JP2017009952A - Imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress an exposure control from occurrence of an illumination area where a correct exposure tracking cannot be locally attained upon the exposure control along with a ND filter.SOLUTION: An imaging device includes: first light reduction means that can adjust an amount of light by causing a size of a diaphragm aperture to vary, in which an adjustment range of the amount of light varies in accordance with a focal length; second light reduction means that can adjust an amount of passing light by varying transmittance, in which an adjustment performance of the second light reduction means is more rough than an adjustment resolving power of the first light reduction means; and control means that controls operations of the first and second light reduction means for making an exposure upon shooting correct. The control means is configured to, when an adjustable range of the amount of light of the first light reduction means is wider than that of the second light reduction means, adjust the amount of light using the first light reduction means and second light reduction means, and when the adjustable range thereof is narrower, adjust the amount of light using the first light reduction means.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an imaging apparatus, a control method thereof, and a program, and more particularly, to an ND filter insertion / extraction timing.

  In an imaging apparatus using a solid-state image sensor such as a video camera or a digital still camera, means for adjusting an aperture area of a diaphragm aperture of a photographing lens, an electronic shutter speed and a mechanical shutter speed of the solid-state image sensor as exposure adjusting means. Means for adjusting, means for adjusting the amplifier gain of the image signal obtained from the individual image sensor, and the like are provided.

  Any of these exposure adjusting means has a limited exposure range in which the exposure can be adjusted without significantly degrading the image quality. In particular, the range in which exposure control can be performed by adjusting the electronic shutter speed and the amplifier gain of the image signal becomes narrower as the individual image sensor becomes smaller and the number of pixels increases. Furthermore, with the variable aperture mechanism that adjusts the aperture area of the aperture aperture, when the aperture aperture is reduced to accommodate very bright subjects, the resolution performance deteriorates due to diffraction when the aperture area decreases to a certain size. As a result, the image quality starts to deteriorate rapidly.

  Therefore, in addition to the above exposure adjustment means, an exposure adjustment means that adjusts the exposure amount by inserting and removing an ND filter in the aperture opening of the taking lens is used in addition to the above exposure adjustment means in an imaging apparatus using a solid-state image sensor. There is what I did. In particular, many patent documents relating to an image pickup apparatus using both an exposure adjusting means using a variable aperture mechanism and an exposure adjusting means using an ND filter have been disclosed.

  In addition, low-priced video cameras include a video camera with a mechanism for adjusting exposure by opening and closing an ND filter that attenuates a certain amount of light in order to reduce costs. In a video camera equipped with such a mechanism, the ND filter can adjust the light amount only by binary values that can be opened and closed, and the amount of light that passes through the ND filter may change greatly at the timing when the ND filter is opened and closed.

  In the exposure control method disclosed in Patent Document 1, an exposure change amount having a magnitude that cancels out the exposure change amount that occurs when a state transition between the fully open state and the fully closed state of the ND filter is generated. By controlling and generating any one of the aperture, the electronic shutter speed of the individual image pickup device, and the amplifier gain amount of the image signal, it is possible to absorb the level difference of the light amount change caused by opening and closing the ND filter. As a result, even with a video camera equipped with an ND filter whose light intensity can be adjusted only in binary units, exposure control with higher follow-up performance can be performed using the ND filter mechanism.

  In recent years, there are Tv priority modes, etc., in which the user designates the shutter speed at the time of shooting and shoots. These modes can be used for shooting that expresses the flow of water by shooting with a long shutter speed. This is particularly effective when shooting a moving subject without blurring by shooting at a high shutter speed.

  There is also a mode in which the user can specify the ISO sensitivity at the time of shooting. In these modes, shooting with low ISO sensitivity is set to reduce image quality degradation due to noise, and conversely, ISO tracking is set to high to improve exposure follow-up performance in low-light scenes. This is particularly effective when shooting.

