means, and the control means has the predetermined amplification in the input / output characteristics of the gradation converting means. It is characterized by adding an amount.

  According to the present invention, the adjustable range of the shooting sensitivity is changed between when the flash is emitted and when the flash is not emitted, and the upper limit of the adjustable range of the shooting sensitivity is limited to be low when the flash is emitted. Even when the subject is at a short distance when the flash is emitted, it is possible to adjust the flash emission amount appropriately so that the subject is not overexposed.

Hereinafter, preferred embodiments of an exposure control method and apparatus and an imaging apparatus according to the present invention will be described in detail with reference to the accompanying drawings.
[Overall configuration of imaging device]
FIG. 1 is a block diagram showing a configuration of an imaging apparatus to which the present invention is applied. As shown in the figure, the imaging apparatus 10 of the present embodiment is a digital camera, and includes a photographing optical system 12, a solid-state imaging device (CCD) 14, such as a CCD, a timing generator (TG) 16, an analog amplifier 18, and an A / A. D converter 20, image input controller 22, image signal processing circuit 24, video encoder 28, image display device 30, compression / decompression processing circuit 32, media controller 34, recording medium 36, AE detection circuit 38, AF detection circuit 40, The operation unit includes a central processing unit (CPU) 42, a memory (SDRAM, ROM, flash ROM, etc.) 44, a shutter release switch 50a, and a mode switch 50b.

  The overall operation of the image pickup apparatus 10 is comprehensively controlled by the CPU 42, and the CPU 42 controls each part of the image pickup apparatus 10 according to a predetermined program based on an input from the operation unit.

  The ROM of the memory 44 stores data necessary for various controls such as a program diagram in addition to the program executed by the CPU 42. The CPU 42 develops the program stored in the ROM on the SDRAM, and executes various processes while using the SDRAM as a working memory. The flash ROM stores various setting information relating to the operation of the imaging apparatus 10 such as user setting information.

  The photographing optical system 12 includes a zoom lens 12z, a focus lens 12f, and a diaphragm (for example, iris diaphragm) 12i, and is driven and controlled via motor drivers 62, 64, and 66 according to commands from the CPU 42, respectively. That is, the zoom lens 12z is driven by the motor driver 62 to move back and forth on the photographing optical axis, thereby changing the focal length. The focus lens 12f is driven by the motor driver 64 to move back and forth on the photographing optical axis, thereby changing the imaging position. Further, the aperture 12i is driven by the motor driver 66, and the opening amount changes stepwise, thereby changing the aperture value.

  The CCD 14 is composed of a color CCD having a predetermined color filter array (for example, a Bayer array). Light incident on the light receiving surface of the CCD 14 via the photographing optical system 12 is converted into signal charges of an amount corresponding to the amount of incident light by each photodiode arranged on the light receiving surface. The signal charges accumulated in each photodiode are read out in accordance with a driving pulse applied via a timing generator (TG) 16 and a CCD driver 17 and sequentially output from the CCD 14 as a voltage signal (image signal).

  The CCD 14 includes a shutter gate and a shutter drain, and the signal charges accumulated in each photodiode can be swept out to the shutter drain by applying a shutter gate pulse to the shutter gate. The CPU 42 controls the charge accumulation time (shutter speed) of the signal charge accumulated in each photodiode by controlling the application of the shutter gate pulse to the shutter gate via the TG 16 and the CCD driver 17 (so-called electronic shutter). function).

The analog amplifier 18 is set with an appropriate photographing sensitivity setting gain by the CPU 42 and amplifies image signals sequentially output from the CCD 14 with the set gain. That is, the analog amplifier 18 functions as a means for adjusting the photographing sensitivity. The A / D converter 20 converts the analog image signal output from the analog amplifier 18 into a digital image signal.

  The image input controller 22 includes a buffer memory having a predetermined capacity, accumulates one frame of the image signal output from the A / D converter 20, and stores the image signal in the memory 44.

