JP5322715B2 - Camera and shutter-second error derivation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allow a user to calibrate and adjust shutter accuracy without using a special measuring device or the like. <P>SOLUTION: A still object TC having temporally nearly constant luminance is imaged for a first shutter opening time to obtain a first image, and is imaged for a second shutter opening time to obtain a second image. An actual exposure ratio is derived based on comparison between the first image and the second image. The error of the shutter speed is derived based on a result of comparing a theoretical exposure ratio obtained based on a ratio of theoretical exposure based on the first shutter opening time to theoretical exposure based on the second shutter opening time, with the actual exposure ratio. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a technique capable of confirming and adjusting shutter accuracy in a completed state in a camera such as an electronic still camera.

  Many digital still cameras have a shutter, such as a focal plane shutter and a lens shutter, that adjusts the amount of light (exposure amount) of subject light incident on the light receiving surface of an image sensor by mechanically operating a light shielding member. These shutters include a light-shielding curtain, mechanical parts for causing the light-shielding curtain to travel (reciprocate) at high speed, a spring, an electromagnet, and the like. For example, in a focal plane shutter, two sets of light shielding members, called a front curtain and a rear curtain, travel at a predetermined time interval (the opening operation is performed by the front curtain traveling and the closing operation is performed by the rear curtain traveling). ), A desired exposure amount can be obtained. In many cases, the time interval when the two sets of light shielding members travel one after another is controlled by a microcomputer or the like.

  Hereinafter, a shutter that mechanically operates the light shielding member described above to adjust the exposure amount of the image sensor is referred to as a mechanical shutter. Most of the mechanical shutters drive the light shielding member with the force obtained by accumulating the spring, so the spring shape, elastic coefficient variation, frictional force acting on the light shielding member when the light shielding member travels, etc. May cause an error in exposure accuracy. In order to minimize such an error in exposure accuracy, adjustment is performed using a shutter tester or the like during camera assembly.

  By the way, many digital still cameras have a continuous shooting function (continuous shooting function). In addition, with the increase in the capacity of memory cards for recording image data obtained by shooting and the improvement in access speed, the number of shooting frames tends to increase compared to silver halide cameras. is there.

  In other words, since a silver halide camera involves the work of loading and rewinding a film, for example, taking 500 frames takes a lot of time and effort, but a digital still camera having a continuous shooting (continuous shooting) function Now it can be completed in a few minutes. A digital still camera does not require a film fee or a development fee. Due to such factors, the number of frames (usage frequency) of digital still cameras tends to increase.

  In general, as the number of frames is increased in this way, the exposure accuracy gradually changes due to a change in friction coefficient or wear of the mechanical shutter mechanism portion. When such a change in accuracy occurs, it is difficult for the user to make adjustments by himself. The reason is that adjustment of the shutter accuracy requires a luminance box, a device for measuring the image plane exposure amount, and the like.

Patent Document 1 discloses a technique for measuring an image plane exposure amount of an accuracy adjustment target camera using an exposure amount measuring device and writing the obtained shutter speed error data in an EEPROM of the accuracy adjustment target camera. According to this technique, if the accuracy adjustment target camera is set on the exposure amount measuring device and the shutter is released, the operator can calibrate the accuracy adjustment target camera without performing difficult work for adjustment.
JP 2000-241849 A

  However, in the technique disclosed in Patent Document 1, it is necessary to use an exposure meter. A typical user does not have such an instrument. Therefore, the user needs to bring the camera to the service station or send it to the manufacturer using a courier service or the like.

  The present invention has been made in view of the above problems, and an object thereof is to provide a technique that enables a user to check and adjust exposure accuracy without using a special adjustment device, a luminance box, or the like. .

(1) According to the first aspect of the present invention, by adjusting the time interval between opening and closing of the image sensor and the light shielding member, the object light incident on the light receiving surface of the image sensor is adjusted. A camera provided with a shutter composed of a focal plane shutter configured to be able to control the amount of light,
A shutter time setting unit for setting an opening time of the shutter;
A shutter timing control unit that controls a time interval from the opening of the shutter to the closing based on the opening time set by the shutter time setting unit;
A first image sensor output obtained by photographing a stationary object having substantially constant luminance in time with a first shutter opening time set by the shutter time setting unit, and the stationary object for the shutter time. An actual exposure amount ratio deriving unit for deriving an actual exposure amount ratio based on a comparison with a second image sensor output obtained by photographing with the second shutter opening time set by the setting unit;
A theoretical exposure amount ratio obtained based on a ratio of a theoretical exposure amount based on the first shutter opening time set by the shutter time setting unit and a theoretical exposure amount based on the second shutter opening time. And a second time error deriving unit for deriving a second time error of the shutter based on a comparison result with the actual exposure amount ratio derived by the actual exposure amount ratio deriving unit ;
Based on the opening time set by the shutter time setting unit, the time interval controlled by the shutter timing control unit is corrected so as to reduce the second time error derived by the second time error deriving unit. A time interval correction unit;
The output of the image sensor is divided into a plurality of regions along the direction of travel of the shutter, and the exposure unevenness of the image sensor is corrected based on the actual exposure amount ratio obtained in each region by the actual exposure amount ratio deriving unit. An uneven exposure correction unit,
By solving, the above-described problems are solved.
(2) According to the second aspect of the present invention, by adjusting the time interval between opening and closing of the image sensor and the light shielding member, the object light incident on the light receiving surface of the image sensor is adjusted. This is applied to a shutter time error deriving method performed by a camera including a focal plane shutter configured to be capable of controlling the amount of light.
Photographing a stationary object having substantially constant luminance in time with a first shutter opening time to obtain a first image sensor output ;
Photographing the stationary object with a second shutter opening time to obtain a second image sensor output ;
The ratio of the exposure amount obtained during the first shutter opening time and the exposure amount obtained during the second shutter opening time from the first image pickup device output and the second image pickup device output. Deriving the exposure ratio,
Deriving a theoretical exposure amount ratio based on a ratio of a theoretical exposure amount obtained by the first shutter opening time and a theoretical exposure amount obtained by the second shutter opening time;
Deriving an error in seconds of the shutter based on a comparison result between the actual exposure amount ratio and the theoretical exposure amount ratio ;
Correcting a predetermined time interval between opening and closing of the shutter to obtain a given shutter opening time so as to reduce the second time error;
Dividing the output of the imaging device into a plurality of regions along the traveling direction of the shutter, and correcting exposure unevenness of the imaging device based on the actual exposure amount ratio obtained in each region;
Have

  According to the present invention, a first object obtained by photographing a stationary object having a substantially constant luminance in time with the first shutter opening time and the second shutter opening time, and with the first shutter opening time. The actual exposure amount ratio derived based on the comparison between the first image and the second image obtained by shooting with the second shutter opening time, the theoretical exposure amount based on the first shutter opening time, and the second Use a luminance box or a special adjustment device, etc. by deriving the error in seconds based on the comparison result with the theoretical exposure amount ratio obtained based on the ratio with the theoretical exposure amount due to the shutter opening time. Therefore, it is possible to measure and adjust the shutter time error.

  FIG. 1 is a block diagram showing a schematic configuration of a camera 10 according to an embodiment of the present invention. In the embodiment of the present invention, the camera 10 will be described as a focal plane shutter type single-lens reflex digital still camera from which the taking lens 180 can be removed. Of course, the present invention is also applicable to other types of cameras, such as cameras with fixed photographing lenses, cameras without a reflex mirror, cameras with lens shutters, and the like.

