JP5914044B2 - Photometric device, imaging device, and photometric method - Google Patents

Description

The present invention relates to a photometric device, an imaging device, and a photometric method, and more particularly to a photometric device, an imaging device, and a photometric method for reducing photometric time under low luminance.

  In an imaging apparatus such as a single-lens reflex camera, a photometric sensor that measures the luminance of a subject with a wide dynamic range by using a LOG characteristic of a photodiode such as a photocurrent of a photodiode is widely used.

  In a photometric circuit using such LOG characteristics, a long waiting time is required to obtain accurate photometric output after receiving the subject light when the power supply voltage is turned on, particularly under the low brightness of the photocurrent. I was trying. In particular, in a system where the mirror is retracted during shooting and the light to the photodiode is shielded, such as a single-lens reflex camera, the deterioration of the photometric performance under low brightness due to the light response causes an increase in the release time lag. This is a very big problem such as a decrease in the continuous shooting speed.

  Furthermore, in recent digital cameras, high-sensitivity cameras with ISO sensitivity of several tens of thousands have appeared due to improved sensitivity of image pickup devices and advanced image processing. It is necessary to improve the photometric performance at

  In order to solve such a problem, for example, in Patent Document 1, a preliminary current is supplied during a non-light-receiving period, and the parasitic capacitance of the photodiode and the logarithmic compression diode is charged, thereby improving the responsiveness of the photometry circuit. What to do is disclosed. Further, for example, in Patent Document 2, preliminary response is performed by a light emitting element during a non-light-receiving period, and photocurrent is generated to precharge the parasitic capacitance of the photodiode and logarithmic compression diode, thereby improving the responsiveness of the photometry circuit. What to do is disclosed.

Japanese Patent Laying-Open No. 2005-077938 JP 2008-309732 A

  However, in the invention described in Patent Document 1, since the difference between the reserve current and the photocurrent becomes an error factor, it is necessary to provide a compensation circuit for compensating for this difference, which increases the circuit scale.

Also in the invention described in Patent Document 2, the difference between the photocurrent generated in the preliminary irradiation and the photocurrent at the time of photometry becomes an error factor. In addition, a light emitting element is necessary for preliminary irradiation, and there is a disadvantage that cost, mounting space, and the like are also required.
The present invention has been made in view of the above problems, and an object thereof is to shorten the time required for photometry under low luminance.

In order to achieve the above object, a photometric device according to the present invention is a photometric means comprising a first light receiving element that generates an electric charge in response to incident light from a subject and a second light receiving element that is shielded from light . The first light receiving element and the second light receiving element each include a photoelectric conversion region and reset means for resetting the photoelectric conversion region to a preset potential, and charge generated in the photoelectric conversion region is a photometric value. A photometric means for converting to and outputting, and a control means for resetting the photoelectric conversion area by the reset means and acquiring a photometric value from each light receiving element of the photometric means after a preset time has elapsed since the reset. Based on the obtained difference between the photometric value of the first light receiving element and the photometric value of the second light receiving element and the conversion characteristics of the photometric means after resetting the photoelectric conversion area, Brightness Luminance conversion means for measuring, and the conversion characteristic of the photometry means is a characteristic representing a relationship between the luminance of a subject and the difference after the preset time has elapsed since the reset. To do.

  According to the present invention, it is possible to shorten the time required for photometry under low luminance.

1 is a block diagram showing a schematic configuration of a single-lens reflex digital camera system according to an embodiment of the present invention. The figure which shows an example of the circuit diagram of the photometry circuit in embodiment. The figure for demonstrating the photometry sensor in embodiment. The figure which represents typically the responsiveness of the photometry circuit with respect to the different brightness | luminance in embodiment. The figure which shows the relationship between the difference of the output of the normal element in an embodiment, and the output of an OB element, and a brightness | luminance. The flowchart which shows the photometry operation | movement in embodiment.

  The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings.