  As shown in FIG. 2, the image signal processing circuit 24 includes an offset correction circuit 24a, an output data luminance integration circuit 24b, a white balance correction circuit 24c, a gamma conversion circuit 24d, a synchronization processing circuit 24e, and a luminance / color difference signal (YC). A processing circuit 24f and the like are included, and an image signal temporarily stored in the memory 44 is processed in accordance with a command from the CPU 42 to generate a YC signal composed of a luminance signal and a color difference signal.

  That is, the R, G, B image signals (RAW image data) input in a point sequential manner to the image signal processing circuit 24 are offset processed by the offset correction circuit 24a, and then output data luminance integration circuit 24b and white balance correction circuit. 24c. The output data luminance integration circuit 24b calculates the luminance value by integrating the input image signals for one frame for each of R, G, and B, and adding these integrated values at a ratio of 3: 6: 1. The calculated luminance value is used to correct a scene that is underexposed during flash emission, and details thereof will be described later.

  The white balance correction circuit 24c is configured by a digital amplifier, and performs white balance correction by applying a white balance correction gain (WB gain) for each color for each of the R, G, and B image signals. The R, G, B image signals output from the white balance correction circuit 24c are added to the gamma conversion circuit 24d.

  The gamma conversion circuit 24d is configured by a look-up table (LUT) having required input / output characteristics, and performs gamma conversion (gradation conversion) and conversion of the number of bits of an image signal (for example, from 10 bits to 8 bits). Conversion).

  The R, G, and B dot sequential image signals output from the gamma conversion circuit 24d are added to the synchronization processing circuit 24e. The synchronization processing circuit 24e interpolates the spatial deviation of the R, G, B signals associated with the color filter arrangement of the single CCD and performs a process of converting the R, G, B signals into a simultaneous expression and synchronizes them. The R, G, and B signals are output to the YC processing circuit 24f.

  The YC processing circuit 24f converts the R, G, and B signals into a luminance signal Y and color difference signals Cr and Cb, and outputs the luminance signal Y and the color difference signals Cr and Cb (YC signal).

  When a through image is displayed on the image display device 30, images are continuously captured by the CCD 14, and the obtained image signal is continuously processed to generate a YC signal. The generated YC signal is applied to the video encoder 28 via the memory 44, converted into a signal format for display, and output to the image display device 30. As a result, a through image is displayed on the image display device 30.

  When recording an image, the CCD 14 captures an image in response to a shooting command from the shutter release switch 50a, and processes the obtained image signal to generate a YC signal. The generated YC signal is added to the compression / decompression processing circuit 32, converted into predetermined compressed image data (for example, JPEG), and then stored in the recording medium 36 via the media controller 34.

  When the mode switch 50b is switched from the shooting mode to the playback mode, the compressed image data stored in the recording medium 36 is read from the recording medium 36 and converted into an uncompressed YC signal by the compression / decompression processing circuit 32. After that, it is output to the image display device 30 via the video encoder 28. As a result, the image recorded on the recording medium 36 is reproduced and displayed on the image display device 30.

  The AE detection circuit 38 calculates a physical quantity necessary for AE control from the input image signal in accordance with a command from the CPU 42. For example, as a physical quantity necessary for AE control, one screen is divided into a plurality of areas (for example, 8 × 8), and an integrated value of R, G, and B image signals is calculated for each divided area. The CPU 42 detects the brightness of the subject based on the aperture value at the time of metering, the shutter speed and the photographing sensitivity, and the integrated value obtained from the AE detection circuit 38 to obtain the EV value, and the photographing is performed based on the obtained EV value. Sets the hour exposure. This exposure setting method will be described in detail later.

  The AF detection circuit 40 calculates a physical quantity necessary for AF control from the input image signal in accordance with a command from the CPU 42. In the imaging apparatus 10 of the present embodiment, AF control is performed based on image contrast, and the AF detection circuit 40 calculates a focus evaluation value indicating the sharpness of the image from the input image signal. The CPU 42 controls the movement of the focus lens 12f by driving the focus motor 60f via the motor driver 64 so that the focus evaluation value calculated by the AF detection circuit 40 is maximized.

