JP2014128021A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an imaging apparatus that is able to automatically maintain appropriate exposure for an image without user's checking it.SOLUTION: When a first unit exposure period passes, an imager 104 outputs an image of a first frame. A DSP105 measures the exposure value of the image and calculates a remaining exposure period. The remaining exposure period is a period for which the imager 104 has to expose a subject image until an appropriate exposure value is obtained. When the unit exposure period is shorter than the remaining exposure period, the imager 104 outputs an image of a second frame after the passage of the unit exposure period from the start of a second unit exposure period. The DSP105 forms a composing image by combining the image of the first frame and the image of the second frame. Then, the exposure value of the composite image is measured and a remaining exposure period is calculated again. When these processes are repeated, there may be a case where the unit exposure period is longer than the remaining exposure period. At this time, the imager 104 outputs an image after the passage of the remaining exposure period and ends the exposure.

Description

  The present invention relates to an imaging apparatus that captures an image.

  2. Description of the Related Art An imaging device is known in which images captured in multiple times are combined into a single composite image. Each time the imaging device captures an image, the captured image is combined with the captured image to create a composite image, which is displayed on the screen. By looking at the composite image displayed on the screen, the user determines whether or not the exposure of the composite image is appropriate. When the user determines that the exposure is appropriate, imaging is terminated by the user's operation (Patent Document 1).

JP 2009-130471 A

  However, in such an imaging apparatus, the user has to wait by the monitor during the exposure period to check the image displayed on the monitor, and is complicated when the exposure period is long. When the user cannot stand by the monitor, exposure cannot be performed for a long time. Similarly, the imaging device cannot determine the shooting conditions such as the shutter speed and the aperture before imaging under conditions where only the light amount below the measurement limit is obtained, so the user checks the image displayed on the monitor and determines the exposure period. Must.

  The present invention has been made in view of these problems, and an object of the present invention is to obtain an imaging apparatus capable of automatically maintaining appropriate exposure without confirmation by a user.

  An imaging device according to the present invention includes an imaging device that captures an image for each unit exposure period and outputs an image during an exposure period, and a monitoring unit that receives an image from the imaging device and monitors an exposure state of the image. During the period, the monitoring unit receives an image from the image sensor, and determines a remaining exposure period based on an exposure state of the received image.

  During the exposure period, it is preferable that the monitoring unit receives a plurality of images from the image sensor and determines the remaining exposure period based on the exposure states of the received plurality of images.

  During the exposure period, it is preferable that the monitoring unit receives images from the image sensor, combines all the received images to create a combined image, and determines the remaining exposure period based on the exposure state of the combined image.

  The monitoring unit preferably ends the imaging when the exposure state of the composite image is more than appropriate.

  The monitoring unit preferably determines the remaining exposure period when the exposure state of the composite image is not more than appropriate.

  When the remaining exposure period is longer than the unit exposure period, the monitoring unit causes the image sensor to capture an image during the unit exposure period. When the remaining exposure period is equal to or less than the unit exposure period, the monitoring unit It is preferable to have the imaging performed.

  The monitoring unit calculates a target exposure period based on the exposure of the subject image before starting the exposure period. If the target exposure period is longer than the unit exposure period, the monitoring unit causes the image sensor to perform imaging in the unit exposure period. When the target exposure period is equal to or shorter than the unit exposure period, it is preferable to cause the image sensor to perform imaging in the target exposure period.

  The unit exposure period is preferably determined according to the characteristics of the image sensor.

  According to the present invention, it is possible to obtain an imaging apparatus capable of automatically maintaining an appropriate exposure without confirmation by a user.

It is the block diagram which showed the imaging device roughly. 6 is a timing chart showing an exposure sequence. It is the graph which showed the relationship between exposure amount and exposure period. It is the flowchart which showed the exposure process. It is the flowchart which showed the exposure period calculation process. It is the flowchart which showed the exposure amount determination process.

  Hereinafter, a digital camera 100 that is an embodiment of an imaging apparatus according to the present invention will be described with reference to FIGS. First, the configuration of the digital camera 100 will be described with reference to FIG.