  The camera 10 includes a system controller 100, an information display unit 102, an operation switch 104, a nonvolatile memory 110, a DRAM 116, an image signal processing unit 120, a display control unit 122, an image display unit 124, an analog A front end 130 and a timing generator 132 are included. The camera 10 further includes an image sensor 134, an optical low-pass filter 136, a shutter 140, a front curtain locking magnet 142, a rear curtain locking magnet 144, a shutter charge mechanism 146, a main mirror 150, and a mirror drive. A shutter locking mechanism 152 and a sub mirror 154 are included. The camera 10 also includes a pentaprism 160, an eyepiece lens 162, a photometry unit 164, and a focus detection device 170. A photographic lens 180 and an image data recording medium 126 are detachably attached to the camera 10.

  The components described above will be described below. The photographing lens 180 includes a lens element 182, a diaphragm device 184, a diaphragm driving unit 186, and a lens driving unit 188. When the photographic lens 180 is attached to the camera 10 and the camera 10 is turned on, power is supplied to the photographic lens 180 from the camera 10 side. At the time of shooting, a control signal is issued from the camera 10 side to the aperture driving unit 186 and the lens driving unit 188 to adjust the aperture (set aperture value) of the aperture device 184 and the position of the lens element 182 in the optical axis direction.

  The main mirror 150 is a so-called quick return type reflex mirror configured to be rotatable about an axis P. The sub mirror 154 provided on the back surface of the main mirror 150 is configured to be rotatable about the axis Q. In a shooting preparation state (a state in which the user performs composition determination, focus adjustment, etc.), the main mirror 150 is positioned in the optical path of subject light that passes through the shooting lens 180 and travels through the camera 10. Most of the subject light transmitted through the photographing lens 180 is reflected by the main mirror 150 toward the pentaprism (pentagonal roof prism) 160. A part of the main mirror 150 is a semi-transparent mirror. When the main mirror 150 is positioned in the optical path of the subject light traveling through the camera 10 as described above, a part of the subject light that has passed through the semi-transparent portion of the main mirror 150 is reflected by the sub-mirror 154 and focused. Guided to the detector 170. The focus detection device 170 can be of a so-called phase difference detection type having a reflecting mirror, a condenser lens, a separator lens, a small image sensor, and the like.

  The subject light incident on the pentaprism 160 is reflected by the three reflecting surfaces provided on the pentaprism 160 and enters the eyepiece 162. The user can observe the subject image magnified by the eyepiece 162 by putting his eye on the eyepiece 162. Part of the subject light reflected and guided by the pentaprism 160 is incident on a photosensor included in the photometry unit 164, and the luminance of the subject is measured by the photometry unit 164.

  The mirror drive / shutter locking mechanism 152 drives the main mirror 150 and the sub mirror 154, and the main mirror 150 and the sub mirror 154 are positioned in the optical path of the subject light, and the subject light is transmitted to the pentaprism 160 and the focus detection device 170. The state is switched to the state of guiding, or the state of retracting from the optical path of the subject light and guiding the subject light toward the image sensor 134.

  The main mirror 150 is driven by the mirror driving / shutter locking mechanism 152, and is moved up to a position where it is retracted from the optical path of the subject light with the axis P as a rotation center at the time of photographing operation. At this time, the sub-mirror 154 is also flipped up to a position where it is retracted from the optical path of the subject light, with the axis Q as the center of rotation. At the end of the photographing operation, the main mirror 150 and the sub mirror 154 are returned to the positions in the photographing preparation state described above.

  The shutter 140 will be described. In the embodiment of the present invention, the shutter 140 is provided between the main mirror 150 and the image sensor 134 and is configured to be able to travel along a plane substantially orthogonal to the optical axis of the photographing lens 180. The description will be made assuming that the focal plane shutter has. The shutter 140 is a so-called longitudinal traveling focal plane shutter, and the curtain travel direction is a direction from top to bottom. That is, when shooting is performed with the camera 10 held in the horizontal position, the front curtain and the rear curtain travel from the upper side to the lower side in the vertical direction to perform the exposure operation. Of course, the running direction of the curtain may be a direction from the lower side to the upper side, or may be a so-called side running type or rotary type.

  The shutter 140 is used as a front curtain, a rear curtain, a mechanism component for moving the front curtain in the vertical direction, a mechanism component for moving the rear curtain in the vertical direction, a front curtain locking mechanism, and a rear curtain locking mechanism (not shown). In addition, the front-curtain locking magnet 142, the rear-curtain locking magnet 144, the front-curtain, and the front-curtain elastic member and the rear-curtain elastic member that store the driving force when the rear curtain travels are provided. it can. The driving force for running the front curtain and the rear curtain may be an electromagnetic force other than the elastic force.

  The front curtain locking magnet 142 and the rear curtain locking magnet 144 are composed of an electromagnet, a movable iron piece (armature), and the like. The stop state is maintained.

  When the shutter 140 is operated, when the energization to the front curtain locking magnet 142 is first released, the attractive force by the electromagnet is lost and the movable iron piece is separated. As a result, the front curtain locking state is released and the front curtain starts to travel. Thereafter, when the energization to the rear curtain locking magnet 144 is released, the rear curtain locking state is released by the same action as described above, and the rear curtain travels. By changing the timing to release the energization of the front curtain locking magnet 142 and the rear curtain locking magnet 144, the timing at which the front curtain starts to travel and the timing at which the rear curtain starts to travel are changed at the desired shutter speed. 140 can be exposed.

  The shutter charge mechanism 146 is a position before the start of traveling of the front and rear curtains of the shutter 140 when or after the mirror driving / shutter locking mechanism 152 returns the main mirror 150 and the sub mirror 154 to the shooting ready state. Return to. At this time, the front curtain elastic member and the rear curtain elastic member are elastically deformed and stored. At the time of shutter charging, the front curtain locking magnet 142 and the rear curtain locking magnet 144 are not energized and no attracting force is generated. However, when the main mirror 150 and the sub-mirror 154 are in the shooting ready state, the mirror driving / shutter locking mechanism 152 mechanically maintains the locked state of the front curtain and the rear curtain. Therefore, the shutter 140 does not operate at an unintended timing. Energization of the front curtain locking magnet 142 and the rear curtain locking magnet 144 is started immediately before the mirror driving / shutter locking mechanism 152 drives the main mirror 150 and the sub mirror 154 to a position where they are retracted from the optical path of the subject light. The Thereby, power consumption is suppressed.

  The optical low-pass filter 136 is configured by combining an optical member having a birefringence action and an optical member having a polarization action, and reduces high spatial frequency components in the transmitted subject light. On the surface of the optical low-pass filter 136, a layer (thin film) having a characteristic of blocking infrared light is formed as necessary. Alternatively, a film having a characteristic of absorbing infrared light, a glass substrate, or the like may be provided separately.

  The image sensor 134 can be a CCD image sensor or a CMOS image sensor. In the embodiment of the present invention, the image sensor 134 will be described as a single-plate CMOS color image sensor in which an on-chip color filter having a Bayer array is formed on the light receiving surface.

  The analog front end 130 (denoted as “AFE” in FIG. 1) performs processing such as correlated double sampling, amplification, and AD conversion on the analog image signal output from the image sensor 134, and performs digital processing. An image signal is generated. The analog front end 130 may be provided in the image sensor 134.

  A timing generator 132 (denoted as “TG” in FIG. 1) generates a timing pulse based on a command output from the image signal processing unit 120 and outputs the timing pulse to the image sensor 134. The image sensor 134 outputs an image signal to the analog front end 130 in a dot sequential manner in synchronization with the timing pulse.

  The DRAM 116 is a volatile memory configured to be accessible from both the image signal processing unit 120 and the system controller 100, and is used as a work area when the image signal processing unit 120 and the system controller 100 perform processing to be described later. It is done.

  The nonvolatile memory 110 is configured by a flash memory or the like. The nonvolatile memory 110 stores adjustment parameters 112, a control program 114, and the like. The adjustment parameter 112 and the control program 114 will be described later.