JP 2005-45648 A

  However, in the mode in which the user specifies the shutter speed and ISO sensitivity at the time of shooting as described above, the exposure change is of a magnitude that cancels out the step of the exposure change caused by opening and closing of the ND filter as described above. It can be generated only by controlling the aperture of the taking lens. Further, a general zoom lens has a feature that the open F value becomes darker as the focal length is moved to the telephoto side by performing a zoom operation.

  Due to the characteristics of the above zoom lens, the open F value gradually darkens due to the zoom operation, and when the exposure change amount between the open F value and the small aperture F value opens and closes the ND filter at a certain focal length It may be smaller than the resulting exposure change step.

  At this time, there is a problem that an exposure change step generated when the ND filter is opened / closed cannot be absorbed only by aperture control of the photographing lens, and an illuminance region in which proper exposure follow cannot be locally generated.

  The present invention has been made in view of such problems. An object of the present invention is that, in a digital camera equipped with an ND filter mechanism that can adjust the light amount only by binary values, an illuminance region that cannot properly follow an appropriate exposure is generated when performing exposure control using an ND filter. It is to suppress exposure control.

  In order to achieve the above object, an imaging apparatus of the present invention has the following configuration. In other words, the optical means for forming the subject image, and the amount of light can be adjusted by changing the size of the aperture opening that exists on the optical axis of the optical means, and the adjustment range thereof according to the focal length The amount of passing light can be adjusted by changing the transmittance that is present on the optical axis of the optical means and the first dimming means that changes, and the adjustment performance is the adjustment of the first dimming means A second dimming means coarser than the resolution, and a control means for controlling the operation of the first and second dimming means in order to make exposure at the time of photographing appropriate, the control means, When the light amount adjustable range of the first dimming means is wider than that of the second dimming means, the light quantity is adjusted using the first dimming means and the second dimming means, The light amount adjustable range of the first dimming means is larger than that of the second dimming means. If narrow and adjusting the amount of light using the first light reduction means.

  According to the imaging apparatus of the present invention, when performing exposure control using an ND filter, it is possible to suppress exposure control in which an illuminance region that cannot locally follow appropriate exposure is generated.

1 is a block diagram illustrating an example of a functional configuration of a digital camera as an example of an imaging apparatus according to an embodiment of the present invention. (a) Example of program diagram according to an embodiment of the present invention, (b) Example of program diagram according to an embodiment of the present invention, (c) Example of program diagram according to an embodiment of the present invention The flowchart for demonstrating operation | movement in the still image recording mode of the digital camera shown in FIG. The flowchart for demonstrating the process which selects the program diagram which determines exposure conditions of the digital camera shown in FIG.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. Hereinafter, an example in which the present invention is applied to a digital camera provided with an exposure control mechanism using an ND filter as an example of an imaging apparatus will be described. However, the present invention can be applied not only to an electronic device having an exposure control mechanism using an ND filter but also to an electronic device having an exposure control mechanism in place of the ND filter. These electronic devices include mobile phones, game machines, tablet terminals, personal computers, etc., but these are merely examples.

[Example 1]
(1 Configuration of imaging device)
FIG. 1 is a block diagram illustrating a functional configuration example of an imaging apparatus 10 according to the present embodiment. One or more of the functional blocks shown in FIG. 1 may be realized by hardware such as an ASIC or a programmable logic array (PLA), or may be realized by a programmable processor such as a CPU or MPU executing software. May be. Further, it may be realized by a combination of software and hardware. Therefore, in the following description, even when different functional blocks are described as the operation subject, the same hardware can actually be realized as the subject.

  In FIG. 1, a photographing lens 101 has a zoom mechanism, and constitutes an optical system that forms an incident light from a subject on an imaging surface. The ND filter 102 attenuates the amount of incident light according to an instruction from the AE (Auto Exposure) processing unit 105. The iris diaphragm 103 and the mechanical shutter 104 control the amount of incident light on the image sensor 108 and the charge accumulation time in accordance with an instruction from an AE (Auto Exposure) processing unit 105. The image sensor 108 converts an optical image formed on the light receiving surface into an electric signal by photoelectric conversion processing such as a CCD element or a CMOS element, and outputs the electric signal to the A / D converter 109. The A / D conversion unit 109 converts the electrical signal (analog signal) output from the image sensor 108 into a digital signal. The A / D converter 109 includes a CDS circuit that removes noise from the received electrical signal, and a nonlinear amplifier circuit that performs nonlinear amplification before converting the received electrical signal into a digital signal.

