JP2006325066A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allow bracket imaging which achieves both correct exposure and dynamic range, in an imaging apparatus that uses imaging elements with a plurality of different photoelectric conversion characteristics. <P>SOLUTION: Such imaging apparatus and imaging method comprises a plurality of bracket imaging modes which achieves both correct exposure and dynamic range by separately controlling the exposure and dynamic range. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an imaging apparatus, and more particularly, to an imaging apparatus that includes a plurality of imaging elements having different photoelectric conversion characteristics and includes a bracket imaging mode.

  Conventionally, by adding a logarithmic conversion circuit having a MOSFET or the like to a solid-state image pickup device in which photoelectric conversion elements such as photodiodes are arranged in a matrix, and utilizing the sub-threshold characteristics of the MOSFET, There is known a logarithmic conversion type imaging device whose output characteristics are such that an electrical signal is logarithmically converted with respect to an incident light amount (see, for example, Patent Document 1).

  Further, in the logarithmic conversion type image pickup device, by applying a specific reset voltage to the MOSFET, a linear operation state in which an electrical signal is linearly converted and output according to the original output characteristics of the solid state image pickup device, that is, the amount of incident light, and There is known a logarithmic conversion type image pickup device capable of automatically switching between the above-mentioned logarithmic operation states (see, for example, Patent Document 2). Furthermore, an imaging apparatus is disclosed that can automatically switch from a linear operation state to a logarithmic operation state, and that can adjust the potential state of the MOSFET by adjusting the reset time of the MOSFET (for example, Patent Document 3). reference).

  By the way, when the logarithmic conversion type imaging device is used in a linear operation state, an output proportional to the amount of electric charge generated by the photoelectric conversion device can be obtained, so that even a low-luminance subject has high contrast (has high gradation). ) There is an advantage that an image signal can be obtained, but there is a disadvantage that the dynamic range becomes narrow. On the other hand, when the logarithmic conversion type imaging device is used in a logarithmic operation state, an output that is naturally logarithmically converted with respect to the amount of incident light can be obtained. Since logarithmic compression is performed, there is an inconvenience that contrast is deteriorated.

  Furthermore, in addition to the logarithmic conversion type image pickup device, an image pickup device (for example, an image having a dynamic range wider than that of each screen can be synthesized by selecting and synthesizing a screen portion of an appropriate level from a plurality of screens having different exposure amounts. And Patent Document 4) and a charge-voltage conversion unit that converts photoelectric conversion signal charges of the image sensor into signal voltages, and the charge-voltage conversion unit includes a plurality of capacitors having different voltage dependencies, and a dynamic range is variable. Some imaging devices (see, for example, Patent Document 5) have also been proposed.

  However, since the image sensor proposed in Patent Document 4 synthesizes images from images with different exposure amounts by image processing, a simple image synthesis results in an unnatural and extremely difficult to see image. Very complex image composition is essential, which makes the cost very high. Further, the image pickup device proposed in Patent Document 5 has a complicated device structure and a high manufacturing cost, and it is difficult to control the voltage dependency of the capacitance, so that adjustment for each device is required, which causes an increase in cost.

  The imaging device and the imaging device according to Patent Documents 1 to 3 only disclose that the imaging device can be automatically switched from the linear operation state to the logarithmic operation state. However, in view of the advantages and disadvantages of the linear operation state and the logarithmic operation state described above, the image capturing operation is performed not only by automatic switching but also by actively utilizing the advantages of each operation state. Is desirable. For example, even in the case of performing automatic exposure control, if the control is performed by associating the luminance of the target subject with the switching point from the linear operation state to the logarithmic operation state of the imaging sensor, the advantages provided by each operation state There is a possibility that the optimum automatic exposure control using the can be performed.

  Therefore, the applicant of the present application, in Japanese Patent Application No. 2004-159760, performs exposure control of the imaging device in association with the photoelectric conversion characteristics of the imaging sensor included in the imaging device, so that the light amount from the subject (subject luminance) is satisfied. Thus, an imaging apparatus and an imaging method capable of imaging a subject with an optimal exposure state and a predetermined dynamic range are proposed.

On the other hand, a digital camera that is a representative example of an imaging apparatus has an imaging mode related to exposure (for example, exposure bracket imaging mode) (for example, see Non-Patent Document 1). Here, exposure bracket imaging refers to taking multiple photos with different exposures by changing the aperture or shutter speed little by little in order to obtain an image of the main subject and background exposure balance that matches the photographer's intention. It is a technique to do.
JP 11-298798 A JP 2002-77733 A JP 2002-300476 A Japanese Patent Publication No. 7-97841 JP 2000-165755 A Konica Minolta Photo Imaging Co., Ltd .: α-7 DIGITAL catalog (http://konicaminolta.jp/products/consumer/digital_camera/catalogue/pdf/a-7digital.pdf) “Exposure Bracketing” on page 9/9 “Shooting Function” ] Column; searched on April 8, 2005)

  However, the method shown in Japanese Patent Application No. 2004-159760 does not mention until the method is applied to an imaging mode related to exposure, for example, exposure bracket imaging. Since the dynamic range also changes in conjunction with the change, in some cases, the dynamic range is insufficient, and there may be a problem that whiteout occurs on the high luminance side.