  The image data recording medium 126 includes a memory card, a small hard disk drive, a floppy (registered trademark) disk, or the like, and is configured to be detachable from the camera 10. Image data generated by the camera 10 is recorded in the image data recording medium 126.

  The image display unit 124 includes a TFT display element and a backlight device, an organic EL display element, or the like, and is configured to be able to display an image obtained by photographing in color. Further, it is possible to display a menu screen as necessary, and to display characters and graphics for transmitting information to the user.

  The display control unit 122 controls the image display unit 124 to display an image based on the signal output from the image signal processing unit 120.

  The image signal processing unit 120 receives the digital image signal output from the analog front end 130 and temporarily stores it in the DRAM 116. When all the digital image signals obtained by one shooting are stored in the DRAM 116, the image signal processing unit 120 performs a process such as demosaic, white balance correction, shading correction, level correction, gradation correction and the like on the digital image signal. To generate image data. In the present specification, the signal before the above processing is referred to as a digital image signal, and the processed signal is referred to as digital image data. The image signal processing unit 120 compresses the digital image data as necessary, and records the processed image data in the image data recording medium 126. The image signal processing unit 120 also generates display image data based on the generated image data and the image data read from the image data recording medium 126 and outputs the display image data to the display control unit 122. The display control unit 122 displays an image based on the received display image data on the image display unit 124.

  The system controller 100 can be configured with a CPU, hardware logic, or the like, but in the present embodiment, it is configured with a CPU. The system controller 100, the front curtain locking magnet 142, the rear curtain locking magnet 144, the shutter charge mechanism 146, the mirror drive / shutter lock mechanism 152, the aperture drive unit 186, the lens drive unit 188, etc. are electrically connected via the bus 106. Connected. The system controller 100 sequentially reads and executes the control program 114 transferred from the nonvolatile memory 110 to the DRAM 116, and controls the operation of each component described above to control the overall operation of the camera 10.

  The adjustment parameter 112 will be described. Mechanical parts and electronic parts constituting the camera 10 have manufacturing variations. Due to these variations, even if the individual cameras 10 are controlled based on the same control program, variations in operation and accuracy may occur. The adjustment parameter 112 is written corresponding to each camera 10 in the manufacturing / adjustment process in order to reduce such variation.

  For example, there may be individual differences in the time from when the energization to the front curtain locking magnet 142 and the rear curtain locking magnet 144 is released until the movable iron piece starts to separate. The elastic force of the elastic member for running may have individual differences. Further, when the front curtain and the rear curtain travel, the frictional force acting on the front curtain and the rear curtain may have individual differences. These individual differences cause variations in the travel distance (slit width) between the front curtain and the rear curtain and the travel speed of the curtain. Therefore, even if the energization to the trailing curtain locking magnet 144 is canceled 1/8000 seconds after the energization of the leading curtain locking magnet is canceled, the obtained shutter time (exposure time) is not necessarily 1/8000 seconds. It does not always become. Therefore, time interval correction information for adjusting (increasing or decreasing) the time interval from when the energization to the front curtain locking magnet 142 is released until the energization to the rear curtain locking magnet 144 is released is used as the adjustment parameter 112. It can be stored in the non-volatile memory 110. Details of the time interval correction information will be described later with reference to FIG.

  In addition to the time interval correction information described above, the adjustment parameter 112 adjusts the photometry accuracy adjustment information of the photometry unit 164, the gain adjustment at the analog front end 130, or the level and linearity during AD conversion. For example, various adjustment information can be stored.

  The information display unit 102 is configured by a monochrome or color liquid crystal display device or the like provided in the upper part or rear surface of the camera 10 or in the viewfinder. The information display unit 102 may also include an LED or the like. In addition to or in place of the information display unit 102, the camera 10 may have a device such as a sounding body and a vibration motor for transmitting sound and vibration to the user.

  The operation switch 104 is a general term for various switches provided in the camera 10 such as a release switch, a slide switch, a dial switch, and a push switch. The user uses the operation switch 104 to perform operations such as setting of an aperture value, shutter speed, equivalent ISO sensitivity, exposure mode, switching of the camera operation mode (recording mode / playback mode, etc.), menu selection, start of shooting operation, etc. It becomes possible to do.

  FIG. 2 is a block diagram illustrating a processing unit included in the system controller 100. FIG. 2 shows only the system controller 100 and some of the components shown in FIG. The system controller 100 includes a shutter time setting unit 200, a shutter timing control unit 202, an actual exposure amount ratio deriving unit 204, a second time error deriving unit 206, a shutter accuracy decrease notification processing unit 208, and a time interval correcting unit 210. And have. When the system controller 100 sequentially reads and executes the control program 114 transferred from the non-volatile memory 110 to the DRAM 116, each processing unit described above functions.

  The shutter time setting unit 200 performs a process of setting the opening time (shutter seconds) of the shutter 140. For example, when the camera 10 is set to the aperture priority exposure mode, the set equivalent ISO sensitivity, the aperture value of the photographing lens 180 set by the user, the photometric result obtained from the photometric unit 164, and the like. Based on this, the shutter time setting unit 200 sets an open time (shutter time) when the shutter 140 operates.

  The shutter timing control unit 202 controls a time interval from when the shutter 140 is opened to when it is closed based on the opening time set by the shutter time setting unit 200. Specifically, the shutter timing control unit 202 releases the energization to the front curtain locking magnet 142 based on the release time set by the shutter time setting unit 200 and then energizes the rear curtain locking magnet 144. A time interval until release (hereinafter, a time interval from when the energization to the front curtain locking magnet 142 is released until the energization to the rear curtain locking magnet 144 is released is referred to as a delay time) is determined. The delay time corresponding to the shutter time set by the shutter time setting unit 200 is stored in the nonvolatile memory 110 in the form of a data table, and can be read out by the shutter timing control unit 202. . Alternatively, a calculation formula for calculating the delay time from the shutter time set by the shutter time setting unit 200 is incorporated in the control program 114, and the delay time is calculated by the shutter timing control unit 202 before the shutter opening / closing operation. You may make it do.

  The actual exposure amount ratio deriving unit 204 stops the subject having substantially constant luminance in time (having substantially constant luminance regardless of the passage of time), and maintains the equivalent ISO sensitivity, etc., in a first manner. A ratio of exposure amounts when shooting is performed with a shutter opening time (for example, 1/8192 seconds) and a second shutter opening time (for example, 1/4096 second) different from the first shutter opening time. This actual exposure amount ratio is not a theoretical exposure amount ratio (in the above example, 2 which is a ratio of 1/8192 seconds and 1/44096 seconds, or 1 Ev by APEX calculation), but actually obtained exposure amount. The ratio of quantities.

  The second time error deriving unit 206 derives the second time error of the shutter 140 based on the comparison result between the actual exposure amount ratio and the theoretical exposure amount ratio. For example, when the theoretical exposure amount ratio is 1 Ev and the actual exposure amount ratio is 0.8 Ev, the exposure amount error is 0.2 Ev. The second time error deriving unit 206 derives the second time error from the exposure amount error by a method described later.

  When the second error derived by the second error deriving unit 206 exceeds a predetermined allowable amount, for example, an allowable amount corresponding to plus or minus 0.3 Ev in the APEX calculation, the shutter accuracy reduction notification processing unit 208 A process of notifying the user to that effect is performed. As a method of notifying the user, it is possible to display on the image display unit 124 that the shutter time error is unacceptable, or to display pictograms or the like on the information display unit 102. Or you may display using a liquid crystal display device, LED, etc. in a finder, or operate a sounding body, a vibration motor, etc., and may notify a user.

