JP6066949B2 - Imaging apparatus, control method therefor, and program - Google Patents

Description

  The present invention relates to a technique for determining an initial exposure condition based on an output of an image sensor and displaying a captured image in an imaging apparatus.

  In general, in an imaging apparatus having a solid-state imaging device such as a CCD or CMOS sensor, in order to interpose processing such as appropriate exposure and correction until the captured image is captured by the imaging device and displayed on the live view screen. A time lag occurs. For example, when the captured image is displayed in live view after the imaging power is turned on, the time lag is noticeable.

  Therefore, in order to shorten the time from when the power is turned on to when the video signal from the imaging device is output to the display screen, processing for increasing the startup time is being studied. Patent Document 1 discloses an imaging apparatus that performs accurate photometry in a short time by using an external photometric sensor and an imaging sensor in parallel.

JP 2008-58704 A

  However, the conventional technique disclosed in Patent Document 1 uses an external photometric sensor in addition to the imaging sensor, which complicates the configuration and leads to an increase in the cost of the entire imaging apparatus, and is also disadvantageous in terms of power consumption. There was a problem.

  The present invention has been made to solve the above-described problems of the prior art, and an object of the present invention is to shorten the time until the start of image display with appropriate exposure while avoiding an increase in cost.

  In order to achieve the above object, the present invention provides an image sensor having a plurality of pixels that output a signal corresponding to an optical image, and a signal read from a first pixel group among the plurality of pixels of the image sensor. A first acquisition unit that acquires one image, and a second image acquired from a signal read from a second pixel group that does not overlap with the first pixel group among the plurality of pixels of the image sensor. 2 acquisition means, and control means for controlling image acquisition by each of the first acquisition means and the second acquisition means, and the control means displays the captured image on the display unit. In the absence of the first image at the first frame rate and the first exposure condition, the first acquisition means acquiring the first image, and a second speed higher than the first frame rate. The first exposure at a frame rate And causing the second acquisition unit to acquire the second image under a second exposure condition that has an exposure time shorter than that of the first acquisition unit. Based on the luminance information obtained from the first image obtained by the above and the luminance information obtained from the second image obtained by the second obtaining means, the captured image is displayed on the display unit. The initial exposure condition is determined.

  A computer-readable storage medium storing the program according to claim 12 constitutes the present invention.

  According to the present invention, it is possible to shorten the time until the start of image display with appropriate exposure while avoiding an increase in cost.

It is a block diagram which shows the structure of the imaging device which concerns on 1st Embodiment. It is a perspective view and a block diagram of an image pick-up part. It is a figure explaining pixel selection in a column signal line in the 1st chip. It is a flowchart of a live display start process when shooting is started. It is a timing chart at the time of the process of a live display start. It is a flowchart of the process of the live display start at the time of imaging | photography start in 2nd Embodiment. It is a timing chart at the time of the process of a live display start. It is a timing chart at the time of the process of a live display start.

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

(First embodiment)
FIG. 1 is a block diagram showing the configuration of the imaging apparatus according to the first embodiment of the present invention.

  The image pickup apparatus is assumed to be the digital camera 100 as an example. However, the image pickup apparatus may be a video camera, and the present invention is applied to an apparatus having a still image or moving image shooting function.

  In the digital camera 100 shown in FIG. 1, the photographing lens 103 is a lens group including a zoom lens and a focus lens. The shutter 101 is a shutter having a diaphragm function. The imaging unit 22 is an imaging device configured with a CCD, a CMOS device, or the like that converts an optical image into an electrical signal. It has a plurality of pixels 201 (FIG. 2A) to be described later and has an A / D conversion processing function. The imaging unit 22 includes an AF evaluation value detection unit 23. The AF evaluation value detection unit 23 calculates an AF evaluation value used when performing autofocus control from the contrast information obtained from the digital image signal, and outputs the obtained AF evaluation value to the system control unit 50. The barrier 105 covers the photographing lens 103 to prevent the imaging system including the photographing lens 103, the shutter 101, and the imaging unit 22 from becoming dirty or damaged.

  The image processing unit 24 performs resize processing and color conversion processing such as predetermined pixel interpolation and reduction on the data output from the imaging unit 22 or the data output from the memory control unit 15. The image processing unit 24 performs predetermined calculation processing using the captured image data, and the system control unit 50 performs exposure control and distance measurement control based on the obtained calculation result. Thus, TTL (through-the-lens) AE (automatic exposure) processing and EF (flash automatic light control emission) processing are performed. The image processing unit 24 performs AF (autofocus) processing. At this time, the output of the AF evaluation value detection unit 23 included in the imaging unit 22 may be used. The image processing unit 24 further performs predetermined arithmetic processing using the captured image data, and also performs TTL AWB (auto white balance) processing based on the obtained arithmetic result.

  Output data of the imaging unit 22 is written to the memory 32 via the image processing unit 24 and the memory control unit 15 or directly via the memory control unit 15. The memory 32 stores image data acquired by the imaging unit 22 and A / D converted, and image data to be displayed on the display unit 28. The memory 32 has a storage capacity sufficient to store a predetermined number of still images, a moving image and sound for a predetermined time.

  The memory 32 also serves as an image display memory (video memory). The D / A converter 13 converts the image display data stored in the memory 32 into an analog signal and supplies the analog signal to the display unit 28. Thus, the display image data written in the memory 32 is displayed on the display unit 28 via the D / A converter 13. The display unit 28 includes a display device such as an LCD, and performs display in accordance with an analog signal from the D / A converter 13. The digital signal once A / D converted by the imaging unit 22 and stored in the memory 32 is converted into an analog signal by the D / A converter 13 and sequentially transferred to the display unit 28 for display, thereby functioning as an electronic viewfinder. Is achieved and a through image can be displayed.