  The present invention has been made in view of the above circumstances, and controls exposure and dynamic range independently or in conjunction when imaging using an image sensor having a photoelectric conversion characteristic composed of a linear characteristic region and a logarithmic characteristic region. Thus, an object of the present invention is to provide an imaging device capable of bracket imaging that achieves both exposure and dynamic range.

  The object of the present invention can be achieved by the following constitution.

(Claim 1)
In an imaging apparatus including an imaging device having a plurality of different photoelectric conversion characteristics,
An exposure control unit that controls exposure when imaging a subject based on luminance information of the subject;
A dynamic range control unit for controlling the dynamic range of the image sensor;
Mode setting means for setting the bracket imaging mode;
When the bracket imaging mode is set by the mode setting means,
An image pickup apparatus, comprising: an image pickup control unit configured to pick up a plurality of images by the image pickup device while causing the exposure control unit to control exposure for each image pickup and causing the dynamic range control unit to control a dynamic range. .

(Claim 2)
The exposure control unit controls exposure to be constant,
The dynamic range control unit controls the dynamic range to a plurality of different values,
The imaging apparatus according to claim 1, wherein the imaging control unit performs imaging for each of the plurality of different dynamic ranges.

(Claim 3)
The exposure control unit controls the exposure to a plurality of different values;
The dynamic range control unit controls the dynamic range to be constant,
The imaging apparatus according to claim 1, wherein the imaging control unit performs imaging for each of the plurality of different exposures.

(Claim 4)
The exposure control unit controls the exposure to a plurality of different values;
The dynamic range control unit controls the dynamic range to a plurality of different values,
The imaging apparatus according to claim 1, wherein the imaging control unit performs imaging for each set of the plurality of different exposures and dynamic ranges.

(Claim 5)
The image sensor generates an electrical signal corresponding to the amount of incident light, a linear characteristic region in which the electrical signal is linearly converted with respect to the amount of incident light, and an electric signal for the amount of incident light. 5. The imaging apparatus according to claim 1, wherein the imaging device has a photoelectric conversion characteristic including a logarithmic characteristic region that is logarithmically converted and output.

(Claim 6)
The image pickup device synthesizes an image having a wider dynamic range than individual screens by selecting and synthesizing a screen portion of an appropriate level from a plurality of screens having different exposure amounts. The imaging apparatus according to any one of 1 to 4.

(Claim 7)
The image sensor has a charge-voltage converter that converts the photoelectric conversion signal charge of the image sensor into a signal voltage, and the charge-voltage converter includes a plurality of capacitors having different voltage dependencies, and has a variable dynamic range. The image pickup apparatus according to claim 1, wherein the image pickup apparatus is an image pickup apparatus.

  According to the first aspect of the present invention, at the time of imaging using a plurality of imaging elements having different photoelectric conversion characteristics, bracketing imaging is performed by controlling the exposure and the dynamic range, thereby making the exposure and the dynamic range compatible. An imaging device capable of bracket imaging can be provided.

  According to the second aspect of the present invention, when imaging using a plurality of imaging elements having different photoelectric conversion characteristics, the exposure and the dynamic range can be obtained by performing bracket imaging while changing only the dynamic range while keeping the exposure constant. It is possible to provide an imaging device capable of bracket imaging that satisfies both of the above.

  According to the third aspect of the present invention, the exposure and the dynamic range can be obtained by performing bracket imaging while changing only the exposure and making the dynamic range constant when imaging using a plurality of imaging elements having different photoelectric conversion characteristics. It is possible to provide an imaging device capable of bracket imaging that satisfies both of the above.

  According to the fourth aspect of the present invention, in imaging using a plurality of imaging elements having different photoelectric conversion characteristics, bracketing imaging is performed by changing both the exposure and the dynamic range, thereby making the exposure and the dynamic range compatible. An imaging device capable of performing bracket imaging can be provided.

  According to the fifth aspect of the present invention, it is possible to perform bracket imaging with both exposure and dynamic range by using an image sensor having photoelectric conversion characteristics including a linear characteristic region and a logarithmic characteristic region as the image sensor. An imaging device can be provided.

  According to the sixth aspect of the present invention, an image having a dynamic range wider than that of each screen is generated by selecting and synthesizing a screen portion having an appropriate level from a plurality of screens having different exposure amounts as the imaging device. By using a device, it is possible to provide an imaging device capable of bracket imaging with both exposure and dynamic range.

  According to the seventh aspect of the present invention, the imaging device includes a charge-voltage conversion unit that converts the photoelectric conversion signal charge of the imaging device into a signal voltage, and the charge-voltage conversion unit includes a plurality of capacitors having different voltage dependencies. Thus, by using a device having a variable dynamic range, it is possible to provide an imaging device capable of bracket imaging with both exposure and dynamic range.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  1A and 1B are schematic external views of a digital camera 1 that is an example of an imaging apparatus according to the present invention. FIG. 1A is a front view and FIG. 1B is a rear view.

  An interchangeable lens 20 is attached to the front surface of the body 10.

  A release button 101, which is an operation member for imaging, is installed on the upper surface of the body 10, and an AF that operates in the first stage of pressing the release button 101 inside the body 10 is below the release button 101. A / AE switch 101a and a two-stage switch constituting the release switch 101b that operates in the second stage of pressing the release button are arranged. A flash 102 is built in the upper part of the body 10 and a mode setting dial 112 for setting the operation mode of the digital camera 1 is arranged.