  The time interval correction unit 210 calculates the second derived by the second time error deriving unit 206 with respect to the time interval (delay time) controlled by the shutter timing control unit 202 based on the open time set by the shutter time setting unit 200. A correction process is performed to reduce the time error.

  FIG. 3 is a diagram showing the relationship between the timing at which the energization to the front curtain locking magnet 142 and the rear curtain locking magnet 144 is released and the travel timing of the front curtain and rear curtain of the shutter 140. FIG. 3A shows a state where an ideal shutter time is obtained with respect to the delay time set by the shutter timing control unit 202. FIG. 3B shows a state in which the obtained shutter time (actual time) has an error with respect to the delay time set by the shutter timing control unit 202 corresponding to the target time. In FIG. 3C, the delay time set by the shutter timing control unit 202 is corrected corresponding to the target time, and the resulting shutter time (actual time) is the target time. It shows a state that almost matches. In each of (a), (b), and (c) of FIG. 3, time is shown in the left-right direction of the figure, and changes in events (front curtain lock release signal, rear curtain function) are shown in the vertical direction. The change of the stop release signal, the state from the start of the leading curtain and the trailing curtain to the completion of traveling) are shown.

  In FIG. 3A, after the energization of the front curtain locking magnet 142 is released, the energization of the rear curtain locking magnet 144 is released after a delay time equal to the target shutter speed, and the resulting shutter is obtained. Second time (actual time) is substantially equal to the target shutter time.

  In FIG. 3B, after the energization to the front curtain locking magnet 142 is released, the delay to the rear curtain locking magnet 144 is performed after the delay time set by the shutter timing control unit 202 corresponding to the target time. The state where the energization is released is shown. The obtained shutter speed (actual time) is deviated from the target time. The difference between the target second time and the actual second time (shutter second time error) is added to the delay time set by the shutter timing control unit 202. In the example shown in FIG. 3B, the actual second time is longer than the target second time. Therefore, in the example shown in FIG. 3C, the value obtained by subtracting the shutter time error (= time interval correction amount) shown in FIG. 3B from the delay time before correction is the delay time after correction. Is set. As a result, the obtained shutter time is approximately equal to the target time.

  The above will be described using specific numbers. For example, the actual shutter speed for the nominal value 1/8000 seconds is 1/8192 seconds, which is 122 microseconds. That is, by releasing the energization to the rear curtain locking magnet 144 after the time interval of 122 microseconds after the energization to the front curtain locking magnet 142 is released, the shutter time (the nominal value 1/8000 seconds) ( 122 microseconds) is assumed to be obtained. This is the state of FIG. However, it is assumed that due to the above-described factors, the shutter time obtained by controlling the shutter 140 at the above time interval is longer and is 142 microseconds. This is the state of FIG. That is, the target second time is 122 microseconds, and the actual second time is 142 microseconds.

  In such a case, the shutter time error, that is, target second time−real second time = 122−142 = −20 (microseconds) is stored in the nonvolatile memory 110 as information of the time interval correction amount for the time interval 1/8192 seconds. do it. In the subsequent shooting operation by the camera 10, for the target time of 1/8192 seconds, −20 microseconds is added to the time interval of 122 microseconds which is the control reference value, and the leading curtain locking magnet 142 is supplied. By setting the time interval from when the energization is released to when the energization to the trailing curtain locking magnet 144 is released to 102 microseconds, the shutter time of 1/8192 seconds (122 microseconds) is obtained as a result. ) Can be obtained. Similarly, for the target time of 1/4096, -20 microseconds is added to the time interval of 244 microseconds, which is the control reference value, and the energization of the front curtain locking magnet 142 is released, and thereafter By setting the time interval until the energization to the curtain locking magnet 144 to be released is 224 microseconds, it is possible to obtain a shutter time of 1/4096 second (244 microseconds) (real time) as a result. Become.

  By the way, the time interval correction amount described above can be directly obtained without providing a sensor (curtain travel sensor) for detecting the travel timing of the front curtain and the rear curtain in the shutter 140 or using an expensive shutter tester or the like. Can not. However, in the camera 10 according to the embodiment of the present invention, the time interval correction amount can be derived without using the curtain travel sensor or the shutter tester by using the method described below.

  FIG. 4 is a diagram conceptually showing a state in which the camera 10 is operated in the shutter calibration mode, which is an operation mode for confirming the shutter accuracy and correcting as necessary. It is desirable that the test chart TC is illuminated with a substantially constant illuminance in time and has a substantially uniform reflectance. As an example, it is possible to use plain paper illuminated by sunlight or DC-driven lighting equipment as the test chart TC. If there is no suitable test chart TC, a stationary object can be used instead of the test chart TC. For example, the camera 10 can be directed to a clear blue sky. Further, the stationary object does not necessarily need to be plain.

  The camera 10 shoots the same scene several times in the shutter calibration mode, and confirms the accuracy of the shutter 140 as will be described later from the difference in the amount of exposure obtained, so it is desirable that the camera 10 be fixed to a tripod TP or the like. . Assume that the camera 10 is equipped with a photographing lens 180. Instead of using the test chart TC, it is possible to cover the light incident portion of the photographing lens 180 with a semi-transparent milky white hemispherical cap. In this case, it is desirable that the amount of light incident on the hemispherical cap is stable in time during the calibration operation.

  FIG. 5 conceptually shows a digital image signal (digital signal before demosaic processing or the like) output from the analog front end 130 after photographing in the state shown in FIG. Alternatively, the pixels may be considered to be two-dimensionally arranged on the image area of the image sensor 134. It is assumed that the front curtain and rear curtain of the shutter 140 travel corresponding to the direction from the upper side to the lower side in FIG. This digital image signal is assumed to be two-dimensionally arranged in p rows × q columns.

  Corresponds to the upper end (the part that is exposed first), the center (the part that is exposed at an intermediate timing), and the lower end (the part that is exposed last) in the image signal obtained by one photographing operation. Image signals of partial areas P1, P2, and P3 to be extracted are extracted. Each partial region has the number of pixels of A pixels in the horizontal direction and B pixels in the vertical direction in FIG. In FIG. 5, one rectangle to which R, Gr, Gb, or B is attached means one pixel. The rectangle with the symbol R means a pixel in which a red on-chip color filter is provided on the photodiode. Similarly, the rectangles labeled Gr and Gb have pixels with a green on-chip color filter provided on the photodiode, and the rectangles labeled B with a blue on-chip color filter provided on the photodiode. Means the selected pixel. In the following, a pixel provided with a red on-chip color filter is an R pixel, a pixel provided with a green on-chip color filter is a G pixel (referred to as Gr pixel and Gb pixel when it is necessary to distinguish), and a blue on-chip color filter is provided. A pixel provided with a chip color filter is referred to as a B pixel. The pixel values corresponding to these R pixel, G pixel, and B pixel can be digital values having a bit depth of, for example, 8 bits, 12 bits, and 14 bits.

  The G output average value is obtained corresponding to each of the partial areas P1, P2, and P3. That is, as shown below, the sum of the pixel values of the Gr pixel and the Gb pixel is obtained corresponding to each partial region P1, P2, and P3, and the G output average value is obtained.

When the sum of the pixel values of the Gr pixels is represented by SumGr and the sum of the pixel values of the Gb pixels is represented by SumGb, the G output average value can be obtained by the following equation. In the following formula, A and B mean the number of pixels in the horizontal and vertical directions of the partial areas P1, P2, and P3. In each partial area P1, P2, P3, the number of G pixels is only half of the total number of pixels (A × B) in each partial area, so 2 is multiplied in the following equation.

