JP2010113291A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress degradation of the quality of a displayed and recorded moving image regardless of a focus adjusting operation that involves wobbling. <P>SOLUTION: An image signal processing section 152 repeatedly inputs an image signal from an imaging element 150 that can output an image signal obtained by photo-electrically converting a subject image formed by a photographic lens 130, and at least displays or records a moving image. With timing between one input timing and the subsequent input timing when the image signal processing section 152 at least displays or records the moving image by repeatedly input an image signal from the imaging element 150, an imaging state detection processing section 154 inputs an image signal output from the imaging element for an imaging state detection process, and detects the imaging state of an image to be formed on the imaging element 150. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an imaging apparatus having an automatic focus adjustment function, and more particularly to an imaging apparatus capable of displaying and / or recording a moving image.

  Some digital still cameras and digital movie cameras capable of displaying and recording moving images perform focus adjustment using a contrast detection method using a wobbling technique. In the technical field related to camera focus adjustment, wobbling continuously adjusts the focus with respect to the movement of the subject, so the focusing lens in the photographic lens is microvibrated (reciprocating) along the optical axis direction of the photographic lens. Meaning technology In other words, wobbling means repeatedly performing an operation of shifting the focus adjustment position of the photographing lens back and forth with respect to the reference focus adjustment position.

  The wobbling described above is performed, and the focus adjustment position is moved back and forth with respect to the reference focus adjustment position. Then, based on the direction in which the focus adjustment position is moved and the tendency of increase or decrease of the contrast value obtained by processing the image signal output from the image sensor, to which direction the focus adjustment position is moved during the focusing operation (focusing lens To which direction to move).

  On the light receiving surface of the image sensor, an array of pixels two-dimensionally arranged along two arrangement directions orthogonal to each other is provided. When calculating a contrast value from an image signal output based on a signal obtained from each pixel of the image sensor, along the direction parallel to one of the arrangement directions from the image signal. In general, a one-dimensionally arranged image signal obtained by reading out pixel values is analyzed.

  In calculating the contrast value, a method is known in which high-pass filtering (HPF) processing is applied to the image signal to extract high-frequency components, and among these, the image signal in the region where focus detection is performed is appropriately integrated. Yes.

  As can be inferred from the above description, if the amplitude of wobbling performed during the display or recording of a moving image is large, blurring of the image due to wobbling becomes remarkable, and the moving image becomes considerably unsightly.

On the other hand, in Patent Document 1, in order to suppress image quality deterioration due to wobbling, the following method, that is,
-Limit wobbling amplitude based on the history of AF evaluation value changes,
-When panning, tilting, and zooming operations are detected, the image is moved greatly by these operations, so the wobbling amplitude limit is canceled based on the idea that image quality degradation due to wobbling is not noticeable.
This method is disclosed.
JP 2008-129255 A

  In recent years, an image sensor such as a CMOS image sensor capable of operating with low power consumption and capable of reading an image signal at high speed has been realized. Therefore, continuous imaging is possible even with a digital single-lens reflex camera that has conventionally been intended for still image shooting. As a result, a digital single lens reflex camera having a live view function for displaying a continuously captured image on a liquid crystal display panel attached to the back of the camera or the like for framing instead of the optical viewfinder is provided.

  In a digital single-lens reflex camera having a function of performing live view display using an image signal read from an image pickup device for photographing, a main mirror for guiding subject light to a viewfinder optical system, and a partial transmission through the main mirror The focal plane shutter is kept fully open by moving the sub-mirror that guides the subject light to the focus detection element of the phase difference detection method to a position where it is retracted from the optical path of the photographing lens. In this case, since the subject light cannot be guided to the focus detection element of the phase difference detection method, focus detection by the phase difference detection method cannot be performed. In order to compensate for this, a contrast detection type focus adjustment operation is performed using an image signal read from the imaging element for photographing.

  Recently, with the increase in the number of pixels of the image sensor and the increase in the image signal readout speed and the image signal processing speed, the resolution of the full HD standard (1920) has been achieved with a digital single lens reflex still camera. A pixel capable of recording a moving image of 30 fps with (pixel × 1080 pixels) is also available on the market.

  However, digital single-lens reflex cameras designed to capture high-quality still images use an image sensor that has an area size that is at least several times larger than that of a general movie camera. A photographic lens having a circle is also large. In addition, in order to obtain the same angle of view, it is necessary to increase the focal length of the photographing lens as the image circle increases. For this reason, the movement stroke and the mass of the lens (focusing lens) driven during the focusing operation tend to be large.

  Furthermore, in order to give priority to reducing the moving stroke and mass of the focusing lens, the photographic lens for a digital single-lens reflex camera is designed to allow a change in imaging magnification due to movement of the focusing lens to some extent. There are many. For this reason, when a focus adjustment operation accompanied by a wobbling operation is performed during moving image shooting, fluctuations in the magnification of the image are conspicuous, and the quality of the moving image may be reduced.

  The present invention has been made in view of the above-described problems, and it is possible to suppress degradation of the quality of a moving image displayed and recorded even when performing a focus adjustment operation with wobbling in a digital camera having a relatively large area size. Aims to provide a new technology.

(1) The present invention is applied to an imaging apparatus, and the imaging apparatus is
The image signal is repeatedly input from an image sensor capable of outputting an image signal obtained by photoelectrically converting a subject image formed by the photographing lens, and at least one of display and recording of a moving image is performed. An image signal processing unit;
When the image signal processing unit repeatedly inputs the image signal from the image sensor and performs at least one of display and recording of a moving image, one input timing and a subsequent input timing An imaging state detection processing unit that inputs an image signal output for imaging state detection processing from the image sensor at a timing in between and detects the imaging state of an image formed on the imaging element; By solving this problem, the above-described problems are solved.

  According to the present invention, an image signal processing unit repeatedly inputs an image signal output from an image sensor that can output an image signal obtained by photoelectrically converting a subject image formed by a photographing lens, At least one of display and recording is performed. When the image signal processing unit repeatedly inputs an image signal from the image sensor and performs at least one of display and recording of a moving image, the interval between one input timing and the subsequent input timing The image formation state detection processing unit inputs an image signal output from the image sensor at the timing for image formation state detection processing, and performs processing for detecting the image formation state of the image formed on the image sensor. As a result, the image signal output from the image sensor for the imaging state detection process is not input to the image signal processing unit, and the influence of the image disturbance caused by the imaging state detection process is prevented from affecting the moving image. Is possible.