The imaging device 10 of the present embodiment is configured as described above.
[Exposure control]
<First Embodiment>
Next, a first embodiment of the exposure control method in the imaging apparatus 10 of the present embodiment will be described.

  FIG. 3 is a flowchart illustrating an operation at the time of shooting of the imaging apparatus including the exposure control method according to the first embodiment.

  In FIG. 3, when the shutter release switch 50a is pressed in the photographing mode, first, the CPU 42 calculates the integrated value of the image signal taken in via the CCD 14 by the AE circuit 38, and this integrated value and the aperture at the time of photometry. The brightness of the subject is detected based on the value, the shutter speed, and the photographing sensitivity, and a standard exposure value (EV value) is calculated based on the detected brightness of the subject (steps S10 and S12).

  Subsequently, the flash is emitted based on the calculated EV value, a camera shake limit shutter speed, which will be described later, and a flash emission mode (low brightness flash automatic emission mode, flash emission inhibition mode, flash forced emission mode, etc.). It is determined whether or not (step S14).

  The flash light emission mode can be selected on the menu screen of the image display device 30 for performing various settings or by using a dedicated setting switch. When the set flash emission mode is the flash emission inhibition mode, the flash does not emit regardless of the EV value or the like, and conversely, in the flash forced emission mode, the flash always emits light. In the case of the low-brightness flash automatic light emission mode, the EV value decreases, and as a result, the flash is emitted when the shutter speed cannot maintain the camera shake limit shutter speed.

  Here, the camera shake limit shutter speed generally depends on the focal length (35 mm film equivalent) and is defined by 1 / focal length [second]. For example, when the focal length is 60 mm in terms of 35 mm film, 1/60 second is the camera shake limit shutter speed. Therefore, the camera shake limit shutter speed changes according to the change in the focal length accompanying the movement of the zoom lens 12z of the photographing optical system 12.

  If it is determined in step S14 that the flash is emitted, the maximum value of the sensitivity with which the appropriate flash emission amount can be adjusted within the range of the imaging sensitivity that can be adjusted by the imaging device 10 (analog amplifier 18) is determined. (Step S16). In this embodiment, the adjustable sensitivity is in the range of ISO 200 to ISO 1600, and the upper limit at the time of flash emission is ISO 800.

  On the other hand, if it is determined that the flash is not emitted, the maximum sensitivity value that can be adjusted by the imaging device 10 is set as the upper limit value of the imaging sensitivity (step S18). In this embodiment, the upper limit value when no flash is emitted is ISO 1600.

  FIG. 4 shows a program diagram when flash is emitted, and FIG. 5 shows a program diagram when flash is not emitted. It is noted that the focal length is 45 mm (35 mm film equivalent) (that is, the camera shake limit shutter speed is 1/45 seconds).

  As shown in the program diagram of FIG. 4, in order to prevent shooting errors due to camera shake and subject blur, the shutter speed is usually set to a specified shutter speed (lower limit shutter speed) or higher, and the EV value is from 12.5. As the aperture value becomes smaller, the aperture value reaches the minimum value, so that the photographing sensitivity is increased by one step. The lower limit shutter speed is a shutter speed set to a value that is faster by a predetermined step than the camera shake limit shutter speed, and is set to a shutter speed that is, for example, three steps faster than the camera shake limit shutter speed.

When the EV value is smaller than 10.5, the photographing sensitivity reaches the lower limit ISO800 during flash emission, so the shutter speed is set slower than the lower limit shutter speed.
When the shutter speed reaches the camera shake limit shutter speed, this is set as a low-intensity flash emission point P1.

  On the other hand, when the flash is not emitted, as shown in the program diagram of FIG. 5, when the EV value is smaller than 9.5, the photographing sensitivity is set to the upper limit ISO 1600, and only the shutter speed is adjusted according to the EV value. Is done.