G output average value = (SumGr + SumGb) ÷ (A × B) × 2 (1)

The G output average value is calculated from each image signal obtained at two different shutter seconds (for example, nominal value 1/4000 sec, nominal value 1/8000 sec) while the equivalent ISO sensitivity and aperture value are fixed. The Therefore, the G output average value calculated from the image signal obtained by photographing at the nominal value of 1/4000 seconds is calculated from G (4000), and the image signal obtained by photographing at the nominal value of 1/8000 seconds. The G output average value is expressed as G (8000). The theoretical value for the second corresponding to the nominal value 1/4000 second is 1/4096 second≈244 microseconds, and the theoretical value for the second corresponding to the nominal value 1/8000 second is 1/8192 second≈122 microseconds. Express.

In general, the shutter time error (FIG. 3B) has a property that is substantially constant even when the shutter time is changed. Now, when the shutter time error is expressed by ΔS (microseconds), the following relational expression is established.

log ₂ (244 + ΔS) −log ₂ (122 + ΔS)
= Log ₂ G (4000) -log ₂ (G8000) ... Formula (2)

In the above formula, the left side is the difference in Tv value in the APEX calculation, and the right side is the difference in Ev value in the APEX calculation. Since the Av value and the Sv value are fixed as described above, the difference in Tv value can be calculated (estimated) from the difference in Ev value. When the right side of the above formula (2) is replaced with ΔEv, the formula (2) can be expressed by the following formula (3).

log ₂ (244 + ΔS) −log ₂ (122 + ΔS) = ΔEv Equation (3)

Hereinafter, the expression (3) is modified.

log ₂ [(244 + ΔS) / (122 + ΔS)] = ΔEv

(244 + ΔS) / (122 + ΔS) = 2Δ <sup>Ev

244 + ΔS = 2Δ Ev × (</sup> 122 + ΔS) = 122 × 2Δ Ev + ΔS × 2Δ Ev

ΔS−ΔS × 2Δ ^Ev = 122 × 2Δ ^Ev −244

ΔS × (1-2Δ ^Ev ) = 122 × 2Δ ^Ev −244

Therefore,

ΔS = (244−122 × 2Δ ^Ev ) / (2Δ ^Ev −1)

That is, the shutter time error can be obtained by the following equation (4).

  Using the above equation (4), the shutter time is obtained from the G average value obtained when the nominal shutter speed is 1/8000 second and the G average value obtained when the nominal value is 1/4000 seconds. An error can be obtained. Note that the combination of the shutter time of 1/4000 seconds and 1/8000 seconds is merely an example, and any combination of seconds can be used within the range of the dynamic range of the image sensor.

  Further, when the aperture accuracy of the taking lens 180 is known, the aperture value may be changed. In other words, it is possible to open the aperture for a relatively short shutter time and close the aperture for a relatively long shutter time. By doing so, it is possible to suppress the occurrence of whiteout and blackout pixels in the image signal, and it is possible to perform more accurate calibration. When the aperture value is also changed, it is necessary to change the constant in the equation (4) in consideration of aperture value combinations and aperture value errors corresponding to different shutter speeds.

  Using the above equation (4), the shutter time error is obtained corresponding to each of the partial areas P1, P2, and P3. The shutter time errors corresponding to these divided areas P1, P2, and P3 are referred to as DEC_upper, DEC_center, and DEC_lower, respectively.

  In the above example, if the results are used once for each of 1/4000 seconds and 1/8000 seconds, there is a case where the influence of so-called uneven cutting may occur. For this reason, it is desirable to obtain the average value, the mode value, etc. by obtaining the shutter time error by repeating the above process several times. For example, in the case of repeating n times, it is possible to obtain the average value of the shutter time error (average shutter time error) using the following equation (5). In the following formula (5), DEC_center (x) means the shutter time error at the xth time (x = 1, 2,... N) when the determination of the shutter time error is repeated n times.

  In the above example, DEC_upper and DEC_lower are not used when obtaining the average shutter-second error, but these values may be used.

  Here, with reference to FIG. 6, a description will be given of the relationship between the shutter time error at the upper end, the center, and the lower end of the image area, that is, the size of DEC_upper, DEC_center, and DEC_lower and the running characteristics of the shutter curtain. For example, when the elastic force acting on the front curtain differs from the elastic force acting on the rear curtain for some reason, the running characteristics of the front curtain and the running characteristics of the rear curtain may be different as shown in FIG. . Alternatively, even when the frictional force applied during the front curtain travel is different from the frictional force applied during the rear curtain travel, the travel characteristics of the front curtain and the rear curtain may be different as shown in FIG. is there.

  FIG. 6A shows three cases in which the driving characteristics of the rear curtain are different from the driving characteristics of the front curtain, and shows a state after the DEC_center is made equal. FIG. 6B shows an example in which the curtain speed of the rear curtain is slower than the curtain speed of the front curtain, the exposure amount is insufficient at the upper end and the exposure amount is excessive at the lower end as compared with the exposure amount at the center. FIG. 6C shows an example in which the curtain speeds of the front curtain and the rear curtain are substantially equal, and a substantially uniform exposure amount is obtained at the upper end, the center, and the lower end. FIG. 6D shows an example in which the curtain speed of the rear curtain is higher than the curtain speed of the front curtain, the exposure amount is excessive at the upper end compared to the exposure amount at the center, and the exposure amount is insufficient at the lower end. Yes. FIGS. 6B, 6C, and 6D also show the state after alignment so that DEC_center is equal, as in FIG. 6A. In the case as shown in FIGS. 6B and 6D, uneven exposure occurs. Hereinafter, a first embodiment and a second embodiment of the present invention will be described.

-First embodiment-
In the first embodiment, an operation for detecting an error in shutter second time is performed in response to the user switching the operation mode of the camera 10 from the normal shooting mode to the shutter calibration mode, and the result is notified to the user. . At this time, if the detected shutter time error deviates from a predetermined allowable amount, a notification to that effect is given to the user, and whether or not the user desires to adjust the shutter time. Confirm that. If the user does not wish to adjust the shutter speed, a message prompting contact to the support center is displayed together with contact information of the support center.

  The above-described operation will be described with reference to the flowcharts of FIGS. The flowchart shown in FIGS. 7 and 8 is an outline of the shutter-second calibration executed by the system controller 100 in response to the user operating the camera 10 and switching its operation mode from the normal shooting mode to the shutter calibration mode. The process procedure is shown. Assume that the camera 10 is set to the state described with reference to FIG. 4 as a premise when the processing shown in FIGS. 7 and 8 is executed. That is, it is assumed that the camera 10 is fixed by a tripod TP or the like and is directed to a stationary object (test chart TP) whose luminance is stable over time. In addition, when the camera 10 has a continuous shooting mode (a mode in which shooting operations are continuously performed while the release switch is pressed), setting the continuous shooting mode can shorten the calibration operation. It is desirable to complete in a short time.

  In S700, the system controller 100 sets the Av value and Sv value of the camera 10. That is, the aperture value of the photographing lens 180 and the gain set by the analog front end 130 when performing the photographing operation in the shutter calibration mode are set to a predetermined value or a value determined by the user. Thereafter, the Av value and the Sv value are kept constant until the shutter calibration mode processing is completed.

  In S702, the system controller 100 clears the counter value C. The counter value C is a counter that counts the number of times when the photographing operation is repeatedly performed in order to derive the shutter time error.

  In S704, the system controller 100 sets the shutter time to a nominal value of 1/8000 seconds. At this time, the shutter timing control unit 202 (FIG. 2) sets a delay time of 1/8192 seconds (122 microseconds).

  In S706, the system controller 100 executes shooting. At this time, the digital image signal output from the image sensor 134 and processed by the analog front end 130 is output to the system controller 100 via the image signal processing unit 120. In step S708, the system controller 100 acquires this digital image signal and temporarily records it in the DRAM.