  The nonvolatile memory 56 is an electrically erasable / recordable memory, and for example, a flash memory or the like is employed. The nonvolatile memory 56 stores constants, programs, and the like for operating the system control unit 50. The program here is a control program for executing various flowcharts described later in the present embodiment.

  The system control unit 50 controls the entire digital camera 100. By executing a program recorded in the nonvolatile memory 56, each process described later is realized. The system memory 52 is, for example, a RAM, and constants and variables for operation of the system control unit 50, programs read from the nonvolatile memory 56, and the like are expanded in the system memory 52. The system control unit 50 also performs display control by controlling the memory 32, the D / A converter 13, the display unit 28, and the like.

  The system timer 53 is a time measuring unit that measures the time used for various controls and the time of a built-in clock. The mode switch 60, the first shutter switch 62, the second shutter switch 64, and the operation unit 70 are operation members for inputting various operation instructions to the system control unit 50.

  The mode switch 60 switches the operation mode of the system control unit 50 to any one of a still image recording mode, a moving image recording mode, a reproduction mode, and the like. Modes included in the still image recording mode include an auto shooting mode, an auto scene discrimination mode, a manual mode, various scene modes for shooting settings for each shooting scene, a program AE mode, a custom mode, and the like. The mode changeover switch 60 can directly switch to one of these modes included in the still image shooting mode. Alternatively, after switching to the still image shooting mode once with the mode switch 60, the mode may be switched to any one of these modes included in the still image shooting mode using another operation member. Similarly, the moving image shooting mode may include a plurality of modes.

  The first shutter switch 62 is turned on when a shutter button 61 provided in the digital camera 100 is being operated, so-called half-press (shooting preparation instruction), and generates a first shutter switch signal SW1. When the first shutter switch signal SW1 is generated, operations such as AF processing, AE processing, AWB processing, and EF processing are started.

  The second shutter switch 64 is turned on when the operation of the shutter button 61 is completed, so-called full press (shooting instruction), and generates the second shutter switch signal SW2. When the second shutter switch signal SW2 is generated, the system control unit 50 starts a series of shooting processing operations from reading a signal from the imaging unit 22 to writing image data on the recording medium 200.

  Each operation member of the operation unit 70 is appropriately assigned a function for each scene by selecting and operating various function icons displayed on the display unit 28, and functions as various function buttons. Examples of the function buttons include an end button, a return button, an image advance button, a jump button, a narrowing button, and an attribute change button. For example, when a menu button is pressed, various setting menu screens are displayed on the display unit 28. The user can make various settings intuitively using the menu screen displayed on the display unit 28, and the four-way button and the SET button.

  The controller wheel 73 is a rotatable operation member included in the operation unit 70, and is used when a selection item is instructed together with a direction button. When the controller wheel 73 is rotated, an electrical pulse signal is generated according to the operation amount, and the system control unit 50 controls each unit of the digital camera 100 based on the pulse signal. From this pulse signal, it is possible to determine the angle at which the controller wheel 73 is rotated, how many rotations, and the like. The controller wheel 73 may be any operation member that can detect a rotation operation. For example, it may be a dial operation member that generates a pulse signal by rotating the controller wheel 73 itself according to the rotation operation of the user. Further, an operation member made of a touch sensor may detect the rotation operation of the user's finger on the controller wheel 73 without rotating the controller wheel 73 itself (so-called touch wheel).

  The power control unit 80 includes a battery detection circuit, a DC-DC converter, a switch circuit that switches a block to be energized, and the like, and detects whether or not a battery is installed, the type of battery, and the remaining battery level. Further, the power control unit 80 controls the DC-DC converter based on the detection result and an instruction from the system control unit 50, and supplies a necessary voltage to each unit including the recording medium 200 for a necessary period. The power switch 72 is operated by the user.

  The power supply unit 40 includes a primary battery such as an alkaline battery or a lithium battery, a secondary battery such as a NiCd battery, a NiMH battery, or a Li battery, an AC adapter, or the like. The recording medium I / F 18 is an interface with the recording medium 200 such as a memory card or a hard disk. The recording medium 200 is a recording medium such as a memory card for recording a captured image, and includes a semiconductor memory, a magnetic disk, or the like.

  FIG. 2 is a diagram for explaining the configuration of the imaging unit 22 shown in FIG. FIG. 2A is a perspective view showing the structure, and FIG. 2B is a block diagram showing the structure.

  In FIG. 2A, the imaging unit 22 includes a first chip 20 and a second chip 21. The first chip 20 is stacked on the second chip 21. The first chip 20 has a plurality of pixels 201 arranged in a matrix, and the first chip 20 is disposed on the light incident side (that is, located on the light receiving side of the optical image). .

  In the second chip 21, pixel driving circuits such as column scanning circuits 213-a and 213-b and a row scanning circuit 212 shown in FIG. 2B are formed, and the above-described AF evaluation value detection unit 23 is provided. Is formed.

  As described above, the semiconductor is divided into two chips, the pixel 201 is formed on the first chip 20, and the pixel driving circuit and the AF evaluation value detection unit 23 are formed on the second chip 21. Thereby, the manufacturing process of the peripheral circuit and the pixel portion of the image sensor 102 can be separated, and the wiring in the peripheral circuit can be thinned, the speed can be increased by increasing the density, the size can be reduced, and the function can be increased.