  Returning to FIG. 3, when the aperture value, shutter speed, and photographing sensitivity are set according to the program diagram of FIG. 4 or FIG. 5, exposure control is performed according to the set exposure conditions (step S20). That is, the aperture of the aperture 12i, the charge accumulation time (shutter speed) in the CCD 14, and the imaging sensitivity setting gain of the analog amplifier 18 are set. Then, shooting is performed according to the set exposure condition (step S22).

  Further, at the time of flash light emission, the flash light is emitted from the flash light emitting device 52 by a target light emission amount according to a command from the CPU. This flash emission control method uses a preliminary light emission of a predetermined amount of light, detects the amount of light returning from the subject, determines the flash emission amount suitable for shooting the subject, and controls the flash emission time during the main emission. And a method of detecting the amount of light returning from the subject with a light control sensor during flash emission and stopping flash emission when the target amount of light is reached.

The R, G, B image signals (RAW image data) photographed for recording as described above are subjected to various signal processing by the image signal processing circuit 24 shown in FIG. 2 (step S24). Then, it is compressed by the compression / decompression processing circuit 32 and recorded on the recording medium 36 via the media controller 34 (step S26).
<Second Embodiment>
Next, a second embodiment of the exposure control method in the imaging apparatus 10 of the present embodiment will be described.

  FIG. 6 is a flowchart illustrating an operation at the time of shooting of the imaging apparatus including the exposure control method according to the second embodiment. In addition, the same step number is attached | subjected to the part which is common in 1st Embodiment shown in FIG. 3, The detailed description is abbreviate | omitted.

  Compared with the first embodiment shown in FIG. 3, the second embodiment shown in FIG. 6 has steps S30, S32, S34 indicated by broken lines between steps S22 and S24, and The difference is that S36 is added.

  In these steps S30 to S36, for example, when shooting a scene with a long night view by emitting a flash, processing for improving the problem of underexposure without the flash reaching the subject is performed.

  In step S30, R, G, and B image signals (RAW image data) photographed by the output data luminance integration circuit 24b shown in FIG. 2 are integrated to obtain an integrated luminance value.

In step S32, it is determined whether or not the flash is fully emitted. This full light emission determination is performed based on whether or not the flash light emission time T satisfies the following equation.
[Equation 1]
T ≧ T1 + T2
However, T1: Range in which the light emission amount shown in FIG. 10 is uncontrollable
T2: Controllable range of the light emission amount shown in FIG. 10 Note that, as described above, when the flash is fully emitted, it is a case where a scene where the flash does not reach the subject is photographed. become.

  If it is determined in step S32 that the flash is not fully emitted (when the subject distance is within a dimmable range), the process proceeds to step S24. On the other hand, if it is determined that the flash is fully emitted, the process proceeds to step S34.

In step S34, the amplification amount Gain is calculated from the target luminance integrated value Ytarget during flash emission and the luminance integrated value (luminance integrated value of output data after A / D conversion) Yad calculated in step S30 as shown in the following equation. calculate.
[Equation 2]
Gain = Ytarget / Yad
However, when the expression (3) indicating the following conditions is not satisfied, the upper limit value and the lower limit value of the amplification amount Gain are clipped.
[Equation 3]
GAINmin ≤ Gain ≤ GAINmax
However, GAINmin: Lower limit of amplification amount
GAINmax: upper limit value of amplification amount For example, when GAINmin = 1.0 and GAINmax = 2.0, the amplification amount Gain obtained by the equation [2] is clipped as shown in FIG. .

  Subsequently, the white balance correction circuit 24c shown in FIG. 2 is multiplied by the calculated gain Gain for the WB gain set for each of R, G, and B, and the multiplication result is set as the WB gain (step S36). .

Thereby, the upper limit value of the photographing sensitivity is limited at the time of flash emission, and even when a subject to which the flash does not reach becomes dark (underexposure), it can be corrected to be bright.
<Third Embodiment>
Next, a third embodiment of the exposure control method in the imaging apparatus 10 of the present embodiment will be described.

  FIG. 8 is a flowchart showing an operation at the time of shooting of the image pickup apparatus including the exposure control method of the third embodiment. In addition, the same step number is attached | subjected to the part which is common in the flowchart which shows 2nd Embodiment shown in FIG. 6, The detailed description is abbreviate | omitted.