  The digital camera 100 includes a photographing lens 101, a return mirror 102, a shutter 103, an image sensor 104 such as a CCD or a CMOS, a DSP 105 constituting a monitoring unit, an internal memory 106, an operation button 107, an LCD 108, an SD card 109, and an exposure sensor 110. Is mainly provided.

  The taking lens 101 is attached to the digital camera 100 so as to be detachable. The return mirror 102 reflects the subject image from the photographing lens 101 toward the viewfinder block 111 in the lowered state. A pentaprism 112 provided in the finder block 111 reflects the subject image toward the finder 113 and the exposure sensor 110. The return mirror 102 is a half mirror, and the subject image transmitted through the return mirror 102 is reflected toward the AF sensor 114. On the other hand, when the return mirror 102 is raised, the subject image from the photographing lens 101 is formed on the image sensor 104.

  The operation button 107 includes, for example, a shutter release. The shutter release is operated by the user and transmits a signal to the DSP 105 to shoot.

  When the shutter release is half-pressed, the exposure sensor 110 measures the exposure of the subject image and sends it to the DSP 105, and the AF sensor 114 sends the contrast information of the subject image to the DSP 105. The DSP 105 determines the shutter speed based on the exposure, and drives the photographing lens 101 based on the contrast information to focus the subject.

  When the shutter release is fully pressed, the shutter 103 has a front curtain and a rear curtain. Based on the shutter speed determined by the DSP 105, the front and rear curtains run at intervals during imaging, thereby causing the image sensor 104 to move. Adjust the exposure amount. The image sensor 104 captures a subject image and outputs the image.

  The DSP 105 receives an image from the image sensor 104, performs image processing using the internal memory 106, and transmits the image processing to the LCD 108 and / or the SD card 109. The LCD 108 displays an image, and the SD card 109 stores the image. The SD card 109 is detachably attached to the digital camera 100.

  The image sensor 104 has a unit exposure period corresponding to its characteristics. The unit exposure period is a value determined in advance by experiment and stored in the internal memory 106. In general, when the image sensor 104 performs long-term exposure, there is a tendency for noise to appear in the output image due to the influence of dark current. The longer the exposure period, the more noise. Therefore, an exposure period in which noise included in an image does not affect image quality is determined as a unit exposure period.

  The digital camera 100 can perform bulb photography. By performing an exposure process to be described later, bulb photographing is realized.

  Next, an exposure sequence in bulb photography will be described with reference to FIG. Before starting the exposure sequence, the digital camera 100 is in a standby state. In the standby state, the return mirror 102 is lowered, the shutter 103 is closed, and the image sensor 104 is placed in the standby state. When the user presses the shutter release halfway, the exposure sensor 110 measures the exposure of the subject image, and the DSP 105 acquires the exposure of the subject image from the exposure sensor 110 and calculates a target exposure period based on the exposure. The target exposure period is a period in which the shutter 103 should be opened until an appropriate exposure amount is obtained, and the image sensor 104 should expose the subject image until an appropriate exposure amount is obtained. Details of the target exposure period calculation will be described later. Since the target exposure period is calculated based on the exposure of the subject image when the shutter release is half-pressed, if the exposure of the subject image increases, the image is correct even if the target exposure period has not elapsed If the exposure of the subject image has decreased, there is a possibility that the image has not reached the proper exposure even after the target exposure period has elapsed.

  When the user fully presses the shutter release, the charge of the image sensor 104 is reset and then starts to accumulate the charge. When the image sensor 104 starts to accumulate charges, the front curtain of the shutter 103 runs and a subject image is formed on the image sensor 104. At this time, exposure is started.

  The image sensor 104 outputs an image of the first frame when the first unit exposure period elapses. The DSP 105 receives the image, measures the exposure amount of the image, and calculates the remaining exposure period. The remaining exposure period is a period in which the shutter 103 should be opened until an appropriate exposure amount is obtained from the current exposure amount, and the image sensor 104 should expose the subject image until an appropriate exposure amount is obtained from the current exposure amount. It is a period. Details of the remaining exposure period calculation will be described later.