− First embodiment −
FIG. 1 is a block diagram illustrating a schematic configuration of an imaging apparatus 100 according to the first embodiment of the present invention. The image pickup apparatus 100 shown in FIG. 1 may be a so-called compact digital still camera or movie camera integrated with a lens, or a digital single-lens reflex using an image pickup element having a relatively large image area with a photographing lens exchange type. It may be a type camera (hereinafter referred to as “digital single-lens reflex camera”).

  Alternatively, the imaging apparatus 100 is a photographic lens interchangeable type, but does not have a reflex mirror, a focusing screen, a pentagonal roof prism, or the like, but instead displays an electronic viewfinder device (EVF) or a live view image. It may be a camera having the display device. The imaging device 100 may also be incorporated into a mobile phone, a personal digital assistant (PDA), or the like.

  In the following description, it is assumed that the image pickup apparatus 100 is a camera that uses an image pickup device having a relatively large image area, which is of a type in which an image is taken while observing a live view image displayed on the display unit 158. do. Here, “having a relatively large image area” means having an image area that is larger than that of a 1/3 type image pickup device of a digital video camera or the like. As an example, the imaging apparatus 100 can have a 4 / 3-type imaging device or a larger imaging device.

  The photographing lens 130 is configured to be detachable from the imaging device 100. The taking lens 130 includes a plurality of lens elements 140 including a focusing lens 134, an aperture unit 132, an aperture actuator 136, and a focus actuator 138. The aperture unit 132 is disposed in the optical path of the photographic lens and is configured so that the aperture shape is variable, and thereby the F value of the photographic lens can be adjusted.

  The aperture actuator 136 includes an actuator such as a stepping motor, for example, and drives the aperture unit 132 based on a control signal output from the imaging apparatus 100 to change the aperture shape. The focus actuator 138 includes, for example, an electromagnetically driven motor, an ultrasonic motor, and the like, and the focusing lens 134 is extended in the direction in which the optical axis of the photographing lens 130 extends based on a control signal output from the imaging device 100. Drive along. Thereby, the focus adjustment position of the photographic lens 130 is moved toward or away from the light receiving surface of the image sensor 150 (hereinafter referred to as a direction approaching or moved away from the light receiving surface of the image sensor 150). Can be simply moved in the “front-rear direction”.

  The recording medium 164 may be a memory card that includes a flash memory or the like and is configured to be removable from the imaging apparatus 100.

  In the embodiment of the present invention, it is assumed that the imaging device 100 is configured such that the photographing lens 130 and the recording medium 164 are detachable. In the following description, it is assumed that the imaging lens 130 and the recording medium 164 are attached to the imaging apparatus 100.

  The imaging apparatus 100 includes a controller 110, an imaging element 150, an image signal processing unit 152, an imaging state detection processing unit 154, a display driver 156, a display unit 158, and a memory 162. Are connected via the system bus 160.

  The controller 110 comprehensively controls the operation of the imaging apparatus 100. For example, when the imaging apparatus 100 is set to the recording mode, the controller 110 performs control such as focus adjustment, photometry, exposure adjustment, and flash emission adjustment. When the imaging apparatus 100 is set to the playback mode, the controller 110 performs a process of accepting a user operation such as switching of an image displayed on the display unit 158, switching of reduced / enlarged display.

  The image sensor 150 photoelectrically converts the subject image formed by the photographing lens 130 and outputs an image signal. In this specification, the image sensor 150 is an array of photoelectric conversion elements arranged two-dimensionally on the light receiving surface, an analog signal output from the array of photoelectric conversion elements is subjected to CDS (correlated double sampling), amplification. A circuit block for performing a process such as A / D conversion and outputting a digital image signal is provided. In the following description, it is assumed that a digital image signal can be output from the image sensor 150. A digital image signal output from the image sensor 150 is transferred to the memory 162 via the system bus 160 and temporarily stored as pre-processed image data.

  The image signal processing unit 152 includes an ASIC (Application Specific Integrated Circuit) and the like. As described above, the pre-processing image data temporarily stored in the memory 162 is subjected to demosaic processing, gradation correction processing, color balance adjustment, Unsharp mask processing is performed to generate image data. The image signal processing unit 152 also performs processing such as JPEG compression on the generated image data for recording, if necessary, and records it on the recording medium 164. The image signal processing unit 152 further performs live view image display processing and processing for reading out image data recorded on the recording medium 164 and generating display image data.

  The imaging state detection processing unit 154 performs contrast detection processing, which will be described in detail later, based on pre-processing image data temporarily stored in the memory 162, and performs processing for detecting the focus adjustment state of the photographic lens 130. . The imaging state detection processing unit 154 may be included in the image signal processing unit 152.

  The memory 162 includes a mask ROM, an EEPROM, a RAM, and the like, and stores a program executed by the controller 110, various control parameters handled in the imaging apparatus 100, various information, and the like. In the RAM in the memory 162, a VRAM area in which display image data is temporarily stored is secured.

  The display driver 156 performs processing for displaying an image based on the display image data stored in the VRAM area secured in the RAM in the memory 162 on the display unit 158. The display unit 158 includes a TFT display panel, a backlight device, and the like, and is configured to display a color image.

  The configuration of the controller 110 will be described. The controller 110 can be configured by an ASIC, hard logic, CPU, or the like. In the embodiment of the present invention, the controller 110 is constituted by a CPU, and the function blocks described below are realized by the CPU executing a program stored in the memory 162.

  The controller 110 includes a gain control unit 112, an electronic shutter control unit 114, a focus control unit 116, a wobble operation control unit 118, an aperture drive control unit 120, and a timing control unit 122.

  The gain control unit 112 outputs a signal designating a gain when the analog signal obtained by photoelectric conversion is amplified inside the image sensor 150 to the image sensor 150. The electronic shutter control unit 114 controls time related to the charge accumulation operation performed by the image sensor 150. That is, the operation time of the electronic shutter of the image sensor 150 (electronic shutter time) is controlled.

  The focus control unit 116 issues a control signal to the focus actuator 138 to drive the focus actuator 138, thereby controlling the front and rear positions of the focusing lens 134 along the optical axis direction.

