JP5400432B2 - IMAGING DEVICE, ITS CONTROL METHOD, AND CAMERA - Google Patents

Description

  The present invention relates to an imaging apparatus, a control method thereof, and a camera.

  2. Description of the Related Art Conventionally, some imaging apparatuses such as digital still cameras perform exposure control (hereinafter referred to as an imaging surface AE) using an imaging element as a photometric sensor. However, in general, an image sensor has a narrow dynamic range compared to a photometric sensor. Therefore, on the imaging surface AE, when there is a scene change such as the subject suddenly becomes brighter, overexposure tends to occur, and the exposure control response may be delayed by performing exposure control from the overexposed state. .

  As a technique for compensating for the narrowness of the dynamic range of the image sensor, which is a factor that slows down the responsiveness of the exposure control on the imaging surface AE, Patent Document 1 discloses that a switch is provided in the image sensor and the output of the pixel is a linear output. Switching to a logarithmic output is disclosed.

JP 2006-14277 A

  However, in the above prior art, when the imaging surface AE is performed, a new switch must be provided in the imaging device, resulting in an increase in cost and an image captured by reducing the light receiving area by the amount required for the switch. May have an effect.

  The present invention has been made for the purpose of solving at least one of the problems of the prior art. An object of the present invention is to perform imaging control using an image sensor as a photometric sensor, and to reduce the dynamic range of the image sensor while suppressing an increase in cost and an influence on a captured image. An apparatus, a control method thereof, and a camera are provided.

The object includes generating a charge according to the amount of received light, accumulating the generated charge, and a holding unit holding the accumulated charge transferred from the photoelectric conversion unit, An imaging unit in which a plurality of pixels that output a pixel signal based on the amount of charge held in the holding unit are arranged, and driving of the imaging unit is controlled, and based on the value of the pixel signal output from the plurality of pixels Control means for performing exposure control, wherein the control means overflows from the photoelectric conversion unit and is held in the holding unit before the charge accumulated in the photoelectric conversion unit is transferred to the holding unit. When the surplus signal based on the charge amount of the charge is acquired and the ratio of the number of pixels that outputs the surplus signal to the total number of pixels of the imaging unit is equal to or greater than a preset first value, or For the total number of pixels of the imaging means That the proportion of the number of pixels that the photoelectric conversion unit has output a pixel signal indicating a value that indicates the state of saturation, the case where the second value or more set in advance, the value of the pixel signal and the surplus signal The image pickup apparatus according to the present invention achieves the exposure control based on the above.

Further, the object is to generate a charge according to the amount of received light, store the generated charge, and a holding unit that holds the accumulated charge transferred from the photoelectric conversion unit. An image pickup apparatus control method comprising an image pickup means in which a plurality of pixels that output a pixel signal based on the amount of charge held in the holding section are arranged, wherein the control means controls driving of the image pickup means. , Including a control step of performing exposure control based on pixel signal values output from the plurality of pixels, the control step including the transfer of the charge accumulated in the photoelectric conversion unit to the holding unit. A surplus signal based on the amount of surplus charge overflowed from the conversion unit and held in the holding unit is acquired, and a ratio of the number of pixels outputting the surplus signal to the total number of pixels of the imaging unit is set in advance. Greater than the first value Or the ratio of the number of pixels that output a pixel signal indicating a value indicating the saturated state of the photoelectric conversion unit to the total number of pixels of the imaging means is equal to or greater than a preset second value. In addition, the exposure control is performed based on the values of the pixel signal and the surplus signal, which is also achieved by the control method for an imaging apparatus according to the present invention.

  According to the present invention, in performing exposure control using an image sensor as a photometric sensor, it is possible to compensate for the narrow dynamic range of the image sensor while suppressing an increase in cost and an influence on a captured image.

It is a block diagram of the imaging device concerning a 1st embodiment. It is a block diagram of the image sensor concerning a 1st embodiment. It is a figure showing the section structure for one pixel of the image sensor concerning a 1st embodiment. 6 is a timing chart for explaining a signal readout operation of the image sensor according to the first embodiment. It is a figure for demonstrating the read-out sequence at the time of the live view imaging of the imaging device which concerns on 1st Embodiment. 6 is a timing chart for explaining a saturated light amount signal read operation according to the first embodiment; It is a flowchart which shows the live view imaging process which concerns on 1st Embodiment. It is a flowchart which shows calculation of the AE control parameter which concerns on 1st Embodiment. 6 is a timing chart for explaining a signal readout operation of the image sensor according to the second embodiment. It is a flowchart which shows the live view imaging process which concerns on 2nd Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments. Further, the embodiment of the present invention shows the most preferable mode of the invention, and does not limit the scope of the invention.

[First Embodiment]
FIG. 1 is a block diagram of an imaging apparatus 100 according to the first embodiment. As illustrated in FIG. 1, the imaging apparatus 100 is a camera that captures an object image formed on an imaging element 103 via an optical system 101 and a mechanical shutter 102 by photoelectric conversion. The optical system 101 is a lens and an aperture, and a lens position and an aperture value are adjusted by a drive unit (not shown) controlled by the drive circuit 107. A mechanical shutter 102 (shown as a mechanical shutter) exposes the image sensor 103 with a predetermined exposure time under the control of the drive circuit 107. The image sensor 103 outputs image data (analog signal) obtained by photoelectrically converting the subject image to the CDS circuit 104 under the control of the drive circuit 107. Details of the image sensor 103 will be described later.