  As shown in FIG. 2B, in the first chip 20, the pixels 201 are arranged in a matrix. The pixel 201 is connected to the transfer signal line 203, the reset signal line 204, and the row selection signal line 205 in the horizontal direction (row direction), and is connected to the column signal lines 202-a and 202-b in the vertical direction (column direction). ing. Note that the connection destinations of the column signal lines 202-a and 202-b differ depending on the readout row unit.

  The image processing unit 24 includes a signal processing unit 104. The description regarding the pixel connection method will be described later with reference to FIG.

  The second chip 21 is provided with a plurality of column ADC blocks 211, and the column ADC block 211 is connected to the column signal line 202-a or the column signal line 202-b. Further, the second chip 21 includes a row scanning circuit 212, column scanning circuits 213-a and 213-b, a timing control circuit 214, horizontal signal lines 215-a and 215-b, a changeover switch 216, a frame memory 217, And an AF evaluation value detection unit 23.

  The timing control circuit 214 receives the control signal from the system control unit 50 and controls the operation timing of the row scanning circuit 212, the column scanning circuits 213-a and 213-b, and the column ADC block 211. The row scanning circuit 212 scans each row, and the column scanning circuits 213a and 213b scan each column.

  The horizontal signal lines 215-a and 215-b transfer the output signal (image signal) of the column ADC block 211 according to the timing controlled by the column scanning circuits 213-a and 213-b, respectively.

  The frame memory 217 temporarily stores an image signal output from the horizontal signal line 215-b. The AF evaluation value detection unit 23 detects (generates) an AF evaluation value according to the image signal stored in the frame memory 217, and sends the AF evaluation value to the control unit 106. The changeover switch 216 is a changeover switch for selectively outputting an image signal output to the horizontal signal line 215-b to either the AF evaluation value detection unit 23 or the signal processing unit 104. The image signal transferred to the horizontal signal line 215-a is given to the signal processing unit 104.

  Next, the configuration and operation of the imaging unit 22 will be described. Although the configuration of each of the plurality of pixels 201 is common, only one pixel 201 is illustrated in detail in FIG. 2B, so that description will be made mainly with reference to it.

  Each of the pixels 201 includes a photodiode PD that is a photoelectric conversion element, a transfer transistor M1, a reset transistor M2, an amplification transistor M3, a selection transistor M4, and an FD (floating diffusion). In the illustrated example, each of the transistors is an n-channel MOSFET (MOS Field-Effect Transistor).

  A transfer signal line 203, a reset signal line 204, and a row selection signal line 205 are connected to the gates of the transfer transistor M1, the reset transistor M2, and the selection transistor M4, respectively. These signal lines 203 to 205 extend in the horizontal direction, and pixels in the same row are driven simultaneously. This makes it possible to control the operation of a line sequential operation type rolling shutter or an all row simultaneous operation type global shutter. Further, the column signal line 202-a or the column signal line 202-b is connected to the source of the selection transistor M4 in units of rows.

  The photodiode PD accumulates electric charges generated by photoelectric conversion. The P side of the photodiode PD is grounded, and the N side is connected to the source of the transfer transistor M1. When the transfer transistor M1 is turned on (ON), the charge of the photodiode PD is transferred to the FD, and since there is a parasitic capacitance in the FD, the charge transferred to the FD is accumulated.

  A power supply voltage Vdd is applied to the drain of the amplification transistor M3, and its gate is connected to the FD. The amplification transistor M3 amplifies the charge (that is, voltage) of the FD and converts it into a voltage signal. The selection transistor M4 is for selecting a pixel from which a signal is read out in units of rows, and its drain is connected to the source of the amplification transistor M3. The source of the selection transistor M4 is connected to the column signal line 202.

  When the selection transistor M4 is turned on, a voltage signal corresponding to the voltage of the FD is output to the column signal line 202. A power supply voltage Vdd is applied to the drain of the reset transistor M2, and its source is connected to the FD. When the reset transistor M2 is turned on, the voltage of the FD is reset to the power supply voltage Vdd.

  In the following description, during imaging, an output path from the column signal line 202-a via the horizontal signal line 215-a is referred to as channel Ch1, and output from the column signal line 202-b via the horizontal signal line 215-b. The route is called channel Ch2.

  Imaging for acquiring an image from the channel Ch1 is referred to as “main imaging”, and an image obtained thereby is referred to as a main captured image. Imaging for acquiring an image from the channel Ch2 is referred to as “sub-imaging”, and an image obtained thereby is referred to as a sub-captured image. The main captured image is used for scan AE or live view. The sub-captured image is for scan AE in the multiple output mode, but is for AF evaluation value detection in the focus control mode.

  An image signal for scan AE or live view by main imaging is output to the column signal line 202-a, and an image signal for scan AE or AF evaluation value detection by sub imaging is output to the column signal line 202-b. .

  FIG. 3 is a diagram for explaining pixel selection in the column signal line 202-a or 202-b in the first chip 20 shown in FIG.

  In FIG. 3, a pixel group of 8 rows × 6 columns is shown, and here, each pixel is arranged in a Bayer array.

  When the focus control mode is set by the operation of the operation unit 70 shown in FIG. 1, the system control unit 50 performs the readout row in the imaging unit 22 so that the main imaging and the sub imaging can be performed simultaneously (in parallel). Divide. That is, the changeover switch 216 is controlled to connect the horizontal signal line 215-b to the frame memory 217.

  In FIG. 3, row numbers 1 and 2 are rows for sub-imaging, and the pixels 201 belonging to these rows are referred to as a “second pixel group”. Row numbers 3 to 8 are rows for main imaging, and the pixels 201 belonging to these rows are referred to as a “first pixel group”. The first pixel group and the second pixel group do not overlap. In the illustrated example, readout scanning is sequentially performed in units of rows, and readout scanning is repeatedly performed in units of 8 rows.

