JP2016224277A - Image pickup apparatus, and control method for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce, in AF control using an image face phase difference system, the load on the system and electric power consumption without sacrificing the accuracy of focus detection.SOLUTION: An image pickup apparatus is equipped with multiple photoelectric converters for each of two-dimensionally arranged multiple micro-lenses, an image pickup element (221) that outputs picture signals matching incident light intensity, designating means (232, 234, 236 and 237) that designate focus detection areas, and an autofocusing signal reading-out control unit (233) that so performs control as to determine from the multiple photoelectric converters the range of reading-out in the sub-scanning direction of divided reading-out on the basis of the designated focus detection areas and image pickup conditions, to read out signals by divided reading-out from the photoelectric converters in the determined range of reading-out, and to read out signals by addition reading-out from the photoelectric converters except the pertinent range of reading-out.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an imaging apparatus and a control method thereof, and more particularly, to a focus adjustment technique using imaging plane phase difference AF.

  2. Description of the Related Art Conventionally, a technique for realizing a focus detection function and image signal acquisition using a single image sensor is known. As an example, an information acquisition pixel for focus detection is used for image acquisition for display / recording. A pixel that can also be used as a pixel has been proposed (see Patent Document 1). According to this technology, at least some of the pixels constituting the image sensor are divided into a plurality of regions in the horizontal and / or vertical directions, and signals obtained from the divided regions are added at the time of image acquisition. To obtain an image signal. Further, at the time of focus adjustment, it is possible to use as a phase difference type focus adjustment signal in which each pixel is divided into pupils by reading out signals for two regions divided in the horizontal or vertical direction.

  Also, in Patent Document 2, signals of a plurality of divided areas are read into a line memory and added for each pixel and output as an image signal, or a signal of each area is output independently and a phase difference focus. An imaging apparatus that switches whether to use as an adjustment signal is disclosed.

JP 2001-083407 A JP 2012-155095 A

  On the other hand, with the increase in the number of pixels of the image sensor, it is required to read out more pixel signals within a predetermined time, but the load on the system due to an increase in the output rate of the image sensor has increased. Yes. In particular, as shown in Patent Document 2, in the case of an image sensor having a pupil division readout function in which each pixel is configured by a plurality of photoelectric conversion units, the number of signal readout increases, so that the readout load and the processing load increase. In addition, the burden on the system increases.

  In Patent Document 2, a signal read for each photoelectric conversion unit is output as it is from the image sensor in the focus adjustment region, and a signal read for each photoelectric conversion unit is added for each pixel in the other regions, and then the image is read from the image sensor. Output. In this way, the number of signal outputs is reduced by switching the output method between the focus adjustment area and the other areas. However, in Patent Document 2, since reading from each photoelectric conversion unit is performed independently, the time required for reading cannot be shortened sufficiently.

  On the other hand, reading as much as possible for each photoelectric conversion unit has advantages in focus detection processing, such as improvement in focus detection accuracy by improving S / N and improvement in the degree of freedom of control method of focus detection. There is a trade-off relationship. For this reason, it has been a problem to determine from which region in the screen the phase adjustment type focus adjustment signal is read out.

  The present invention has been made in view of the above-described problems. In the AF control using the imaging surface phase difference method, the system load is reduced and the power consumption is reduced without reducing the focus detection accuracy. Objective.

  In order to achieve the above object, an imaging device according to the present invention includes a plurality of photoelectric conversion units for each of a plurality of two-dimensionally arranged microlenses, and an image sensor that outputs an image signal corresponding to the amount of incident light. From the plurality of photoelectric conversion units corresponding to each microlens based on a designation unit that designates a focus detection region for performing focus detection, the focus detection region designated by the designation unit, and an imaging condition, Determining means for determining a readout range in the sub-scanning direction in the imaging device, performing first readout capable of obtaining an addition signal obtained by adding a pair of signals having parallax and signals of the plurality of photoelectric conversion units; A signal is read out by the first reading from the photoelectric conversion unit in the reading range determined by the determining unit, and a pair of signals is read from the photoelectric conversion unit excluding the reading range. A control means for controlling to read out the signal, the a second read to obtain a sum signal without obtaining.

  According to the present invention, in AF control using the imaging surface phase difference method, the system load can be reduced and the power consumption can be reduced without reducing the accuracy of focus detection.