  When the unit exposure period is shorter than the remaining exposure period, the image sensor 104 enters the second unit exposure period, and outputs the second frame image after the unit exposure period elapses. The DSP 105 combines the first frame image and the second frame image to create a combined image. Then, the exposure amount of this composite image is measured, and the remaining exposure period is calculated again.

  If these processes are repeated, the unit exposure period may be longer than the remaining exposure period. At this time, the image sensor 104 outputs an image after the remaining exposure period elapses, the rear curtain runs to close the shutter 103, the return mirror 102 moves down, and the exposure ends.

  Next, a method for calculating the remaining exposure period will be described in detail with reference to FIG.

  The exposure amount for obtaining an appropriate image that can withstand observation is generally a value obtained by a known method, and is referred to as a target exposure amount Et here. The remaining exposure period calculation method is a method of calculating the remaining exposure period using the current exposure amount En and the target exposure amount Et every time the image sensor 104 outputs an image.

  First, the case where the first unit exposure period t1 has elapsed will be described. The DSP 105 receives the first frame image and measures the exposure amount E1 of the image. In general, the relationship between the exposure amount E and the period t is expressed by a linear linear expression E = at + b. Therefore, the coefficients a and b are obtained based on the first unit exposure period t1 and the exposure amount E1 of the first frame image. Then, a period tt = (Et−b) / a necessary to obtain the target exposure amount is obtained using the obtained expression. Then, the remaining exposure period is obtained by subtracting the unit exposure period t1 from the period tt.

  A case where the n-th unit exposure period tn has elapsed will be described. The DSP 105 receives the image of the nth frame and combines it with the images from the first frame to the (n−1) th frame to create a composite image. Then, the exposure amount En of the composite image is measured. Further, the coefficients a and b of the equation E = at + b are obtained based on the total of the unit exposure periods from the first time to the nth time and the exposure amount En of the composite image. Then, a period tt = (En−b) / a necessary to obtain the target exposure amount is obtained using the obtained expression. Then, the remaining exposure period is obtained by subtracting the total of the unit exposure periods from the first to the n-th from the period tt.

  When the unit exposure period becomes longer than the remaining exposure period, the image sensor 104 outputs an image after the remaining exposure period elapses, the rear curtain runs to close the shutter 103, the return mirror 102 moves down, and the exposure ends. To do. The DSP 105 combines all the output images to create a combined image.

  Next, the exposure process will be described with reference to FIG. The exposure process is executed when the user half-presses the shutter release.

  In the first step S41, the exposure sensor 110 measures the exposure of the subject image, and the DSP 105 acquires the exposure of the subject image from the exposure sensor 110.

  In the next step S42, it is determined whether or not the shutter release has been fully pressed. If it is fully pressed, the process proceeds to step S43. If it is not fully pressed, the process returns to step S41.

  In step S43, an exposure period calculation process described later is executed. The exposure period calculation process is a process for calculating a target exposure period and a unit exposure period.

  In the next step S44, the image sensor 104 performs exposure for the unit exposure period, and in the next step S45, the DSP 105 reads an image of one frame from the image sensor 104.

  In the next step S46, an exposure amount determination process to be described later is executed. The exposure amount determination process is a process for determining whether or not to end the exposure according to the exposure amount of the image.

  In the next step S47, it is determined whether or not to end the exposure based on the result of the exposure amount determination process. If the exposure ends, the process ends. If the exposure does not end, the process returns to step S44 to perform the exposure again.

  Next, the exposure period calculation process will be described with reference to FIG. The exposure period calculation process is executed in step S43 of the exposure process.

  In the first step S51, the unit exposure period is read from the internal memory 106.