  On the back of the body 10, there are a power switch 111 for turning on / off the power of the digital camera 1 and five switches, up, down, left, right, and center, and a jog dial for performing various settings in each operation mode of the digital camera 1. 115, a viewfinder eyepiece 121a, and an image display unit 131 for displaying a recorded image.

  FIG. 2 is a block diagram showing an example of a circuit of the digital camera 1 shown in FIG. In the figure, the same parts as those in FIG.

  A camera control unit 150 that is a control unit of the digital camera 1 includes a CPU (central processing unit) 151, a work memory 152, a storage unit 153, and the like, and reads a program stored in the storage unit 153 to the work memory 152. Each part of the digital camera 1 is centrally controlled according to the program. In addition, the camera control unit 150 receives inputs from the power switch 111, the mode setting dial 112, the jog dial 115, the AF / AE switch 101a, the release switch 101b, and the like, and communicates with the photometry module 121b on the optical viewfinder 121. Controls the photometry operation, controls the focusing operation by communicating with the AF module 144, drives the reflex mirror 141 and the sub mirror 142 via the mirror drive unit 143, and controls the shutter 145 via the shutter drive unit 146 (Here, the camera control unit 150 functions as an exposure control unit in the present invention), controls the flash 102 via the flash control unit 147, and controls the imaging operation by communicating with the imaging control unit 161. The image display unit 1 displays captured image data and various information. It is displayed on the 1, displays various information to the in-finder display section 132.

  Further, the camera control unit 150 functions as a communication unit between the body 10 and the interchangeable lens 20, and a BL communication unit (body side) 172 provided on the mount (body side) 171 and a mount (lens side) 271. A lens control unit 241 for controlling the focus and zoom of the lens 211 and a diaphragm control unit for controlling the aperture 221 via the lens interface 251 of the interchangeable lens 20 via the BL communication unit (lens side) 272 provided above. 222, the entire interchangeable lens 20 is controlled by communicating with a lens information storage unit 231 storing unique information of the interchangeable lens 20 (here, the camera control unit 150 functions as an exposure control unit in the present invention). To do).

  An image formed by the lens 211 of the interchangeable lens 20 is photoelectrically converted by the image sensor 162, amplified by an amplifier 163, converted to digital data by an analog / digital (A / D) converter 164, and image processing is performed. The image data is converted into digital image data subjected to predetermined image processing by the unit 165, temporarily recorded in the image memory 181, and finally recorded in the memory card 182. These operations are controlled by the imaging control unit 161 under the control of the camera control unit 150 (here, the camera control unit 150 and the imaging control unit 161 function as a dynamic range control unit in the present invention).

  Next, bracket imaging in the digital camera 1 which is an example of the imaging apparatus according to the present invention will be described. 3 to 6 are flowcharts showing the flow of the bracket imaging operation according to the present invention. FIG. 3 is a main routine, and FIGS. 4 to 6 are subroutines showing each bracket imaging mode.

  In FIG. 3, when the power switch 111 is operated in step S101 to turn on the camera power, the operation mode of the digital camera 1 set by the mode setting dial 112 is confirmed in step S111. When the camera mode is set (step S111; YES), the process proceeds to step S121. If it is set to a mode other than the camera mode (for example, the image reproduction mode) (step S111; NO), the control proceeds to each mode according to the setting. Description is omitted.

  In step S121, it is confirmed whether or not the imaging mode in the camera mode of the digital camera 1 is set to the bracket imaging mode. When the bracket imaging mode is set (step S121; YES), the process proceeds to step S131. When an imaging mode other than the bracket imaging mode (for example, continuous shooting mode) is set (step S121; NO), the control proceeds to each mode according to the setting. Description is omitted.

  In step S131, it is confirmed whether or not the exposure is set to be constant in the bracket imaging mode. If the exposure is set to be constant (step S131; YES), the process proceeds to step S132, the “bracket A mode” subroutine of FIG. 4 is executed, and the process returns to step 111, where the operation mode of the digital camera 1 is set. It is confirmed whether the camera mode has been changed. Thereafter, the above-described operation flow is repeated.

  If the setting for making the exposure constant is not made in step S131 (step S131; NO), it is confirmed in step S141 whether or not the setting for making the dynamic range constant is made in the bracket imaging mode. When the dynamic range is set to be constant (step S141; YES), the process proceeds to step S142, the “bracket B mode” subroutine of FIG. 5 is executed, and the process returns to step 111. Repeat the flow.

  If the setting for making the dynamic range constant is not made in step S141 (step S141; NO), the process proceeds to step S151, the "bracket C mode" subroutine of FIG. 6 is executed, the process returns to step 111, and thereafter The above operation flow is repeated.

  FIG. 4 is a subroutine of the “bracket A mode” in step S132 described above, that is, a mode for performing bracket imaging with constant exposure.

  In step S301, it is confirmed whether or not the release button 101 is operated and the AF / AE switch 101a is turned on. It waits in step S301 until it is turned on. If it is turned on (step S301; YES), an AF operation is performed in step S311 to focus. In step S312, photometry is performed by the photometry module 121b. In step S313, the exposure, that is, the aperture value of the aperture 221 of the interchangeable lens 20 and the shutter speed of the shutter 145 are set from the photometry result.

