JP5013954B2 - Imaging device - Google Patents

Description

  The present invention relates to an imaging apparatus such as a digital camera, and more particularly to an imaging apparatus having a bracket shooting function.

  Recent digital cameras have a function of automatically controlling various shooting conditions. For example, an auto exposure adjustment function (auto iris function) that automatically sets an optimal exposure amount, an auto white balance function that automatically adjusts white balance, an auto focus function that automatically adjusts focus, and the like are provided.

  Such automatic control is very convenient, but shooting by the automatic control does not always result in shooting as intended by the photographer. For example, an automatically set exposure amount may result in an image that is too bright or too dark than the photographer intended. In order to cope with such a problem, bracket shooting for shooting a plurality of still images while gradually changing shooting conditions such as exposure conditions has been put into practical use.

  In bracket shooting, after the optimum control value is determined by automatic control at the time of shooting the first image, shooting is performed by changing the control value to the plus side and the minus side around the optimum control value. By using bracket shooting, it is possible to acquire an image under shooting conditions that match the photographer's intention.

  However, although conventional bracket photography is suitable for changing the contrast of an image, it cannot be said that it is suitable for photographing a moving subject. That is, in bracket shooting, the optimal timing of a moving subject may not be captured.

  A continuous shooting function is used to capture the optimal timing of a moving subject. In continuous shooting, an optimum control value is usually determined at the time of shooting the first image, and the optimum control value is applied to the shooting of the second and subsequent images to perform high-speed continuous shooting. By using this continuous shooting, it is possible to capture the optimal timing of a moving subject without missing a so-called shutter chance. However, continuous shooting with a fixed control value cannot cope with the problem that bracket shooting tries to solve.

  Patent Document 1 below discloses a method related to exposure correction during bracket photography. In this method, an appropriate exposure value is obtained based on the brightness of the subject, and the first image is taken with the appropriate exposure value. Thereafter, it is determined whether or not the appropriate exposure value is appropriate based on the shooting result of the first image, and the second and subsequent images are shot based on the determination result.

JP 2004-245923 A

  SUMMARY An advantage of some aspects of the invention is that it provides an image pickup apparatus that supports image acquisition under shooting conditions in accordance with a photographer's intention without missing a photo opportunity.

  An imaging apparatus according to the present invention includes a continuous bracket imaging unit that performs bracket imaging continuously for a plurality of cycles in an imaging apparatus that performs bracket imaging in which a predetermined number of imaging operations are performed while changing a predetermined type of imaging condition. It is characterized by that.

  By executing bracket shooting continuously for a plurality of cycles, it is possible to receive both the benefits of bracket shooting and the benefits of continuous shooting. That is, for example, it is possible to acquire an image under shooting conditions in accordance with a photographer's intention without missing an optimal shutter chance.

  And, for example, the continuous bracket photographing means determines the photographing condition for bracket photographing in the target cycle in the second cycle and later, in consideration of the image characteristics of each photographed image acquired in the past cycle of the target cycle. To do.

  More specifically, for example, the imaging apparatus includes an evaluation value deriving unit that derives a luminance evaluation value corresponding to the brightness of each captured image, and the predetermined type of imaging condition is an exposure condition, and the continuous The bracket photographing means determines the photographing condition for the bracket photographing in the target cycle after the second cycle in consideration of the luminance evaluation value in the past cycle of the target cycle.

  Thereby, it is possible to control the exposure condition to have continuity. For example, it is possible to obtain a series of images having smooth image changes that follow changes in illumination and composition.

  As a specific configuration, for example, in one bracket shooting, the reference shooting for shooting under the reference exposure condition, the plus correction shooting with the exposure amount larger than the reference exposure condition, and the exposure amount than the reference exposure condition. The continuous bracket photographing means compares the average luminance evaluation value for the past one cycle of the target cycle with the luminance evaluation value for the reference photographing in the past one cycle, In consideration of the comparison result, the shooting condition for bracket shooting of the target cycle is determined.

  As a specific configuration, for example, in one bracket shooting, the reference shooting for shooting under the reference exposure condition, the plus correction shooting with the exposure amount larger than the reference exposure condition, and the exposure amount than the reference exposure condition. The continuous bracket photographing means compares the average luminance evaluation value for the past one cycle of the target cycle with the luminance evaluation value for the reference photographing in the past one cycle, If the difference between the former and the latter is greater than a predetermined threshold, the reference exposure condition is corrected in a direction to reduce the change in the former with respect to the latter, and the corrected reference exposure condition is applied to the target cycle. When the difference is smaller than the threshold, the reference exposure condition for the past cycle is also applied to the target cycle.

  In addition, for example, one bracket shooting includes a reference shooting in which shooting is performed under the reference shooting conditions, a plus correction shooting in which shooting conditions are changed by the bracket width in opposite directions around the reference shooting conditions, and minus shooting. The continuous bracket photographing means includes an evaluation means for evaluating the suitability of the bracket width applied to the bracket photographing from image characteristics of each photographed image in one bracket photographing, and a second cycle. Bracket width setting means for determining the bracket width for bracket shooting in the subsequent focus cycle based on the evaluation result of the evaluation means for the past cycle of the focus cycle.

  Thereby, the bracket width can be adjusted in a better direction.

  Further, for example, the predetermined type of shooting condition is an exposure condition, and one bracket shooting is performed by a reference shooting for shooting under a reference exposure condition and a bracket width set by the reference exposure condition. Including a positive correction shooting with a large amount and a negative correction shooting in which the exposure amount is smaller by the bracket width than the reference exposure condition, and a captured image by the reference shooting, a captured image by the positive correction shooting, and the negative correction shooting. , The continuous bracket photographing means sets each cycle as an evaluation cycle, and the bracket exposure in the evaluation cycle is the reference exposure image of the reference exposure image, the positive exposure image, the positive correction image, and the negative correction image, respectively. Luminance histogram of dark area, luminance histogram of dark area of the positive correction image, and reference exposure image Evaluation means for evaluating the suitability of the bracket width applied to bracket shooting in the evaluation cycle based on the brightness histogram of the bright area and the brightness histogram of the bright area of the minus correction image, and the second cycle Bracket width setting means for determining the bracket width for bracket shooting in the subsequent focus cycle based on the evaluation result of the evaluation means for the past cycle of the focus cycle.

  Thereby, the bracket width can be adjusted in a better direction.

  Specifically, for example, the evaluation unit includes a first luminance difference between a mode value and a maximum luminance value in a luminance histogram of a bright area of the reference exposure image, and a luminance histogram of a bright area of the minus correction image. While comparing the second luminance difference between the mode value and the maximum luminance value, the third luminance difference between the mode value and the minimum luminance value in the luminance histogram of the dark area of the reference exposure image, and the positive correction image The fourth luminance difference between the mode value and the minimum luminance value in the luminance histogram of the dark area is compared, and the suitability of the bracket width is evaluated based on the comparison result.

  And, for example, the continuous bracket photographing means sets the exposure amount for the reference photographing of the target cycle in consideration of the first to fourth luminance differences when the past cycle of the target cycle is the evaluation cycle. .

  Thereby, the exposure amount can be adjusted in a better direction.

  According to the present invention, it is possible to support image acquisition under shooting conditions in accordance with a photographer's intention without missing a photo opportunity.

  The significance or effect of the present invention will become more apparent from the following description of embodiments. However, the following embodiment is merely one embodiment of the present invention, and the meaning of the term of the present invention or each constituent element is not limited to that described in the following embodiment. .

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. In each of the drawings to be referred to, the same part is denoted by the same reference numeral, and redundant description regarding the same part is omitted in principle. The first to fourth embodiments will be described later. First, matters that are common to each embodiment or items that are referred to in each embodiment will be described.

  FIG. 1 is an overall block diagram of an imaging apparatus 1 according to an embodiment of the present invention. The imaging device 1 is a digital video camera that can capture moving images and still images. However, the imaging device 1 may be a digital still camera that can capture only still images. As shown in FIG. 1, the imaging device 1 includes each part referred to by reference numerals 11 to 28.