  The CDS circuit 104 performs analog signal processing such as correlated double sampling on the image data output from the image sensor 103 and outputs the result to the A / D converter 105. The A / D converter 105 converts the image data (analog signal) output from the CDS circuit 104 into a digital signal and outputs the digital signal to the signal processing circuit 108. The timing signal generation circuit 106 generates timing signals for operations of the image sensor 103, the CDS circuit 104, and the A / D converter 105 under the control of the control unit 114. The drive circuit 107 controls driving of the optical system 101, the mechanical shutter 102, and the image sensor 103 under the control of the control unit 114.

  The signal processing circuit 108 performs necessary signal processing on the image data captured by the image sensor 103 and output from the A / D converter 105 under the control of the control unit 114. The image memory 109 stores image data that has undergone signal processing under the control of the control unit 114. The recording medium 110 is a semiconductor memory or a hard disk drive, and is detachably connected to the imaging device 100 via an interface such as a connector (not shown). The recording circuit 111 records the signal-processed image data on the recording medium 110 under the control of the control unit 114.

  The image display device 112 is an LCD (Liquid Crystal Display) or the like, and displays signal-processed image data. The display circuit 113 outputs the signal-processed image data to the image display device 112 under the control of the control unit 114 and causes the image display device 112 to display an image.

  The control unit 114 is a CPU (Central Processing Unit) or the like, and develops the program code stored in the non-volatile memory 115 in the work area of the volatile memory 116 and sequentially executes the operation, whereby the operation of each unit of the imaging apparatus 100 is performed. Central control. The nonvolatile memory 115 (ROM) indicates a program code describing a control method executed by the control unit 114, control data such as parameters and tables used when executing the program code, and defective pixels of the image sensor 103. Correction data such as a flaw address is stored. The volatile memory 116 (RAM) transfers and stores the program code, control data, and correction data stored in the non-volatile memory 115, and work used when the control unit 114 controls the imaging apparatus 100. Provide area.

  Here, an imaging operation performed using the mechanical shutter 102 using the imaging apparatus 100 described above will be described. Prior to the imaging operation, necessary program code, control data, and correction data are transferred from the nonvolatile memory 115 to the volatile memory 116 and stored at the start of the operation of the control unit 114 when the imaging apparatus 100 is powered on. Shall be kept. These program codes and data are used when the control unit 114 controls the imaging apparatus 100. Further, the control unit 114 transfers additional program code and data from the nonvolatile memory 115 to the volatile memory 116 as necessary, or directly reads and uses the data in the nonvolatile memory 115.

  First, the optical system 101 drives a diaphragm and a lens by a control signal from the control unit 114 to form a subject image set to an appropriate brightness on the image sensor 103. Next, the mechanical shutter 102 is driven by a control signal from the control unit 114 so as to shield the image sensor 103 in accordance with the operation of the image sensor 103 so that a necessary exposure time is reached. At this time, when the image sensor 103 has an electronic shutter function, it may be used together with the mechanical shutter 102 to secure a necessary exposure time.

  The image sensor 103 is driven downward by an operation pulse (timing signal) generated by the timing signal generation circuit 106 controlled by the control unit 114, converts the subject image into an electric signal by photoelectric conversion, and outputs an analog image signal (image data). ). The analog image signal output from the image sensor 103 is subjected to an operation pulse generated by the timing signal generation circuit 106 controlled by the control unit 114, the clock synchronization noise is removed by the CDS circuit 104, and the A / D converter 105 It is converted into a digital image signal.

  Next, in the signal processing circuit 108 controlled by the control unit 114, image processing such as color conversion, white balance, and gamma correction, resolution conversion processing, image compression processing, and the like are performed on the digital image signal. The image memory 109 is used for temporarily storing a digital image signal being subjected to signal processing and storing image data which is a digital image signal subjected to signal processing.

  The image data signal-processed by the signal processing circuit 108 and the image data stored in the image memory 109 are converted into data suitable for the recording medium 110 (for example, file system data having a hierarchical structure) by the recording circuit 111 and recorded on the recording medium. 110. The image data is subjected to resolution conversion processing by the signal processing circuit 108 and then converted into a signal suitable for the recording circuit 111 (for example, an NTSC analog signal) by the display circuit 113 and displayed on the recording circuit 111. Or

  Here, the signal processing circuit 108 may output the digital image signal as it is as image data to the image memory 109 or the recording circuit 111 without performing signal processing by the control signal from the control unit 114. When there is a request from the control unit 114, the signal processing circuit 108 outputs to the control unit 114 information on a digital image signal or image data generated in the signal processing process in response to the request. For example, the information output to the control unit 114 includes information such as the spatial frequency of the image, the average value of the brightness of the designated area, the amount of compressed image data, or information extracted from them. Further, when there is a request from the control unit 114, the recording circuit 111 outputs information such as the type and free capacity of the recording medium 110 to the control unit 114.