  The aperture drive control unit 120 issues a control signal to the aperture actuator 136 to drive the aperture actuator 136, thereby controlling the aperture diameter of the aperture unit 132.

  The wobble operation control unit 118 issues a control signal to the focus control unit 116 and the aperture drive control unit 120 based on the timing signal output from the timing control unit 122. Based on a signal (hereinafter referred to as a wobble control signal) output from the wobble operation control unit 118 to the focus control unit 116, the focusing lens 134 is driven in the front-rear direction along the optical axis direction of the photographing lens 130. Based on a signal (hereinafter referred to as an aperture control signal) output from the wobble operation control unit 118 to the aperture drive control unit 120, the aperture of the aperture unit 132 is changed.

  The wobble operation control unit 118 may also be configured to be able to issue a control signal to at least one of the gain control unit 112 and the electronic shutter control unit 114. When configured to be able to issue a control signal from the wobble operation control unit 118 to the gain control unit 112, the gain control unit 112 is set by the image sensor 150 based on the gain control signal output from the wobble operation control unit 118. The gain to be changed can be changed. Similarly, when it is configured to be able to issue a control signal from the wobble operation control unit 118 to the electronic shutter control unit 114, the electronic shutter control unit 114 is based on the electronic shutter control signal output from the wobble operation control unit 118. The time of the electronic shutter set by the image sensor 150 can be changed.

  The timing control unit 122 transmits a control signal for controlling the timing of operations performed by each of the wobble operation control unit 118, the image sensor 150, the image signal processing unit 152, and the imaging state detection processing unit 154 to the wobble operation control unit 118. , Output to each of the image sensor 150, the image signal processing unit 152, and the imaging state detection processing unit 154. The timing control unit 122 can be implemented as a so-called software timer. Alternatively, a hardware timer provided inside or outside the controller 110 may be used.

  The contrast value of the subject image will be described with reference to FIG. The graph shown in FIG. 2 conceptually shows the relationship between the focus adjustment position of the photographic lens 130 and the contrast value of the subject image formed on the light receiving surface of the image sensor 150. In the graph shown in FIG. 2, when the focus adjustment position is on the left side of the focusing position a, the position where the subject light is focused (imaging position) is the side closer to the subject (hereinafter referred to as the light receiving surface of the image sensor 150). , This is called “front side”). Similarly, when the focus adjustment position is on the right side of the focus position a, the imaging position is on the side away from the subject with respect to the light receiving surface of the image sensor 150 (hereinafter referred to as “rear side”). Means.

  When the focus adjustment position of the photographic lens 130 is at the focus position a, that is, when the subject light emitted from the photographic lens 130 is focused on the light receiving surface of the image sensor 150, the subject image i1 becomes sharp and has a contrast. The value is relatively high.

  When the focus adjustment position of the photographic lens 130 is at positions b1 and b2 that are shifted to the front side or the rear side with respect to the focus position a, the sharpness of the subject image i2 slightly decreases, and the contrast value also decreases accordingly.

  When the focus adjustment position of the photographic lens 130 is at positions c1 and c2 that are further shifted to the front side or the rear side with respect to the focus position a, the sharpness of the subject image i3 further decreases, and the contrast value further decreases accordingly. To do.

  That is, when the change in the contrast value is examined by changing the focus adjustment position from c1 to b1 for the same subject, the contrast value increases, so that the focus position a is behind the focus adjustment position b1. Can be guessed. Alternatively, if the change in contrast value is examined by changing the focus adjustment position from c2 to b2 for the same subject, the contrast value also increases, so that the in-focus position a is in front of the focus adjustment position b2. Can be guessed. Similarly, when the change in the contrast value is examined by changing the focus adjustment position from b1 to b2 (b2 to b1) for the same subject, the change in the contrast value is hardly seen. It can be estimated that the position is between the adjustment positions b1 and b2.

  Using the above-described properties, focusing is performed by examining wobbling, that is, by changing the contrast value while shifting the focus adjustment position of the photographing lens 130 back and forth with respect to the reference focus adjustment position. It is possible to know whether the imaging position of the subject light can be brought close to the in-focus position by moving the lens 134 forward or backward.

  FIG. 3 illustrates an example of an automatic focus adjustment operation (AF operation) performed when the imaging apparatus 100 is displaying a live view image on the display unit 158 or when the imaging apparatus 100 is in an operation mode for recording a moving image. Indicates. In FIG. 3, the horizontal axis indicates the passage of time, and the vertical axis indicates the focus adjustment position by the focusing lens 134. In the vertical axis, the direction in which the coordinate value increases is the front side, and the opposite is the rear side. That is, FIG. 3 shows a state in which the focus adjustment position of the photographic lens 130 tends to move closer to the subject side as time passes.

  From time t0 to t1, there is no change in the shooting scene, and the focusing lens 134 is stopped. Assume that there is a scene change at time t1. The scene change means a case where the distance (shooting distance) between the main subject and the imaging device 100 changes, or a case where the shooting distance changes as a result of the photographer panning or tilting the imaging device 100. .

  As described above, there is a scene change at time t1, and as a result, the contrast value detected by the imaging state detection processing unit 154 decreases. The controller 110 starts an imaging state detection process with a wobbling operation, and performs control for executing an operation for determining whether the in-focus position is on the front side or the rear side. In the example illustrated in FIG. 3, it is determined that the contrast value tends to increase when the focus adjustment position is moved forward by the wobbling operation performed between the times t1 and t2.

  From time t2 to t3, the controller 110 moves the focusing lens 134 without performing a wobbling operation, and performs control for sequentially detecting a change in contrast value during that time. Based on the relationship between the amount of movement of the focusing lens 134 and the change in contrast value, the controller 110 determines that the focus adjustment position is approaching the in-focus position, and starts imaging state detection processing with a wobbling operation again at time t3. To control.

  From time t3 to time t4, the controller 110 performs a wobbling operation while slightly changing the reference focus adjustment position, and performs control for adjusting the focus adjustment position of the photographing lens 130 to the in-focus position. At time t4, the controller 110 determines that the operation for adjusting the focus adjustment position to the in-focus position is completed, and stops the driving of the focusing lens 134.