  FIG. 1 is a block diagram showing a schematic configuration of a single-lens reflex digital camera system according to an embodiment of the present invention. As shown in FIG. 1, the digital camera system according to the present embodiment is configured such that a photographic lens unit 200 is detachably attached to a camera body 100 via a mount mechanism (not shown). The mount portion has an electrical contact group 210. The contact group 210 has a function of transmitting control signals, status signals, data signals, and the like between the camera body 100 and the photographic lens unit 200 and supplying currents of various voltages. The contact group 210 further has a function of transmitting a signal to the system controller 120 when the photographing lens unit 200 is connected to the camera body 100. Accordingly, communication can be performed between the camera body 100 and the photographing lens unit 200, and the photographing lens 201 and the diaphragm 202 in the photographing lens unit 200 can be driven. The contact group 210 may be configured to transmit not only electrical communication but also optical communication, voice communication, and the like. In FIG. 1, the photographing lens 201 is shown as a single lens for convenience, but it is well known that it is actually composed of a large number of lenses.

  A light beam from a subject image (not shown) is guided to a quick return mirror 102 that can be driven in a direction indicated by an arrow through a photographing lens 201 and a diaphragm 202. The central portion of the quick return mirror 102 is a half mirror, and a part of the light beam is transmitted when the quick return mirror 102 is lowered. The transmitted light beam is reflected downward by the sub mirror 103 installed behind the quick return mirror 102.

  Reference numeral 104 denotes a well-known phase difference type AF sensor unit including a field lens (not shown), a reflecting mirror, a secondary imaging lens, a diaphragm, a line sensor composed of a plurality of CCDs, and the like arranged near the imaging surface. It is. The focus detection circuit 105 controls the AF sensor unit 104 based on a control signal from the system controller 120 to perform well-known phase difference type focus detection.

  On the other hand, the light beam reflected by the quick return mirror 102 reaches the eyes of the photographer via the pentaprism 101 and the eyepiece 106.

  The photometric circuit 107 includes a photometric sensor for measuring the luminance of a subject disposed in the vicinity of the eyepiece lens 106, and its output is supplied from the photometric circuit 107 to the system controller 120.

  When the quick return mirror 102 is raised, the sub mirror 103 is folded and retracted from the optical path. The light beam incident through the photographing lens 201 and the diaphragm 202 reaches the image sensor 112 through the focal plane shutter 108 and the filter 109 which are mechanical shutters. Examples of the image sensor 112 include a CCD image sensor, a MOS image sensor, a CdS-Se contact image sensor, an a-Si (amorphous silicon) contact image sensor, a bipolar contact image sensor, and the like. Good.

  The filter 109 has two functions. One is a function of cutting infrared rays and guiding only visible light to the image sensor 112, and the other is a function as an optical low-pass filter. The focal plane shutter 108 has a front curtain and a rear curtain, and controls transmission and blocking of a light beam through the photographing lens 201 and the diaphragm 202.

  The camera body 100 according to the present embodiment is a control unit for the entire digital camera system, and includes a system controller 120 configured by a CPU that controls the control, and appropriately controls the operation of each unit described below.

  A lens control circuit 204 and an aperture control circuit 206 are connected to the system controller 120 via a lens control microcomputer 207. The lens control circuit 204 controls the lens driving mechanism 203 for moving the photographing lens 201 in the optical axis direction to perform focusing, and the diaphragm control circuit 206 controls the diaphragm driving mechanism 205 for driving the diaphragm 202. The lens control microcomputer 207 includes a lens storage device that stores lens-specific information such as a focal length, an open aperture, and a lens ID assigned to each lens, and information received from the system controller 120. The system controller 120 forms a subject image on the image sensor 112 by controlling the lens driving mechanism 203 via the lens control microcomputer 207. Further, the system controller 120 controls the diaphragm driving mechanism 205 that drives the diaphragm 202 based on the set Av value, and outputs a control signal to the shutter control circuit 111 based on the set Tv value. To control exposure. The shutter control circuit 111 controls the traveling of the front curtain and rear curtain of the focal plane shutter 108 based on the Tv value.

  The system controller 120 is connected to a shutter charge / mirror drive mechanism 110 that controls the up / down drive of the quick return mirror 102 and the shutter charge of the focal plane shutter 108. The drive source of the front curtain and rear curtain of the focal plane shutter 108 is constituted by a spring, and after the shutter travels, a spring charge is required for the next operation. The shutter charge / mirror drive mechanism 110 controls this spring charge. Also, the quick return mirror 102 is raised and lowered by the shutter charge / mirror drive mechanism 110.