  Next, details of the image sensor 103 in which a plurality of pixels for capturing a subject image are arranged will be described with reference to FIG. FIG. 2 is a block diagram of an element when a CMOS (Complementary Metal Oxide Semiconductor) solid-state image sensor is used as the image sensor 103. Each circuit element constituting the solid-state imaging device is formed on a single semiconductor substrate such as single crystal silicon, although it is not particularly limited by the manufacturing technology of the semiconductor integrated circuit. In the example of FIG. 2, the pixel array 1 has 3 rows and 3 columns for the sake of simplicity, but the solid-state imaging device is not limited to this size.

  As shown in FIG. 2, in the pixel array 1, photodiodes D11 to D33, which are photoelectric conversion units that generate optical signal charges corresponding to the amount of received light, are grounded on the anode side in this example. The cathode sides of the photodiodes D11 to D33 are connected to the sources of transfer MOSs M111 to M133 for transferring the optical signal charges accumulated in the photodiodes. The gate of the transfer MOS M111 is connected to a first row selection line (vertical scanning line) PTX1 that extends in the horizontal direction. The gates of similar transfer MOSs M121 and M131 of other pixel cells arranged in the same row are also commonly connected to the first row selection line PTX1. The gates of the amplification MOSs M311 to M333 are connected to the drains of the transfer MOSs M111 to M133.

  The gates of the amplification MOSs M311 to M333 are connected to the sources of reset MOSs M211 to M233 for resetting them, and the drains of the reset MOSs M211 to M233 are connected to a reset power source. Further, the drains of the amplification MOSs M311 to M333 are connected to selection MOSs M411 to M433 for supplying a power supply voltage. The gate of the reset MOS M211 is connected to a second row selection line (vertical scanning line) PRES1 that extends in the horizontal direction. The gates of similar reset MOSs M221 and M231 of other pixel cells arranged in the same row are also commonly connected to the second row selection line PRES1. The gate of the selection MOS M411 is connected to a third row selection line (vertical scanning line) PSEL1 arranged extending in the horizontal direction. Gates of similar selection MOSs M421 and M431 of other pixel cells arranged in the same row are also commonly connected to the third row selection line PSEL1.

  These first to third row selection lines are connected to the vertical scanning circuit block 2 and supplied with a signal voltage based on an operation timing described later. Also in the row shown in FIG. 2, pixel cells having a similar configuration and row selection lines are provided. PRES1 to PRES3 and PSEL1 to PSEL3 formed by the vertical scanning circuit block 2 are supplied to these row selection lines.

  The source of the amplification MOS M311 is connected to a vertical signal line V1 that extends in the vertical direction. The sources of similar amplification MOSs M312 and M313 of pixel cells arranged in the same column are also connected to the vertical signal line V1. The vertical signal line V <b> 1 is connected to a load MOS M <b> 51 that is a load element via a gate-grounded MOS M <b> 71 that is a constant voltage unit 3. The gate of the common-gate MOS M71 is connected to a voltage input terminal 6 for supplying a gate voltage. Similarly, the remaining vertical signal lines V2 to V3 shown in FIG. 2 are connected to the amplification MOS, the grounded gate MOS, and the load MOS.

  Further, the sources of the load MOSs M51 to M53 are connected to the common GND line 4, and the gate is connected to the gate of the input MOS M50 and to the voltage input terminal 5. Further, the vertical signal line V1 is held in the noise signal holding capacitor CTN1 for temporarily holding the noise signal via the noise signal transfer switch M11, and is held for temporarily holding the optical signal via the optical signal transfer switch M21. Are simultaneously connected to the optical signal holding capacitor CTS1.

  The opposite terminals of the noise signal holding capacitor CTN1 and the optical signal holding capacitor CTS1 are grounded. A connection point between the noise signal transfer switch M11 and the noise signal holding capacitor CTN1 and a connection point between the optical signal transfer switch M21 and the optical signal holding capacitor CTS1 are grounded via holding capacitor reset switches M31 and M32. Further, the connection points are connected to the differential circuit block 8 for taking the difference between the optical signal and the noise signal via the horizontal transfer switches M41 and M42, respectively.

  The gates of the horizontal transfer switches M41 and M42 are commonly connected to the column selection line H1 and connected to the horizontal scanning circuit block 7. In the remaining columns V2 to V3 shown in FIG. 2, readout circuits having the same configuration are provided. The gates of the noise signal transfer switches M11 to M13 and the optical signal transfer switches M21 to M23 connected to each column are commonly connected to PTN and PTS, respectively, and a signal voltage is supplied based on an operation timing described later. .

  Next, FIG. 3 shows a configuration of a cross-sectional structure of a photoelectric conversion element (photodiode) for one pixel of the constant voltage unit 3. As shown in FIG. 3, in the photodiode for one pixel, a p-type well 3002 is formed on an n-type substrate 3001, an n-layer 3004 of the photodiode is formed thereon, and a p-layer of the photodiode is formed thereon. 3005 is formed with a deep surface. In the photodiode for one pixel, the gate region of the transfer MOS transistor 3003 is formed on the side surface of the photodiode via an insulating layer.

  Between the gate region of the transfer MOS transistor 3003 and the side surface of the photodiode, a bypass region 3006 continuous from the n layer of the photodiode is formed. Further, a diffusion floating region (Floating Diffusion region: FD region) 3007 is formed below the side surface of the gate region of the transfer MOS transistor 3003.

  The diffusion floating region 3007 is connected to the gate of the amplification MOS transistor 3010 of the output circuit. The diffusion floating region 3007 is connected to a source 3008 of a reset MOS transistor for resetting the diffusion floating region 3007, and a drain is connected to a reset power source 3009.