  In sub-imaging, three out of four pixels of the same vertical color are skipped and read in order to emphasize the frame rate. On the other hand, in main imaging, 1 pixel out of 4 pixels of the same vertical color is thinned out and 3 pixels are added to emphasize image quality.

  In other words, in the main imaging, the first pixel group is read at the first frame rate. In sub-imaging, the second pixel group is read out at a second frame rate that is faster than the first frame rate.

  As described above, by separating the main imaging and the sub imaging for each selected row, it is possible to acquire image signals of different frame rates with different data sizes in different charge accumulation times. In the example shown in FIG. 3, the sub imaging has a frame rate three times that of the main imaging. For example, when the main imaging frame rate is 30 fps, the sub-imaging frame rate is 90 fps.

  The voltage signals (analog signals) output to the column signal lines 202-a and 202-b are converted from analog signals to digital signals (image signals) in the column ADC block 211 (FIG. 2).

  The image signal that is the output of the column ADC block 211 is read from the column ADC block 211 to the horizontal signal line 215-a or the horizontal signal line 215-b by the column scanning circuit 213-a or the column scanning circuit 213-b. The image signal read out to the horizontal signal line 215-a is sent to the signal processing unit 104.

  On the other hand, the image signal read to the horizontal signal line 215-b is output to the changeover switch 216, and is output to the signal processing unit 104 or the frame memory 217 in accordance with the control signal from the system control unit 50. Switching by the changeover switch 216 is performed in units of frames.

  In the multiple output mode, the selector switch 216 switches the output destination of the signal of the second pixel group output to the horizontal signal line 215-b to the signal processing unit 104. In this case, the image signals of the first pixel group and the second pixel group are output to the signal processing unit 104 in parallel through the horizontal signal line 215-a and the horizontal signal line 215-b, respectively.

  In the focus control mode, the changeover switch 216 switches the output destination of the signal of the second pixel group output to the horizontal signal line 215-b to the frame memory 217. In this case, the image signal of the first pixel group is output to the signal processing unit 104 through the horizontal signal line 215-a, and the image signal of the second pixel group is output to the frame memory 217 through the horizontal signal line 215-b. Is output.

  In the AF evaluation mode (autofocus control mode), an image signal for AF evaluation value detection by sub imaging is supplied from the horizontal signal line 215-b to the frame memory 217 via the changeover switch 216 and recorded. . The AF evaluation value detection unit 23 detects an AF evaluation value based on contrast information in the image signal recorded in the frame memory 217. The AF evaluation value is sent from the AF evaluation value detection unit 23 to the system control unit 50.

  Next, scan type exposure control will be described. Here, a scan type exposure control in which photometry is performed three times will be described as an example.

Photometry is performed using three control values Bv1, Bv2, and Bv3 having different exposure values. The average luminance value of the digital data obtained by each control value is Y1, Y2, Y3, respectively, and the target luminance value is Yref. The three control values ΔBv1, ΔBv2, and ΔBv3 can be obtained by the following formulas 1, 2, and 3.
[Equation 1]
ΔBv1 = log ₂ (Y1 / Yref)
[Equation 2]
ΔBv2 = log ₂ (Y2 / Yref)
[Equation 3]
ΔBv3 = log ₂ (Y3 / Yref)
Next, the exposure control value BvS is obtained based on the smallest one of ABS (ΔBv1), ABS (ΔBv2), and ABS (ΔBv3), which are the absolute values of the control values ΔBv1, ΔBv2, and ΔBv3. For example, when ABS (ΔBv1) is the smallest among ABS (ΔBv1), ABS (ΔBv2), and ABS (ΔBv3), the exposure control value BvS is obtained by Equations 4 and 5. However, Av1, Tv1, and Sv1 are an aperture control value, an electronic shutter control value, and a sensitivity control value of the imaging unit 22 when the exposure value of photometry is the control value Bv1, respectively.
[Equation 4]
Bv1 = Av1 + Tv1-Sv1
[Equation 5]
BvS = Bv1 + ΔBv1
Therefore, if the smallest one is ABS (ΔBv2) or ABS (ΔBv2), Bv2 or Bv3 is entered instead of Bv1 in Formulas 3 and 4, and ΔBv2 or ΔBv3 is entered instead of ΔBv1. Further, a value corresponding to Bv2 or Bv3 is entered instead of Av1, Tv1, and Sv1. The exposure control value BvS obtained here is sent to the imaging unit 22 as the initial exposure value Bvs, and the aperture and shutter are controlled to perform the main exposure shooting.

  If the imaging operation is performed with the control values Bv1, Bv2, and Bv3 according to the scan type exposure control and the respective average luminance values Y1, Y2, and Y3 can be quickly obtained, the time lag until the live display starts in the proper exposure state Shortening is possible.

  Here, the method for obtaining the initial exposure condition (initial exposure value Bvs) when performing the photometry three times in the case of performing the scan type exposure control and displaying the preview of the captured image on the display unit 28 has been described. However, the number of photometry is not limited to three, and may be reduced to two, or increased to four or five. 4 and 5, a case where the number of photometry is two will be described.

  FIG. 4 is a flowchart of live display start processing at the start of shooting. Each process in the following flowcharts including FIG. 4 is realized by the system control unit 50 executing a program stored in the nonvolatile memory 56.

  In this live display start, scanning AE control is performed twice after photometry is started and before live display is started. Further, the sub-captured image output from the channel Ch2 is not used for AF evaluation value detection, but is used for performing the AE operation before the start of live display at high speed. As a premise for performing the scan AE, the imaging sensitivities in the channels Ch1 and Ch2 are controlled to be the same (or equivalent), and the diaphragms are also the same.