  In S710, the system controller 100 inputs the photometric value immediately before or after the shooting is performed in S706 from the photometric unit 164, and stores it as B1.

  In S712, the system controller 100 derives the G output average value from the digital image signal acquired in S708 using Expression (1). At this time, it is desirable to derive the G output average value from the pixel value of the partial region P2 shown in FIG. 5 using Equation (1).

  In S714, the system controller 100 sets the shutter time to a nominal value of 1/4000 seconds. At this time, the shutter timing control unit 202 (FIG. 2) sets a delay time of 1/4096 second (244 microseconds).

  In step S716, the system controller 100 executes shooting. At this time, the digital image signal output from the image sensor 134 and processed by the analog front end 130 is output to the system controller 100 via the image signal processing unit 120. In step S718, the system controller 100 acquires this digital image signal and temporarily records it in the DRAM.

  In S720, the system controller 100 inputs the photometric value immediately before or after the photographing is performed in S716 from the photometric unit 164, and stores it as B2.

  In S722, the system controller 100 derives the G output average value from the digital image signal acquired in S718 using Expression (1). At this time, it is desirable to derive the G output average value from the pixel value of the partial region P2 shown in FIG. 5 using Equation (1).

  In S724, the system controller 100 determines whether or not the absolute value of the value obtained by subtracting B2 from B1 is smaller than a predetermined value B. If this determination is affirmative, the system controller 100 proceeds to S726 and is denied. If so, the process returns to S702. That is, the difference between the subject brightness when shooting is performed at the nominal shutter speed of 1/8000 seconds and the subject brightness when shooting is performed at the nominal shutter speed of 1/4000 seconds is predetermined. If it is determined that the value is larger than the reference value B, all the data obtained up to the time of this determination is discarded, and a series of processing procedures relating to the shutter second time calibration is restarted from the beginning.

  A large difference in the subject brightness means that the subject brightness is not stable. For example, when the test chart TC (FIG. 4) is illuminated with a fluorescent lamp or the like, the above difference may increase due to the influence of flicker or the like. The predetermined reference value B can be about 0.1 in terms of the Bv value of the APEX calculation. On the other hand, when the difference in subject brightness is small, the subject brightness is stable (has substantially constant brightness over time).

  The reason for performing the processes of S710, S720, and S724 is to enable more accurate calibration at the shutter speed. In other words, since the error in the shutter speed is obtained from the difference in the exposure amount, shooting with an unstable subject brightness causes a variation in the exposure amount, and the resulting reliability of the error in the shutter time is obtained. This is because there is a possibility of lowering the degree.

  In S726, the system controller 100 calculates the shutter time error using the equation (4) from the G output average value G (8000) derived in S712 and the G output average value G (4000) derived in S722. To derive.

  In S728, the system controller 100 increments the counter value C. In subsequent S730, it is determined whether or not the incremented counter value C is greater than or equal to a positive integer N. If this determination is affirmed, the process proceeds to S732. If the determination is negative, the process returns to S704, and the above-described process is repeated. That is, the above process is repeated N times, which is a preset number of times. N can be set to 5, for example. When N = 5, a total of 10 shooting operations are performed. However, if the camera 10 is set to the continuous shooting mode and the subject brightness is stable, the process from S704 to S730 is performed within a few seconds. It is possible to complete a series of processes.

  In S732, the system controller 100 derives the average value of the shutter time error from the N shutter time error derivation results derived in S726.

  In S734, the system controller 100 determines whether or not the average value of the shutter time error derived in S732 is within the allowable range. If this determination is affirmative, the process proceeds to S742, and if it is negative, S736 is determined. Proceed to That is, if the average value of the shutter time error is within a predetermined allowable range (for example, about 0.3 in terms of Tv value in the APEX calculation), the process proceeds to S742, and there is no need to readjust the shutter time. The system controller 100 performs a process for displaying the effect on the image display unit 124. FIG. 9 shows an example of the content displayed on the image display unit 124, and the example shown in FIG. 9A corresponds to the display processing result in S742.

  In S742, the system controller 100 determines whether or not the user has performed a “return” operation. While this determination is denied, the system controller 100 repeats the process of S744, and when the determination of S742 is affirmed, the shutter speed calibration is performed. Complete the process. For example, it is detected that a “return” character as shown in FIG. 9A is displayed on the image display unit 124 and that the user who sees this display presses the operation switch 104 to perform a determination operation. Then, the determination in S744 is affirmed.

  When the determination in S734 is negative, that is, in S736, which is a branch destination when the shutter time error is not within the allowable range, a process for confirming to the user whether or not to perform the shutter time adjustment is performed. The system controller 100 does this. Corresponding to the processing of S736, the image display unit 124 displays as illustrated in FIG. 9B. When the display as shown in FIG. 9B is performed, the shutter time error may be displayed by an APEX display or the like. For example, a display such as “There is an error equivalent to +0.35 Ev in 1/8000 second” can be displayed.

  In step S <b> 738, the system controller 100 determines whether the user desires execution of the shutter speed adjustment. For example, in the display of “Yes” and “No” as shown in FIG. 9B, the user may select “Yes” by operating the operation switch 104 and then perform the determination operation. If detected, the determination in S738 is affirmed. If the determination in S738 is affirmative, the process proceeds to S740, and a process for updating the adjustment parameter is performed. For example, when the time interval correction amount before the update is plus 40 microseconds and the average value of the shutter time error derived in S732 is minus 55 microseconds, the time interval correction amount after the update is plus 95 microseconds. . When the process of S740 is completed, a series of shutter time calibration processes is completed.

  In S746, which is a branch destination when the determination in S738 is negative, the system controller 100 displays an image of a message prompting contact with the support center as exemplified in FIG. Processing to be displayed on the unit 124 is performed.

  In step S748, the system controller 100 determines whether or not the user has performed a “close” operation. While this determination is negative, the system controller 100 repeats the processing in step S748, and if the determination in step S748 is affirmative, calibration is performed at the shutter speed. Complete the process. For example, it is detected that the character “Close” as shown in FIG. 9C is displayed on the image display unit 124, and the user who sees this display presses the operation switch 104 and performs a determination operation. Then, the determination in S748 is affirmed.

  According to the first embodiment described above, confirmation of the shutter speed and adjustment as necessary are performed without using a device such as a luminance box, a shutter tester, or an image surface exposure meter. Is possible.

  In the above, an example of performing a series of calibration operations with the camera 10 fixed on a tripod has been described. However, if the user holds the camera 10 facing the clear blue sky or the like when the user switches the camera 10 to the continuous shooting mode, within a few seconds. It is also possible to complete a series of shutter speed calibration and adjustment.

  In the above, the focal plane shutter is configured as a shutter configured to be able to control the amount of subject light incident on the light receiving surface of the image sensor by adjusting the time interval from when the light shielding member is opened to when it is closed. The example used is described. However, the present invention is not limited to this example. In other words, the present invention is applied to cameras having all types of shutters that can control the amount of subject light incident on the light receiving surface of the image sensor by adjusting the time interval from when the light shielding member is opened to when it is closed. Is possible.

  In the above description, an example in which the digital image signal before the demosaic process is performed by the image signal processing unit 120 when the shutter time error is derived has been described. It is also possible to derive the shutter time error using the digital image signal.

-Second Embodiment-
In the second embodiment, an operation for detecting an error in shutter second time is performed in response to the user switching the operation mode of the camera 10 from the normal shooting mode to the shutter calibration mode. If the detected shutter time error deviates from a predetermined allowable amount, the shutter time adjustment is automatically performed. Further, based on the size of the exposure unevenness described with reference to FIG. 6, it is determined whether or not the exposure unevenness needs to be adjusted. If it is determined that the exposure unevenness is necessary, a process for correcting the exposure unevenness is performed.