  The signal amplified by the amplification MOS transistor 3010 is taken out through the pixel selection MOS transistor 3011. In addition, an aluminum light shielding plate 3013 is provided on the upper part of the element so that light does not enter other than the photodiode.

  Next, a general signal reading operation in the constant voltage unit 3 will be described with reference to the configuration of FIG. 2 and the timing chart of FIG. As shown in FIG. 4, prior to reading out the optical signal charges from the photodiodes D11 to D33, the gates PRES1 of the reset MOSs M211 to M231 are set to the high level. As a result, the gates of the amplification MOSs M311 to M331 are reset to the reset power source.

  Next, after the gates PRES1 of the reset MOSs M211 to M231 return to the low level, the gates PSEL1 of the selection MOSs M411 to M431 and the gates PTN of the noise signal transfer switches M11 to M13 become high level. As a result, the reset signal (noise signal) on which the reset noise is superimposed is read out to the noise signal holding capacitors CTN1 to CTN3.

  Next, the gates PTN of the noise signal transfer switches M11 to M13 return to the low level. Next, the gate PTX1 of the transfer MOSs M111 to M131 becomes high level, and the optical signal charges of the photodiodes D11 to D33 are transferred to the gates of the amplification MOSs M311 to M331.

  Next, after the gate PTX1 of the transfer MOSs M111 to M131 returns to the low level, the gates PTS of the optical signal transfer switches M21 to M23 become the high level. As a result, the optical signal is read out to the optical signal holding capacitors CTS1 to CTS3.

  Next, the gates PTS of the optical signal transfer switches M21 to M23 return to the low level. With the operation so far, the noise signal and the optical signal of the pixel cell connected to the first row are held in the noise signal holding capacitors CTN1 to CTN3 and the optical signal holding capacitors CTS1 to CTS3 connected to the respective columns. The

  Next, the gates PRES1 of the reset MOSs M211 to M231 and the gates PTX1 of the transfer MOSs M111 to M131 become high level, and the optical signal charges of the photodiodes D11 to D33 are reset. Thereafter, the signals of the horizontal transfer switches M41 to M46 in each column are sequentially set to the high level by the signals H1 to H3 from the horizontal scanning circuit block 7. As a result, voltages based on the charge amounts held in the noise holding capacitors CTN1 to CTN3 and the optical signal holding capacitors CTS1 to CTS3 are sequentially read out to the differential circuit block 8. In the differential circuit block 8, the difference between the optical signal and the noise signal is taken, and the pixel signals are sequentially output to the output terminal OUT. Thus, reading of the pixels connected to the first row is completed.

  Thereafter, prior to reading of the second row, the gates PCTR of the reset switches M31 to M36 of the noise signal holding capacitors CTN1 to CTN3 and the optical signal holding capacitors CTS1 to CTS3 are set to the high level and reset to GND. Similarly, pixel signals of pixels connected in the second and subsequent rows are sequentially read by signals from the vertical scanning circuit block 2, and reading of all pixels is completed.

  Next, a readout sequence of the imaging apparatus 100 during normal live view imaging in which imaging is performed by sequentially driving the imaging element 103 will be described with reference to FIG. FIG. 5 is a diagram illustrating scanning of the entire image sensor 103 with the vertical axis representing the vertical scanning position and the horizontal axis representing time.

  As shown in FIG. 5, first, prior to live view imaging, the image sensor 103 is reset (in order from the pixel at the reset scanning position 501). Next, the device is exposed for a preset accumulation time 504 from the row where the reset is completed. Next, readout is performed sequentially from the pixel at the signal readout scanning position 502 that has reached the accumulation time 504. The reading method at this time is the same as the normal pixel reading method described with reference to FIG.

  The time required for this reading is called a reading period 505, and the difference between the time of one frame and the reading period is called a blanking period 506. During this period, parameters used in the subsequent frames such as the accumulation time are determined. In particular, when performing imaging surface AE that is exposure control (AE) using the image sensor 103 as a photometric sensor, it is necessary to set exposure control values such as aperture, sensor gain, and accumulation time in the next frame during this period. .

  Thereafter, the reset is performed again from the pixel for which one frame has elapsed since the previous reset (sequentially from the pixel at the reset scanning position 503), and the exposure for the second frame is started. Live view imaging is a repetition of the sequence described above.

  The signal read in this way will be described with reference to FIG. 1. First, the signal is converted into a digital signal by the A / D converter 105, and recorded in the image memory 109 through the signal processing circuit 108. Data recorded in the image memory 109 is processed by the display circuit 113, and an image of each frame is displayed by the image display device 112 (electronic viewfinder display (EVF display)). Through the processing described above, the imaging apparatus 100 can perform live view imaging.

  Next, an FD signal that is a saturation light amount signal according to the present embodiment will be described with reference to FIG. As shown in FIG. 3, the light that has passed through the opening of the aluminum light shielding plate 3013 is photoelectrically converted by a photodiode configured immediately below the opening, and is accumulated as an electric charge in the n layer 3004 of the photodiode.