  FIG. 4 is a diagram conceptually illustrating a state in which the above-described wobbling operation is performed in conjunction with an imaging operation (accumulation operation) performed by the imaging element 150. In a time zone before the time t1 when the scene change is detected, for example, an imaging operation is performed at a frame rate of 30 frames per second (30 fps), and image data output from the imaging device 150 is output by the image signal processing unit 152. Sequential processing is performed to perform at least one of display and moving image recording.

  On the other hand, after time t1 when the execution of the wobbling operation is started, the imaging operation is performed at a frame rate of 60 fps. Then, the wobbling operation is performed in synchronization with the imaging timing of the hatched frame in FIG. 4 (in FIG. 4, the accumulation operation for obtaining the image of the hatched frame is performed by the imaging device 150). Hereinafter, the hatched frame image in FIG. 4 is referred to as an AF image, and the non-hatched frame image, that is, the display image or the recording image is collectively referred to as a display / recorded image. .

  As shown in FIG. 4, at the imaging timing for obtaining a display / recording image, the controller 110 controls the position of the focusing lens 134 so that the focus adjustment position is at a reference position (reference position). The controller 110 also performs wobbling so that the focus adjustment position is shifted to the front side or the rear side from the reference position at the imaging timing for obtaining the AF image.

  The AF image is processed by the imaging state detection processing unit 154, and a contrast value is obtained. This AF image is not used as a display / recording image. The display / recording image is processed by the image signal processing unit 152 to generate display image data and recording image data. Since the display image data and the recording image data are generated from the display / recording image obtained when the focus adjustment position is at the reference position, image quality deterioration due to wobbling does not occur.

  As described above, in the first embodiment, when wobbling is not performed, the imaging operation is performed at the frame rate of 30 fps, and the display / recording image is generated at the frame rate of 30 fps. After starting wobbling, the frame rate is doubled to 60 fps, and the obtained image signal is alternately distributed as an AF image and a display / recording image. Then, at the imaging timing at which an AF image is obtained, wobbling control is performed to move the focusing lens 134 so that the focus adjustment position is shifted to the front side or the rear side from the reference position. At the imaging timing at which a display / recording image is obtained, the position of the focusing lens 134 is controlled so that the focus adjustment position is at the reference position.

  Since the controller 110 controls the wobbling operation timing in this manner, the display / recorded image is not affected by the wobbling. Then, an AF image can be obtained at a sufficient speed (interval) to perform a quick AF operation.

  The example in which the frame rate of the image sensor 150 is increased to twice the frame rate before the start of wobbling as the wobbling starts has been described. However, the present invention is not limited to this. For example, the frame rate before starting wobbling may be 60 fps. In this case, display image data and recording image data can also be generated at a frame rate of 60 frames per second. Then, after the start of wobbling, for example, an odd-numbered frame image is used as a display / recording image, and an even-numbered frame image is used as an AF image. In this way, after starting wobbling, display image data and recording image data can be obtained only for 30 frames per second. However, an image corresponding to a missing image can be generated using an interpolation technique. That is, it is possible to generate an image corresponding to a missing image by performing an interpolation process using an image signal of a certain even-numbered frame and an image signal of the next even-numbered frame following this. .

  Note that the frame rate values disclosed before and after the start of wobbling disclosed above are merely examples, and there are various values depending on the specifications of the imaging device 150, the image signal processing unit 152, and the photographing lens 130 incorporated in the imaging device 100. It can be a value. In addition, when obtaining a moving image, the present invention is not limited to an apparatus that performs frame imaging, and the present invention can also be applied to an imaging apparatus that performs field imaging.

− Second Embodiment −
Also in the second embodiment, as in the first embodiment, after the start of wobbling, the wobbling operation is performed so that the focus adjustment position is at the reference position at the imaging timing for obtaining the display / recording image. Then, at the imaging timing for obtaining the AF image, the wobbling operation is performed so that the focus adjustment position is shifted forward and backward with respect to the reference position. The second embodiment is different from the first embodiment in that the aperture of the taking lens 130 is changed in conjunction with the wobbling operation as described below.

  While recording a moving image, the main subject may move in a direction toward or away from the imaging apparatus. In such a case, it is a general practice to reduce the aperture of the taking lens so that the image does not blur much even if the focus adjustment does not catch up with the movement of the subject. However, when the aperture of the photographic lens is reduced in this way, the depth of focus increases, and the imaging state detection process with wobbling may be difficult.

  Here, referring to Table 1 showing an example comparing a digital single-lens reflex camera and a consumer movie camera, the area size of the image sensor and the shift amount of the focus adjustment position required for wobbling (hereinafter referred to as wobbling (Referred to as amplitude). As shown in Table 1, the image sensor size of a digital single-lens reflex camera has an image area size about four times that of a movie camera, even if it is relatively small. Therefore, in order to obtain an angle of view equivalent to that of a movie camera with a digital single-lens reflex camera, it is necessary to use a lens having a focal length that is four times the shooting lens of the movie camera in proportion to the size of the imaging device. In addition, in order to obtain a depth of field equivalent to that of a movie camera at an equivalent subject distance, it is necessary to set the F value to four times the F value set by the shooting lens of the movie camera. Arise.

  In movie shooting, as described above, there are many cases where a moving subject is shot. Therefore, the aperture is set so that the depth of field is deeper than when shooting a still image as a work that takes advantage of the blur. It is common to narrow down.

  At this time, in order to obtain blur equivalent to that of a movie camera by wobbling, the wobbling amplitude needs to be approximately proportional to the depth of focus on the image sensor surface. The depth of focus is determined by the setting F value of the photographing lens and the allowable confusion circle diameter. Assuming that the size of the permissible circle of confusion is proportional to the area size of the image sensor, if the diagonal dimension of the image sensor is four times, the permissible circle of confusion is also four times, so the same set F value Requires four times the wobbling amplitude. Furthermore, in order to obtain the same depth of field, the setting F value of the photographing lens needs to be quadrupled as described above. In other words, the digital single-lens reflex camera shown in Table 1 is 16 times as large as a standard digital movie camera, 4 times due to a difference in allowable confusion circle diameter, and 4 times due to a difference in a set aperture value. It is necessary to wobble with the amplitude of.