  Each part in the imaging apparatus 1 exchanges signals (data) between the parts via the bus 24 or 25. The TG 22 generates a timing control signal for controlling the timing of each operation in the entire imaging apparatus 1, and provides the generated timing control signal to each unit in the imaging apparatus 1. The timing control signal includes a vertical synchronization signal Vsync and a horizontal synchronization signal Hsync.

  The CPU 23 comprehensively controls the operation of each unit in the imaging apparatus 1. The operation unit 26 receives an operation by a user. The operation unit 26 includes a recording button 26a, a shutter button 26b, an operation key 26c, and the like. The operation content given to the operation unit 26 is transmitted to the CPU 23. The SDRAM 17 functions as a frame memory. Each unit in the imaging apparatus 1 temporarily records various data (digital signals) in the SDRAM 17 during signal processing as necessary. The memory card 18 is an external recording medium, for example, an SD (Secure Digital) memory card. In this embodiment, the memory card 18 is illustrated as an external recording medium. However, the external recording medium is composed of one or a plurality of randomly accessible recording media (semiconductor memory, memory card, optical disk, magnetic disk, etc.). can do.

  FIG. 2 is an internal configuration diagram of the imaging unit 11 of FIG. By using a color filter or the like for the imaging unit 11, the imaging device 1 is configured to generate a color image by shooting.

  The imaging unit 11 includes an optical system 35, a diaphragm 32, an imaging element 33, and a driver 34. The optical system 35 includes a plurality of lenses including the zoom lens 30 and the focus lens 31. The zoom lens 30 and the focus lens 31 are movable in the optical axis direction. The driver 34 controls the movement of the zoom lens 30 and the focus lens 31 based on the control signal from the CPU 23, and controls the zoom magnification and focal length of the optical system 35. The driver 34 controls the opening degree (aperture value) of the diaphragm 32 based on a control signal from the CPU 23.

  Incident light from the subject enters the image sensor 33 through the lenses and the diaphragm 32 constituting the optical system 35. Each lens constituting the optical system 35 forms an optical image of the subject on the image sensor 33. The TG 22 generates a drive pulse for driving the image sensor 33 in synchronization with the timing control signal, and applies the drive pulse to the image sensor 33.

  The image pickup device 33 is composed of, for example, a CCD (Charge Coupled Devices) image sensor, a CMOS (Complementary Metal Oxide Semiconductor) image sensor, or the like. The image sensor 33 photoelectrically converts an optical image incident through the optical system 35 and the diaphragm 32 and outputs an electrical signal obtained by the photoelectric conversion to the AFE 12. More specifically, the imaging device 33 includes a plurality of pixels (light receiving pixels; not shown) that are two-dimensionally arranged in a matrix, and in each photographing, each pixel receives a signal charge having a charge amount corresponding to the exposure time. store. The electrical signal from each pixel having a magnitude proportional to the amount of the stored signal charge is sequentially output to the subsequent AFE 12 in accordance with the drive pulse from the TG 22.

  The AFE 12 amplifies the analog signal output from the imaging unit 11 (image sensor 33), and converts the amplified analog signal into a digital signal. The AFE 12 sequentially outputs the digital signals to the video signal processing unit 13.

  The video signal processing unit 13 generates a video signal representing an image captured by the imaging unit 11 (hereinafter also referred to as “captured image”) based on the output signal of the AFE 12. The video signal is composed of a luminance signal Y representing the luminance of the photographed image and color difference signals U and V representing the color of the photographed image. The video signal generated by the video signal processing unit 13 is sent to the compression processing unit 16 and the video output circuit 20.

  Further, the video signal processing unit 13 detects an AF evaluation value according to the contrast amount in the focus detection area in the captured image and an AE evaluation value (luminance evaluation value) according to the brightness of the captured image, and these are detected by the CPU 23. To communicate. The CPU 23 adjusts the position of the focus lens 31 via the driver 34 in FIG. 2 according to the AF evaluation value, thereby forming an optical image of the subject on the image sensor 33. Further, the CPU 23 adjusts the opening degree of the diaphragm 32 (and the amplification degree of signal amplification in the AFE 12 as necessary) via the driver 34 of FIG. 2 according to the AE evaluation value, so that the received light amount (brightness of the image). Control).

  The microphone 14 converts audio (sound) given from the outside into an analog audio signal and outputs the analog audio signal. The audio signal processing unit 15 converts an analog audio signal output from the microphone 14 into a digital audio signal. This digital audio signal is sent to the compression processing unit 16.

  The compression processing unit 16 compresses the video signal from the video signal processing unit 13 using a predetermined compression method. At the time of capturing and recording a moving image or a still image, the compressed video signal is sent to the memory card 18 and recorded on the memory card 18. The compression processing unit 16 compresses the audio signal from the audio signal processing unit 15 using a predetermined compression method. At the time of shooting and recording a moving image, the video signal from the video signal processing unit 13 and the audio signal from the audio signal processing unit 15 are compressed in the compression processing unit 16 while being temporally related to each other, and after compression, Is recorded in the memory card 18.

  The operation mode of the imaging apparatus 1 includes a shooting mode capable of shooting and recording a moving image or a still image, and a playback mode for reproducing and displaying the moving image or the still image stored in the memory card 18 on the display unit 27. included. Transition between the modes is performed according to the operation on the operation key 26c. In accordance with an operation on the recording button 26a, shooting and recording of moving images are started or ended. Further, a still image is taken and recorded in accordance with an operation on the shutter button 26b.

  In the shooting mode, shooting is sequentially performed at a predetermined frame period (for example, 1/60 seconds). When the user presses the recording button 26a in the shooting mode, under the control of the CPU 23, the video signal of each frame after the pressing and the corresponding audio signal are sequentially recorded on the memory card 18 via the compression processing unit 16. Is done. When the recording button 26a is pressed again, the moving image shooting ends. That is, the recording of the video signal and the audio signal to the memory card 18 is completed, and the shooting of one moving image is completed.

  In the shooting mode, when the user presses the shutter button 26b, a still image is shot. Specifically, under the control of the CPU 23, the video signal of one frame after being pressed is recorded on the memory card 18 via the compression processing unit 16 as a video signal representing a still image.

  In the playback mode, when the user performs a predetermined operation on the operation key 26 c, a compressed video signal representing a moving image or a still image recorded on the memory card 18 is sent to the expansion processing unit 19. The decompression processing unit 19 decompresses the received video signal and sends it to the video output circuit 20. In the shooting mode, even if the recording button 26a or the shutter button 26b is not pressed, a shot image is acquired at a predetermined frame period (for example, a 1/60 second period). This captured image is particularly referred to as a through image. In the shooting mode, a video signal of a through image is sequentially sent to the video output circuit 20 so as to perform a so-called preview.

  The video output circuit 20 converts a given digital video signal into a video signal (for example, an analog video signal) in a format that can be displayed on the display unit 27 and outputs the video signal. The display unit 27 is a display device such as a liquid crystal display, and displays an image corresponding to the video signal output from the video output circuit 20.

  In addition, when a moving image is reproduced in the reproduction mode, a compressed audio signal corresponding to the moving image recorded on the memory card 18 is also sent to the expansion processing unit 19. The decompression processing unit 19 decompresses the received audio signal and sends it to the audio output circuit 21. The audio output circuit 21 converts a given digital audio signal into an audio signal in a format that can be output by the speaker 28 (for example, an analog audio signal) and outputs the audio signal to the speaker 28. The speaker 28 outputs the sound signal from the sound output circuit 21 to the outside as sound (sound).

  By the way, the imaging device 1 can execute bracket shooting. As is generally known, bracket shooting is shooting in which a predetermined number of shootings are continuously performed while changing predetermined types of shooting conditions. In the present embodiment, for the sake of concrete explanation, the case where the photographing condition to be changed is the exposure condition is handled. The imaging apparatus 1 can execute continuous bracket shooting in which one bracket shooting is set as a unit cycle and bracket shooting is repeated a plurality of cycles continuously.

  FIG. 3 shows a conceptual diagram of continuous bracket shooting. In the present embodiment, it is assumed that one bracket shooting, that is, one cycle of bracket shooting, is formed from three shootings (three still image shootings). In FIG. 3, three still images with a reference numeral 201 are a group of images captured by bracket shooting in the first cycle, and three still images with a reference numeral 202 are bracketed in the second cycle. Is a group of images taken by bracket photography in the third cycle, and three still images attached by reference numeral 204. It is the image group image | photographed by bracket photography of the 4th cycle. When an operation for instructing execution of continuous bracket shooting is performed on the operation unit 26 in FIG. 1, bracket shooting for the first cycle is performed first, and then bracket shooting for the second, third, fourth, and so on is performed. Are executed sequentially.