  The AE processing unit 105 controls the operations of the ND filter 102, the iris diaphragm 103, and the mechanical shutter 104 according to an instruction from the system control unit 114, and changes the exposure state.

  The focus lens 106 focuses on the imaging surface of the image sensor 108 to form an optical image in accordance with a control signal from an AF (Auto Focus) processing unit 107.

  The image processing unit 110 performs resize processing and color conversion processing such as predetermined pixel interpolation and image reduction on the digital signal output from the A / D conversion unit 109, and outputs image data. The image processing unit 110 reads and writes image data from the image recording unit 113 via the format conversion unit 111. The image processing unit 110 reads image data based on an instruction from the system control unit 114, and performs face detection processing and authentication processing. The authentication process in the present embodiment includes an authentication process that performs a matching process using authentication dictionary data. The image processing unit 110 updates the dictionary data used for authentication when the authentication processing is successful based on an instruction from the system control unit 114.

  The format conversion unit 111 performs format conversion of the image data generated by the image processing unit 110 in order to store the image data in the DRAM 112. The DRAM 112 is an example of a high-speed built-in memory, and is used as a high-speed buffer that manages temporary storage of image data, or as a working memory in image data compression / decompression processing.

  The image recording unit 113 includes a recording medium such as a memory card for recording captured images (still images and moving images) and an interface thereof, and includes a recording medium and a circuit for reading and writing data from and to the recording medium.

  The system control unit 114 includes a CPU, a ROM, and a RAM. The CPU expands and executes a program stored in the ROM in a work area of the RAM, thereby performing overall operation control of the imaging apparatus. In addition to the control of each functional unit for obtaining image data corresponding to one exposure, the control of the AE processing unit 105 for acquiring image data corresponding to a plurality of exposures with different shooting conditions and the amount of light of the strobe 118 To control. In addition, a mode to be used is controlled from a plurality of imaging drive modes of the imaging element 108. The VRAM 115 is an image display memory.

  The display unit 116 is, for example, an LCD or the like, and displays an image, a display for assisting operation, a status display of the imaging device, and an index indicating a shooting screen and a focus detection area at the time of shooting.

  The operation unit 117 includes, for example, a menu switch for performing various settings such as shooting mode, exposure correction, aperture value setting, image playback setting, zoom lever for instructing the zoom operation of the shooting lens, shooting mode and playback mode. The operation mode changeover switch is provided. The user gives various settings and instructions to the imaging apparatus by operating the operation unit 117.

  The strobe 118 emits light at an appropriate timing and light emission amount according to an instruction from the system control unit 114. The first switch (SW1) 119 is a switch for performing shooting preparation operations such as AE processing and AF processing. The second switch (SW2) 120 is connected to the system control unit 114 after the operation of the first switch 119. Switch for instructing to start shooting.

(2 Imaging device exposure control)
In the above configuration, the ND filter 102 and the AE processing unit 105 constitute a first exposure adjusting unit of the imaging device 10, and the iris diaphragm 103 and the AE processing unit 105 are the second exposure adjustment of the imaging device 10. Means. The mechanical shutter 104 and the AE processing unit 105 constitute a third exposure adjustment unit of the imaging device 10, and the A / D conversion unit 109 adjusts the fourth exposure adjustment of the imaging device 10 by adjusting the amplifier gain of the image signal. Means. Then, the system control unit 114 controls the first exposure adjustment unit, the second exposure adjustment unit, the third exposure adjustment unit, and the fourth exposure adjustment unit according to the exposure control method of the present invention. Perform exposure control.