  However, when incident light enters beyond the capacity of the photodiode, a phenomenon occurs in which the photoelectrically converted charge cannot be accumulated in the photodiode and overflows. Discharging this overflowing charge (hereinafter referred to as surplus charge) is called overflow. As this overflow, vertical overflow and horizontal overflow are mainly known.

  In the case of the image sensor 103 illustrated in FIG. 3, when a large amount of light is incident and an excessive signal is generated in the photodiode, excess charge passes through the p-type well 3002 from the layer 3004 and is absorbed by the n-type substrate. It is structured. Such an overflow structure is called a vertical overflow / drain, and is common in the current structure of an image sensor.

  However, in reality, it is difficult to discharge all surplus charges by this vertical overflow / drain, and some surplus charges overflow into the adjacent diffusion floating region 3007. This overflowing to the adjacent capacity is called a horizontal overflow. The ratio of surplus charge that causes a horizontal overflow differs for each image sensor, but can be controlled to some extent by the gate voltage of the transfer MOS transistor 3003.

  Incidentally, in normal imaging, surplus charges accumulated in the diffusion floating region 3007 due to horizontal overflow do not affect the image by normal imaging by being reset before reading. Hereinafter, in this case, a saturation light amount signal indicating surplus charge overflowing in the diffusion floating region 3007 is referred to as an FD signal (FD: Floating Diffusion), and a charge signal (pixel signal) accumulated in the photodiode is referred to as a PD signal (PD : Photodiode).

  In the present embodiment, in order to compensate for the narrow dynamic range of the photodiode that affects the imaging surface AE, the FD signal indicating the surplus charge due to the lateral overflow described above is used for controlling the imaging surface AE. Therefore, in this embodiment, since it is not necessary to provide a new switch in the image sensor, the manufacturing cost can be suppressed. Further, in this embodiment, the light receiving area is not reduced by the amount required for the switch, so that the influence on the captured image can be suppressed.

  Next, with respect to how to read out the FD signal, referring to FIG. 6 showing a timing chart for reading out the FD signal and FIG. 2 showing the configuration of the image sensor 103, while comparing FIG. explain. As shown in FIG. 4, at the time of normal reading, first, PRES1 is set to high level, the gates of the amplification MOSs M311 to M331 are reset, that is, the potential of the diffusion floating region 3007 in FIG. 3 is returned to the reset level. However, when it is desired to read the surplus charge overflowing into the diffusion floating region 3007 as in the present embodiment, it is not necessary to reset first as in the normal reading in FIG.

  That is, when reading the FD signal, as shown in FIG. 6, before the transfer of the charge accumulated in the photodiode, the gate PTS of the optical signal transfer switches M21 to M23 is set to the high level before the diffusion floating region 3007 is reset. To level. As a result, the FD signal including noise is read out to the optical signal holding capacitors CTS1 to CTS3.

  Next, the gates PTS of the optical signal transfer switches M21 to M23 are returned to the low level. Thereafter, PRES1 is set to high level, and the gates of the amplification MOSs M311 to M331 are reset. When the reset is completed, PRES1 is set to the low level, and then the gates PTN of the noise transfer switches M11 to M13 are set to the high level. As a result, the reset signal is read out to the noise signal holding capacitors CTN1 to CRN3.

  Next, the gates PRES1 of the reset MOSs M211 to M231 and the gates PTX1 of the transfer MOSs M111 to M131 are set to the high level. The subsequent signal reading is the same as the normal reading described with reference to FIG.

  In this case, it should be noted that the noise components accumulated in the noise signal holding capacitors CTN1 to CRN3 subtracted from the signal components accumulated in the optical signal holding capacitors CTS1 to CTS3 in the differential circuit block 8 are the signal components. There is a different reset noise. Further, since the dark current noise component generated during the accumulation time is not included, the SN ratio of the output signal is worse than that of a normal read signal. However, when the FD signal is used for exposure control as in the present embodiment, this level of deterioration of the SN ratio is not a problem level.

  Next, a flow of live view imaging processing for performing the imaging surface AE in the first embodiment will be described with reference to the flowchart of FIG. As shown in FIG. 7, when live view imaging processing is started under the control of the control unit 114, first, AE control parameters such as an accumulation time of one frame, an aperture value, and a sensor gain in the image sensor 103 are set. (S701). In S701, the AE control parameter calculated in the previous frame (in this case, the (n-1) th frame) is set. Note that in a frame immediately after the start of the live view imaging process, a default value preset in a memory or the like is used as the AE control parameter.

  Next, under the control of the control unit 114, imaging is performed with the AE control parameter set in S701, and the PD signal is read out by the normal reading method described in FIG. 4 (S702). Next, under the control of the control unit 114, the image (n-th frame) read in S702 is displayed on the image display device 112 (S703).

  In the next frame (the (n + 1) th frame), under the control of the control unit 114, the FD signal is read by the reading method described with reference to FIG. 6 (S704). Since the FD signal read here has a signal only for the pixels to which the light amount exceeding the saturation light amount of the photodiode is incident, the image becomes dark when displayed on the image display device 112. Therefore, the image displayed on the image display device 112 is continuously displayed without updating the PD signal of the previous frame (nth frame).

  Next, the control unit 114 calculates an AE control parameter for imaging in the next frame from the signal values obtained in S702 and S704 (S705). The calculation method of the AE control parameter in S705 is not particularly limited, but an example will be described later.