  For bracket photography, the first cycle, the second cycle, the third cycle,... Are also referred to as the first cycle, the second cycle, the third cycle,.

  Below, the 1st-4th Example is described as a concrete Example regarding continuous bracket photography. The matter described in one embodiment is applicable to other embodiments as long as there is no contradiction. The following description is an explanation of the operation in the shooting mode unless otherwise specified.

<< First Example >>
First, a first embodiment relating to continuous bracket shooting will be described. FIG. 4 shows a partial block diagram of the image pickup apparatus 1 involved in continuous bracket shooting according to the first embodiment. For example, the AE evaluation unit 41 is mounted in the video signal processing unit 13 in FIG. 1, and the exposure control unit 42 is mounted in the CPU 23 in FIG. Although not specifically shown in FIG. 4, the function of each part (such as the imaging unit 11) of the imaging device 1 is naturally used when executing continuous bracket imaging.

  The AE evaluation unit 41 is given a luminance signal for each captured image. The AE evaluation unit 41 calculates an AE evaluation value (luminance evaluation value) corresponding to the brightness of the captured image. For example, the average value (or integrated value) of the luminance values of each pixel located in a predetermined AE evaluation area of the focused image is calculated, and the average value is used as the AE evaluation value of the focused image. The AE evaluation area is a predetermined rectangular area set in the captured image or the entire area of the captured image. The luminance value is the value of the luminance signal. For a certain pixel, the brightness of the pixel increases as the luminance value increases. The AE evaluation value is calculated for each captured image, and the calculated AE evaluation value is sequentially transmitted to the exposure control unit 42.

  Based on the received AE evaluation value, the exposure control unit 42 performs exposure control (that is, control of exposure conditions) for controlling the exposure amount in the next and subsequent shootings. The exposure control includes control over the shutter speed in the electronic shutter, control over the aperture (aperture value) of the diaphragm 32, and control over the sensitivity of the image capture (the degree of signal amplification in the AFE 12 or the video signal processing unit 13). The shutter speed in the electronic shutter (hereinafter simply referred to as shutter speed) is represented by the exposure time for each pixel of the image sensor 33 in FIG. An exposure control signal for realizing exposure control is transmitted to the imaging unit 11 and the like. In a certain shooting, if the exposure time or the aperture of the diaphragm 32 is increased, the exposure amount for the shooting is increased, and if the exposure time or the opening of the aperture 32 is decreased, the exposure amount for the shooting is decreased. Note that the exposure amount is generally expressed as an exposure value (therefore, the exposure amount can also be read as an exposure value).

  FIG. 18 shows a conceptual diagram of one bracket shooting (that is, bracket shooting for one cycle). One bracket shooting includes a reference exposure shooting for shooting under a standard exposure condition, a positive correction shooting with a larger exposure amount than the reference exposure shooting, and a negative correction shooting with a smaller exposure amount than the reference exposure shooting. . The exposure amount in the reference exposure shooting is referred to as a reference exposure amount, and the reference exposure amount is defined by the reference exposure condition. The captured image acquired by reference exposure shooting, the captured image acquired by plus correction shooting, and the captured image acquired by minus correction shooting are referred to as a reference exposure image, a plus correction image, and a minus correction image, respectively. Each captured image acquired by continuous bracket shooting is stored in the memory card 18 of FIG.

  In the present embodiment, as described above, it is assumed that one bracket shooting is formed from three shootings (three still image shootings). For this reason, one bracket shooting is formed by one reference exposure shooting, one plus correction shooting, and one minus correction shooting. The exposure amount in plus correction shooting is increased by an amount corresponding to a predetermined bracket width from the reference exposure amount, and the exposure amount in minus correction shooting is decreased by an amount corresponding to the bracket width from the reference exposure amount.

  In the following description including all the embodiments, for convenience of explanation, the shutter speed (exposure time) is controlled in order to control the exposure amount of the plus correction shooting and the minus correction shooting around the exposure amount of the reference exposure shooting. And Of course, in order to control the exposure amount, the aperture value may be controlled instead of the shutter speed.

  With reference to FIG. 5, the operation | movement procedure of continuous bracket imaging | photography concerning 1st Example is demonstrated. FIG. 5 is a flowchart showing this operation procedure.

  When it is detected that the shutter button 26b (see FIG. 1) is pressed in the shooting mode, execution of each process in FIG. 5 is started. First, processing such as initialization of necessary variables is performed in step S11, and an AE evaluation value for the latest through image is acquired in step S12. Subsequently, in step S13, the exposure control unit 42 determines an appropriate exposure condition (that is, an appropriate aperture value and an appropriate shutter speed) based on the AE evaluation value acquired in step S12. For example, an aperture value and a shutter speed that should be set to set the AE evaluation value to a desired value are calculated as an appropriate aperture value and an appropriate shutter speed. In this embodiment, the latest appropriate exposure condition determined in step S13 is set as the reference exposure condition.

  Then, after the actual aperture value is controlled to an appropriate aperture value in accordance with the exposure control signal from the exposure control unit 42, the reference exposure shooting based on the reference exposure condition is performed in step S14, and the plus correction shooting is performed in the subsequent step S15. In step S16, minus correction photography is performed. The exposure time in the plus correction shooting is longer than the exposure time in the reference exposure shooting by a time corresponding to a predetermined bracket width, and the exposure time in the minus correction shooting is equivalent to the bracket width than the exposure time in the reference exposure shooting. It is shortened by the time to do. As a result, the exposure amount for plus-correction shooting is increased by an amount corresponding to the bracket width than that for reference exposure shooting, and the exposure amount for minus-correction shooting is only an amount corresponding to the bracket width than that for reference exposure shooting. Less.

  One cycle of bracket photographing is performed in one process of steps S14 to S16. After the minus correction photographing is performed in step S16, the process proceeds to step S17, and the CPU 23 confirms whether the shutter button 26b is kept depressed. If the shutter button 26b is depressed in step S17, the process returns to step S12, and bracket shooting consisting of steps S12 to S16 is executed again. That is, the bracket shooting of the next cycle is executed. If the shutter button 26b has not been depressed, the processing in FIG. 5 is terminated. The operation of continuously depressing the shutter button 26b corresponds to an operation of instructing continuous execution of continuous bracket shooting.

  By performing the processing as described above, continuous bracket shooting is executed for a cycle corresponding to a period during which the shutter button 26b is pressed.

  Originally, bracket photographing is an effective photographing technique when it is difficult to set optimum photographing conditions by automatic control, or when the photographing conditions desired by the photographer cannot be met by automatic control. However, since the conventional bracket shooting is only one cycle shooting, the optimal timing of a moving subject may not be captured. A continuous shooting function is prepared to capture the optimal timing of a moving subject, but it is difficult to avoid the problem that bracket shooting is trying to solve with the normal continuous shooting function. In continuous bracket photography taking these into account, it is possible to enjoy both the benefits of bracket photography and the benefits of continuous photography. That is, for example, it is possible to acquire an image according to the shooting conditions intended by the photographer without missing an optimal shutter chance.

<< Second Example >>
In the first embodiment described above, since the reference exposure condition is set independently for each cycle, the exposure amount may vary greatly between cycles. An example of this situation is shown in FIG. In the example shown in FIG. 6, there is a large gap in the exposure amount due to a change in illumination or a change in composition between the second cycle and the third cycle. The imaging apparatus 1 itself sets an exposure amount that is considered optimal in each cycle, but the imaging apparatus 1 cannot know where the exposure amount that the photographer really wants is. It is also assumed that there is an exposure amount that the photographer really wants between the exposure amounts of the second and third cycles in FIG.

  Further, when the exposure amount is suddenly changed, an abrupt image change occurs in a series of photographed image groups by continuous bracket photography. In continuous shooting, smooth image changes are required, and continuous bracket shooting also has the aspect of continuous shooting. Therefore, it is preferable that exposure adjustment is continuous even in continuous bracket shooting.