  Furthermore, an EEPROM 122 is connected to the system controller 120. The EEPROM 122 stores parameters that need to be adjusted to control the camera body 100, camera ID information that enables individual identification of the digital camera, AF correction data adjusted by the reference lens, automatic exposure correction values, and the like. .

  An image data controller 115 is connected to the system controller 120. The image data controller 115 is configured by a DSP (digital signal processor), and executes control of the image sensor 112 and correction and processing of image data input from the image sensor 112 based on a command from the system controller 120. is there. The item of image data correction / processing includes auto white balance, and the correction amount can be changed by a command from the system controller 120.

  Further, the image data controller 115 can divide the image signal into regions, supply a value obtained by integrating each Bayer pixel in each region to the system controller 120, and measure the integrated signal by the system controller 120 for photometry. .

  A timing pulse generation circuit 114, an A / D converter 113, a DRAM 121, a D / A converter 116, and an image compression circuit 119 are connected to the image data controller 115. The timing pulse generation circuit 114 outputs a pulse signal necessary for driving the image sensor 112. The A / D converter 113 receives the timing pulse generated by the timing pulse generation circuit 114 together with the image sensor 112, and converts an analog signal corresponding to the subject image output from the image sensor 112 into a digital signal (image data). . The DRAM 121 is used for temporarily storing the image data converted by the A / D converter 113 and for temporarily storing the image data before being processed or converted into a predetermined format. The

  The image compression circuit 119 is a circuit for performing compression and conversion (for example, JPEG) of image data stored in the DRAM 121. A recording medium 401 is connected to the image compression circuit 119, and the image data converted by the image compression circuit 119 is stored in the recording medium 401. As the recording medium 401, for example, a hard disk, a flash memory, a micro DAT, a magneto-optical disk, an optical disk such as a CD-R and a CD-WR, a phase change optical disk such as a DVD, and the like are used. is not.

  In addition, an image display circuit 118 is connected to the D / A converter 116 via an encoder circuit 117. The image display circuit 118 is a circuit for displaying image data picked up by the image sensor 112, and is generally composed of a color liquid crystal display element. The image data controller 115 controls the image data on the DRAM 121 to be converted into an analog signal by the D / A converter 116 and output to the encoder circuit 117. The encoder circuit 117 converts the output of the D / A converter 116 into a video signal (for example, NTSC signal) necessary for driving the image display circuit 118.

  The image data controller 115 passes a filter having a predetermined frequency characteristic to the corrected image data, evaluates a contrast in a predetermined direction of an image signal obtained by performing a predetermined gamma process, and sends the result to the system controller 120. Supply. The system controller 120 communicates with the lens control circuit 204 and adjusts the focal position so that the contrast evaluation value is higher than a predetermined level, thereby performing contrast-based focus adjustment.

  Further, the system controller 120 has an operation display circuit 123 for displaying information on the operation mode of the camera body 100, exposure information (shutter time, aperture value, etc.) on the external liquid crystal display device 124 and the internal liquid crystal display device 125. It is connected. Further, a shooting mode selection button 130 for setting a mode for causing the digital camera system to execute a desired operation by the user, a main electronic dial 131, and a determination SW 132 are connected. Further, a distance measuring point selection button 133 for selecting a focus detection position to be used from a plurality of focus detection positions of the AF sensor unit 104, an AF mode selection button 134, and a photometry mode selection button 135 are connected. . Furthermore, a release switch SW1 (136) for starting a photographing preparation operation such as photometry and focus adjustment, a release switch SW2 (137) for starting an imaging operation, and a finder mode selection switch SW138 are connected. .

  The viewfinder mode selection switch SW138 switches between an optical viewfinder mode in which a subject can be confirmed by the eyepiece lens 106 and a live view display mode in which image signals from the image sensor 112 are sequentially displayed on the image display circuit 118.

  Further, the strobe device 300 can be detachably attached to the camera body 100 via a mount mechanism (not shown). The mount portion has an electrical contact group 310. The contact group 310 includes an X terminal (light emitting terminal) that transmits a control signal, a status signal, a data signal, and the like between the camera body 100 and the flash device 300 and controls the light emission timing. Further, it has a function of transmitting a signal to the system controller 120 when the strobe device 300 is connected to the camera body 100. Accordingly, communication between the camera body 100 and the flash device 300 can be performed, and the flash emission control can be performed. The contact group 310 may be configured to transmit not only electrical communication but also optical communication, voice communication, and the like.