  First, in step S401, the system control unit 50 supplies power to the imaging unit 22 to turn on the imaging power source, further opens the shutter 101 and the barrier 105, and moves the photographing lens 103 to the initial position.

  In step S402, the system control unit 50 performs settings for operating in a multiple output mode in which main imaging and sub imaging are performed in parallel, and starts driving the imaging unit 22 and the like. Specifically, the system control unit 50 sets the output destination of the channel Ch2 by the changeover switch 216 as the signal processing unit 104. At this time, the system control unit 50 sets the exposure times (shutter speeds) T1 and T2 (T1> T2) derived from the control values Bv1 and Bv2 in the above-described scan type exposure control to the main imaging and the sub imaging, respectively. Against.

  Hereinafter, the sub-captured image obtained from the second pixel group exposed at the exposure time T2 (second exposure condition) is referred to as a second image P2, and is exposed at the exposure time T1 (first exposure condition). The main captured image obtained from the first pixel group is referred to as a first image P1.

  Next, the system control unit 50 waits for the completion of the reading (capture) operation from the imaging unit 22 of the second image P2 exposed at the exposure time T2 by the sub imaging (step S403). When the reading operation of the second image P2 is completed (second acquisition step), the system control unit 50 uses the luminance evaluation value Y (P2), which is luminance information for the second image P2 acquired by the reading, to perform image processing. Obtained from the unit 24 (step S404). At the same time, the system control unit 50 sets the operation mode to the AF evaluation mode, and sets the output destination of the channel Ch2 by the changeover switch 216 to the frame memory 217.

  Next, the system control unit 50 waits for the completion of the reading operation from the imaging unit 22 for the first image P1 exposed at the exposure time T1 by the main imaging (step S405). When the read operation of the first image P1 is completed (first acquisition step), the system control unit 50 uses the luminance evaluation value Y (P1), which is the luminance information for the first image P1 acquired by the reading, to perform image processing. Obtained from the unit 24 (step S406).

  Next, the system control unit 50 obtains an initial exposure value Bvs from the control values Bv1 and Bv2 based on the above-described calculation in the scan type exposure control (Equations 1 to 5) (step S407). Next, the system control unit 50 determines an initial exposure time T0 for preview display from the initial exposure value BvS and the program diagram stored in the nonvolatile memory 56, and sets it in the imaging unit 22 ( Step S408).

  Next, the system control unit 50 continuously transfers the main captured image output from the imaging unit 22 to the image processing unit 24 via the signal processing unit 104, performs display development processing, and writes it to the memory 32. Come on. Then, the system control unit 50 starts live display by transferring the image in the memory 32 to the display unit 28 via the memory control unit 15 and the D / A converter 13 (step S409), and the processing of FIG. End.

  Next, details of the imaging timing after the start of imaging corresponding to the processing of FIG. 4 will be described using FIG.

  FIG. 5 is a timing chart at the time of live display start processing. In FIG. 5, PVD represents a vertical synchronizing signal for display, VD1 represents a vertical synchronizing signal for main imaging in the channel Ch1, and VD2 represents a vertical synchronizing signal for sub-imaging in the channel Ch2. Until time t507, the captured image is not displayed on the display unit 28.

  Reading of the second image P2 exposed at the exposure time T2 by the sub imaging is completed at time t501, and the luminance evaluation value Y (P2) is obtained from the second image P2 by calculation in the image processing unit 24. It is done. Thereafter, the operation mode becomes the AF evaluation mode. Therefore, after time t501, the sub imaging is used for original AF evaluation value detection.

  On the other hand, the reading of the first image P1 exposed at the exposure time T1 by the main imaging in parallel with the sub imaging is completed at time t502, and the luminance evaluation value Y (P1) is image-processed from the first image P1. It is obtained by calculation in the unit 24 (time t503).

  After time t503, the initial exposure value BvS is derived from the luminance evaluation values Y (P1) and Y (P2) by the above-described arithmetic expression, and the initial exposure time T0 is determined from the initial exposure value BvS and the program diagram ( Time t504).

  The initial exposure time T0 is reflected from the vertical period of the next main imaging, that is, the imaging for the next live display, and the exposure is started from time t505. Thereafter, reading of the exposure image P0 is completed at time t506, and live display can be started from time t507 in synchronization with the next vertical synchronizing signal PVD for display.

  In this way, in scan-type exposure control, a mechanism that allows main imaging that can be used for live display and sub-imaging that can be used for AF evaluation value detection in parallel is used, and sub-imaging is performed rather than main imaging. Is a high frame rate. In the scanning exposure control operation, the exposure time T2 is shorter than the exposure time T1, and the main imaging is on the long seconds side and the sub imaging is on the short seconds side.

  Exposure in both main imaging and sub imaging is controlled to be completed within 1 V period (one vertical scanning period) of channel Ch1. Accordingly, the acquisition of the second image P2 by the sub imaging is completed before the acquisition of the first image P1 by the main imaging is completed. Thereby, the time required for the scanning exposure control operation is shortened. That is, conventionally, the scanning type exposure control that required 2V period (2 vertical scanning periods) in imaging for live display can be completed in 1V period.