  A second embodiment will be described as an embodiment considering the continuity of exposure adjustment. A partial block diagram of the image pickup apparatus 1 involved in continuous bracket shooting according to the second embodiment is the same as that according to the first embodiment (that is, FIG. 4).

  With reference to FIG. 7, the operation | movement procedure of continuous bracket imaging | photography concerning 2nd Example is demonstrated. FIG. 7 is a flowchart showing this operation procedure.

  By detecting that the shutter button 26b (see FIG. 1) is pressed in the shooting mode, execution of each process in FIG. 7 is started. First, processing such as initialization of necessary variables is performed in step S21, and an AE evaluation value for the latest through image is acquired in step S22. Subsequently, in step S23, the exposure control unit 42 determines an appropriate exposure condition (that is, an appropriate aperture value and an appropriate shutter speed) based on the AE evaluation value acquired in step S22. The proper exposure condition determined here is set as the reference exposure condition for the first cycle.

  Then, after the actual aperture value is controlled to an appropriate aperture value in accordance with the exposure control signal from the exposure control unit 42, the reference exposure shooting based on the reference exposure condition is performed in step S24, and the plus correction shooting is performed in the subsequent step S25. In step S26, minus correction photography is performed. The exposure time in the plus correction shooting is longer than the exposure time in the reference exposure shooting by a time corresponding to a predetermined bracket width, and the exposure time in the minus correction shooting is equivalent to the bracket width than the exposure time in the reference exposure shooting. It is shortened by the time to do.

  The standard exposure condition in the first cycle matches the appropriate exposure condition determined in step S23, and the standard exposure amount applied to the standard exposure shooting in the first cycle is the exposure amount according to the proper exposure condition. However, the reference exposure conditions in the second and subsequent cycles can be corrected from the appropriate exposure conditions determined in step S23 (see step S30 or S32 described later).

  Further, the exposure control unit 42 introduces variables V [0], V [1], and V [2]. Then, the AE evaluation value of the reference exposure image acquired in the latest reference exposure shooting is substituted into the variable V [0] (step S24), and the AE evaluation value of the plus correction image acquired in the latest plus correction shooting. Is substituted into the variable V [1] (step S25), and the AE evaluation value of the minus correction image acquired in the latest minus correction photographing is substituted into the variable V [2] (step S26).

  After the process of step S26, the process proceeds to step S27, and the CPU 23 confirms whether the shutter button 26b remains depressed. If the shutter button 26b is not depressed, the process of FIG. 7 is terminated. If the shutter button 26b is depressed, the process proceeds to step S28.

  In steps S28 to S32, a reference exposure condition for the next cycle is set based on the AE evaluation value for one cycle. Steps S28 to S32 are executed by the exposure control unit 42 in FIG. The outline of the setting process will be described with reference to FIG. FIG. 8 is a diagram for explaining the concept of the setting process.

  Since the bracket width for the plus-correction shooting and the minus-correction shooting centering on the reference exposure shooting is the same, if there is no change in the illumination state and the shooting composition around the imaging device 1, the AE evaluation value V [ 1] and the average value of the AE evaluation value V [2] of the negative correction image substantially coincide with the AE evaluation value V [0] of the reference exposure image. If there is a change in illumination or composition during one bracket shooting, a change occurs in the relationship of the AE evaluation values.

  For example, after the reference exposure shooting and the plus correction shooting are performed, when the illumination brightness increases when the minus correction shooting is performed, the AE evaluation value V [2] of the minus correction image is larger than the assumed value, and V [1 ] And V [2] have an average value larger than V [0]. When the image becomes bright due to an increase in illumination brightness or the like, the exposure amount should be corrected to the minus side (that is, the image becomes darker) in order to return to an appropriate exposure in the next shooting. Although the case where the image becomes bright due to an increase in illumination brightness or the like is illustrated, the case where the image becomes dark should be dealt with similarly.

  In order to realize such a correction, “V [0] − (V [1] + V [2]) / 2” is compared with a predetermined threshold value.

Specifically, in step S28, it is determined whether the following formula (1) is satisfied. The threshold value TH1 is a negative predetermined value (see also FIG. 8). If the expression (1) is satisfied, the process proceeds to step S30, the reference exposure amount applied in the reference exposure shooting of the current cycle is decreased by a predetermined amount α, and the process returns to step S24. The reference exposure amount after the reduction is applied to the reference exposure shooting in the next cycle. When the control over the exposure amount is realized by the control over the exposure time, the exposure time applied to the reference exposure shooting in the current cycle is corrected to be shortened by an amount corresponding to α, and the exposure time after the shortening correction is performed. Is applied to the reference exposure shooting of the next cycle. If the exposure time applied to the reference exposure shooting in the next cycle is shortened, of course, the exposure time for plus correction shooting and minus correction shooting in the next cycle is also corrected. If equation (1) is not satisfied, the process proceeds to step S29.
V [0] − (V [1] + V [2]) / 2 <TH1 (1)

In step S29, it is determined whether the following formula (2) is satisfied. The threshold value TH2 is a positive predetermined value (see also FIG. 8). If the expression (2) is satisfied, the process proceeds to step S32, the reference exposure amount applied in the reference exposure shooting of the current cycle is increased by a predetermined amount α, and the process returns to step S24. The increased reference exposure amount is applied to reference exposure shooting in the next cycle. When the control over the exposure amount is realized by the control over the exposure time, the exposure time applied to the reference exposure shooting of the current cycle is corrected so as to increase by an amount corresponding to α, and the exposure time after the increase correction Is applied to the reference exposure shooting of the next cycle. If the exposure time applied to the reference exposure shooting of the next cycle increases, of course, the exposure time of the plus correction shooting and the minus correction shooting in the next cycle is also increased and corrected.
V [0] − (V [1] + V [2]) / 2> TH2 (2)

  If the expression (2) is not satisfied in step S29, the reference exposure amount applied in the reference exposure shooting of the current cycle is not changed (step S31), and the process returns to step S24. Therefore, in this case, the exposure time applied to the reference exposure shooting of the current cycle is applied to the reference exposure shooting of the next cycle as it is.

As shown in the following formula (3), “V [0] − (V [1] + V [2]) / 2” is the average value of the AE evaluation values for one cycle and the standard of the cycle. Since it is proportional to the difference from the AE evaluation value of the exposed image, the comparison based on the above formula (1) or (2) is equivalent to comparing this difference with a predetermined threshold value.
V [0]-(V [1] + V [2]) / 2
= 3/2 {V [0]-(V [0] + V [1] + V [2]) / 3} (3)

Thus, the average value of AE evaluation values for one cycle (V [0] + V [1] + V [2]) /
3 was compared with V [0]. If the former was larger than the latter, the exposure amount of the next cycle was corrected in the direction to cancel the increase of the former, and the former was smaller based on the latter. Then, the exposure amount of the next cycle is corrected so as to cancel the former decrease. By repeating this, it is possible to follow a change in illumination or composition while avoiding an abrupt change in exposure conditions, and a series of images having smooth image changes can be obtained.

  In the process shown in FIG. 7, once the appropriate exposure condition is set in step S23, the reference exposure condition (reference exposure amount) for each cycle is determined depending only on step S30 or S32. However, the reference exposure condition for each cycle may be determined in consideration of the AE evaluation value of the through image between adjacent cycles. That is, for example, when attention is paid to the first and second cycles, the through image obtained after the processing of steps S24 to S26 for the first cycle and before the processing of step S24 for the second cycle is executed. The reference exposure condition (reference exposure amount) for bracket shooting in the second cycle may be determined with reference to the AE evaluation value V [3].

  For example, when both of the above formulas (1) and (2) are not established for the first cycle and the process reaches step S31, V [0] or (V [0] + V [1] + V [ 2]) / 3 and V [3]. If V [0] −V [3]> ΔV, or (V [0] + V [1] + V [2]) / 3−V [3]> ΔV, then after step S26, Since it is anticipated that a decrease in illumination brightness or the like has occurred, the same processing as step S32 is performed, and then the process returns to step S24 (where ΔV is a positive predetermined value). That is, after the reference exposure amount applied in the reference exposure shooting of the first cycle is increased by the predetermined amount α, the process returns to step S24. The increased reference exposure amount is applied to the second cycle reference exposure shooting.