  In step S314, the dynamic range of the first frame for bracket imaging is set in accordance with the exposure set in step S313. In step S321, it is confirmed whether the release button 101 is operated and the release switch 101b is turned on. Until it is turned on, the operation flow from step S301 to step S321 is repeated. When turned on (step S321; YES), in step S322, imaging is performed with the aperture value and shutter speed set in step S313 and the dynamic range set in step S314. In step S323, the captured image Attached information of the image (a flag indicating that the image is captured in the bracket A mode) is temporarily recorded in the image memory 181. The exposure, that is, the aperture value and the shutter speed are held at the same setting until bracket imaging with a predetermined number of frames is completed.

  In step S331, it is confirmed whether or not the predetermined number of frames for bracket imaging has been completed. If not completed (step S331; NO), in step S341, the currently set dynamic range is shifted by a predetermined value and reset, and the process returns to step S322 to return the held exposure and the reset dynamic range. Imaging is performed in the range, and in step S323, the captured image and information attached to the image are temporarily recorded in the image memory 181. When the predetermined number of frames for bracket imaging has been completed (step S331; YES), images for the number of bracket imaging frames recorded in the image memory 181 are recorded in the memory card 182 in step S332, and the process returns to the main routine.

  FIG. 5 is a subroutine of the “bracket B mode” in step S142 described above, that is, a mode for performing bracket imaging with a constant dynamic range. Steps that are the same as in FIG. 4 are given the same numbers, and descriptions thereof are omitted.

  In the “bracket B mode”, in step S422, imaging is performed with the aperture value and shutter speed set in step S313 and the dynamic range set in step S314, and the dynamic range is bracket imaging with a predetermined number of frames. It is held at the same setting until the end. In step S441, the currently set exposure, that is, the combination of the aperture value and the shutter speed is shifted by a predetermined value and reset, and the process returns to step S422 to perform imaging with the held dynamic range and the reset exposure. Is called.

  FIG. 6 is a sub-routine of the above-described “bracket C mode” in step S151, that is, a mode in which bracket imaging is performed without making exposure and dynamic range constant. The same steps as those in FIG. 4 and FIG.

  In the “bracket C mode”, in step S522, imaging is performed with the aperture value and shutter speed set in step S313 and the dynamic range set in step S314. However, both exposure and dynamic range are constant during bracket imaging. In step S541, the currently set exposure, that is, the combination of the aperture value and the shutter speed is shifted by a predetermined value and reset, and in step S542, the currently set dynamic range is set to the default value. The setting is shifted and reset, and the process returns to step S522, and imaging is performed with the reset exposure and the reset dynamic range.

  In the above description, the resetting of the exposure is performed by shifting the combination of the aperture value and the shutter speed by a predetermined value, but only the aperture value or only the shutter speed may be changed. The exposure and dynamic range are reset by shifting the current setting value by a predetermined value. Of course, the shift amount may be set by the user from the outside or may be programmable. .

  Next, a first example of the image sensor 162 having photoelectric conversion characteristics including a linear characteristic area and a logarithmic characteristic area in the present invention will be described with reference to FIGS.

  FIG. 7 is a block diagram showing the internal configuration of the image sensor 162. In the figure, the same parts as those in FIG. Pixels 162 a are two-dimensionally arranged on the image sensor 162. The photoelectric conversion output VP of the horizontal pixel 162a selected by the vertical scanning circuit 162b is output to the vertical signal line 306, simultaneously held for one row in the sample hold circuit 162c, and scanned by the horizontal scanning circuit 162e to output circuit The image is sequentially output from 162 d as an image output 307 and input to the amplifier 163. Each operation of the image sensor 162 is controlled by a timing generator (TG) 162f in accordance with an imaging control signal 305 from the imaging controller 161.

  FIG. 8 is a circuit diagram illustrating a first example of a circuit of a pixel 162a that constitutes the imaging element 162 and has a photoelectric conversion characteristic including a linear characteristic region and a logarithmic characteristic region.

  The pixel 162a includes a photodiode PD, transistors T1 to T6 as MOSFETs (Metal Oxide Semiconductor Field Effect Transistors), and a capacitor C as a capacitor for integration. In this example, P-channel MOSFETs are used for the transistors T1 to T6. φVD, φV, φVPS, φRST, φS, and RSB indicate signals (voltages) to the respective transistors and capacitors C, and GND indicates ground.

  The photodiode PD is a photoelectric conversion unit and outputs a photocurrent IPD corresponding to the amount of incident light from the subject.

  The transistor T1 is a switch used when a pixel variation signal indicating an error component between pixels generated due to the manufacturing variation of the transistor T2 is taken out. The transistor T1 is normally turned on, and is between the transistor T2 and the photodiode PD. The photocurrent IPD flows through the first electrode. When taking out the pixel variation signal, the transistor T1 is turned off, the photocurrent IPD of the photodiode PD is cut off, and only the pixel variation signal is taken out.

  The transistor T2 has a gate and a drain connected to each other, and utilizes a subthreshold characteristic in the MOSFET (a characteristic in which a minute current called a subthreshold current flows when the gate voltage is equal to or lower than a threshold value). It serves to generate a linearly or logarithmically converted voltage for the current IPD.

  Specifically, when the subject to be imaged is dark, that is, when the incident light quantity incident on the photodiode PD is small, the gate potential of the transistor T2 is higher than the source potential of the transistor, so that the transistor T2 is a so-called cut-off state, the subthreshold current does not flow in the transistor T2, the photocurrent IPD generated in the photodiode PD flows in the parasitic capacitance CPD of the photodiode PD, the photocurrent IPD is integrated, and the integrated charge amount is obtained. A corresponding voltage is generated.