  The strobe device 300 includes a light emission control circuit 303 including a xenon (Xe) tube 301, a reflective shade 302, an IGBT for controlling light emission of the Xe tube 301, a charging circuit 304, a power source 305, and a strobe control microcomputer 306. The The charging circuit 304 generates a voltage of about 300 V to supply power to the Xe tube 301. The power supply 305 is a battery that supplies power to the charging circuit 304, and the strobe control microcomputer 306 controls light emission and charging of the strobe and also controls communication with the system controller 120 on the camera body 100 side.

  FIG. 2 is an example of a circuit diagram showing a detailed configuration of the photometry circuit 107 shown in FIG. In FIG. 2, Q1 is an NPN phototransistor having a photoelectric conversion region that generates charges in response to incident light, MP1 is a PMOS for fixing the base potential of the phototransistor Q1, and I is a PMOS ( MP1) is a current source that is a load. MP2 is a PMOS for feeding back the gate potential of the PMOS (MP1) to the drain of MP1, and MP3 is a PMOS for a reset operation for forcibly injecting carriers into the phototransistor Q1. Reference numeral 256 denotes a logarithmic compression circuit for logarithmically compressing the emitter current of the phototransistor Q1.

  Note that the configuration of the photometry circuit 107 is not limited to the circuit configuration illustrated in FIG. 2, and may be any circuit configuration that can reset the base potential (photoelectric conversion region) of the phototransistor. For example, the photometric circuit 107 is used as a configuration capable of resetting the base potential of a phototransistor of a circuit described in Japanese Patent Application Laid-Open Nos. 2000-77644, 2010-45293, 2010-45294, and the like. be able to.

  Since the gate voltage of the PMOS (MP1) through which the constant current has flowed has a constant potential difference Vth with respect to the voltage VCC, the base potential of the phototransistor Q1 is also constant regardless of the light intensity incident on the phototransistor Q1. . Further, the base potential of the phototransistor Q1 is further stabilized by forming feedback using the PMOS (MP2). This eliminates the need to charge / discharge the large base capacitance Vcb. Therefore, the responsiveness of the photometric circuit of FIG. 2 is determined by the emitter capacitance Veb and the drain capacitance of the PMOS (MP2) and the photocurrent, which are smaller than the collector capacitance. Therefore, under low luminance where the influence of responsiveness begins to appear, the photometric value becomes higher than the actual luminance. Therefore, by performing exposure control based on the photometric value higher than the actual luminance, an underexposed image Will be imaged.

  FIG. 3 is a diagram for explaining a photometric sensor of the photometric circuit 107 of the present invention. FIG. 3A shows a layout diagram of the photometric sensors of the photometric circuit 107. As is clear from FIG. 3A, the light receiving elements include a total of 12 light receiving elements of 4 × 3. Among the light receiving elements, the light receiving elements ob1, ob2, and ob3 are optical black light receiving elements (hereinafter referred to as “light receiving elements”) configured such that the entire surface of the light receiving elements is covered with a light shielding member such as aluminum and light reflected from a subject is not incident. These are called “OB elements”. Further, nine light receiving elements s1 to s9 (hereinafter referred to as “normal elements” for distinction) are light receiving elements configured such that the output changes according to the intensity of reflected light from the subject. It is. Of course, it goes without saying that the arrangement and number of OB elements and normal elements are not limited to those shown in FIG. FIG. 3B shows the relationship between the photometric sensor of the photometric circuit 107 and the imaging range 30 of the image sensor 112.

  FIG. 4 is a diagram schematically showing the responsiveness (conversion characteristics) of the photometry circuit 107 for different luminances. FIG. 4A shows the relationship between the subject brightness and the stabilization waiting time from the reset operation of the photometry circuit 107 shown in FIG. 2 until the steady output is reached. The emitter capacitance Veb and the drain capacitance of the PMOS (MP2) described above. And the relationship of photocurrent. As apparent from FIG. 4 (a), when the Ev value corresponding to the luminance is around 0, the stabilization waiting time starts to increase so as to affect the operation sequence of the camera, and the Ev value becomes darker than 0. As a result, the stabilization waiting time increases exponentially.