  In the next step S52, it is determined whether or not the AE data is valid. That is, in step S41 of the exposure process, the exposure sensor 110 determines whether or not the exposure of the subject image is properly measured. If it is valid, the process proceeds to step S55, and if it is not valid, the process proceeds to step S56. When performing bulb photography, the exposure of the subject image may be small. For this reason, the exposure sensor 110 may not be able to properly measure AE data. In such a case, it is determined that the AE data is not valid.

  In the next step S53, a target exposure period is calculated based on the exposure of the subject image.

  In the next step S54, it is determined whether or not the target exposure period is longer than the unit exposure period. If it is long, the process proceeds to step S56. If it is not long, the process proceeds to step S55.

  In step S55, a target exposure period is set as the remaining exposure period. When the target exposure period is not longer than the unit exposure period, that is, when the target exposure period is equal to or shorter than the unit exposure period, when the unit exposure period is exposed, the exposure amount of the image exceeds the appropriate exposure amount. Therefore, a target exposure period is set as the remaining exposure period, and the image sensor 104 is exposed only during the target exposure period. Then, the process ends.

  In step S56, a unit exposure period is set as the remaining exposure period. If the AE data is not valid, the target exposure amount cannot be accurately calculated. Therefore, the unit exposure period is set as the remaining exposure period, and imaging is performed while monitoring the exposure state of the image. Even when the target exposure period is longer than the unit exposure period, the unit exposure period is set as the remaining exposure period, and imaging is performed while monitoring the exposure state of the image. Then, the process ends.

  Next, the exposure amount determination process will be described with reference to FIG. The exposure amount determination process is executed in step S46 of the exposure process.

  In the first step S61, it is determined whether or not the image read in step S45 of the exposure process is the first frame. If it is the first frame, the process proceeds to step S63 with the image of the first frame as a composite image. If it is not the first frame, the process proceeds to step S62, and the image read so far and the image read this time are combined to create a composite image.

  In step S63, the exposure amount of the composite image is measured. In the next step S64, it is determined whether or not the exposure is appropriate based on the measured exposure amount.

  In step S65, it is determined whether or not the exposure amount determined in step S64 exceeds the target exposure amount. If so, the process proceeds to step S66 to set 1 to the exposure completion flag. When the exposure completion flag is 1, it indicates that the exposure is completed. By determining whether or not the exposure amount exceeds the target exposure amount in step S65, shooting can be interrupted when the exposure of the subject image suddenly changes, and an image with an appropriate exposure can be obtained. If the exposure amount does not exceed the target exposure amount in step S65, the process proceeds to step S67.

  In step S67, the remaining exposure period is calculated based on the exposure amount measured in step S63.

  In the next step S68, it is determined whether or not the remaining exposure period is longer than the unit exposure period. If so, the process proceeds to step S69. If not, the process proceeds to step S70.

  In step S69, a unit exposure period is set as the next exposure period. Thereby, imaging can be performed while monitoring the exposure state of the image.

  In step S70, the remaining exposure period is set in the next exposure period. Thus, the exposure can be completed while keeping the exposure amount of the image appropriate.

  In the next step S71, the exposure completion flag is set to 0. When the exposure completion flag is 0, it means that the exposure is not completed. Then, the process ends.

  According to the present embodiment, since the digital camera can perform shooting while appropriately monitoring the exposure state of the image, an image with an appropriate exposure can be automatically obtained during shooting. Further, when the exposure of the subject image suddenly changes, shooting can be interrupted to obtain an image with an appropriate exposure.

  When performing bulb photography using the conventional digital camera 100, the user must press the shutter release for a desired period of time. However, according to this embodiment, the user can perform bulb photography by depressing the shutter release once and obtain an image with an appropriate exposure amount.

  In addition, when imaging is performed in a situation where only a light amount less than the measurement limit is obtained, the imaging device cannot determine imaging conditions such as shutter speed and aperture before imaging. However, according to the present embodiment, the exposure period can be automatically determined by analyzing the captured image.

  The unit exposure period may be calculated in step S43 of the exposure period calculation process.