  Next, the control unit 114 determines whether or not to end the live view mode from the setting of an operation unit (not shown) that receives an input instruction of a mode operation from the user (S706). If the process does not end in S706, the control unit 114 returns the process to S701 and sets the AE control parameter calculated in S705. In the imaging apparatus 100, the above-described flow is continued until the live view mode ends.

  Here, an example of the calculation method of the AE control parameter in S705 will be described with reference to FIG. As shown in FIG. 8, in the calculation process of the AE control parameter, first, the FD signal read in S704 of FIG. 7 is analyzed. Whether or not the number of pixels of the FD signal that is equal to or larger than a predetermined value is equal to or larger than a predetermined ratio (N% of the total) (first value or larger) set in advance with respect to the total number of pixels. Is determined (S801).

  If it is determined in S801 that the number of pixels equal to or greater than a predetermined ratio is detected from all the pixels of the image sensor 103 using the FD signal, the image captured by the image sensor 103 is determined as an overexposed image. Therefore, the control unit 114 does not calculate the AE control parameter by calculating the luminance value of the image captured from only the PD signal, but sets an appropriate AE control parameter based on both the PD signal and the FD signal. Calculate (S802). The AE control parameter is calculated based on the brightness value of the captured image and a control diagram related to exposure. In S802, the AE control parameter is calculated with reference to not only the brightness value based on the PD signal but also the brightness value based on the FD signal. Is done.

  Specifically, in S802, it is preferable to obtain an AE control parameter in which the FD signal value indicating that the photodiode overflows due to overexposure decreases and the PD signal value does not become too dark. For example, the AE control parameter is set such that the exposure period is shortened and the aperture value is increased so that the FD signal value is decreased, and the range in which the exposure period is shortened and the aperture value is increased is such that the PD signal value does not become too dark. Ask. The degree of shortening the exposure period and increasing the aperture value so that the FD signal value is decreased not only depends on the magnitude of the FD signal value but also the ratio of pixels of the FD signal that are equal to or greater than a predetermined value. You may respond. For example, the exposure period may be shortened or the aperture value may be increased as the proportion of pixels of the FD signal that is equal to or greater than a predetermined value is greater.

  On the other hand, if the number of pixels equal to or greater than a predetermined ratio is not detected from the FD signal from all the pixels of the image sensor 103 based on the determination in S801, the image captured by the image sensor 103 may be an overexposed image. It is judged that there are few. Accordingly, the control unit 114 calculates the luminance value of the image captured from the PD signal and calculates the AE control parameter in the same manner as the normal AE control parameter calculation method (S803).

  By performing the processing described above, the imaging apparatus 100 calculates the AE control parameter based on the PD signal and the FD signal. Therefore, it is difficult to calculate an appropriate AE control parameter using only the PD signal. However, an appropriate AE control parameter can be acquired. For this reason, especially when the scene is suddenly changed to a bright scene during live view imaging, the time required for controlling to proper exposure is greatly reduced. Further, in the imaging apparatus 100, in all pixels of the imaging element 103, calculation of the AE control parameter including the FD signal is performed when the pixel in which the photoelectrically converted signal charge is saturated and overflows is a predetermined ratio or more. Is done. Therefore, the calculation of the AE control parameter including the FD signal is performed only in the over-exposure state where it is difficult to calculate an appropriate AE control parameter using only the PD signal.

  In the present embodiment, the FD signal is always read in the next frame after reading the PD signal, and the image of the image display device 112 is not updated in the frame from which the FD signal is read. For this reason, the image displayed on the image display device 112 may become unnatural when the reading process or the display process is not fast. However, the frame from which the FD signal is read is not limited to the next frame from which the PD signal has been read. For example, normally, only the PD signal may be read, and the FD signal may be read in the next frame only when the saturation pixel of the PD signal exceeds a predetermined ratio.

[Second Embodiment]
Next, a second embodiment in which the FD signal readout method is different from the first embodiment will be described. In the second embodiment, only parts different from those in the first embodiment will be described, and the same parts as those in the first embodiment such as the configuration of the imaging apparatus 100 described with reference to FIGS. I will omit the explanation.

  The reading method of the FD signal according to the second embodiment is to read by mixing (synthesizing) the PD signal and the FD signal in the image sensor 103. When such a reading method is used, since the PD signal and the FD signal can be combined and read out, there is an advantage that the calculation of the AE control parameter can be performed at once. Furthermore, since there is no time lag between the PD signal and the FD signal used for calculating the AE control parameter, exposure control can be performed with higher accuracy. Regarding how to read the combined signal of the PD signal and the FD signal according to the second embodiment, refer to FIG. 9 showing a timing chart for reading the combined signal and FIG. 2 showing the configuration of the image sensor 103. explain.

  First, as shown in FIG. 9, the gate PTX1 of the transfer MOSs M111 to M131 is set to the high level to synthesize the PD signal and the FD signal. Then, the signal PTX1 is read out to the optical signal holding capacitors CTS1 to CTS3 with the gates PTS of the optical signal transfer switches M21 to M23 being set to the high level with the high level maintained.

  Next, after returning the PTS to the low level, the reset signal PRES1 is set to the high level to return to the reset potential. After the reset is completed, the gates PTN of the noise transfer switches M11 to M13 are set to the high level, and the reset signal is read out to the noise signal holding capacitors CTN1 to CRN3. Thereafter, after PTN is returned to the low level, the gates PTX1 of the transfer MOSs M111 to M131 are returned to the low level. The subsequent processing is the same as the reading of the FD signal described with reference to FIG. 6 in the first embodiment.