  FIG. 4B shows how the output of the photometric circuit 107 stabilizes with time. The vertical axis indicates the result of A / D conversion of the output of the photometry circuit 107, and the horizontal axis indicates the elapsed time from the reset operation, and the output (photometry output) of the photometry circuit 107 is read at a predetermined time interval. And plot the values. The series of graphs is luminance, and represents changes in the output from the normal element of the photometry circuit 107 and the output from the OB element when the Ev values are 2, 0, -2, and -4, respectively. Note that the output from the OB element shows responsiveness as shown in the figure regardless of the subject brightness. As is clear from FIG. 4B, the locus from the reset operation to the steady output varies depending on the Ev value. However, if the Ev value is the same, there is almost no variation in the locus. For this reason, reading is performed a plurality of times during the period until the steady state is reached, and the difference between the output of the normal element and the output of the OB element is calculated, so that the metering output in the steady state can be obtained without setting a sufficient stabilization waiting time. It is possible to predict.

  FIG. 5 shows the difference between the output of the normal element and the output of the OB element when the photometric time is 10 ms in FIG. The horizontal axis represents luminance, and the vertical axis represents the difference between the output of the normal element and the output of the OB element. As shown in FIG. 5, there is a good correlation between the luminance and the difference, and sufficient fitting is possible with a high-order function such as a cubic function. As described above, by using the function, the photometry time can be shortened to about 10 ms until the Ev value of about -4, which conventionally required a stabilization waiting time of several hundred ms. In addition, by using the difference between the output of the normal element and the output of the OB element, there is an advantage that it is not necessary to consider a fluctuation factor such as a temperature change of the dark current component.

  FIG. 6 is a flowchart showing the photometric operation in the present embodiment. The system controller 120 performs control of the photometric circuit 107 and calculation of luminance based on the photometric output from the photometric circuit 107. Therefore, the system controller corresponds to control means, luminance calculation means, and exposure control means. In S601, the reset operation of all twelve light receiving elements including the OB element is performed. Specifically, the PMOS (MP1) in FIG. 2 is turned on, carriers are injected into the base of the phototransistor Q1, and resetting is performed.

  In S602, a predetermined photometry stabilization waiting time T is provided. As shown in FIG. 4B, after resetting all twelve light receiving elements, the light receiving elements converge their outputs in a steady state with response characteristics corresponding to the respective amounts of received light. Therefore, in order to predict the steady-state output by prediction, an output difference must occur between the light receiving elements, and thus a predetermined waiting time is provided. In the present embodiment, this time may be as short as about 10 ms.

  In S603, when the photometric stabilization waiting time T has elapsed (after a predetermined time has elapsed), the photometric values of all 12 light receiving elements are acquired. In S604, among the obtained photometric values, the photometric values of the OB elements ob1, ob2, and ob3 are averaged and stored in the memory as OB_AVE. The responsiveness of the OB element is determined according to the amount of carriers injected by the reset operation and the amount of dark current generated in the OB element. Further, since the dark current has a predetermined variation for each light receiving element, the variation in prediction accuracy can be suppressed by averaging in order to alleviate this.

  In S605, the difference ΔAEx (x = 1, 2,..., 9) between the photometric value sx (x = 1, 2,..., 9) of the normal elements s1 to s9 and the photometric value OB_AVE of the OB element is calculated. To do. In S606, it is determined whether or not the difference ΔAEx has been calculated for all photometric values sx. If there is a photometric value sx that has not been calculated, the process returns to S605, and if calculation has been completed for all photometric values sx, the process proceeds to S607. In S607, it is determined whether the prediction calculation can be applied using the value of ΔAEx. Here, if ΔAEx ≧ β (the second value), the process proceeds to S608. If 0 <ΔAEx <β (the first value), the process proceeds to S609, and ΔAEx ≦ 0 (the third value). ) Branch to S610.

  In S608, ΔAEx is a predetermined value β or more, for example, the subject brightness is an Ev value of 2 or more, and the response of the normal element is sufficiently good as shown in FIG. In this case, since it is better to use the photometric value sx of the normal element as it is than using the prediction formula, the photometric calculation is performed using the photometric value sx to calculate the Bv value indicating the luminance.