  At this time, since T1 is turned on, a voltage corresponding to the photocurrent IPD integrated into the parasitic capacitance CPD is generated as a voltage VG at the gates of the transistors T2 and T3. The voltage VG causes a current to flow through the transistor T3, and an amount of charge proportional to the voltage VG is accumulated in the capacitor C (the transistor T3 and the capacitor C constitute an integrating circuit). A voltage linearly proportional to the integral value of the photocurrent IPD appears at the connection node a between the transistor T3 and the capacitor C, that is, the output VOUT. This is the operation in the linear characteristic region.

  On the other hand, when the subject to be imaged is bright and the amount of incident light incident on the photodiode PD is large, the gate potential of the transistor T2 becomes lower than the source potential of the transistor, and the transistor T2 operates in the subthreshold region. A threshold current flows, and a voltage VG having a value obtained by natural logarithm conversion of the photocurrent IPD is generated at the gates of the transistors T2 and T3. The voltage VG causes a current to flow through the transistor T3, and a charge equivalent to a value obtained by natural logarithmically converting the integrated value of the photocurrent IPD is accumulated in the capacitor C. As a result, a voltage proportional to a value obtained by natural-logarithmically converting the integral value of the photocurrent IPD is generated at the connection node a (output VOUT) between the capacitor C and the transistor T3. This is the operation of the imaging sensor 30 in the logarithmic characteristic region.

  As described above, whether the operation of the pixel 162a has a linear characteristic or a logarithmic characteristic is determined by the relationship between the gate potential VG and the source potential φVPS of the transistor T2. Since the gate potential VG is determined by the photocurrent IPD as described above, the point (inflection point) at which the linear characteristic and the logarithmic characteristic are switched can be controlled by controlling the source potential φVPS.

  As described above, a voltage linearly or naturally logarithmically proportional to the integrated value of the photocurrent IPD is generated for each pixel in accordance with the brightness of the subject, that is, the amount of incident light.

  The transistor T4 is a transistor for resetting the capacitor C, and operates as a switch that is turned on / off according to the voltage φRST applied to the gate of the transistor T4. When the transistor T4 is turned on, the reset voltage RSB is applied to the capacitor C, and the accumulated charge is returned to the state before the start of integration.

  The transistor T5 constitutes a source follower amplifier circuit, and functions to lower the output impedance by performing current amplification on the output VOUT described above.

  The transistor T6 is a signal reading transistor, and operates as a switch that is turned on and off in accordance with the voltage φV applied to the gate. The source of the transistor T6 is connected to the output signal line 306. When the transistor T6 is turned on, the photoelectric conversion output VP that has been subjected to current amplification by the transistor T5 and reduced in impedance is led to the output signal line 306.

  Next, the photoelectric conversion characteristics of the image sensor 162 using the pixel 162a shown in FIG. 8, and the resetting method of exposure control and dynamic range control based on the bracket imaging will be described in detail. FIG. 9 is a schematic diagram showing a change in photoelectric conversion characteristics of the pixel 162a of the image sensor 162 when only the dynamic range is controlled with constant exposure, and FIG. 10 is a case where only the exposure is controlled with constant dynamic range. FIG. 11 is a schematic diagram showing a change in photoelectric conversion characteristics of the pixel 162a of the image sensor 162 when controlling both the dynamic range and exposure. is there. 9 to 11, the horizontal axis represents the logarithmic coordinates of the subject luminance B (logarithm value of the subject luminance), and the vertical axis represents the photoelectric conversion output VP.

  First, the bracket A mode imaging (corresponding to the flowchart of FIG. 4) in which exposure is constant and only the dynamic range is controlled will be described with reference to FIG. Here, in order to simplify the description, the bracket imaging will be described assuming that a total of three frames are captured, one for each of the wide dynamic range and the narrow side with respect to one frame of the appropriate dynamic range.

  The photoelectric conversion characteristic 402 is a photoelectric conversion characteristic indicating an appropriate dynamic range determined by, for example, the method described in Japanese Patent Application No. 2004-159760 described above from the result of the photometric operation in step S312 of FIG. The photoelectric conversion characteristic 402 is divided into a linear characteristic area (the dark side of the subject brightness) and a logarithmic characteristic area (the bright side) at the inflection point 412 (the photoelectric conversion output at this time is Vth42).

  Control of the source potential φVPS of the transistor T2 in FIG. 8 which is set as a dynamic range shift amount at the time of imaging in the bracket A mode with respect to the photoelectric conversion characteristic 402 and is necessary for shifting the dynamic range by a predetermined value. The reset value of is calculated. At this time, the exposure, that is, the aperture value and the shutter speed are kept the same as the photoelectric conversion characteristic 402. The photoelectric conversion characteristic 401 is a characteristic with a narrow dynamic range, the photoelectric conversion characteristic 403 is a characteristic with a wide dynamic range, and the photoelectric conversion output at an inflection point is Vth41 with respect to the photoelectric conversion characteristic 402 with an appropriate dynamic range. Are shifted to DR41 narrower than DR42 and DR43 wider than DR42, respectively.