  As described above, the area size of the image sensor greatly affects the wobbling operation at the time of moving image display / photographing, and such a problem may be a new problem not found in the conventional movie camera. The second embodiment of the present invention is suitable for use in such a situation.

  Since the imaging apparatus according to the second embodiment of the present invention is also the same as the imaging apparatus 100 described with reference to FIG. 1 in the first embodiment, illustration and description thereof are omitted. FIG. 5 is a diagram illustrating a state where the wobbling operation and the aperture adjustment operation are performed in synchronization with the timing of image capturing (accumulation) performed by the image sensor 150. In the following description, it is assumed that the aperture value of the photographic lens 130 attached to the imaging apparatus 100 is set to F8 and the imaging operation is performed.

  In FIG. 5, when the set aperture value of the taking lens 130 is F8, the wobbling amplitude necessary for obtaining a blur amount sufficient for the imaging state detection processing unit 154 to detect the contrast change is a. It is represented. On the other hand, when the set aperture value of the taking lens 130 is F2, the wobbling amplitude necessary to obtain the same blur amount as in the case of F8 is 1/4, that is, a / 4. That is, the wobbling amplitude necessary to obtain the same blur amount is proportional to the aperture value set by the photographing lens 130.

  In the second embodiment, the aperture area of the aperture unit 132 is increased in synchronization with shifting the focus adjustment position in the front-rear direction with respect to the reference position by wobbling. In the example shown in FIG. 5, the aperture value is set to F8 when the focus adjustment position is at the reference position, and the aperture value is set to F2 when the focus adjustment position is at a position shifted in the front-rear direction from the reference position. . An image obtained by imaging with the imaging device 150 when the set aperture value of the photographing lens 130 is F8 is used as a display / recording image, and an image obtained by imaging with the imaging device 150 when F2 is set. Are used as AF images. Then, the wobbling amplitude is set to a / 4, and the imaging state detection process accompanied by the wobbling operation is performed.

  As a result, the display / recording image has a relatively large depth of field, such as an image denoted by reference numeral i51 in FIG. The image denoted by reference numeral i51 indicates that both the image of the person as the main subject and the image of the tree as the background subject located behind the person are clearly visible. On the other hand, the AF image has a relatively narrow depth of field, like an image indicated by reference numeral i52 in FIG. The image denoted by reference numeral i52 shows that the image of the person who is the main subject looks clear, while the image of the tree which is the background subject located behind the person is blurred.

  Thus, by making the aperture value set at the imaging timing for obtaining the AF image smaller than the aperture value set at the imaging timing for obtaining the display / recording image (opening the aperture to increase the aperture area) Even if the wobbling amplitude during the wobbling operation is reduced, a sufficient amount of image blur can be secured (a sufficient change in contrast can be obtained), and thus sufficient imaging state detection sensitivity can be obtained. Is possible. In addition, since the wobbling amplitude can be reduced, the moving stroke of the focusing lens 134 can be reduced. By reducing the moving stroke of the focusing lens 134 in this way, it is possible to suppress power consumed by the imaging apparatus 100 and to reduce vibrations and sounds generated by the wobbling operation of the focusing lens 134. Become.

  In order to change the aperture of the photographing lens 130 as described above, the aperture unit 132 can be mechanically driven by the aperture actuator 136 based on the control signal output from the aperture drive control unit 120. Alternatively, the aperture unit 132 may be configured by using a liquid crystal or an electrochromic element so that the aperture size of the aperture can be electrically changed.

  By the way, when opening and closing the diaphragm, the opening shape may not maintain a similar state. For example, it may have a circular shape when it is close to the full aperture, and may have a shape different from the circular shape when it is small, such as an oval shape. In such a case, it is appropriate to express that the aperture shape is changed rather than changing the aperture size when changing the aperture area of the stop. That is, when changing the aperture area of the stop of the photographic lens 130, the aperture size may be changed, or the aperture shape may be changed.

  Regarding control when switching the frame rate when wobbling is not performed or when the image signal output from the image sensor 150 is distributed for AF image generation and display / recording image generation, It may be the same as that described in the first embodiment.

  As described above, when the wobbling operation and the aperture adjustment operation are performed in synchronization with the timing of image capturing (accumulation) performed by the image sensor 150, the aperture is opened (the aperture area is increased). Since the image plane illuminance increases, the subject light incident on the light receiving surface of the image sensor 150 increases. A method corresponding to this increase in the amount of incident light will be described with reference to FIGS.

  FIG. 6 shows a method of reducing the gain when amplifying an analog image signal obtained by imaging with the imaging device 150 when the aperture of the photographing lens 130 is opened. In the example shown in FIG. 6, a relatively large gain is set for the signal obtained when the focus adjustment position is at the reference position and the set aperture is F8, and the equivalent ISO sensitivity of the image sensor 150 is set. The (exposure index) is equivalent to 1600. On the other hand, the gain is set lower for the signal obtained when the focus adjustment position is shifted in the front-rear direction with respect to the reference position and the set aperture is F2, and the image sensor 150 The equivalent ISO sensitivity (exposure index) is equivalent to 100.

  The above operation will be described with reference to FIG. 1. When the wobble operation control unit 118 in the controller 110 issues a control signal to the focus control unit 116 and the aperture drive control unit 120, the control signal is also issued to the gain control unit 112. . The focus control unit 116 controls the focus actuator 138 to wobble the focusing lens 134 so that a wobbling amplitude based on the control signal input from the wobble operation control unit 118 is obtained. The aperture drive control unit 120 outputs a control signal to the aperture actuator 136 so that an aperture value based on the control signal input from the wobble operation control unit 118 is obtained. The gain control unit 112 outputs a gain setting signal based on the control signal input from the wobble operation control unit 118 to the image sensor 150.

  As described above, by changing the gain corresponding to the change of the set aperture value, it is possible to reduce the possibility that the image signal output from the image sensor 150 is saturated.

  FIG. 6 shows an example in which the gain set by the image sensor 150 is rapidly changed between two values. However, the gain is continuously changed corresponding to the change in the aperture area in the aperture unit 132. You may do it.

  FIG. 7 shows a method of shortening the time of the imaging operation performed by the imaging device 150 when the aperture is opened, that is, the time related to the charge accumulation operation. In the example shown in FIG. 7, when the focus adjustment position is at the reference position and the set diaphragm is F8, a relatively long imaging operation time (electronic shutter time) is set. On the other hand, when the focus adjustment position is shifted in the front-rear direction with respect to the reference position and the set aperture is F2, a relatively short imaging operation time is set.