  The target exposure value of the image capturing apparatus 10 is determined according to the brightness of the subject. Therefore, the AE control unit 105 performs the first exposure adjustment unit, the second exposure adjustment unit, and the third exposure according to the brightness of the subject. The adjusting means and the fourth exposure adjusting means are controlled. Then, the total exposure amount determined by the exposure control by each exposure adjustment unit becomes the exposure amount as a whole of the imaging apparatus 10.

  In the imaging apparatus 10, in order to obtain the target exposure value, it is defined what value the exposure amount of each of the first exposure adjustment unit, the second exposure adjustment unit, the third exposure adjustment unit, and the fourth exposure adjustment unit should be controlled to. The program diagram data is stored.

(3 Program diagram)
As such a program diagram, the first program diagram and the second program diagram when the user sets an arbitrary ISO sensitivity and shoots in the Tv priority mode (the mode in which the user specifies the shutter speed at the time of shooting). Two program diagram data of the program diagram are stored, and the AE processing unit 105 selects one program diagram from the two program diagrams according to the condition, and the selected program diagram To control each exposure adjusting means.

  FIG. 2 shows the contents of the first program diagram and the second program diagram in the form of a graph. For ease of explanation and understanding, here, the exposure time (shutter speed) and ISO sensitivity are set to arbitrary values set by the user, and the relationship between the insertion / extraction state of the ND filter and the F value by the diaphragm is shown. In the graph of FIG. 2, the horizontal axis indicates the exposure amount generated by the first exposure adjusting means, and shows the binary value of the state where the ND filter is removed (ND OFF) and the state where it is inserted (ND ON). The exposure amount is smaller when the ND filter is inserted. The vertical axis indicates the exposure amount generated by the second exposure adjusting means, and indicates that the iris diaphragm blade is closed (the F value is large (dark)) as it goes upward, and the exposure amount decreases. In addition, the small aperture F value (F value when the iris diaphragm is closed to the limit) in FIG. 2A is F16, and the open F value (F value when the iris diaphragm is opened to the limit) is F1.4. In FIG. 2B, the small aperture F value is F16, and the open F value is F4.6. The oblique axis indicates the total exposure amount (EV = ExposureValue) generated by controlling the first exposure adjustment unit and the second exposure adjustment unit, and the exposure amount becomes smaller toward the upper right.

In the example of FIG. 2 (a), in the range where the subject brightness (hereinafter, subject brightness) is high (bright), the iris diaphragm is reduced as the subject brightness decreases (darkens) with the ND filter removed (OFF). Insert the ND filter (ON) at the timing when the exposure amount is attenuated by 3EV with the iris diaphragm (timing when F4 is reached), and open the iris diaphragm to the open position. When the subject brightness further decreases, the iris diaphragm is narrowed down to a small aperture (F11) accordingly.
(4 Still image recording processing sequence)
FIG. 3 is a flowchart for explaining the processing operation in the still image recording mode of the imaging apparatus shown in FIG. In the still image recording mode, a so-called live view function may be realized by continuously capturing still images and displaying the captured moving images on the display unit 116.

  Hereinafter, a series of processes of the still image recording sequence in the present embodiment will be described with reference to FIG. The processing corresponding to the flowchart of FIG. 3 can be realized by the system control unit 114 reading, for example, a processing program stored in the ROM, developing it in the RAM, and executing it.

  The system control unit 114 determines whether or not the switch SW1 119 is ON (S301). If the switch SW1 119 is ON, the system control unit 114 advances the process to S302, and if not, repeats the process of S301.

  In S302, the system control unit 114 performs photometry processing and calculates subject luminance. The subject luminance value is calculated from the luminance signal of the image data (digital signal) output from the A / D conversion unit 109 and the exposure conditions used.

  When the photometry process is completed, in S303, the system control unit 114 determines the focus detection exposure based on the subject brightness calculated in S302, and controls the determined focus detection exposure. A focus detection program diagram is used to determine the focus detection exposure, and an aperture near the open position is used as much as possible to reduce the depth of the subject.