  According to the present embodiment, acquisition of the first image P1 and acquisition of the second image P2 by the signal processing unit 104 of the image processing unit 24 in a state where the captured image is not displayed on the display unit 28. , Done in parallel in time. The first image P1 is acquired at the first frame rate and the first exposure condition. The second image P1 has a second frame rate that is higher than the first frame rate and a second exposure condition (exposure time T2) that is shorter in exposure time than the first exposure condition (exposure time T1). Obtained at Then, based on the luminance information (Y (P1)) and (Y (P2)) obtained from the acquired images P1 and P2, the initial exposure time T0 is used as an initial exposure condition when displaying the captured image on the display unit 28. Is determined. As a result, it is possible to shorten the time until the start of image display with appropriate exposure while avoiding an increase in cost without degrading the display image quality. Since it is not necessary to separately provide an external photometric sensor as in the prior art, it is possible to avoid a complicated configuration and an increase in cost, which is advantageous in terms of power consumption.

  After time t501, the original AF evaluation value detection operation can be performed for channel Ch2. Therefore, by operating the photographing lens 103 and completing the focusing operation before the live display is started at time t507, it is possible to keep the focused state from the start of the live display. . Further, as compared with the conventional method of sequentially reading images, the exposure timing of the first image P1 and the second image P2 is almost synchronized, so that the calculation accuracy for automatic exposure control is improved. There is also.

  The signal read from the second pixel group is used for scan AE and also for generation (detection) of an AF evaluation value by the AF evaluation value detection unit 23 by switching with the changeover switch 216. Accordingly, since the second pixel group is not dedicated to the scan AE, the configuration can be prevented from becoming complicated.

  In the case of performing the scan type exposure control, the method of obtaining the initial exposure condition by performing the photometry twice has been described, but the number of photometry is not limited to two. In consideration of the dynamic range of the imaging unit 22 and the like, the number of photometry may be three or more as described in the second embodiment.

(Second Embodiment)
In the first embodiment described above, the number of times of photometry when performing the scan type exposure control is two, but in the second embodiment, the number of times is three. Also, the luminance evaluation value Y is calculated from the image that has been previously captured in the channel Ch2, and if the luminance evaluation value Y is a satisfactory value, the output destination of the signal of the channel Ch2 in the changeover switch 216 is stored in the frame memory 217. Switch immediately.

  FIG. 6 is a flowchart of live display start processing at the time of shooting activation according to the second embodiment.

  In steps S601 to S604, the system control unit 50 executes the same processes as in steps S401 to S404 in FIG. However, in step S602, the exposure time T1 derived from the control value Bv1 in the above-described scan type exposure control is set for the main imaging. At the same time, the exposure times T2 and T3 derived from the control values Bv2 and Bv3 are set for the sub imaging. The relationship between the lengths of the exposure time T is T1> T3> T2. Regarding sub imaging, imaging with an exposure time T2 on the short second side is performed prior to imaging with an exposure time T3.

  In step S605, the system control unit 50 compares the luminance evaluation value Y (P2) acquired in step S604 with the target luminance value Yref, and the difference d (P2) between the luminance evaluation value Y (P2) and the target luminance value Yref. Is determined to be within a predetermined range.

  As a result of the determination, if the difference d (P2) is outside the predetermined range, the system control unit 50 completes the reading operation from the imaging unit 22 of the third image P3 exposed at the exposure time T3 by the sub imaging. It waits to do (step S606). Here, the third image P3 is a sub-captured image obtained from the second pixel group exposed at the second frame rate and at the exposure time T3 (third exposure condition). When the reading operation of the third image P3 is completed, the system control unit 50 acquires the luminance evaluation value Y (P3) for the third image P3 acquired by the reading from the image processing unit 24 (step S607).

  Then, the system control unit 50 compares the acquired luminance evaluation value Y (P3) with the target luminance value Yref, and the difference d (P3) between the luminance evaluation value Y (P3) and the target luminance value Yref is within a predetermined range. It is determined whether or not there is (step S608). As a result of the determination, if the difference d (P3) is outside the predetermined range, the system control unit 50 completes the reading operation from the imaging unit 22 of the first image P1 exposed at the exposure time T1 by the main imaging. It waits to do (step S609).

  When the reading operation of the first image P1 is completed, the system control unit 50 acquires the luminance evaluation value Y (P1) for the first image P1 acquired by reading from the image processing unit 24 (step S610). Then, the system control unit 50 obtains the initial exposure value Bvs from the control values Bv1, Bv2, and Bv3 based on the calculations in the scanning exposure control (Equations 1 to 5) (step S611).

  When the process proceeds to step S612 via step S611, the system control unit 50 performs initial exposure when displaying a preview from the initial exposure value BvS obtained in step S611 and the program diagram stored in the nonvolatile memory 56. Time T0 is determined. Then, the system control unit 50 sets the obtained initial exposure time T0 in the imaging unit 22.

  Thereafter, in step S613, the system control unit 50 executes a process similar to that in step S409 in FIG. 4 to start live display, and ends the process in FIG.

  On the other hand, if the difference d (P2) is within the predetermined range as a result of the determination in step S605, the system control unit 50 sets the operation mode to the AF evaluation mode and starts the operation for detecting the original AF evaluation value ( In step S614, the process proceeds to step S612. As a result of the determination in step S608, even when the difference d (P3) is within the predetermined range, the system control unit 50 sets the operation mode to the AF evaluation mode and starts the operation for detecting the original AF evaluation value (step S614). ), The process proceeds to step S612.

  When the process proceeds to step S612 via step S614, in step S612, the system control unit 50 determines the initial exposure time T0 without obtaining the initial exposure value BvS and sets it in the imaging unit 22. That is, when the process proceeds from step S605 to S614 to S612, the system control unit 50 determines the initial exposure time T0 based on the difference d (P2). On the other hand, when the process proceeds from step S608 to S614 to S612, the system control unit 50 determines the initial exposure time T0 based on the difference d (P3).

  Next, with reference to FIG. 7, the details of the imaging timing after the start of imaging corresponding to the case where the process in FIG. 6 has shifted from step S611 to S612 will be described.