  The above operation will be described with reference to FIG. 1. When the wobble operation control unit 118 in the controller 110 issues a control signal to the focus control unit 116 and the aperture drive control unit 120, the control signal is also sent to the electronic shutter control unit 114. To emit. The focus control unit 116 controls the focus actuator 138 to wobble the focusing lens 134 so that a wobbling amplitude based on the control signal input from the wobble operation control unit 118 is obtained. The aperture drive control unit 120 outputs a control signal to the aperture actuator 136 so that an aperture value based on the control signal input from the wobble operation control unit 118 is obtained. The electronic shutter control unit 114 controls the imaging operation of the image sensor 150 in response to the electronic shutter time based on the control signal input from the wobble operation control unit 118.

  As described above, it is possible to reduce the possibility that the image signal output from the image sensor 150 is saturated by changing the time of the electronic shutter in response to the change in the set aperture value. . Furthermore, by shortening the electronic shutter time when obtaining an image signal used for AF image generation compared to the electronic shutter time when obtaining an image signal used for display / recording image generation, The effects described below can be obtained.

  FIG. 8A is a diagram conceptually illustrating an example in which image blurring occurs in the obtained image due to the relatively long time of the electronic shutter. FIG. 8B conceptually shows the relationship between the focus adjustment position of the taking lens 130 and the contrast value of the subject image formed on the light receiving surface of the image sensor 150. As shown in FIG. 8B by a broken line, the contrast value obtained from an image in which image blurring occurs as shown in FIG.

  According to the second embodiment of the present invention, the aperture is opened when an image signal used for AF image generation is obtained, so that the electronic shutter speed can be set at a relatively high speed. , Image blur is reduced. As a result, when performing the imaging state detection process based on the AF image, it becomes possible to obtain a sharper change in the contrast value as the focus state changes from the out-of-focus state. The detection accuracy of the image state is increased, and the AF speed and focusing accuracy can be improved.

  On the other hand, when the image is taken for display / recording image generation, since the set aperture is set to a small aperture (so that the F value is increased), the image blur is caused as shown in FIG. Is likely to occur. In still images, image blurring is a factor that reduces image quality, except when it is the intention of drawing, but in moving images, it is more likely that the individual images that make up the moving image have slight image blurring. For an observer who watches the video, it is possible to obtain an effect that the moving image can be felt smoothly.

− Third embodiment −
Also in the third embodiment, as in the first and second embodiments, after starting wobbling, the wobbling operation is performed so that the focus adjustment position is at the reference position at the imaging timing for obtaining the display / recording image. Do. Then, at the imaging timing for obtaining the AF image, the wobbling operation is performed so that the focus adjustment position is shifted forward and backward with respect to the reference position. As in the second embodiment, in the third embodiment, the diaphragm set by the diaphragm unit 132 is changed in conjunction with the wobbling operation. The difference from the second embodiment is that, when changing the aperture value, the aperture shape of the aperture is made to be a non-similar shape before and after the aperture value is changed.

  Since the imaging apparatus according to the third embodiment of the present invention is also the same as the imaging apparatus 100 described with reference to FIG. 1 in the first embodiment, illustration and description thereof are omitted.

  FIG. 9 illustrates how a subject image is formed in the light receiving region 150a of the image sensor 150, an image signal reading direction when reading an image signal corresponding to the subject image, and a pixel value obtained by reading the image signal. It is a figure which shows distribution conceptually. In the light receiving region 150a of the image pickup device 150, pixels are two-dimensionally arranged along the X direction and the Y direction shown in FIG. 9, thereby forming an array of pixels. The imaging state detection processing unit 154 determines the object image based on the distribution 150b of pixel values obtained from a plurality of pixels arranged along one of the X direction and the Y direction, for example, a direction parallel to the X direction. It is assumed that processing for detecting a contrast value is performed. That is, the contrast value detection direction is assumed to be a direction parallel to the X direction.

  FIG. 10 is a conceptual diagram showing the relationship between the change of the aperture shape and the contrast value detection direction when the aperture value is changed in conjunction with the wobbling operation. In FIG. 10, in F8, the shape of the opening 1000a is a substantially perfect circle. However, when the aperture value is changed by increasing the opening area, the opening shape is changed in the Y direction when the opening shape is changed to 1000b and 1000c. The opening area is increased so that the opening dimensions (X1, X2) along the direction parallel to the X direction are larger than the opening dimension (Y1) along the parallel direction. Thus, by increasing the aperture area of the stop of the taking lens 130, it is possible to achieve the effects described below.

  As described above, when the aperture size is changed so that the aperture size (X1, X2) along the direction parallel to the X direction is larger than the aperture size (Y1) along the direction parallel to the Y direction, the image The amount of variation in surface illuminance is relatively small. This is because the opening dimension in the X direction changes to F4 (when the opening dimension is X1) and F2 (when the opening dimension is X2), but the Y dimension remains Y1. Because. That is, even if the opening shape is changed from 1000a to 1000b and 1000c, the equivalent F value calculated from the ratio of the opening areas is approximately equivalent to F5.6 for the opening 1000b and approximately equivalent to F4 for the opening 1000c. . Accordingly, it is possible to reduce the amount of change at the time of changing the gain or changing the second time of the electronic shutter described in the second embodiment.

  This is effective in further simplifying the specifications required for the image sensor 150. On the other hand, when the opening shape is changed so that the opening dimensions (X1, X2) along the direction parallel to the X direction are larger than the opening dimension (Y1) along the direction parallel to the Y direction, It is possible to increase the amount of blur in a direction parallel to the direction. Therefore, it is possible to obtain the same effect as described in the second embodiment. In other words, when performing the imaging state detection process based on the AF image, it becomes possible to obtain a sharper change in the contrast value as the focus state changes from the out-of-focus state. The speed and focusing accuracy can be improved.