  As a result, it is possible to obtain a bracket-captured image with a different appearance by changing the dynamic range even when the exposure is constant for the same subject.

  In actual bracket imaging, based on the result of the photometric operation in step S312, first, in step S314, a control value of the source potential φVPS of the transistor T2 that sets the dynamic range DR41 of the photoelectric conversion characteristic 401 is set, and step S322 is performed. Then, imaging is performed using the control value. Next, in step S341, the control value of the source potential φVPS of the transistor T2 that sets the dynamic range DR42 of the photoelectric conversion characteristic 402 is reset, and imaging is performed in step S322. Next, in step S341, the control value of the source potential φVPS of the transistor T2 that sets the dynamic range DR43 of the photoelectric conversion characteristics 403 is reset, and imaging is performed in step S322. Since the predetermined three frames have been imaged, the process exits the loop and ends the subroutine in step S331.

  Next, bracket B mode imaging (corresponding to the flowchart of FIG. 5) in which only the exposure is controlled with a constant dynamic range will be described with reference to FIG. Here, in order to simplify the description, the bracket imaging will be described assuming that a total of three frames are imaged, one for each of the overexposed side and the underexposed side, with respect to one properly exposed frame.

  The photoelectric conversion characteristic 502 is a photoelectric conversion characteristic with appropriate exposure obtained by the photometric operation in step S312 of FIG. The photoelectric conversion characteristic 502 is divided into a linear characteristic area (the dark side of the subject brightness) and a logarithmic characteristic area (the same bright side) with an inflection point 512 (the photoelectric conversion output value at this time is Vth52) as a boundary.

  For this photoelectric conversion characteristic 502, an aperture value and a shutter speed necessary to shift the exposure by a predetermined overexposure amount and underexposure amount set as an exposure shift amount at the time of imaging in the bracket B mode are calculated. The At this time, if the control value of the source potential φVPS of the transistor T2 in FIG. 8 is kept at Vth52, only the slope of the curve of the linear characteristic region changes, and the switching point between the linear characteristic region and the logarithmic characteristic region and the logarithmic characteristic region are changed. Since the dynamic range changes due to the parallel movement in the horizontal direction of FIG. 10, in order to make the dynamic range DR51 constant, the source potential φVPS of the transistor T2 of FIG. 8 is matched with the calculated aperture value and shutter speed. The control value is also reset. The photoelectric conversion characteristics 501 are overexposed and the photoelectric conversion characteristics 503 are underexposed, and the inflection points are changed from Vth52 to Vth51 and Vth53, respectively.

  Thus, by making the dynamic range constant, the subject luminance range that can be imaged does not change even when the exposure is changed, that is, imaging that is not crushed on the high luminance side is possible.

  In actual bracket imaging, based on the result of the photometric operation in step S312, first, in step S313, an aperture value and shutter speed corresponding to the photoelectric conversion characteristics 501 are set, and in step S314, the dynamic range becomes DR51. Is set to the control value of the source potential φVPS of the transistor T2, and imaging is performed in step S422. Next, in step S441, the aperture value and shutter speed corresponding to the photoelectric conversion characteristic 502 are reset, and in step S442, the control value of the source potential φVPS of the transistor T2 is reset so that the dynamic range is kept constant at DR51. In step S422, imaging is performed. Next, in step S441, the aperture value and shutter speed corresponding to the photoelectric conversion characteristics 503 are reset, and in step S442, the control value of the source potential φVPS of the transistor T2 is reset so that the dynamic range is kept constant at DR51. In step S422, imaging is performed. Since the predetermined three frames have been imaged, the process exits the loop and ends the subroutine in step S331.

  Finally, bracket C mode imaging (corresponding to the flowchart of FIG. 6) for controlling both the dynamic range and exposure will be described with reference to FIG. Here, for the sake of simplicity, bracket imaging is performed for a total of 3 frames, one frame with overexposure and a narrow dynamic range and one frame with underexposure and a wide dynamic range for an appropriate frame. It will be described as being.

  The photoelectric conversion characteristic 602 is a photoelectric conversion characteristic with appropriate exposure obtained by the photometric operation in step S312 of FIG. The photoelectric conversion characteristic 602 is divided into a linear characteristic region (the dark side of the subject luminance) and a logarithmic characteristic region (the same, the bright side) with the inflection point 612 (the photoelectric conversion output value at this time is Vth62) as a boundary.

  For this photoelectric conversion characteristic 602, an aperture value and a shutter speed necessary to shift the exposure by a predetermined overexposure amount and underexposure amount set as an exposure shift amount at the time of imaging in the bracket C mode are calculated. The Further, the control value of the source potential φVPS of the transistor T2 in FIG. 8 for resetting the dynamic range from DR62 to D61 or D63 is reset according to the calculated aperture value and shutter speed. The photoelectric conversion characteristics 601 are overexposed and the photoelectric conversion characteristics 603 are underexposed, and the inflection points are changed from Vth62 to Vth61 and Vth63, respectively.

  As a result, even in an imaging device using an imaging device having a photoelectric conversion characteristic composed of a linear characteristic region and a logarithmic characteristic region, a bracket captured image that is close to a bracketed image captured by a normal silver salt film camera or a normal digital camera Is obtained.