  FIG. 7 is a timing chart at the time of live display start processing.

  Reading of the second image P2 exposed at the exposure time T2 by the sub imaging is completed at time t701, and the luminance evaluation value Y (P2) is obtained from the second image P2 by calculation in the image processing unit 24. It is done. Sub-imaging with exposure time T3 is started after sub-imaging with exposure time T2. Reading of the third image P3 exposed at the exposure time T3 by the sub imaging is completed at time t702, and the luminance evaluation value Y (P3) is obtained from the third image P3 by calculation in the image processing unit 24. It is done.

  On the other hand, main imaging with exposure time T1 is performed in parallel with sub imaging with exposure time T2 and sub imaging with exposure time T3. Reading of the first image P1 exposed at the exposure time T1 by the main imaging is completed at time t703, and the luminance evaluation value Y (P1) is obtained from the first image P1 by calculation in the image processing unit 24. (Time t704).

  Thereafter, an initial exposure value BvS is derived from the obtained luminance evaluation values Y (P1), Y (P2), and Y (P3) by the above-described arithmetic expression of the scanning exposure control, and the initial exposure value BvS and the program diagram are displayed. Thus, the initial exposure time T0 is determined (time t705).

  The initial exposure time T0 is reflected from the vertical period of the next main imaging, that is, the imaging for live display, and the exposure is started from time t706. Thereafter, reading of the exposure image P0 is completed at time t707, and live display can be started from time t708 in time with the next vertical synchronizing signal PVD for display.

  Next, with reference to FIG. 8, the details of the imaging timing after the start of imaging corresponding to the case where the process in FIG. 6 has shifted from step S605 to S614 to S612 will be described.

  FIG. 8 is a timing chart at the time of live display start processing.

  Reading of the second image P2 exposed at the exposure time T2 by the sub imaging is completed at time t801, and the luminance evaluation value Y (P2) is obtained from the second image P2 by calculation in the image processing unit 24. It is done. Since the difference d (P2) between the luminance evaluation value Y (P2) and the target luminance value Yref is within a predetermined range, the initial exposure time T0 is determined based on the difference d (P2).

  Accordingly, the subsequent scan-type exposure control is unnecessary, and sub-imaging with the exposure time T3 is not necessary. Therefore, at time t802, the operation mode becomes the AF evaluation mode, and an acquisition of the original AF evaluation value is instructed. Then, AF control is possible from time t803. The exposure for live display starts from time t805. Reading of the exposure image P0 is completed at time t806. The live display can be started after t807, which is the timing of the next display vertical synchronizing signal PVD.

On the other hand, when the process in FIG. 6 proceeds from step S608 to S614 to S612,
Reading of the third image P3 exposed at the exposure time T3 by the sub imaging is completed at time t901. Therefore, before the acquisition of the first image P1 by the main imaging is completed, the acquisition of the third image P3 that is exposed after the sub imaging is completed. Then, the luminance evaluation value Y (P3) is obtained from the third image P3. Since the difference d (P3) between the luminance evaluation value Y (P3) and the target luminance value Yref is within a predetermined range, the initial exposure time T0 is determined based on the difference d (P3).

  As described above, the acquisition of the images P2 and P3 by the sub imaging on the short second side is performed at a higher frame rate than the acquisition of the image P1 by the main imaging on the long second side, and within the 1V period of the channel Ch1. Complete. Thereby, scan-type exposure control, which conventionally required a 3V period, is completed in a 1V period in the present embodiment.

  In addition, the luminance evaluation value Y is calculated from the second image P2 or the third image P3 that has been captured earlier than the first image P1, and the difference d between the luminance evaluation value Y and the target luminance value Yref is predetermined. If it is within the range, the operation immediately shifts to the AF operation. Therefore, it is possible to advance the start timing of the AF operation. Further, if the difference d is within a predetermined range, the initial exposure time T0 can be determined during the exposure for the main imaging performed for the scan type exposure even during the exposure for the main imaging. Therefore, the effect of shortening the time until the start of display by appropriate exposure is great.

  In addition, by performing reading of the second image P2 on the short second side among the images P2 and P3, live display and AF operation can be started more quickly under high luminance.

  According to the present embodiment, the same effect as that of the first embodiment can be achieved with respect to shortening the time until the start of image display with appropriate exposure. However, in addition to this, when the luminance evaluation value Y calculated from the second image P2 or the third image P3 is a satisfactory value, the initial exposure time T0 can be determined without requiring acquisition of the image P1. This further contributes to shortening the time until image display starts. In particular, in the sub-imaging, the second image P2 on the short second side is read first, so that the possibility of obtaining a large time reduction effect can be increased.

  In the first and second embodiments, the sequence from the start of shooting to the start of live view has been described. However, the sequence is not limited to live view, and is effective for shortening the time lag at the time of moving image shooting immediately after startup. The time lag when shooting using the optical viewfinder is also shortened.

  In the second embodiment, even when the process of FIG. 6 proceeds from step S608 to S614 to S612, the initial exposure time T0 is set based on the difference d (P2) instead of the difference d (P3). It is possible to adopt a configuration of determining.

  In the second embodiment, the sub imaging is performed on two images P2 and P3 having different exposure times. However, three or more images are targeted for exposure / readout within the 1V period of the channel Ch1. Also good. In this case, in order to easily obtain a large time shortening effect, it is desirable to start acquisition of an image under the exposure condition with the shortest exposure time (short seconds) first.