  The third embodiment shown in FIG. 8 is different from the second embodiment shown in FIG. 6 in that step S40 is provided instead of step S36.

  That is, in the second embodiment, the white balance correction circuit 24c formed of a digital amplifier multiplies the R, G, and B image signals by the amplification amount Gain. In the third embodiment, The difference is that the gamma conversion circuit 24d in the image signal processing circuit 24 shown in FIG. 2 multiplies the amplification amount Gain.

  As described above, the gamma conversion circuit 24d is configured by an LUT, and has an input / output characteristic as shown in FIG. 9A, for example, when the amplification amount Gain = 1.

  The gamma conversion circuit 24d has a gamma curve gamma conversion table (reference gamma conversion table) as shown in FIG. 9A. In this conversion table, 10-bit image data is converted into 8-bit data. Is also converted into image data.

  When the amplification amount Gain is Gain> 1, the amplification amount Gain is multiplied by the amplification amount Gain by the conversion value of the reference gamma conversion table shown in FIG. 9A, and the amplification amount Gain is reflected. Create a conversion table. The gamma conversion table created in this way is set in the gamma conversion circuit 24d.

  FIG. 9B shows the input / output characteristics of the gamma conversion table created when the amplification amount Gain = 2. As shown in the figure, when the converted value multiplied by the amplification amount Gain exceeds 255 (the maximum value of 8 bits), it is clipped to 255.

  Accordingly, an image signal amplified by the amplification amount Gain is generated at the time of signal processing (gamma conversion) in step S24.

  In the image pickup apparatus 10 of the above embodiment, the EV value is obtained based on the image signal obtained from the CCD 14, but the method for obtaining the EV value is not limited to this, and other photometric sensors. Etc., the EV value may be obtained.

  Further, the present invention is not limited to the exposure control by the program diagrams shown in FIGS. 4 and 5, and the range of the photographing sensitivity that can be further adjusted is not limited to this embodiment.

FIG. 1 is a block diagram illustrating a configuration of the imaging apparatus. FIG. 2 is a block diagram showing the internal configuration of the image signal processing circuit. FIG. 3 is a flowchart illustrating an operation at the time of shooting of the imaging apparatus including the exposure control method according to the first embodiment. FIG. 4 is a diagram showing an example of a program diagram during flash emission. FIG. 5 is a diagram showing an example of a program diagram when no flash is emitted. FIG. 6 is a flowchart illustrating an operation at the time of shooting of the imaging apparatus including the exposure control method according to the second embodiment. FIG. 7 is a chart used for explaining the clipping processing of the upper limit value and the lower limit value of the calculated amplification amount Gain. FIG. 8 is a flowchart showing an operation at the time of shooting of the image pickup apparatus including the exposure control method of the third embodiment. FIG. 9 is a diagram used for explaining an example of changing the gamma conversion table according to the amplification amount Gain. FIG. 10 is a graph showing the relationship between the flash emission time of the flash emitted from the flash light emitting device and the light emission amount.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Imaging device, 12 ... Imaging optical system, 14 ... CCD, 16 ... Timing generator (TG), 18 ... Analog amplifier, 20 ... A / D converter, 22 ... Image input controller, 24 ... Image signal processing circuit, 24b ... Output data luminance integration circuit, 24c ... White balance correction circuit, 24d ... Gamma conversion circuit, 28 ... Video encoder, 30 ... Image display device, 32 ... Compression / decompression processing circuit, 34 ... Media controller, 36 ... Recording medium, 38 ... AE detection circuit, 40 ... AF detection circuit, 42 ... Central processing unit (CPU), 44 ... Memory, 50a ... Shutter release switch, 52 ... Flash light emitting device

Claims (13)