  On the other hand, if V [3] −V [0]> ΔV, the same processing as step S30 is performed, and then the process returns to step S24. That is, after the reference exposure amount applied in the reference exposure shooting in the first cycle is decreased by the predetermined amount α, the process returns to step S24. The reference exposure amount after the reduction is applied to the reference exposure shooting in the second cycle.

<< Third Example >>
Next, a third embodiment will be described. The third embodiment corresponds to a modification of the second embodiment, and the same effect as that of the second embodiment can be obtained even when the third embodiment is used. A partial block diagram of the image pickup apparatus 1 related to continuous bracket shooting according to the third embodiment is the same as that according to the first embodiment (that is, FIG. 4).

  With reference to FIG. 9, the operation | movement procedure of continuous bracket imaging | photography concerning 3rd Example is demonstrated. FIG. 9 is a flowchart showing this operation procedure.

  When it is detected that the shutter button 26b (see FIG. 1) is pressed in the shooting mode, execution of each process in FIG. 9 is started. First, in step S41, necessary variables are initialized. In particular, a variable P is introduced, and zero is substituted for the variable P. Also, as in the second embodiment, variables V [0] to V [2] into which the AE evaluation values of the reference exposure image, the plus correction image, and the minus correction image are to be substituted are also introduced.

  In step S42, the AE evaluation value for the latest through image is acquired. In subsequent step S43, the exposure control unit 42 determines the appropriate exposure condition (that is, the appropriate exposure condition) based on the AE evaluation value acquired in step S42. A proper aperture value and an appropriate shutter speed). The reference exposure condition in the first cycle matches the appropriate exposure condition determined in step S43, and the reference exposure amount applied to the first cycle reference exposure shooting is the exposure amount according to the appropriate exposure condition. It becomes. However, the reference exposure conditions in the second and subsequent cycles can be corrected from the appropriate exposure conditions determined in step S43 (see step S46 or S48 described later).

  Further, based on the AE evaluation value acquired in step S42, the AE evaluation values of the reference exposure image, the positive correction correction image, and the negative correction image in the first cycle are predicted, and each prediction value is set to the variable V [0. ] To V [2] are substituted as initial values. Since the bracket width is fixed, the exposure control unit 42 can predict each AE evaluation value of the reference exposure image, the plus correction correction image, and the minus correction image in the first cycle in advance. Here, it is assumed that the equation “V [0] − (V [1] + V [2]) / 2 = 0” is predicted.

  After the actual aperture value is controlled to an appropriate aperture value according to the exposure control signal from the exposure control unit 42, in steps S44 to S48, the exposure control unit 42 performs the same processing as steps S28 to S32 in FIG. .

  First, in step S44, it is determined whether the above equation (1) is satisfied. If the expression (1) is satisfied, the process proceeds to step S46, where the process of reducing the reference exposure amount to be applied to the next reference exposure shooting by the predetermined amount α is performed, and then the process proceeds to step S49. If the expression (1) is not satisfied, the process proceeds to step S45.

  In step S45, it is determined whether the above equation (2) is satisfied. Then, when the expression (2) is satisfied, the process proceeds to step S48, and after performing the process of increasing the reference exposure amount to be applied to the next reference exposure shooting by the predetermined amount α, the process proceeds to step S49. If the expression (2) is not satisfied, the process proceeds to step S49 without changing the reference exposure amount (step S47).

  In step S49, the remainder of P / 3 is obtained. And when the remainder is 0, it transfers to step S50, when it is 1, it transfers to step S51, and when it is 2, it transfers to step S52.

  In step S50, reference exposure shooting is performed under the reference exposure condition, and the AE evaluation value of the reference exposure image obtained by the reference exposure shooting is substituted into V [0]. The reference exposure amount applied to the reference exposure shooting in step S50 is obtained by correcting the reference exposure amount according to the appropriate exposure condition determined in step S43 by the processing in step S46 or S48 (however, in step S46 or S48). (There is no correction when the process is not executed)

  In step S51, plus correction shooting is performed, and the AE evaluation value of the plus correction image obtained by the plus correction shooting is substituted into V [1]. In step S52, minus correction shooting is performed, and the AE evaluation value of the minus correction image obtained by the minus correction shooting is substituted into V [2]. The exposure amount for plus correction shooting in step S51 is larger than the current reference exposure amount by an amount corresponding to a predetermined bracket width, and the exposure amount for negative correction shooting in step S52 is the bracket width larger than the current reference exposure amount. The amount corresponding to is small.

  After the process of step S50, S51 or S52, the process proceeds to step S53, and the CPU 23 confirms whether the shutter button 26b remains depressed. If the shutter button 26b is not depressed, the processing in FIG. 9 is terminated. If the shutter button 26b is depressed, 1 is added to the variable P, and the process returns to step S44 (step S54). Each process after S44 is repeatedly executed.

  When the reference exposure amount is corrected to decrease in the process of step S46, the correction result is immediately reflected in the shooting of S50, S51 or S52. Due to this, the above formula (1) is also established in the next step S44, and the process proceeds to step S46, and there is a possibility that the reduction correction of the reference exposure amount is executed again. There is a similar concern for step S48. In order to avoid these, after executing the process of step S46 or S48 once, the correction to the reference exposure amount in steps S46 and S48 is prohibited until the variable P is increased by 3 from the execution time. It is preferable to mask the correction in step S46 or S48.

  Instead of performing this prohibition process, the following may be performed. After correcting the reference exposure amount in step S46 or S48, the process of step S50, S51 or S52 is executed via step S49. In step S50, S51 or S52, the variable V [0] to All V [2] are updated. For example, after correcting the reference exposure amount in step S46 or S48, when the process reaches step S50 via step S49, the reference exposure shooting is performed as described above, and the AE evaluation value of the reference exposure image is set to V [0. ], The AE evaluation values of the plus correction image and the minus correction image corresponding to the corrected reference exposure amount are predicted from the latest V [0] and a predetermined bracket width, and each prediction value is set to V [1. ] And V [2], the process proceeds to step S53.

<< 4th Example >>
By the way, when the imaging apparatus 1 determines the exposure condition, usually, the captured image is divided into a plurality of regions, average brightness is measured for each region, and a simple average value or weight of each measured average brightness is measured. The exposure is determined from the average value. Although the photographer may desire to better capture the subject in the specific area, it is difficult for the imaging apparatus 1 to infer the photographer's intention. For example, when considering the photographed image 250 shown in FIG. 10, the photographer wants to improve the gradation expression of the relatively bright area 251 or to improve the gradation expression of the relatively dark area 252. Often the intention.

  Bracket photography exists in order to assist in obtaining an image in accordance with such an intention. In order to improve the gradation expression of the area 251 or 252, the bracket width needs to be set appropriately. In conventional bracket photography, the photographer himself can only evaluate whether the bracket width is appropriate after photography, and the true desired image cannot often be acquired.

  In the imaging apparatus 1 according to the present embodiment, the bracket width can be automatically adjusted using a special function called continuous bracket shooting. A fourth embodiment will be described as an embodiment for realizing the automatic adjustment of the bracket width.

  First, the principle of automatic bracket width adjustment will be described with reference to FIGS. Focus on bracket photography in one cycle. FIG. 11 shows the reference exposure image 300, the plus correction image 301, the minus correction image 302, and four luminance histograms corresponding to these images in the cycle of interest. Reference numerals 310a, 312a, 320a and 321a indicate four graphs representing four luminance histograms. FIG. 12 is a list of variables used when the bracket width is automatically adjusted.

  In the reference exposure image 300, an area where the image is relatively bright is referred to as a bright area 310, and an area where the image is relatively dark is referred to as a dark area 320. The bright area 310 and the dark area 320 do not have overlapping areas, and they are a part of the entire area of the reference exposure image 300. Also, a bright area 312 is set in the minus correction image 302 and a dark area 321 is set in the plus correction image 301. The position and size of the bright area 310 in the reference exposure image 300 and the position and size of the bright area 312 in the minus correction image 302 are the same, and the position and size of the dark area 320 in the reference exposure image 300 and the plus correction image 301. The position and size of the dark area 321 are the same.