  In the above description, when changing the opening shape from 1000a to 1000b and 1000c, only the opening dimension in the X direction is changed and the opening dimension in the Y direction is constant. However, the opening dimension in the Y direction is also changed. May be. In addition, the opening dimensions in the X direction and the Y direction may be changed, and the opening shape may be changed so that the resulting opening area is substantially constant. For example, when the aperture shape is changed from 1000a to 1000d, the aperture size is increased by a factor of 4 in the X direction, while the aperture size is reduced by a factor of 1/4 in the Y direction, thereby making the aperture area substantially constant. Can keep. By doing so, it is not necessary to change the gain of the image sensor 150 and the electronic shutter speed described with reference to FIGS. 6 and 7.

  In addition, unlike the case shown in FIG. 9, when processing for detecting the contrast value of a subject image based on a distribution of pixel values obtained from a plurality of pixels arranged along a direction parallel to the Y direction is performed, It is possible to change the opening shape so that the opening dimension in the Y direction greatly changes compared to the opening dimension in the X direction.

  With reference to FIGS. 11 and 12, an example of a configuration that allows the aperture shape to be changed by the aperture unit 132 will be described. FIG. 11 is a diagram for explaining an example having two sector blades 1100a and 1100b arranged along a plane orthogonal to the optical axis of the photographing lens 130. FIG. The aperture unit 132A includes two sector blades 1100a and 1100b and a drive pin 1112. The sector blades 1100a and 1100b are formed with holes 1102a and 1102b, long holes 1104a and 1104b, and notches 1106a and 1106b, respectively.

  The two sector blades 1100a and 1100b are arranged so that the notches 1106a and 1106b face each other, and are rotatable about shafts 1110a and 1110b fitted into the holes 1102a and 1102b. A drive pin 1112 is provided so as to penetrate the long holes 1104a and 1104b. The drive pin 1112 is moved along the vertical direction in FIG. 11 by a diaphragm actuator 136 (not shown in FIG. 11, refer to FIG. 1), so that the opening shape formed by the sector blades 1100a and 1100b is changed to FIG. The state shown in (b) or (c) can be changed. In FIG. 11, a fixed diaphragm 1120 is indicated by a two-dot chain line.

  FIG. 11A shows a state where the aperture unit 132A is set to the open state. FIG. 11B shows a state in which the opening 1000a described with reference to FIG. 10 is formed. FIG. 11C shows a state in which the opening 1000c described with reference to FIG. 10 is formed.

  FIG. 12 is a diagram illustrating a configuration example in which a sector blade having a plurality of openings is rotated so that the opening shape can be switched to a turret type. The aperture unit 132B has sector blades 1200 that are rotationally driven by an aperture actuator 136. The sector blade 1200 is disposed along a plane orthogonal to the optical axis of the photographic lens 130 and is configured to be rotatable around a point P. The sector blade 1200 is provided with a plurality of openings 1000a, 1000c, and 1202. FIG. 12A shows a state in which the opening 1202 is at the position of the fixed aperture 1120 and is set to the open state. FIG. 12B shows a state in which the opening 1000c described with reference to FIG. FIG. 12C shows a state in which the opening 1000a described with reference to FIG.

  By the way, in the aperture unit 132B, the ND filter 1204 can be provided in the through hole portion in which the opening 1000c of the sector blade 1200 is formed. The optical density of this ND filter has a value approximately equal to the area ratio between the opening 1000a and the opening 1000c. That is, the ND filter so that the F value of the photographing lens 130 determined by the aperture 1000a and the equivalent F value (which can be considered as the T value) of the photographing lens 130 determined by the optical density of the aperture 1000c and the ND filter 1204 are substantially equal. It is desirable to define an optical density of 1204. By doing so, when changing the aperture shape of the diaphragm between 1000a and 1000c in conjunction with the wobbling operation, the gain change of the image sensor 150 and the electronic device described with reference to FIGS. It is not necessary to change the shutter speed.

  Regarding the above ND filter 1204, it is also possible to dispose a variable optical density filter described below with reference to FIG. 13 in the photographing lens.

  In FIG. 13, the photographing lens 130 </ b> A has a variable optical density filter (density variable filter) 1302, and the controller 110 </ b> A of the imaging apparatus 100 </ b> A includes a light reduction control unit 1304 for adjusting the optical density of the optical density variable filter 1302. It is a block diagram explaining the example of the structure which has. In FIG. 13, the same components as those shown in FIG. 1 are denoted by the same reference numerals, description thereof is omitted, and differences from the configuration shown in FIG. 1 will be mainly described.

  A density variable filter 1302 is disposed along with the aperture unit 132 and the lens element 140 in the optical path of the photographic lens 130A. As the density variable filter, for example, a liquid crystal element or an EC element in which a liquid crystal or a material having electrochromic (EC) physical properties is sealed in two opposing transparent substrates can be used.

  The controller 110 </ b> A of the imaging apparatus 100 </ b> A includes a dimming control unit 1304 that controls the optical density of the density variable filter 1302. The wobble operation control unit 118 issues control signals to the focus control unit 116, the aperture drive control unit 120, and the dimming control unit 1304 based on the timing signal output from the timing control unit 122. Based on the wobble control signal output from the wobble operation control unit 118 to the focus control unit 116, the focusing lens 134 is driven in the front-rear direction along the optical axis direction of the photographing lens 130A. At this time, the aperture shape of the aperture unit 132 is changed based on the aperture control signal output from the wobble operation control unit 118 to the aperture drive control unit 120. When the equivalent F value of the taking lens 130 </ b> A changes as the aperture shape of the aperture unit 132 is changed, a density control signal is output from the wobble operation control unit 118 to the dimming control unit 1304. Based on this density control signal, the dimming control unit 1304 controls the optical density of the density variable filter 1302, and as a result, the T value of the photographing lens 130A is kept substantially constant.

  As described above, the optical density of the density variable filter 1302 is adjusted in response to the change in the F value of the photographing lens 130A due to the change in the aperture shape of the aperture unit 132 during the wobbling operation. Then, the T value of the taking lens 130 is kept substantially constant when the aperture shape of the aperture unit 132 is changed in conjunction with the wobble operation. This eliminates the need for changing the gain of the image sensor 150 and changing the electronic shutter speed described with reference to FIGS. 6 and 7.

  The example in which the aperture shape of the aperture unit 132 is mechanically changed has been described above. For example, a liquid crystal element in which a liquid crystal or a substance having electrochromic (EC) physical properties is sealed in two opposing transparent substrates, An EC element can also be used. In this case, the opening shape can be changed relatively freely, and the opening shape can be switched at a relatively high speed.