In the exposure control method of controlling the exposure by adjusting the aperture value, shutter speed and photographing sensitivity, and controlling the exposure by adjusting the flash emission amount at the time of flash emission,
The upper limit of sensitivity when adjusting the shooting sensitivity is the maximum value within the adjustable range of the shooting sensitivity when the flash is not flashing.
An exposure control method characterized by setting a maximum value of sensitivity that is smaller than the maximum value during flash light emission and that can appropriately adjust the flash light emission amount.   2. The exposure control method according to claim 1, wherein the maximum value of the adjustable range of the photographing sensitivity is ISO1600, and the maximum value of the sensitivity capable of adjusting the appropriate flash light emission amount is ISO800. Determine whether the flash emission amount reached the maximum at the time of flash emission,
2. The exposure control method according to claim 1, wherein when the flash light emission amount reaches a maximum, the image signal acquired at the time of flash light emission is amplified by a predetermined amplification amount.   The exposure control method according to claim 3, wherein the predetermined amplification amount is calculated from a preset target integrated value and an integrated value obtained by integrating image signals acquired at the time of flash emission.   5. The exposure control method according to claim 3, wherein the amplification of the image signal by the predetermined amplification amount is performed together with white balance correction by a white balance correction unit that performs white balance correction.   5. The exposure control method according to claim 3, wherein the amplification of the image signal by the predetermined amplification amount is performed together with the gradation conversion by a gradation conversion unit that performs predetermined gradation conversion. Flash light emitting means;
Light control means for adjusting the amount of flash light emitted from the flash light emitting means;
A metering means for metering the brightness of the subject;
Calculation means for calculating an exposure value based on the brightness of the subject measured by the photometry means;
Exposure control for controlling exposure by adjusting the aperture value, shutter speed and photographing sensitivity based on the calculated exposure value, and controlling exposure by adjusting the amount of flash emission via the light control means during flash emission Means, and
The exposure control means sets the upper limit of sensitivity when adjusting the photographing sensitivity to the maximum value within the adjustable range of the photographing sensitivity when emitting flash from the flash light emitting means, and sets the flash from the flash light emitting means. An exposure control device characterized in that when the light is not emitted, the exposure control device is set to a value smaller than the maximum value and a sensitivity maximum value capable of appropriately adjusting the flash light emission amount by the light control means.   The exposure control means defines, as a lower limit shutter speed, a shutter speed that is a predetermined speed faster than a camera shake limit shutter speed when determining an aperture value, a shutter speed, and a photographing sensitivity based on the calculated exposure value. The aperture value, shutter speed, and shooting sensitivity are set so that the speed is equal to or higher than the lower limit shutter speed. When the aperture value reaches the minimum value and the shooting sensitivity reaches the maximum value, the shutter speed is set to the lower limit shutter speed. The exposure control device according to claim 7, wherein the exposure control device can be set later.   9. The exposure control apparatus according to claim 8, wherein the exposure control means causes the flash light emission means to emit a flash when the shutter speed reaches a camera shake limit shutter speed in the low brightness flash light emission mode. An exposure control device according to any one of claims 7 to 9,
Imaging means for acquiring an image signal in a state in which exposure is controlled by the exposure control device;
Signal processing means for performing signal processing on the image signal acquired by the imaging means;
A discriminating means for discriminating whether or not the flash light emission amount reaches a maximum when the flash is emitted from the flash light emitting means;
Control means for amplifying the image signal acquired at the time of flash emission by a predetermined amplification amount in the signal processing means when it is determined that the flash emission amount has reached the maximum;
An imaging apparatus comprising:   An integrated value calculating means for calculating an integrated value by integrating the image signals acquired at the time of flash emission, and the control means is based on a preset target integrated value and the integrated value calculated by the integrated value calculating means; The imaging apparatus according to claim 10, wherein the predetermined amplification amount is determined.   12. The imaging according to claim 10, wherein the signal processing unit includes a white balance correction unit, and the control unit adds the predetermined amplification amount to a white balance correction value in the white balance correction unit. apparatus.   12. The imaging apparatus according to claim 10, wherein the signal processing unit includes a gradation conversion unit, and the control unit adds the predetermined amplification amount to an input / output characteristic of the gradation conversion unit. .

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