  What should be noted in this reading method is that a signal is read while the transfer gate PTX1 is at a high level, thereby increasing the apparent capacity of the FD, resulting in a problem that the output voltage decreases. That is. That is, with respect to the read voltage, the voltage drop portion must be compensated during signal processing. Another point to be noted is that in this reading, the FD signal and the PD signal are combined and read out, but the sensitivity differs between the PD signal and the FD signal. That is, when calculating the AE control parameter, it is necessary to perform an operation in consideration of that point for a high-intensity signal of a predetermined value or more corresponding to the FD signal portion.

  Next, a flow of live view imaging processing for performing the imaging surface AE in the second embodiment will be described with reference to the flowchart of FIG. As shown in FIG. 10, when the live view imaging process is started under the control of the control unit 114, first, the AE control parameter calculated in the previous frame (in this case, the (n-1) th frame) is set. (S1001). In S1001, a predetermined default value is set for the first frame at the start of processing.

  Next, under the control of the control unit 114, imaging is performed with the AE control parameter set in S1001, and the captured PD signal of the nth frame is read (normal reading) (S1002). Next, the control unit 114 analyzes the PD signal read in S1002. The number of saturated pixels whose PD signal value is equal to or greater than a predetermined value (a value that can be regarded as a saturated signal) is equal to or greater than a predetermined ratio (N%) (second value or greater) set in advance with respect to the total number of pixels. It is determined whether or not there is (S1003).

  In S1003, if the number of saturated pixels is equal to or greater than a predetermined ratio (N%), the PD signal and the FD signal are output by the readout method described with reference to FIG. 9 in the next frame (the (n + 1) th frame). The synthesized signal is read out (S1004). Then, the control unit 114 calculates an AE control parameter from the read composite signal (S1005). As described above, when calculating the AE control parameter, the calculation considering the voltage drop and the sensitivity change is performed.

  Further, if the composite signal is displayed on the image display device 112 for the above-described reason, an unnatural image is formed. Therefore, the control unit 114 controls the image display device 112 to display the previous frame (the nth frame). Is displayed (S1006).

  On the other hand, if the number of saturated pixels is less than the predetermined ratio in S1003, under the control of the control unit 114, the PD signal is read as usual in the next frame (n + 1th frame) (S1007). . Next, the control unit 114 performs calculation of the AE control parameter as usual (S1008). In this case, under the control of the control unit 114, an image of the (n + 1) th frame based on the PD signal read in S1007 is displayed on the image display device 112 (S1009).

  After S1009 or S1006 ends, the control unit 114 determines whether or not to end the live view mode (S1010), and ends the live view imaging process if it ends. If the live view mode is continued without ending in S1010, the process returns to S1001, and the AE control parameter calculated in S1008 or S1005 is set. In the imaging apparatus 100, the above-described flow is continued until the live view mode ends.

  As described above, in the second embodiment, since the AE control parameter is calculated from the combined signal of the PD signal and the FD signal, it is an overexposure state in which it is difficult to calculate an appropriate AE control parameter using only the PD signal. Can also acquire appropriate AE control parameters. For this reason, when the scene suddenly changes to a bright scene during live view imaging, the time until control for proper exposure is significantly shortened. In the second embodiment, since the AE control parameter is calculated from a signal obtained by synthesizing the PD signal and the FD signal of the same frame, the difference in acquisition time between the PD signal and the FD signal that existed in the first embodiment. Does not exist. Therefore, it is possible to calculate the AE control parameter with higher reliability.

  In the second embodiment, the PD signal of each pixel is read out in the nth frame, and the ratio of the number of pixels indicating the state in which the value of the PD signal is saturated to the total number of pixels is set to a predetermined value (first number). 2) or more. As a result of this determination, when the ratio is equal to or higher than a predetermined value, that is, when the scene suddenly changes to a bright scene, the composite signal of each pixel is read out at the (n + 1) th frame, and the AE control parameter is calculated. The value is used for exposure control. Further, if it is less than the predetermined value in the above determination, the PD signal of each pixel is read out even in the (n + 1) th frame, and normal exposure control and frame image display are performed. There is no influence on the.

  Note that the description in the above-described embodiment shows an example, and the present invention is not limited to this. The configuration and operation in the embodiment described above can be changed as appropriate.

(Other embodiments)
The above-described embodiment can also be realized in software by a computer of a system or apparatus (or CPU, MPU, etc.). Therefore, the computer program itself supplied to the computer in order to implement the above-described embodiment by the computer also realizes the present invention. That is, the computer program itself for realizing the functions of the above-described embodiments is also one aspect of the present invention.

  The computer program for realizing the above-described embodiment may be in any form as long as it can be read by a computer. For example, it can be composed of object code, a program executed by an interpreter, script data supplied to the OS, but is not limited thereto. A computer program for realizing the above-described embodiment is supplied to a computer via a storage medium or wired / wireless communication. Examples of the storage medium for supplying the program include a magnetic storage medium such as a flexible disk, a hard disk, and a magnetic tape, an optical / magneto-optical storage medium such as an MO, CD, and DVD, and a nonvolatile semiconductor memory.