  FIG. 10 is a block diagram centering on differences from the camera 10 shown in FIG. 1 in the camera 10A according to the second embodiment of the present invention. Components not shown in FIG. 10 are the same as those shown in FIG. Also, in FIG. 10, components having the same reference numerals as those shown in FIG. 1 are the same as those shown in FIG. 1. Therefore, description of these components is omitted. In FIG. 10, the components with the alphabetic letter A added to the three-digit number have basically the same functions and configurations as the components with the same three-digit number in FIG. 1. Is different.

  The timing generator 132A is different from that shown in FIG. 1 in that its output is also output to the system controller 100A. DRAM 116A is different from that shown in FIG. 1 in that a storage area for gain memory 117 is further secured in the storage area.

  The system controller 100A differs from that shown in FIG. 1 in that it further includes a multiplication processing unit 121 and an address designating unit 101. The multiplication processing unit 121 and the address designating unit 101 also function when the system controller 100A reads and executes the program transferred from the nonvolatile memory 110A to the DRAM 116A.

  The nonvolatile memory 110A has an area for storing an adjustment parameter 112A, and is different in that gain information for correcting uneven exposure is recorded in the adjustment parameter 112A.

  The camera 10A differs from the components shown in FIG. 1 in that it has the above-described components 132A, 116A, 100A, and 110A instead of the timing generator 132, the DRAM 116, the system controller 100, and the nonvolatile memory 110.

  The system controller 100A obtains the actual exposure amount ratio in each of the partial areas P1, P2, and P3 shown in FIG. That is, the system controller 100A uses the expression (1) to calculate the G output average value corresponding to each of the partial areas P1, P2, and P3 in the two image signals obtained by photographing at different set shutter times. Ask. Then, from the ratio of the G output average values (actual exposure amount ratio) obtained corresponding to different shutter times and the theoretical exposure amount ratio obtained from different set shutter times, the partial areas P1, P2, and P3 Corresponding to each, an error in seconds is obtained.

  By the way, as described with reference to FIG. 6, the fact that there is uneven exposure means that the second time error is different in each of the partial areas P1, P2, and P3. First, the system controller 100A determines the time interval correction amount based on the second time error obtained in the partial region P2. As a result, there is no shutter time error in the partial region P2. On the other hand, in the partial areas P1 and P3, after the time interval correction amount determined based on the second time error obtained in the partial area P2 is applied, the exposure amount error changes.

  For example, it is assumed that the shutter 140 has a leading curtain traveling characteristic and a trailing curtain traveling characteristic as shown in FIG. The shutter time error is −40 microseconds near the upper end (near the partial area P1), −30 microseconds near the center (near the partial area P2), and −20 microseconds near the lower end (near the partial area P3). Suppose that In such a case, correction is performed based on the shutter time error in the partial region P2. Therefore, the shutter time error after the shutter time correction is −10 microseconds near the upper end, 0 microseconds near the center, and +10 microseconds near the lower end. In other words, the entire screen has uneven exposure for 20 microseconds at the shutter speed. When this unevenness in exposure is converted into an Ev value, it becomes −0.12 Ev in the vicinity of the upper end, 0 Ev in the center, and +0.11 Ev in the vicinity of the lower end.

  When the exposure unevenness exceeds a predetermined reference value (for example, 0.2 Ev), the system controller 100A derives gain unevenness correction gain information and adds it to the adjustment parameter 112A as described below. .

  Referring to FIG. 5, the system controller 100A performs exposure unevenness correction gain information applied to image signals that are two-dimensionally arranged in the row direction (left-right direction in FIG. 5) and the column direction (up-down direction in FIG. 5). As a result, gain information to be applied to each row is derived. That is, the first row (the uppermost row in FIG. 5), the second row,..., The pth row (the lowermost row in FIG. 5) are interpolated from the exposure amount errors in the partial areas P1, P2, and P3. ), Gain information can be derived.

  The shutter time error correction process and the exposure unevenness correction gain information derivation process described above will be described with reference to FIGS. The processing shown in FIGS. 7 and 11 is executed by the system controller 100A in response to the user operating the camera 10 and switching the operation mode from the normal photographing mode to the shutter calibration mode.

  The flowchart shown in FIG. 11 shows a processing procedure executed following the processing of the flowchart shown in FIG. That is, also in the second embodiment, when shooting is performed at different shutter times, and the G average value is derived to derive the shutter time error, the same processing as shown in FIG. 7 is performed. Done. Therefore, during the processing shown in FIG. 7, the description of the same processing as that of the first embodiment is omitted, and the description will focus on differences from the first embodiment.

  During the process shown in FIG. 7, the processes of S712, S722, and S726 are different from those of the first embodiment in the second embodiment. In other words, in the processes of S712, S722, and S726, only the pixel values of the partial area P2 are processed in the first embodiment, but in the second embodiment, the partial areas P1, P2, and P3 are respectively processed. Pixel values are to be processed.

  In S1100 subsequent to the processing of FIG. 7, the system controller 100A determines that each of the partial areas P1, P2, and P3 is based on the N shutter second time error derivation results derived in S726 corresponding to the partial areas P1, P2, and P3. The average value of the corresponding shutter speed error is derived.

  In S1102, the system controller 100A determines whether or not the average value of the shutter time error of the partial region P2 is within the allowable range among the average value of the shutter time error derived in S732, and this determination is affirmative. If YES, the process proceeds to S1104, and if NO, the process proceeds to S1110. That is, if the average value of the shutter time error in the partial area P2 is within a predetermined allowable range (for example, about 0.3 in terms of Tv value in the APEX calculation), the process proceeds to S1104. On the other hand, when it is determined that the shutter time error of the partial region P2 exceeds the allowable range, the system controller 100A branches to S1110 and performs a process of updating the adjustment parameter. For example, when the time interval correction amount before the update is set to minus 30 microseconds and the average value of the shutter time error in the partial region P2 derived in S1100 is minus 55 microseconds, the time interval after the update The correction amount is plus 25 microseconds. When the process of S1110 ends, the process proceeds to S1104.

  In step S1104, the system controller 100A determines whether exposure unevenness adjustment is necessary based on the shutter time error in the partial areas P1, P2, and P3. For example, when the exposure unevenness exceeds 0.2 Ev, the determination in S1104 is affirmed. If the determination in step S1104 is affirmative, the process proceeds to step S1106, and an exposure unevenness correction amount derivation process is performed. The contents of this process are as described above with reference to FIG. If the determination in S1104 is negative, the process shown in FIG. 11 is completed.

  In S1108, the system controller 100A sets the uneven exposure correction flag to 1 and completes the processing shown in FIG. The uneven exposure correction flag will be described later with reference to FIG.

  FIG. 12 is a flowchart schematically showing the contents of the uneven exposure reduction process executed by the system controller 100A. The process of FIG. 12 is executed each time the camera 10A is set to the normal shooting mode (recording mode) and the user performs a shooting operation. When the camera 10A is switched to the normal photographing mode, gain unevenness correction gain information recorded in the adjustment parameter 112A in the nonvolatile memory 110A is transferred into the DRAM 116A and stored as the gain memory 117. It shall be.

  In S1200, the system controller 100A determines whether or not the uneven exposure correction flag is set to 1, and if this determination is negative, the processing of FIG. 12 is completed. If the determination in S1200 is affirmative, the process proceeds to S1202, and a line address value corresponding to the pulse counting result output from the timing generator 132A is generated. That is, a row address value that identifies which row of the first to pth rows is the processing target in the two-dimensional array of digital image signals shown in FIG. 5 is generated.

  In step S1204, the system controller 100A acquires a gain corresponding to the line address from the gain memory 117. In S1206, the system controller 100A performs a process of multiplying each (pixel value) of the digital image signals for one row (for one line) by the gain acquired in S1204.