  Whether or not the bracket width is appropriate in bracket shooting in the focused cycle can be evaluated from the luminance histogram for each region. This will be described more specifically. For the sake of concrete explanation, it is assumed that the luminance value of each pixel of the photographed image takes a digital value in the range of 0-255.

A histogram of luminance values of each pixel forming an image in the bright area 310 is represented by a curve denoted by reference numeral 310b in the graph 310a.
A histogram of luminance values of each pixel forming an image in the bright area 312 is represented by a curve denoted by reference numeral 312b in the graph 312a.
A histogram of luminance values of each pixel forming an image in the dark area 320 is represented by a curve denoted by reference numeral 320b in the graph 320a.
A histogram of luminance values of pixels forming an image in the dark area 321 is represented by a curve denoted by reference numeral 321b in the graph 321a.
In each graph (310a, 312a, 320a, and 321a), the horizontal axis represents the luminance value, and the vertical axis represents the frequency in the histogram.

In the histogram 310b, the mode value (that is, the luminance value with the highest frequency) is represented by L _A0 , the largest luminance value is represented by L _B0 , and this is called the luminance maximum value.
In the histogram 312b, the mode value (that is, the luminance value with the highest frequency) is represented by L _A2 , and the largest luminance value is represented by L _B2 , which is called the luminance maximum value.
In the histogram 320b, the mode value (that is, the luminance value with the highest frequency) is represented by L _C0 , and the smallest luminance value is represented by L _D0 , which is called the luminance minimum value.
In the histogram 321b, the mode value (that is, the luminance value with the highest frequency) is represented by L _C1 , and the smallest luminance value is represented by L _D1 , which is called the luminance minimum value.
The maximum luminance value L _B0 or L _B2 may or may not match 255 (in the example of FIG. 11, L _B0 = 255 and L _B2 <255). The minimum luminance value L _D0 or L _D1 may or may not match 0 (in the example of FIG. 11, L _D0 = 0 and L _D1 > 0).

As can be seen from the histogram 310b, in the bright area 310 in the reference exposure image 300, the overall brightness value is too large, and the white-side gradation expression is poor and the contrast is low. In the bright area 312 in the minus correction image 302, the gradation expression and contrast on the white side are improved. Now, variables R _L and R _{L (−)} are introduced, and R _L = L _B0 −L _A0 and R _{L (−)} = L _B2 −L _A2 (see FIG. 12). R _L is an evaluation value representing the white side contrast and gradation expression goodness of the bright area 310, and _{RL (−)} is the white side contrast of the bright area 312 and good gradation expression. Is an evaluation value. The respectively below, the evaluation value R _L and R _{L -} R _L and R _{L () (-),} also referred to.

It can be said that the larger the evaluation value R _L is, the better the contrast and gradation expression for the bright area 310 is. The larger the evaluation value R _{L (−)} is, the better the contrast and gradation expression for the bright area 312 is. You can say that. When it is considered that the gradation expression on the white side is improved by the minus correction shooting, ( _{RL (−) − RL} ) represents the degree of improvement. Therefore, Q _L = (R _{L (−)} −R _L ) is set, and Q _L is referred to as a bright portion improvement degree (see FIG. 12).

The dark region is also considered in the same manner, and variables R _D and R _{D (+)} are introduced so that R _D = L _C0 −L _D0 and R _{D (+)} = L _C1 −L _D1 (see FIG. 12). . R _D is an evaluation value indicating the black side contrast and good gradation expression of the dark area 320, and R _{D (+)} represents the black side contrast and good gradation expression of the dark area 321. It is an evaluation value. R _D and R _D a _(+), respectively, hereinafter also referred to as evaluation value R _D and R _{D (+).} Further, Q _D = (R _{D (+)} −R _D ) is set, and Q _D is referred to as a dark area improvement degree (see FIG. 12).

When the bracket width is appropriate and the gradation expression on the white side is appropriately improved by the minus correction photographing, the bright portion improvement degree Q _L takes an appropriate value. Similarly, when the bracket width is appropriate and the gradation expression on the black side is appropriately improved by the plus correction shooting, the dark area improvement degree Q _D takes an appropriate value. For this reason, by referring to each of the histograms described above, it is possible to determine whether or not the bracket width used for bracket shooting in the focused cycle is appropriate. Then, the bracket width applied to bracket shooting in the next cycle may be adjusted according to the determination result.

  The configuration and operation for realizing the above-described automatic adjustment of the bracket width will be described. FIG. 13 shows a partial block diagram of the image pickup apparatus 1 involved in continuous bracket shooting according to the fourth embodiment. In FIG. 13, an AE evaluation unit 41 is the same as that in FIG. 4, and the exposure control unit 42a has the same function as the exposure control unit 42 in FIG. The function of the bracket width evaluation unit 43 will be apparent from the following description. In FIG. 13, for example, the AE evaluation unit 41 is mounted in the video signal processing unit 13 in FIG. 1, and the exposure control unit 42a and the bracket width evaluation unit 43 are mounted in the CPU 23 in FIG. Although not specifically shown in FIG. 13, the function of each part (such as the imaging unit 11) of the imaging device 1 is naturally used when executing continuous bracket imaging.

  With reference to FIG.14 and FIG.15, the operation | movement procedure of continuous bracket imaging | photography concerning 4th Example is demonstrated. 14 and 15 are flowcharts showing this operation procedure.

When it is detected that the shutter button 26b (see FIG. 1) is pressed in the shooting mode, execution of the processes in FIGS. 14 and 15 is started. First, processing such as initialization of necessary variables is performed in step S61 of FIG. In particular, a variable W representing the bracket width and a variable E _C representing the exposure correction value are introduced, and a predetermined initial value (initial bracket width) is substituted for W and zero is substituted for E _C.

In step S62, an AE evaluation value for the latest through image is acquired. In subsequent step S63, the exposure control unit 42a determines an appropriate exposure condition (that is, an appropriate exposure condition) based on the AE evaluation value acquired in step S62. A proper aperture value and an appropriate shutter speed). Subsequently, in step S64, the exposure control unit 42a sets the appropriate exposure amount plus the exposure correction value E _C as the reference exposure amount. The appropriate exposure amount is defined by the appropriate exposure condition determined in step S63 (that is, specified by an appropriate aperture value and an appropriate shutter speed). As will be apparent from the description below, E _C is zero, positive or negative, and when E _C is positive, the reference exposure amount is the exposure amount represented by | E _C | rather than the appropriate exposure amount. When E _C is negative, the reference exposure amount is made smaller than the appropriate exposure amount by the exposure amount represented by | E _C |. In the first cycle, since E _C = 0, the reference exposure amount matches the appropriate exposure amount.

  After the actual aperture value is controlled to an appropriate aperture value in accordance with the exposure control signal from the exposure control unit 42a, reference exposure shooting is performed based on the reference exposure condition (reference exposure amount) in step S65, and in the subsequent step S66, plus correction is performed. Shooting is carried out, and further negative correction shooting is carried out in step S67. The exposure time in the plus correction shooting is longer than the exposure time in the reference exposure shooting by the time corresponding to the bracket width W, and the exposure time in the minus correction shooting corresponds to the bracket width W than the exposure time in the reference exposure shooting. Shortened by the amount of time.

  Thereafter, the bracket width evaluation unit 43 evaluates the contrast (gradation expression) of the bright area in the image using the reference exposure image and the minus correction image in step S68, and in step S69, the reference exposure image and the plus correction image are added. The contrast (gradation expression) of the dark area in the image is evaluated using the corrected image. For these evaluation methods, the above-described method based on the luminance histogram is used. From this evaluation result, the suitability of the current bracket W is determined.

  Now, for concrete explanation, attention is paid to bracket shooting of a certain cycle. Then, assuming that the images acquired in steps S65, S66, and S67 of the focused cycle are the reference exposure image 300, the plus correction image 301, and the minus correction image 302 in FIG. 11, respectively, steps S68 and S69. This process and the processes of steps S70 to S77 in the subsequent stage will be described.

  Prior to the processing of steps S68 and S69, the bracket width evaluation unit 43 sets the bright area 310 and the dark area 320 in the reference exposure image 300, and the dark area 321 and the negative exposure image of the positive exposure image 301 according to the setting contents. A bright area 312 of 302 is set.