  The imaging apparatus according to the present invention is applicable to a still camera and a movie camera. Further, the present invention can also be applied to a camera incorporated in a mobile phone, a personal digital assistant (PDA), a notebook PC, an in-vehicle camera, a surveillance camera, and the like.

It is a block diagram explaining the structure of the imaging device which concerns on embodiment of this invention. It is a figure which illustrates notionally the relationship between the focus adjustment position of a photographic lens, and the contrast value of a to-be-photographed image. It is a figure explaining the focus adjustment operation performed corresponding to the change of a photography scene. It is a figure explaining a mode that a frame rate increases with the start of a wobbling operation | movement, and a one part frame image is used as an image for AF. It is a figure explaining the example which changes an aperture stop in conjunction with a wobbling operation. It is a figure explaining a mode that the gain at the time of amplifying an image signal is changed corresponding to the change of an aperture stop. It is a figure explaining a mode that the time of the electronic shutter set with an image pick-up element is changed corresponding to the change of an aperture stop. It is a figure explaining a mode that the contrast of an image falls by image blurring, (a) is a figure which shows a mode that the image obtained by imaging has produced image blurring, (b) is obtained by imaging. It is a figure which shows a mode that the contrast value calculated | required from the obtained image falls. It is a figure which illustrates notionally a mode that the process which detects the contrast value of a to-be-photographed image based on the distribution of the pixel value obtained from the several pixel located in a line along a X direction. It is a figure which illustrates notionally the relationship between the arrangement direction of the pixel of the object which performs the process which detects a contrast value, and the shape change at the time of changing the aperture shape of a diaphragm in conjunction with wobbling. It is a figure explaining the structural example of the aperture_diaphragm | restriction apparatus which makes it possible to change the aperture shape of an aperture stop. It is a figure explaining another structural example of the aperture_diaphragm | restriction apparatus which makes it possible to change the aperture shape of an aperture_diaphragm | restriction. It is a block diagram explaining the structural example of the imaging device which makes it possible to make T value of a photographic lens substantially constant when the aperture shape of a diaphragm is changed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100, 100A ... Imaging device 110, 110A ... Controller 112 ... Gain control part 114 ... Electronic shutter control part 116 ... Focus control part 118 ... Wobble operation control part 120 ... Aperture drive control part 122 ... Timing control part 130, 130A ... Shooting lens 132, 132A, 132B ... Aperture unit 134 ... Focusing lens 136 ... Aperture actuator 138 ... Focus actuator 140 ... Lens element 150 ... Imaging element 152 ... Image signal processing unit 154 ... Imaging state detection processing unit 156 ... Display driver 158 ... Display unit 160 ... System bus 162 ... Memory 164 ... Recording media 1000a, 1000b, 1000c, 1000d ... Opening shapes 1100a, 1100b, 120 0 ... Sector blade 1204 ... ND filter 1302 ... Density variable filter 1304 ... Dimming control unit

Claims (7)

The image signal is repeatedly input from an image sensor capable of outputting an image signal obtained by photoelectrically converting a subject image formed by the photographing lens, and at least one of display and recording of a moving image is performed. An image signal processing unit;
When the image signal processing unit repeatedly inputs the image signal from the image sensor and performs at least one of display and recording of a moving image, one input timing and a subsequent input timing An imaging state detection processing unit that inputs an image signal output for imaging state detection processing from the image sensor at a timing in between and detects the imaging state of an image formed on the imaging element; An imaging device comprising:   A wobble operation control unit that performs a wobbling operation that shifts the focus adjustment position of the photographing lens back and forth with respect to a reference focus adjustment position, and is used for the imaging state detection process. 2. A wobble operation control unit that performs the wobble operation in synchronization with photoelectric conversion for generating an image signal output to an image state detection processing unit being performed by the image sensor. The imaging device described in 1.   The aperture shape of the stop of the photographing lens is changed in synchronism with the photoelectric conversion for obtaining the image signal for the imaging state detection processing input by the imaging state detection processing unit. The imaging apparatus according to claim 1, further comprising a diaphragm drive control unit that increases an aperture area. A gain control unit for controlling a gain applied in an amplification process performed when the image signal is output from the image sensor;
The gain control unit is configured so that the aperture control unit is synchronized with the photoelectric conversion performed by the imaging device for obtaining the image signal for the imaging state detection process input by the imaging state detection processing unit. 4. The gain is decreased in response to the excessive exposure amount when the exposure amount is excessive by changing the aperture shape of the aperture of the photographing lens or increasing the aperture area. The imaging device described in 1. An electronic shutter control unit for controlling a time related to a charge accumulation operation performed by the image sensor;
The electronic shutter control unit is configured so that the diaphragm control unit synchronizes with the fact that photoelectric conversion for obtaining the image signal for the imaging state detection processing input by the imaging state detection processing unit is performed by the imaging element. When excessive exposure occurs by changing the aperture shape of the stop of the photographing lens or increasing the aperture area, the time for the charge accumulation is shortened in response to the excessive exposure. The imaging apparatus according to claim 3. A light reduction control unit that reduces the amount of light that passes through the photographing lens and enters the image sensor using a light reduction member;
The dimming control unit is configured so that the diaphragm control unit synchronizes with the fact that photoelectric conversion for obtaining the image signal for the imaging state detection processing input by the imaging state detection processing unit is performed by the imaging element. When an excessive amount of exposure occurs by changing the aperture shape of the stop of the photographing lens or increasing the aperture area, the amount of light incident on the image sensor is decreased in response to the excessive amount of exposure. The imaging apparatus according to claim 3. The imaging element has an array of pixels two-dimensionally arranged along two arrangement directions orthogonal to each other, and the imaging state detection processing unit is parallel to one arrangement direction in the two arrangement directions. Configured to detect the imaging state by performing a process of detecting a contrast value of a subject image based on a distribution of pixel values obtained from a plurality of pixels arranged along a certain direction,
The aperture shape of the stop of the photographing lens is changed or the aperture area so that an aperture size along a direction parallel to the one arrangement direction is larger than an aperture size along a direction orthogonal to the one arrangement direction. The imaging device according to claim 3, wherein the imaging device is increased.