  As a computer program supply method using wired / wireless communication, there is a method of using a server on a computer network. In this case, a data file (program file) that can be a computer program forming the present invention is stored in the server. The program file may be an executable format or a source code. Then, the program file is supplied by downloading to a client computer that has accessed the server. In this case, the program file can be divided into a plurality of segment files, and the segment files can be distributed and arranged on different servers. That is, a server apparatus that provides a client computer with a program file for realizing the above-described embodiment is also one aspect of the present invention.

  In addition, a storage medium in which the computer program for realizing the above-described embodiment is encrypted and distributed is distributed, and key information for decrypting is supplied to a user who satisfies a predetermined condition, and the user's computer Installation may be allowed. The key information can be supplied by being downloaded from a homepage via the Internet, for example. Further, the computer program for realizing the above-described embodiment may use an OS function already running on the computer. Further, a part of the computer program for realizing the above-described embodiment may be configured by firmware such as an expansion board attached to the computer, or may be executed by a CPU provided in the expansion board. Good.

Claims (6)

It has a photoelectric conversion unit that generates electric charge according to the amount of received light and accumulates the generated electric charge, and a holding unit that holds the accumulated electric charge transferred from the photoelectric conversion unit, and holds it in the holding unit Imaging means in which a plurality of pixels that output a pixel signal based on the amount of electric charges that are arranged,
Control means for controlling the driving of the imaging means and performing exposure control based on the values of pixel signals output from the plurality of pixels;
With
The control unit obtains a surplus signal based on a charge amount of surplus charge overflowing from the photoelectric conversion unit and held in the holding unit before transferring the charge accumulated in the photoelectric conversion unit to the holding unit. When the ratio of the number of pixels that output the surplus signal to the total number of pixels of the imaging means is equal to or greater than a preset first value, the exposure is performed based on the value of the pixel signal and the surplus signal. An imaging apparatus characterized by performing control. It has a photoelectric conversion unit that generates electric charge according to the amount of received light and accumulates the generated electric charge, and a holding unit that holds the accumulated electric charge transferred from the photoelectric conversion unit, and holds it in the holding unit Imaging means in which a plurality of pixels that output a pixel signal based on the amount of electric charges that are arranged,
Control means for controlling the driving of the imaging means and performing exposure control based on the values of pixel signals output from the plurality of pixels;
With
The control unit obtains a surplus signal based on a charge amount of surplus charge overflowing from the photoelectric conversion unit and held in the holding unit before transferring the charge accumulated in the photoelectric conversion unit to the holding unit. When the ratio of the number of pixels that output a pixel signal indicating a value indicating the saturated state of the photoelectric conversion unit to the total number of pixels of the imaging unit is equal to or greater than a second value set in advance, the pixel features and to that imaging device that performs the exposure control on the basis of the value of the signal and the surplus signal. The control unit transfers the charge accumulated in the photoelectric conversion unit to the holding unit in a state where the surplus charge is held in the holding unit, and synthesizes the charge accumulated in the photoelectric conversion unit and the surplus charge. 3. The imaging apparatus according to claim 1, wherein a combined signal based on the amount of charges obtained is acquired from the plurality of pixels, and the exposure control is performed based on a value of the combined signal. It has a photoelectric conversion unit that generates electric charge according to the amount of received light and accumulates the generated electric charge, and a holding unit that holds the accumulated electric charge transferred from the photoelectric conversion unit, and holds it in the holding unit An image pickup apparatus control method comprising an image pickup unit in which a plurality of pixels that output a pixel signal based on the amount of electric charges are arranged,
The control means includes a control step of controlling the driving of the imaging means and performing exposure control based on pixel signal values output from the plurality of pixels,
The control step acquires a surplus signal based on a charge amount of surplus charges overflowing from the photoelectric conversion unit and held in the holding unit before transferring the charge accumulated in the photoelectric conversion unit to the holding unit. When the ratio of the number of pixels that output the surplus signal to the total number of pixels of the imaging means is equal to or greater than a preset first value, the exposure is performed based on the value of the pixel signal and the surplus signal. A control method for an imaging apparatus, characterized by performing control.   It has a photoelectric conversion unit that generates electric charge according to the amount of received light and accumulates the generated electric charge, and a holding unit that holds the accumulated electric charge transferred from the photoelectric conversion unit, and holds it in the holding unit An image pickup apparatus control method comprising an image pickup unit in which a plurality of pixels that output a pixel signal based on the amount of electric charges are arranged,
  The control means includes a control step of controlling the driving of the imaging means and performing exposure control based on pixel signal values output from the plurality of pixels,
  The control step acquires a surplus signal based on a charge amount of surplus charges overflowing from the photoelectric conversion unit and held in the holding unit before transferring the charge accumulated in the photoelectric conversion unit to the holding unit. When the ratio of the number of pixels that output a pixel signal indicating a value indicating the saturated state of the photoelectric conversion unit to the total number of pixels of the imaging unit is equal to or greater than a second value set in advance, the pixel A control method for an imaging apparatus, wherein the exposure control is performed based on a signal and a value of the surplus signal. The imaging apparatus according to any one of claims 1 to 3 ,
Display means for displaying image data obtained using the imaging device;
Recording means for recording the image data on a recording medium;
A camera comprising:

Images