  In S1208, the system controller 100A stores the digital image signal obtained by the multiplication process in S1206 in the DRAM 116A. In S1210, the system controller 100A determines whether or not all the lines (first to pth rows) have been processed. If the result is negative, the system controller 100A returns to S1202 and repeats the above-described processing. If the determination in S1210 is affirmative, the process in FIG. 12 is completed.

  In the processing of FIG. 12, the example in which the digital image signal stored in the DRAM 116A through the image signal processing unit 120A is multiplied by the gain has been described. However, the present invention is not limited to this, and it is also possible to control the gain when the analog front end 130 amplifies the analog image signal. Alternatively, the image data generated by processing by the image signal processing unit 120A may be multiplied by a gain.

  Also in the second embodiment of the present invention, the example in which the digital image signal before the demosaic process is performed by the image signal processing unit 120 when the shutter time error is derived has been described. It is also possible to derive the shutter time error by using the digital image signal obtained by performing the demosaic processing in FIG.

  According to the camera according to the first and second embodiments of the present invention, it is possible to calibrate and adjust the shutter accuracy by the user's hand without using a special device such as a luminance box or a calibration device. It becomes possible.

  The embodiment of the present invention has been described above, but the present invention is not limited to this, and it is needless to say that various improvements and modifications can be made without departing from the spirit of the present invention.

  The present invention has a shutter configured to be able to control the amount of subject light incident on the light receiving surface of an image sensor by adjusting the time interval from when the light shielding member is opened to when it is closed. If there is, it can be applied not only to a digital still camera but also to various image recording apparatuses having a still image recording function.

It is a block diagram explaining the internal structure of the digital camera to which this invention is applied. It is a block diagram explaining the functional block in a system controller. FIG. 6 is a timing chart for explaining the relationship between the change timing of the leading curtain and trailing curtain locking release signal and the leading curtain and trailing curtain travel timing in the focal plane shutter, and FIG. ) Is a diagram for explaining the timing when the shutter time error is generated, and (c) is a diagram for explaining the timing when the shutter time error is corrected. It is a figure explaining the example of installation of a camera and a test chart at the time of performing calibration at the time of shutter second. It is a figure which illustrates notionally a mode that a partial area | region is provided in the two-dimensionally arranged digital image signal, and a process is made. FIG. 6 is a timing diagram for explaining how exposure unevenness occurs due to a difference in traveling speed between the front curtain and the rear curtain, and (a) shows a case where the rear curtain traveling speed is higher than the front curtain traveling speed and is the same. (B) shows a case where the trailing curtain traveling speed is slower than the leading curtain traveling speed, and (c) shows a case where the leading curtain traveling speed is equal to the trailing curtain traveling speed. (D) is a figure which respectively shows the case where rear curtain travel speed is quick compared with front curtain travel speed. It is a schematic flowchart explaining the procedure of the shutter second time calibration process performed by a system controller. It is a flowchart following the flowchart of FIG. It is a figure explaining the example which displays the shutter time calibration result, (a) when adjustment of a shutter is unnecessary, (b) when adjustment is desirable, (c) is a contact to a support center It is a figure explaining the example of a display when is recommended. It is a block diagram which mainly shows a different point from the component of the camera which concerns on 1st Embodiment in the component in the camera which concerns on the 2nd Embodiment of this invention. It is a schematic flowchart explaining the procedure of the shutter time calibration process performed by the system controller in the camera which concerns on the 2nd Embodiment of this invention. Similarly, it is a schematic flowchart for explaining a procedure of uneven exposure reduction executed by the system controller during a photographing operation.

DESCRIPTION OF SYMBOLS 10, 10A ... Digital camera 100, 100A ... System controller 101 ... Address designation part 102 ... Information display part 104 ... Operation switch 106 ... Bus 110 ... Non-volatile memory 112 ... Adjustment parameter 114 ... Control program 116, 116A ... DRAM
117: Gain memory 120, 120A: Image signal processing unit (DSP)
121: Multiplication processing unit 124 ... Image display unit 130 ... Analog front end 132 ... Timing generator 134 ... Image sensor 140 ... Shutter 142 ... Front curtain locking magnet 144 ... Rear curtain locking magnet 146 ... Shutter charge mechanism 150 ... Main Mirror 152 ... Mirror drive / shutter locking mechanism 160 ... Penta prism 164 ... Photometric part 180 ... Shooting lens 182 ... Lens element 184 ... Aperture device 186 ... Aperture drive part 188 ... Lens drive part 200 ... Shutter time setting part 202 ... Shutter timing Control unit 204 ... Actual exposure amount ratio deriving unit 206 ... Second-time error deriving unit 208 ... Shutter accuracy reduction notification processing unit 210 ... Time interval correction unit

Claims (3)

An image sensor;
A shutter composed of a focal plane shutter configured to be able to control the amount of subject light incident on the light receiving surface of the image sensor by adjusting a time interval from when the light shielding member is opened to when it is closed. A camera comprising:
A shutter time setting unit for setting an opening time of the shutter;
A shutter timing control unit that controls a time interval from the opening of the shutter to the closing based on the opening time set by the shutter time setting unit;
A first image sensor output obtained by photographing a stationary object having substantially constant luminance in time with a first shutter opening time set by the shutter time setting unit, and the stationary object for the shutter time. An actual exposure amount ratio deriving unit for deriving an actual exposure amount ratio based on a comparison with a second image sensor output obtained by photographing with the second shutter opening time set by the setting unit;
A theoretical exposure amount ratio obtained based on a ratio of a theoretical exposure amount based on the first shutter opening time set by the shutter time setting unit and a theoretical exposure amount based on the second shutter opening time. And a second time error deriving unit for deriving a second time error of the shutter based on a comparison result with the actual exposure amount ratio derived by the actual exposure amount ratio deriving unit ;
Based on the opening time set by the shutter time setting unit, the time interval controlled by the shutter timing control unit is corrected so as to reduce the second time error derived by the second time error deriving unit. A time interval correction unit;
The output of the image sensor is divided into a plurality of regions along the direction of travel of the shutter, and the exposure unevenness of the image sensor is corrected based on the actual exposure amount ratio obtained in each region by the actual exposure amount ratio deriving unit. An uneven exposure correction unit,
A camera characterized by comprising:   2. The shutter accuracy decrease notification processing unit that notifies a user of the camera when the second time error exceeds a predetermined allowable amount. camera. An image sensor;
A shutter composed of a focal plane shutter configured to be able to control the amount of subject light incident on the light receiving surface of the image sensor by adjusting a time interval from when the light shielding member is opened to when it is closed.
A method for deriving an error in shutter second time performed by a camera comprising:
Photographing a stationary object having substantially constant luminance in time with a first shutter opening time to obtain a first image sensor output;
Photographing the stationary object with a second shutter opening time to obtain a second image sensor output;
The ratio of the exposure amount obtained during the first shutter opening time and the exposure amount obtained during the second shutter opening time from the first image pickup device output and the second image pickup device output. Deriving the exposure ratio,
Deriving a theoretical exposure amount ratio based on a ratio of a theoretical exposure amount obtained by the first shutter opening time and a theoretical exposure amount obtained by the second shutter opening time;
Deriving an error in seconds of the shutter based on a comparison result between the actual exposure amount ratio and the theoretical exposure amount ratio;
Correcting a predetermined time interval between opening and closing of the shutter to obtain a given shutter opening time so as to reduce the second time error;
Dividing the output of the imaging device into a plurality of regions along the traveling direction of the shutter, and correcting exposure unevenness of the imaging device based on the actual exposure amount ratio obtained in each region;
A method for deriving an error in shutter second time, characterized by comprising:

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