  The DSP 105 obtains the coefficients a and b of the equation E = at + b using the exposure amount of the n−1th frame image and the nth frame image, and obtains the target exposure amount using the obtained equation. A necessary period tt = (En−b) / a may be obtained. Further, the coefficients a and b of the equation E = at + b are obtained using the exposure amount of the n-th frame image, and the period tt = (En−b) / b necessary for obtaining the target exposure amount using the obtained equation. You may ask for a. The coefficients a and b are calculated from the exposure amount obtained during the unit exposure period, and the time until the target exposure amount is reached can be calculated.

  Further, the DSP 105 obtains the coefficients a and b of the equation E = at + b based on the exposure amounts of a plurality of images using a method such as a least square method, and obtains the target exposure amount using the obtained equations. A necessary period tt = (En−b) / a may be obtained.

  In the present embodiment, the case where the present invention is applied to bulb shooting has been described. However, the present invention can be applied to normal shooting and a shutter speed of, for example, 1 second or less. The same effect as bulb shooting is obtained.

  In addition, in the conventional automatic exposure, it is difficult to calculate an appropriate exposure value for a long exposure period, but according to the present embodiment, even when a very long exposure period is required, it is appropriate and accurate. A high exposure value can be obtained.

  Note that the photographic lens 101 is not detachable from the digital camera 100 and may be fixed so as not to be detachable.

  Further, the image sensor 104 may include a solid-state image sensor such as a CMOS instead of a CCD.

  Note that the shutter 103 does not have both or one of the front curtain and the rear curtain. An electronic shutter may be used. If there is no one, the electronic shutter performs an operation corresponding to either the front curtain or the rear curtain.

  The unit exposure period may not be determined in advance by experiment, and may be dynamically changed during the exposure period according to a change in the imaging environment. The imaging environment is the temperature of the image sensor 104, the temperature of the digital camera, or the like.

  In this embodiment, an image is acquired from the image sensor 104 at predetermined intervals to create a composite image, and the target exposure period is calculated using the exposure amount of the composite image. Alternatively, an image may be acquired and the target exposure period may be calculated from the increase in the exposure amount of the image.

DESCRIPTION OF SYMBOLS 100 Digital camera 101 Shooting lens 102 Return mirror 103 Shutter 104 Image pick-up element 105 DSP
106 Internal memory 107 Operation buttons 108 LCD
109 SD card 110 Exposure sensor

Claims (8)

An imaging element that captures an image for each unit exposure period and outputs an image during the exposure period;
A monitoring unit that receives an image from the image sensor and monitors an exposure state of the image;
During the exposure period, the monitoring unit receives an image from the image sensor and determines a remaining exposure period based on an exposure state of the received image.   The imaging apparatus according to claim 1, wherein during the exposure period, the monitoring unit receives a plurality of images from the image sensor and determines a remaining exposure period based on an exposure state of the received plurality of images.   The monitoring unit receives an image from the image sensor during the exposure period, generates a composite image by combining all the received images, and determines a remaining exposure period based on an exposure state of the composite image. Item 3. The imaging device according to Item 1 or 2.   The imaging apparatus according to claim 1, wherein the monitoring unit ends imaging when the exposure state of the composite image is more than appropriate.   The imaging apparatus according to claim 1, wherein the monitoring unit determines the remaining exposure period when an exposure state of the composite image is not appropriate or higher.   When the remaining exposure period is longer than the unit exposure period, the monitoring unit causes the image sensor to perform imaging during the unit exposure period, and when the remaining exposure period is equal to or less than the unit exposure period. The imaging device according to claim 1, wherein the imaging device performs imaging in the remaining exposure period.   The monitoring unit calculates a target exposure period based on exposure of a subject image before starting the exposure period, and when the target exposure period is longer than the unit exposure period, the imaging is performed during the unit exposure period. The imaging device according to claim 1, wherein when an image is picked up by an element and the target exposure period is equal to or shorter than the unit exposure period, the image pickup element is picked up by an image during the target exposure period.   The imaging apparatus according to claim 1, wherein the unit exposure period is determined according to characteristics of the imaging element.

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