  Note that, as in the first and second embodiments, imaging with a high frame rate is acquired in parallel by the imaging unit 22 in addition to imaging for live display, and a photometric evaluation value is output from the data at high speed. Any configuration other than the illustrated configuration can be employed. Therefore, the way of dividing the pixel group is not limited to the way of dividing the first and second pixel groups as illustrated, and it may be divided into a plurality of pixel groups so as not to overlap. Further, in the first chip 20, the pixels 201 are not limited to a configuration arranged in a matrix.

  Further, for example, in the sub-imaging on the short-second side, the image may be captured with the angle of view narrowed so that the central portion is cut out with respect to the angle of view of the live display image by the main imaging. That is, the pixel group used for the sub-imaging may not be divided into rows with respect to the pixel group used for the main imaging, but may have a narrow angle of view cut out from the center of the arrangement range of the pixels 201. With this configuration, it is possible not only to further reduce the time required for image reading, but also to reduce the effect of vignetting on exposure control that occurs before the photographing lens 103 moves from the retracted state to the initial photographing position. There are benefits.

  The present invention is also realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, etc.) of the system or apparatus reads the program code. It is a process to be executed. In this case, the program and the storage medium storing the program constitute the present invention.

  Although the present invention has been described in detail based on preferred embodiments thereof, the present invention is not limited to these specific embodiments, and various forms within the scope of the present invention are also included in the present invention. included. A part of the above-described embodiments may be appropriately combined.

22 Imaging unit 24 Image processing unit 50 System control unit 201 Pixel P1 First image P2 Second image Y Luminance evaluation value

Claims (12)

An image sensor having a plurality of pixels that output signals according to an optical image;
First acquisition means for acquiring a first image from a signal read from a first pixel group among the plurality of pixels of the imaging element;
Second acquisition means for acquiring a second image from a signal read from a second pixel group that does not overlap with the first pixel group among the plurality of pixels of the imaging element;
Control means for controlling image acquisition by each of the first acquisition means and the second acquisition means,
The control unit causes the first acquisition unit to acquire the first image at a first frame rate and a first exposure condition in a state where the captured image is not displayed on the display unit. The second image is sent to the second acquisition means at a second frame rate that is faster than the first frame rate and under a second exposure condition that has an exposure time shorter than the first exposure condition. And obtaining the luminance information obtained from the first image acquired by the first acquisition means, and the acquired by the second acquisition means An imaging apparatus, wherein an initial exposure condition for displaying a captured image on the display unit is determined based on luminance information obtained from a second image.   The control means controls the acquisition of the second image by the second acquisition means before the acquisition of the first image by the first acquisition means is completed. The imaging device according to claim 1.   The control means is a state in which the captured image is not displayed on the display unit, the exposure time is shorter than the first exposure condition at the second frame rate, and the second exposure condition. Having the second acquisition unit acquire the third image under a different third exposure condition, after causing the second image to be acquired, and acquired by the first acquisition unit. The luminance information obtained from the first image, the luminance information obtained from the second image obtained by the second obtaining unit, and the third image obtained by the second obtaining unit. The image pickup apparatus according to claim 1, wherein the initial exposure condition is determined based on luminance information obtained from the information.   The control unit controls the acquisition of the third image by the second acquisition unit before the acquisition of the first image by the first acquisition unit is completed. The imaging device according to claim 3.   The imaging apparatus according to claim 3 or 4, wherein the second exposure condition has a shorter exposure time than the third exposure condition.   When the luminance information obtained from the second image acquired by the second acquisition unit is within a predetermined range in a state where the captured image is not displayed on the display unit, The initial exposure condition is determined based on the luminance information obtained from the second image regardless of the luminance information obtained from the first image and the luminance information obtained from the third image. Item 6. The imaging device according to any one of Items 3 to 5. The image sensor has a generation unit that generates an evaluation value used when performing autofocus control based on a signal read from the second pixel group,
When the luminance information obtained from the second image acquired by the second acquisition unit is within a predetermined range in a state where the captured image is not displayed on the display unit, Controlling that the output destination of the signal read from the second pixel group is switched from the second acquisition unit to the generation unit without causing the second acquisition unit to acquire the third image. The imaging device according to any one of claims 3 to 6.   The said image pick-up element has a production | generation means to produce | generate the evaluation value used when performing autofocus control based on the signal read from the said 2nd pixel group, The Claim 1 or 2 characterized by the above-mentioned. Imaging device.   2. The plurality of pixels of the image sensor are arranged in a matrix, and the first pixel group and the second pixel group are different from each other in rows in the matrix arrangement. The imaging apparatus of any one of -8.   The first pixel group and the second pixel group are set so that the angle of view of the second image is smaller than that of the first image. The imaging device according to any one of 8. A method for controlling an imaging apparatus including an imaging device having a plurality of pixels that output a signal according to an optical image,
A first acquisition step of acquiring a first image from a signal read from a first pixel group among the plurality of pixels of the image sensor;
A second acquisition step of acquiring a second image from a signal read from a second pixel group that does not overlap with the first pixel group among the plurality of pixels of the imaging element;
A control step for controlling image acquisition by each of the first acquisition step and the second acquisition step,
The control step causes the first acquisition step to acquire the first image at a first frame rate and a first exposure condition in a state where the captured image is not displayed on the display unit. In the second acquisition step, the second image is acquired at a second frame rate that is higher than the first frame rate and under a second exposure condition that has an exposure time shorter than the first exposure condition. And acquiring the luminance information obtained from the first image acquired in the first acquisition step and the acquired in the second acquisition step. A control method for an imaging apparatus, comprising: determining an initial exposure condition when displaying a captured image on the display unit based on luminance information obtained from a second image.   A program for causing a computer to execute the method for controlling an imaging apparatus according to claim 11.

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