  In this setting, the function of the AE evaluation unit 41 is used. As shown in FIG. 16, the AE evaluation unit 41 divides the photographed image into a plurality of regions by dividing the photographed image of interest in the vertical and horizontal directions. Each area obtained by this division is called an element area. Then, for each element area, an average value of luminance values of each pixel belonging to the element area is calculated, and an AE evaluation value of the focused image taken from the average value of each element area is calculated. The bracket width evaluation unit 43 refers to the average value of the luminance values for each element area, and sets a relatively bright area as a bright area and a relatively dark area as a dark area in the focused captured image.

  For example, the average value of the luminance values of each element region is compared with a predetermined bright portion threshold value, and a group of element regions whose average luminance value is equal to or greater than the bright portion threshold value is determined to be a bright portion region In the case of the reference exposure image 300, it is set as the bright area 310), while the average value of the luminance value of each element area is compared with a predetermined dark area threshold value, and the average luminance value is equal to or less than the dark area threshold value. A group of element areas is set as a dark area (a dark area 320 when the focused captured image is the reference exposure image 300). Here, the bright part threshold is larger than the dark part threshold. The bright area 310 and the dark area 320 may be determined by performing an area division process based on the luminance value on the reference exposure image 300.

After setting the bright region and the dark region, the bracket width evaluation unit 43 creates the histograms 310b, 312b, 320b, and 321b of FIG. 11, evaluates values R _L and R _{L (−)} , and R _D and R _{D (+ )} through a calculation of calculating a bright portion improvement Q _L and the dark portion improvement Q _D, to assess the degree of bright portions improvement Q _L and the dark portion improvement Q _D (see FIG. 12).

Specifically, with respect to the bright portion improvement degree Q _L, it is determined whether or not the following formulas (4a) and (4b) are satisfied. When the expression (4a) is satisfied, it is determined that the bright portion improvement degree Q _L is too small. When the expression (4b) is satisfied, it is determined that the bright part improvement degree Q _L is excessive, and the expression ( When both 4a) and (4b) are not established, it is determined that the bright portion improvement level Q _L is appropriate. Q _TH1 and Q _TH2 are an under-determination threshold value and an over-determination threshold value set in advance, respectively, and as shown in FIG. 17, 0 <Q _TH1 <Q _TH2 <Q _TH3 . Q _TH3 is a predetermined limit value.
Q _L <Q _TH1 (4a)
Q _L > Q _TH2 (4b)

Similarly, it is determined whether or not the following formula (5a) and formula (5b) are satisfied with respect to the dark portion improvement degree Q _D. When the formula (5a) is satisfied, it is determined that the dark area improvement degree Q _D is too small. When the expression (5b) is satisfied, it is determined that the dark area improvement degree Q _D is excessive, and the expression (5a) and both of the formula (5b) is while if it is negative, the dark portion improvement Q _D is judged to be appropriate.
Q _D <Q _TH1 (5a)
Q _D > Q _TH2 (5b)

When the evaluation for the bright portion improvement degree Q _L and the dark portion improvement degree Q _D is finished, the process proceeds from step S69 of FIG. 14 to step S70 of FIG. The evaluation result is transmitted to the exposure control unit 42a (see FIG. 13). Hereinafter, the light portion improvement Q _L and the dark portion improvement Q _D, respectively, simply referred to as Q _L and Q _D. Each process of steps S70 to S77 is executed by the exposure control unit 42a based on the evaluation results for Q _L and Q _D.

At step S70, the whether Q _L is determined to excessively small is determined, while if Q _L is determined under-program shifts to Step S71, if Q _L is not determined to under-goes to step S74 To do. In step S71, whether Q _D is determined to excessive is determined, while if Q _D is determined excessive to shift to step S73, if Q _D is not determined to excessive proceeds to step S72 To do. At step S74, the whether Q _L is determined to excessive is determined, while if Q _L is determined excessive to shift to step S75, the case where Q _L is not determined to excessive proceeds to step S78 To do. At step S75, the whether Q _D is determined to excessively small is determined, while if Q _D is determined under-moving to step S77, the case where Q _D is not determined to under-goes to step S76 To do.

If it is determined that the bright portion improvement degree Q _L is too small and the dark portion improvement degree Q _D is too small (or appropriate), the process proceeds to step S72. In this case, it is considered that the current bracket width W is too small. Accordingly, in step S72, correction is performed so as to increase the current bracket width W. Specifically, the current bracket width W is substituted into W on the right side of Expression (6) below, and the value of W _{1 on} the left side obtained according to Expression (6) is set as a new bracket width W. Here, W _MAX is a predetermined maximum value that the bracket width W can take.
W ₁ = W + (W _MAX −W) × (1−Q _L / Q _TH1 ) (6)

If it is determined that the bright area improvement level Q _L is excessive and the dark area improvement level Q _D is also excessive (or appropriate), the process proceeds to step S76. In this case, it is considered that the current bracket width W is too large. Accordingly, in step S76, the current bracket width W is corrected so as to decrease. Specifically, the current bracket width W is substituted into W on the right side of Expression (7) below, and the value of W _{2 on} the left side obtained according to Expression (7) is set as a new bracket width W. Here, W _MIN is a predetermined minimum value that the bracket width W can take.
W ₂ = W− (W−W _MIN ) × Q _L / Q _TH3 (7)

If it is determined that the bright area improvement level Q _L is too small and the dark area improvement level Q _D is excessive, the process proceeds to step S73. In this case, it is considered that the amount of exposure in this cycle is too large. Accordingly, in step S73, correction for reducing the exposure correction value E _C is performed. For example, a predetermined value ΔE is subtracted from the current exposure correction value E _C, and a value obtained by this subtraction is set as a new exposure correction value E _C. However, ΔE> 0.

If it is determined that the bright area improvement level Q _L is excessive and the dark area improvement level Q _D is excessive, the process proceeds to step S77. In this case, it is considered that the amount of exposure in this cycle is too small. Accordingly, in step S77, correction for increasing the exposure correction value E _C is performed. For example, a predetermined value ΔE is added to the current exposure correction value E _C , and a value obtained by this addition is set as a new exposure correction value E _C.

  By performing the processing as described above, a more appropriate bracket width and exposure amount are set in bracket shooting in the next cycle. As a result, it is possible to acquire an image more in line with the photographer's intention.

  When the process of step S72, S73, S76 or S77 is completed, the process proceeds to step S78. In step S78, the CPU 23 confirms whether or not the shutter button 26b remains depressed. When the shutter button 26b is not pressed down, the processing in FIGS. 14 and 15 is terminated. However, when the shutter button 26b is pressed down, the processing returns to step S62 in FIG. 14, and each processing after step S62 is repeated. Execute.

<< Deformation, etc. >>
The specific numerical values shown in the above description are merely examples, and as a matter of course, they can be changed to various numerical values. As modifications or annotations of the above-described embodiment, notes 1 to 4 are described below. The contents described in each comment can be arbitrarily combined as long as there is no contradiction.

[Note 1]
As described above, bracket shooting is shooting in which a predetermined number of shootings are continuously performed while changing predetermined types of shooting conditions. In the above-described embodiment, the case has been dealt with when the shooting condition to be changed is the exposure condition. However, the types of shooting conditions to be changed in the continuous bracket shooting include various types, and when performing a known bracket shooting. Includes any type of imaging condition that can be changed.

  For example, the shooting conditions that can be changed include a color balance condition that affects white balance, a focus condition, and a zoom condition in addition to the exposure condition. Regardless of the type of shooting conditions to be changed, first, a reference shooting condition is determined, and plus correction shooting in which the shooting conditions are changed by a predetermined bracket width in the opposite direction centering on the reference shooting condition and Perform negative correction shooting.

  Although the case where one cycle of bracket shooting consists of shooting for three times has been described above, the present invention is of course not limited to this. Assuming that the number of times of shooting for forming one cycle of bracket shooting is referred to as the number of times of bracket shooting, the number of times of bracket shooting may be three times as described above, or two times or four times or more.