In S609, it is in the range of 0 <ΔAEx <β, and prediction calculation is possible. For example, 0 <ΔAEx <β corresponds to the Ev value in FIG. 4 from −4 to Ev2. In this area, for example, fitting is performed by a cubic equation,
AEx = a × ΔAEx ³ + b × ΔAEx ² + c × ΔAEx + d (1)
The Bv value is calculated using AEx predicted as described above.

  In S610, since ΔAE ≦ 0, it is a low luminance or dark state in which it is difficult to discriminate between the output of the normal element and the output of the OB element, and prediction cannot be applied. Therefore, in this case, the Bv value is clipped to a predetermined value, for example, the measurement limit Bv value−9 (Ev value−4) or less.

  In S611, it is checked whether or not the calculation of the Bv value has been completed for all the pixels. If not completed, the process returns to S607 to continue the calculation of the Bv value, and if completed, the process proceeds to S612.

  In S612, a final photometric calculation is performed using the obtained nine Bv values, and the photometric operation is terminated. The photometric calculation is calculated from nine photometric values as appropriate according to the camera mode such as center weight and evaluation photometry, and the final exposure control value is determined.

  As described above, according to the present embodiment, it is possible to predict the photometric output based on the difference between the output of the normal element and the output of the OB element constituting the photometric circuit even when the subject brightness is low. It is possible to shorten the time required for photometry under luminance.

Claims (7)

Photometric means having a first light receiving element that generates an electric charge in response to incident light from a subject and a second light receiving element shielded from light , wherein the first light receiving element and the second light receiving element are: A photoelectric conversion region, and a reset unit that resets the photoelectric conversion region to a preset potential, and a photometric unit that converts the charge generated in the photoelectric conversion region into a photometric value and outputs the photometric value,
The photoelectric conversion area is reset by the reset means, and after a preset time has elapsed since the reset, control means for obtaining a photometric value from each light receiving element of the photometric means,
Based on the obtained difference between the photometric value of the first light receiving element and the photometric value of the second light receiving element, and the conversion characteristics of the photometric means after resetting the photoelectric conversion area, the luminance of the subject Brightness calculating means for predicting,
The photometric device is characterized in that the conversion characteristic of the photometric means is a characteristic representing a relationship between a luminance of a subject and the difference after the preset time has elapsed since the reset.   The photometric device according to claim 1, wherein the luminance calculation unit performs the prediction when the difference is within a predetermined range, and does not perform the prediction when the difference is not within the range.   The brightness calculation means performs the prediction when the difference is a first value within the range, and the brightness calculation means performs the prediction when the difference is a second value that is greater than the first value and not within the range. The photometric device according to claim 2, wherein the brightness is calculated based on a photometric value obtained from one light receiving element.   The luminance calculation means performs the prediction when the difference is a first value within the range, and determines in advance when the difference is a third value smaller than the first value and not within the range. 4. The photometric device according to claim 2, wherein the brightness is set. A plurality of the second light receiving elements are provided,
5. The luminance calculation unit takes a difference between a photometric value of the first light receiving element and a value obtained by averaging the photometric values of the plurality of second light receiving elements. 6. The photometric device according to item. A photometric device according to any one of claims 1 to 5;
An image pickup apparatus comprising: an exposure control unit that controls exposure based on the luminance obtained by the luminance calculation unit. Photometric means having a first light receiving element that generates an electric charge in response to incident light from a subject and a second light receiving element shielded from light , wherein the first light receiving element and the second light receiving element are: Photometry using an output from a photometric unit that has a photoelectric conversion region and a reset unit that resets the photoelectric conversion region to a preset potential and converts the charge generated in the photoelectric conversion region into a photometric value and outputs it. A method,
The photoelectric conversion region is reset by the reset unit, and after a preset time has elapsed since the reset, an acquisition step of acquiring a photometric value from each light receiving element of the photometric unit;
Based on the obtained difference between the photometric value of the first light receiving element and the photometric value of the second light receiving element, and the conversion characteristics of the photometric means after resetting the photoelectric conversion area, the luminance of the subject And a luminance calculation step for predicting
The photometry method according to claim 1, wherein the conversion characteristic of the photometry means is a characteristic representing a relationship between a luminance of a subject and the difference after the preset time has elapsed since the reset.

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