  In step S304, the system control unit 114 performs focus detection processing based on image data captured under exposure conditions for focus detection. Specifically, the system control unit 114 controls the AF processing unit 107 to perform shooting while moving the focus lens 106, and indicates the contrast of the image data (digital signal) output from the A / D conversion unit 109. Obtain an evaluation value. Then, the AF control unit 107 sets the focus lens position where the AF evaluation value is maximized to the in-focus position. Here, focus detection using the contrast detection method is performed, but focus detection using the phase difference detection method may be performed.

  In step S305, the system control unit 114 controls the AF control unit 107 to move the focus lens to the in-focus position calculated in step S304.

  In S306, the system control unit 114 determines whether the currently set shooting mode is the shutter speed priority mode (hereinafter referred to as Tv priority mode). If the Tv priority mode is set, the system control unit 114 advances the process to S307, and if other modes are set, advances the process to S309.

  In step S307, the system control unit 114 determines whether the ISO sensitivity at the time of shooting is currently set by the user. If an arbitrary ISO sensitivity is set, the system control unit 114 advances the process to S308, and if the automatic ISO sensitivity determination mode (Auto) is set, advances the process to S309.

  In S308 and S309, the system control unit 114 controls the AE processing unit 105 to determine an exposure condition during still image shooting (main shooting), and then advances the process to S310.

  In S310, the system control unit 114 changes the exposure set for focus detection in S303 to the exposure for main photographing. In order to reduce the time lag from when the switch SW2 120 is turned on until the actual shooting is performed, the system control unit 114 controls the AE processing unit 105, and at this time, the iris diaphragm 103 is determined in S308 or S309. Control the aperture value for exposure conditions.

  In step S311, the system control unit 114 determines whether the switch SW2 120 is ON. If the switch SW2 120 is OFF, the system control unit 114 proceeds to step S312; otherwise, the process proceeds to step S313.

  In step S312, the system control unit 114 determines whether or not the switch SW1 119 is ON. If the switch SW1 119 is ON, the process proceeds to step S311. If the switch SW1 119 is OFF, the process returns to step S301. That is, while the switch SW1 119 is ON and the switch SW2 120 is OFF, the system control unit 114 repeatedly executes the processes of S311 to S312.

  When the switch SW2 120 is turned on and a main photographing start instruction is given, the system control unit 114 controls the AE processing unit 105 to control the exposure conditions determined in S308 or S309 in S313, and then performs main exposure ( S314) is performed.

In S315, the system control unit 114 applies processing according to the recording format, such as development processing in the image processing unit 110 and encoding processing in the format conversion unit 111, to the image data obtained in the main exposure in S314, and the image data Generate a file.
In step S316, the system control unit 114 records the image data file on a recording medium such as a semiconductor memory card using the image recording unit 113.
(5 Calculation of exposure conditions)
FIG. 4 is a flowchart for explaining the details of the “Tv priority mode & ISO sensitivity designation exposure condition determination” (S308) processing operation of the flowchart shown in FIG.

  Hereinafter, the “Tv priority mode & ISO sensitivity designation exposure condition determination” process in this embodiment will be described with reference to FIG. The processing corresponding to the flowchart of FIG. 4 can be realized by the system control unit 114 reading, for example, a processing program stored in the ROM, developing it in the RAM, and executing it.

  In S401, the system control unit 114 controls the AE processing unit 105 to acquire the open F value of the iris diaphragm 103 in the current digital camera state, and then the process proceeds to S402.

  In S402, the system control unit 114 controls the AE processing unit 105 to change the exposure change amount that is generated when the iris diaphragm 103 is driven from the open position to the small stop, and the exposure change that is generated when the ND filter 102 is driven. It is determined whether or not the amount is larger than the amount. If larger, the process proceeds to S403, and if smaller, the process proceeds to S404.

  In S403 and S404, the system control unit 114 controls the AE processing unit 105 to determine exposure conditions using the program diagrams shown in FIGS. 2 (a) and 2 (b), respectively.