[Note 2]
When performing continuous bracket shooting, a method of performing camera control setting and bracket control setting independently for each cycle can be used. The camera control setting is, for example, a setting for exposure amount and focusing. The bracket control setting includes setting of the type of shooting condition changed in bracket shooting, setting of the bracket width, setting of the number of times of bracket shooting, and the like. However, this method is easy to mount on the imaging apparatus 1, but requires calculation time for each camera control setting. Moreover, there is a possibility that the shooting conditions may change greatly in bracket shooting between adjacent cycles, and it cannot be reflected in the next cycle whether the set shooting conditions are appropriate.

  In consideration of this, in the second to fourth embodiments, the imaging conditions of the target cycle are set in consideration of the image characteristics of each captured image (reference exposure image, positive correction image, and negative correction image) in the past cycle of the target cycle. Has been decided. In the second to fourth embodiments, attention is paid to the image feature relating to the luminance, and the shooting condition of the attention cycle is determined using the AE evaluation value and the histogram of the luminance, but the attention cycle is based on the image feature other than the luminance. The shooting conditions may be determined.

  For example, an image feature related to the color of each photographed image is evaluated from the color difference signal of each photographed image (reference exposure image, plus-corrected image, and minus-corrected image) in the cycle immediately before the subject cycle, and the image feature is taken into consideration. You may make it determine the imaging condition of a cycle. The image feature relating to the color is expressed as a color evaluation value, for example, and white balance adjustment is performed according to the color evaluation value, for example.

[Note 3]
The imaging apparatus 1 in FIG. 1 can be realized by hardware or a combination of hardware and software. In particular, the function of each part shown in FIG. 4 or FIG. 13 can be realized by hardware, software, or a combination of hardware and software. When the imaging apparatus 1 is configured using software, a block diagram of a part realized by software represents a functional block diagram of the part. Also, all or part of the functions realized in each part shown in FIG. 4 or FIG. 13 is described as a program, and the function is executed by executing the program on a program execution device (for example, a computer). You may make it implement | achieve all or one part.

[Note 4]
For example, it can be considered as follows. The continuous bracket photographing means for realizing the continuous bracket photographing includes the exposure control unit 42 in FIG. 4 or the exposure control unit 42a in FIG. It can also be considered that the continuous bracket photographing means includes the imaging unit 11 and / or the CPU 23 of FIG. 4 or 13 functions as an evaluation value deriving unit.

  The bracket width evaluation unit 43 in FIG. 13 functions as an evaluation unit that evaluates the suitability of the bracket width. And the exposure control part 42a of FIG. 13 functions as a bracket width setting means which sets a bracket width based on the evaluation result of the evaluation means. The bracket width evaluation unit 43 also has a function as a luminance histogram derivation unit that obtains a luminance histogram.

1 is an overall block diagram of an imaging apparatus according to an embodiment of the present invention. It is an internal block diagram of the imaging part of FIG. It is a key map of continuous bracket photography concerning an embodiment of the present invention. FIG. 2 is a partial block diagram of the image pickup apparatus of FIG. 1 according to the first embodiment of the present invention and involved in continuous bracket shooting. It is a flowchart showing the operation | movement procedure of continuous bracket imaging | photography concerning 1st Example of this invention. It is a figure which shows that the amount of exposure can change a lot between adjacent cycles regarding continuous bracket photography according to the first embodiment of the present invention. It is a flowchart showing the operation | movement procedure of continuous bracket imaging | photography concerning 2nd Example of this invention. It is a figure for demonstrating the method which concerns on 2nd Example of this invention and sets the exposure condition of the following cycle based on the imaging | photography result of this cycle. It is a flowchart showing the operation | movement procedure of continuous bracket imaging | photography concerning 3rd Example of this invention. It is a figure which shows a mode that a comparatively bright area | region and a comparatively dark area | region are mixed within the one picked-up image. It is a figure for demonstrating the principle of automatic adjustment of bracket width concerning 4th Example of this invention. It is the figure which concerns on 4th Example of this invention and showed each variable utilized in the case of the automatic adjustment of a bracket width as a table | surface. It is a partial block diagram of the imaging device of FIG. 1 according to the fourth embodiment of the present invention and involved in continuous bracket shooting. It is a flowchart showing the operation | movement procedure of continuous bracket imaging | photography concerning 4th Example of this invention. It is a flowchart showing the operation | movement procedure of continuous bracket imaging | photography concerning 4th Example of this invention. It is a figure which shows that a picked-up image is divided | segmented into a some area | region in the AE evaluation part of FIG. It is a figure which shows the magnitude relationship of the threshold value referred in the bracket width evaluation part of FIG. It is a figure which shows the conceptual diagram of one bracket imaging | photography (namely, bracket imaging | photography for 1 cycle) concerning embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Imaging device 11 Imaging part 32 Aperture 33 Imaging element 41 AE evaluation part 42, 42a Exposure control part 43 Bracket width evaluation part

Claims (4)

In an imaging device that performs bracket shooting for shooting a predetermined number of times while changing a predetermined type of shooting condition,
Continuous bracket photographing means for continuously executing the bracket photographing for a plurality of cycles;
Evaluation value deriving means for deriving a luminance evaluation value according to the brightness of each captured image;
With
The continuous bracket photographing means includes
The shooting conditions for bracket shooting of the target cycle in the second and subsequent cycles are determined in consideration of the luminance evaluation value in the past cycle of the target cycle,
One bracket shooting includes reference shooting in which shooting is performed under reference shooting conditions, plus correction shooting and minus correction shooting in which shooting conditions are changed by the bracket width in opposite directions around the reference shooting conditions. Including,
The continuous bracket photographing means includes
An evaluation means for evaluating the suitability of the bracket width applied to the bracket shooting from the image characteristics of each shot image in one bracket shooting;
Bracket width setting means for determining the bracket width with respect to bracket shooting in the second and subsequent cycles based on the evaluation results of the evaluation means for the past cycles of the target cycle. An imaging device that is characterized. In an imaging device that performs bracket shooting for shooting a predetermined number of times while changing a predetermined type of shooting condition,
Continuous bracket photographing means for continuously executing the bracket photographing for a plurality of cycles;
Evaluation value deriving means for deriving a luminance evaluation value according to the brightness of each captured image;
With
The continuous bracket photographing means includes
The shooting conditions for bracket shooting of the target cycle in the second and subsequent cycles are determined in consideration of the luminance evaluation value in the past cycle of the target cycle,
One bracket shooting includes reference shooting in which shooting is performed under the reference exposure condition, plus-correction shooting in which the exposure amount is larger by the bracket width set than the reference exposure condition, and the bracket width than the reference exposure condition. Including negative correction shooting with a small exposure amount,
When the photographed image by the reference photographing, the photographed image by the plus correction photographing, and the photographed image by the minus correction photographing are a reference exposure image, a plus correction image, and a minus correction image, respectively.
The continuous bracket photographing means includes
Each cycle is an evaluation cycle, and in the bracket shooting of the evaluation cycle, the luminance histogram of the dark area of the reference exposure image, the luminance histogram of the dark area of the plus correction image, the luminance histogram of the bright area of the reference exposure image, and the Evaluation means for evaluating the suitability of the bracket width applied to bracket shooting in the evaluation cycle, based on the brightness histogram of the bright area of the minus correction image;
Bracket width setting means for determining the bracket width for bracket shooting of the target cycle in the second and subsequent cycles based on the evaluation result of the evaluation means for the past cycle of the target cycle.
An imaging apparatus characterized by that . The evaluation means includes
A second difference between the first luminance difference between the mode value and the maximum luminance value in the luminance histogram of the bright area of the reference exposure image, and the mode value and the maximum luminance value in the luminance histogram of the bright area of the minus correction image. While contrasting the brightness difference,
A third luminance difference between the mode value and the minimum luminance value in the luminance histogram of the dark area of the reference exposure image, and a fourth luminance difference between the mode value and the minimum luminance value in the luminance histogram of the dark area of the positive correction image. And
Evaluate the suitability of the bracket width based on the comparison results
The imaging apparatus according to claim 2 . The continuous bracket photographing means sets the exposure amount for the reference photographing of the target cycle in consideration of the first to fourth luminance differences when the past cycle of the target cycle is the evaluation cycle.
The imaging apparatus according to claim 3 .