  In actual bracket imaging, based on the result of the photometric operation in step S312, first, in step S313, an aperture value and a shutter speed corresponding to the photoelectric conversion characteristic 601 are set, and in step S314, the dynamic range becomes DR61. Is set to the control value of the source potential φVPS of the transistor T2, and imaging is performed in step S522. Next, in step S541, the aperture value and shutter speed corresponding to the photoelectric conversion characteristic 602 are reset, and in step S542, the control value of the source potential φVPS of the transistor T2 is reset so that the dynamic range is changed to DR62. In step S522, imaging is performed. Next, in step S541, the aperture value and shutter speed corresponding to the photoelectric conversion characteristic 603 are reset, and in step S542, the control value of the source potential φVPS of the transistor T2 is reset so that the dynamic range is changed to DR63. In step S522, imaging is performed. Since the predetermined three frames have been imaged, the process exits the loop and ends the subroutine in step S331.

  Next, a second example of the image sensor 162 having photoelectric conversion characteristics including a linear characteristic area and a logarithmic characteristic area in the present invention will be described with reference to FIG. FIG. 12 is a circuit diagram illustrating a second example of a circuit of a pixel 162a that constitutes the imaging element 162 and has a photoelectric conversion characteristic including a linear characteristic region and a logarithmic characteristic region.

  The pixel 162a includes a buried photodiode PD10 and transistors T11 to T14 as N-channel MOSFETs. A connection portion between the drain of the transistor T1 and the source of T2 is formed of a floating diffusion FD. φRSB, φRST, φTX, and φV indicate signals (voltages) for the respective transistors, VDD indicates a power supply, and GND indicates ground.

  The embedded photodiode PD10 is a photoelectric conversion unit, and generates a photocurrent IPD corresponding to the amount of incident light from the subject. Since the embedded photodiode cannot directly extract the photoelectrically converted photocurrent, it outputs it through a transfer gate and an extraction portion called a floating diffusion.

  The transistor T11 is called a transfer gate, and is an element for transferring the photoelectric charge photoelectrically converted by the embedded photodiode PD10 to the floating diffusion FD. The transistor T11 is normally turned on, and is between the transistor T12 and the photodiode PD10. The photocurrent IPD flows through the first electrode.

  The transistor T12 is called a reset gate, and resets the buried photodiode PD10 and the floating diffusion FD to a high potential, and a subthreshold characteristic in the MOSFET (a small current called a subthreshold current is generated when the gate voltage is equal to or lower than a threshold value). Using the flow characteristic), the source of the transistor functions to generate a voltage that is linearly or logarithmically converted with respect to the photocurrent IPD.

  Specifically, when the subject to be imaged is dark, that is, when the amount of incident light incident on the photodiode PD10 is small, the reset operation causes the gate potential of the transistor T12 to be lower than the source potential of the transistor. In addition, the transistor T12 is in a so-called cut-off state, the subthreshold current does not flow through the transistor T12, and the photocurrent IPD generated in the embedded photodiode PD10 is reset to a high potential, and the parasitic capacitance CPD10 of the embedded photodiode PD10 is reset. , The photocurrent IPD is integrated, and a voltage VFD corresponding to the integrated charge amount is generated in the floating diffusion FD. This is the operation in the linear characteristic region.

  On the other hand, when the subject to be imaged is bright and the amount of incident light incident on the photodiode PD10 is large, the gate potential of the transistor T12 becomes equal to or higher than the source potential of the transistor, and the transistor T12 operates in the subthreshold region. A threshold current flows, and a voltage VFD obtained by natural logarithm conversion of the photocurrent IPD is generated in the floating diffusion FD. This is the operation in the logarithmic characteristic region. Since the second example does not have the integrating capacitor C as in the first example shown in FIG. 8, the output VFD in the logarithmic characteristic region is not obtained by logarithmically converting the integral value of the photocurrent IPD. It is not a logarithmic conversion value of the photocurrent IPD at that moment.

  As described above, whether the operation of the pixel 162a has a linear characteristic or a logarithmic characteristic depends on the relationship between the gate potential and the source potential of the transistor T12. Therefore, the point (inflection point) at which the linear characteristic and the logarithmic characteristic are switched can be controlled by appropriately controlling the gate potential φRST.

  The transistor T13 constitutes a source follower amplifier circuit, and functions to lower the output impedance by performing current amplification on the output VFD described above.

  The transistor T14 is a signal reading transistor, and operates as a switch that is turned on and off in accordance with the voltage φV applied to the gate. The source of the transistor T14 is connected to the output signal line 306. When the transistor T14 is turned on, the photoelectric conversion output VP that has been amplified by the transistor T13 and reduced in impedance is led to the output signal line 306.

  When bracket imaging is performed using the pixel circuit of the second example, φVPS in the flowcharts shown in FIGS. 4 to 6 may be read as φRST. However, when the control shown in the flowchart of FIG. 5 is performed, if φRST is set in step S314, as described above, in the logarithmic characteristic region, the photoelectric conversion output is the logarithmic conversion value of the photocurrent IPD at the moment of imaging. Therefore, by changing the exposure (aperture value and shutter speed) in step S441, Vth automatically changes without changing φRST in step S442, and the dynamic range is kept constant. 10 can be obtained.