  Here, for example, the amount of exposure change caused by the insertion / extraction driving of the ND filter 102 in the program diagram shown in FIG. 2 is 3EV. The program diagram of FIG. 2A is a program diagram in the case where the exposure change amount (F1.4 to F11) generated when the iris diaphragm 103 is driven from the open position to the small diaphragm is 6 EV. Further, the program diagram of FIG. 2 (b) shows the exposure change amount (F4) generated when the iris diaphragm 103 is driven from the full open to the small stop, such as when the full aperture F value is increased (darkened) by a zoom operation or the like. .6 to F11) is a program diagram when 2.5 EV.

  Here, in order to help understanding of the effect of the present embodiment, the exposure change amount generated when the iris diaphragm 103 is driven from the open position to the small stop is smaller than the exposure change amount generated when the ND filter 102 is driven to be inserted and removed. In this case, an example of a program diagram when the exposure amount is adjusted using the ND filter 102 together is shown. In the program diagram shown in FIG. 2C, the exposure change amount generated when the iris diaphragm 103 is driven from the open position to the small stop is smaller than the exposure change amount generated when the ND filter 102 is driven to be inserted and removed. The exposure amount for EV in the section P (area indicated by the dotted line) in FIG. 2C cannot be secured. In such a case, it becomes impossible to perform exposure with an appropriate exposure amount in a scene having some subject luminance.

  On the other hand, in the present embodiment, whether or not the exposure change amount generated when the iris diaphragm 103 is driven from the open position to the small stop in S402 is larger than the exposure change amount generated when the ND filter 102 is driven to be inserted and removed. Since the program diagram shown in FIG. 2A in which the ND filter 102 is also used together to determine the exposure condition is used only when the judgment is large, there is no section like P.

  Although the present invention has been described in detail based on preferred embodiments thereof, the present invention is not limited to these specific embodiments, and various forms within the scope of the present invention are also included in the present invention. included. A part of the above-described embodiments may be appropriately combined. Also, when a software program that realizes the functions of the above-described embodiments is supplied from a recording medium directly to a system or apparatus having a computer that can execute the program using wired / wireless communication, and the program is executed Are also included in the present invention.

  Accordingly, the program code itself supplied and installed in the computer in order to implement the functional processing of the present invention by the computer also realizes the present invention. That is, the computer program itself for realizing the functional processing of the present invention is also included in the present invention. In this case, the program may be in any form as long as it has a program function, such as an object code, a program executed by an interpreter, or script data supplied to the OS. As a recording medium for supplying the program, for example, a magnetic recording medium such as a hard disk or a magnetic tape, an optical / magneto-optical storage medium, or a nonvolatile semiconductor memory may be used.

  As a program supply method, a computer program that forms the present invention is stored in a server on a computer network, and a connected client computer downloads and programs the computer program.

101 photographic lens, 102 ND filter, 103 iris diaphragm,
104 mechanical shutter, 105 processing unit

Claims (3)

Optical means for forming a subject image;
A first dimming unit that is on the optical axis of the optical unit and capable of adjusting the amount of light by changing the size of the aperture opening, and whose adjustment range changes according to the focal length;
The amount of passing light can be adjusted by changing the transmittance existing on the optical axis of the optical means, and the adjustment performance thereof is the second dimming means coarser than the adjustment resolution of the first dimming means. ,
Control means for controlling the operation of the first and second dimming means in order to make exposure at the time of photographing proper,
The control means uses the first dimming means and the second dimming means when the light quantity adjustable range of the first dimming means is wider than that of the second dimming means. Adjusting the light quantity, and adjusting the light quantity using the first dimming means when the light quantity adjustable range of the first dimming means is narrower than that of the second dimming means, An imaging device.   The imaging apparatus according to claim 1, wherein the control unit performs the control only in a mode in which photographing is performed at a predetermined shutter speed.   The imaging apparatus according to claim 2, wherein the control unit performs the control only in a mode in which photographing is performed with a predetermined ISO sensitivity.