  In addition, as shown in Patent Document 4, an image sensor that synthesizes an image having a wider dynamic range than individual screens by selecting and synthesizing a screen portion of an appropriate level from a plurality of screens having different exposure amounts. The image sensor shown in Patent Document 5 has a charge-voltage conversion unit that converts photoelectric conversion signal charges into signal voltages, and the charge-voltage conversion unit is composed of a plurality of capacitors having different voltage dependencies and has a variable dynamic range. The present invention can also be applied to an imaging apparatus using a wide dynamic range imaging element other than a logarithmic conversion type such as an imaging element.

  As described above, according to the present invention, when bracket imaging using an image sensor having a plurality of different photoelectric conversion characteristics, exposure and dynamic range are controlled independently, so that appropriate exposure and dynamic range can be controlled. It is possible to provide an image pickup apparatus and an image pickup method having a plurality of bracket image pickup modes in which both are compatible.

  The detailed configuration and detailed operation of each component constituting the imaging apparatus according to the present invention can be changed as appropriate without departing from the spirit of the present invention.

1 is a schematic external view of a digital camera that is an example of an imaging apparatus according to the present invention. It is a block diagram which shows an example of the circuit of the digital camera shown in FIG. It is the main routine of the flowchart which shows the flow of operation | movement of bracket imaging in this invention. It is a subroutine (1/3) of the flowchart which shows the flow of operation | movement of the bracket imaging in this invention. It is a subroutine (2/3) of the flowchart which shows the flow of operation | movement of bracket imaging in this invention. It is a subroutine (3/3) of the flowchart which shows the flow of operation | movement of the bracket imaging in this invention. It is a block diagram which shows the internal structure of the image pick-up element used for the imaging device which concerns on this invention. FIG. 3 is a circuit diagram illustrating a first example of a pixel circuit having a photoelectric conversion characteristic including a linear characteristic region and a logarithmic characteristic region. FIG. 5 is a schematic diagram illustrating changes in photoelectric conversion characteristics of pixels of the image sensor according to the control flow illustrated in FIG. 4. It is a schematic diagram which shows the change of the photoelectric conversion characteristic of the pixel of an image pick-up element by the control flow shown in FIG. It is a schematic diagram which shows the change of the photoelectric conversion characteristic of the pixel of an image pick-up element by the control flow shown in FIG. It is a circuit diagram which shows the 2nd example of the pixel circuit which has the photoelectric conversion characteristic which consists of a linear characteristic area | region and a logarithmic characteristic area | region.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Digital camera 10 Body 20 Interchangeable lens 101 Release button 101a AF / AE switch 101b Release switch 102 Flash 111 Power switch 112 Mode setting dial 115 Jog dial 121 Viewfinder 121a Viewfinder eyepiece 121b Photometric module 131 Image display section 132 Infinder display section 141 Release Flex mirror 142 Sub mirror 143 Mirror drive unit 144 AF module 145 Shutter 146 Shutter drive unit 147 Flash control unit 150 Camera control unit 151 CPU (central processing unit)
152 Work Memory 153 Storage Unit 161 Imaging Control Unit 162 Imaging Device 163 Amplifier 164 Analog / Digital (A / D) Converter 165 Image Processing Unit 171 Mount (Body Side)
172 BL communication part (Body side)
181 Image memory 182 Memory card 211 Lens 221 Aperture 222 Aperture control unit 231 Lens information storage unit 241 Lens control unit 251 Lens interface 271 Mount (lens side)
272 BL communication part (lens side)

Claims (7)

In an imaging apparatus including an imaging element having a plurality of different photoelectric conversion characteristics,
An exposure control unit that performs exposure control when imaging the subject based on the luminance information of the subject;
A dynamic range control unit for controlling the dynamic range of the image sensor;
Mode setting means for setting the bracket imaging mode;
When the bracket imaging mode is set by the mode setting means,
An image pickup apparatus comprising: an image pickup control unit configured to pick up a plurality of images by the image pickup device while causing the exposure control unit to control exposure for each image pickup and causing the dynamic range control unit to control a dynamic range. . The exposure control unit controls exposure to be constant,
The dynamic range control unit controls the dynamic range to a plurality of different values,
The imaging apparatus according to claim 1, wherein the imaging control unit performs imaging for each of the plurality of different dynamic ranges. The exposure control unit controls the exposure to a plurality of different values;
The dynamic range control unit controls the dynamic range to be constant,
The imaging apparatus according to claim 1, wherein the imaging control unit performs imaging for each of the plurality of different exposures. The exposure control unit controls the exposure to a plurality of different values;
The dynamic range control unit controls the dynamic range to a plurality of different values,
The imaging apparatus according to claim 1, wherein the imaging control unit performs imaging for each set of the plurality of different exposures and dynamic ranges. The image sensor generates an electrical signal corresponding to the amount of incident light, linearly converts the electrical signal with respect to the amount of incident light, and outputs the linear characteristic region. 5. The imaging device according to claim 1, wherein the imaging device has a photoelectric conversion characteristic including a logarithmic characteristic region that is logarithmically converted and output. The image pickup device synthesizes an image having a wider dynamic range than individual screens by selecting and synthesizing a screen portion of an appropriate level from a plurality of screens having different exposure amounts. The imaging apparatus according to any one of 1 to 4. The image sensor has a charge-voltage converter that converts a photoelectric conversion signal charge of the image sensor into a signal voltage. The charge-voltage converter includes a plurality of capacitors having different voltage dependencies, and has a variable dynamic range. The image pickup apparatus according to claim 1, wherein the image pickup apparatus is an image pickup apparatus.

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