1 is a block diagram showing a schematic configuration of an imaging system according to a first embodiment of the present invention. 1 is a diagram showing a schematic configuration of an image sensor in an embodiment of the present invention. FIG. 2 is a conceptual diagram and a circuit diagram illustrating a configuration example of a pixel of an image sensor in an embodiment. 7 is a flowchart showing imaging processing in the first to third embodiments. 9 is a flowchart showing still image shooting processing in the first to third embodiments. 9 is a flowchart showing focus state detection processing in the first to third embodiments. 5 is a flowchart showing a divided readout range setting process in the first embodiment. FIG. 5 is a diagram illustrating an example of a relationship between a focus detection area and a divided readout range in the first embodiment. The figure which showed an example of the setting method of the division | segmentation readout range in case the division | segmentation readout line numbers in 1st Embodiment are each an odd number and an even number. The figure which shows the relationship before and behind the change of the focus detection area | region in 1st Embodiment. The block diagram which shows schematic structure of the imaging system which concerns on 2nd Embodiment. 9 is a flowchart showing a divided readout range setting process in the second embodiment. 10 is a flowchart showing a divided readout range setting process in the third embodiment. The figure which shows an example of the relationship between the some focus detection area | region and division | segmentation readout range in 3rd Embodiment.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components exemplified in this embodiment should be changed as appropriate according to the configuration of the apparatus to which the present invention is applied and various conditions. However, the present invention is not limited to these examples.

<First Embodiment>
Configuration of Imaging System FIG. 1 is a block diagram showing a schematic configuration of an imaging system according to the first embodiment of the present invention. In the first embodiment, the imaging system is described as an interchangeable lens system, but an imaging apparatus having a fixed lens may be used.

  As shown in FIG. 1, the imaging system in the present embodiment includes a lens unit 10 and a camera body 20. The lens control unit 106 that controls the overall operation of the lens unit 10 and the camera control unit 232 that controls the overall operation of the imaging system including the lens unit 10 exchange data with each other through terminals provided on the lens mount. Are communicating.

  First, the configuration of the lens unit 10 will be described. The lens unit 10 has a photographing optical system including a fixed lens 101, a diaphragm 102, a focus lens 103, and the like. The diaphragm 102 is driven by the diaphragm driving unit 104 and controls the amount of light incident on the image sensor 221 described later. The focus lens 103 is driven by the focus lens driving unit 105 and is used for focus adjustment. In addition, you may comprise so that focus adjustment may be performed by driving the position of the image pick-up element 221 mentioned later to an optical axis direction. The aperture driving unit 104 and the focus lens driving unit 105 are controlled by the lens control unit 106, and the aperture diameter of the aperture 102 and the position of the focus lens 103 are controlled.

  When an operation such as a focus is performed by a user operating a focus ring or the like provided in the lens operation unit 107, the lens control unit 106 performs control according to the user operation. In addition, the lens operation unit 107 allows the user to make settings related to the operation of the lens unit 10 such as switching between auto focus (AF) / manual focus (MF) modes, setting of a shooting distance range, and setting of a camera shake correction mode. it can.

  The lens control unit 106 controls the aperture driving unit 104 and the focus lens driving unit 105 according to a control command and control information received from a camera control unit 232 described later, and transmits lens information to the camera control unit 232. .

  Next, the configuration of the camera body 20 will be described. In the camera body 20, the image sensor 221 is configured by a CCD or CMOS sensor, and a light beam that has passed through the photographing optical system of the lens unit 10 is imaged on the light receiving surface of the image sensor 221. Then, the formed subject image is photoelectrically converted into an electric charge corresponding to the amount of incident light by the photodiode (photoelectric conversion unit) of the image sensor 221 and accumulated. The electric charge accumulated in each photodiode is sequentially read out from the image sensor 221 as a voltage signal corresponding to the electric charge based on a driving pulse given from the timing generator 235 in accordance with an instruction from the camera control unit 232. Although the detailed configuration of the image sensor 221 will be described later, the image sensor 221 in the present embodiment can be used for phase difference type focus detection in addition to a normal image signal (recording / display signal). A pair of AF signals having parallax can be output.

  The imaging signal and AF signal read from the imaging element 221 are input to the CDS / AGC / AD circuit 222, and correlated double sampling for removing reset noise, gain adjustment, and signal digitization are performed. Then, the CDS / AGC / AD circuit 222 outputs the processed imaging signal to the image signal processing unit 223 and the AF signal to the AF signal processing unit 224.

  The image signal processing unit 223 performs various types of image processing on the imaging signal output from the CDS / AGC / AD circuit 222, generates an image signal, and stores the image signal in the SDRAM 229 via the bus 21. The image signal stored in the SDRAM 229 is read by the display control unit 225 via the bus 21 and displayed on the display unit 226. In the operation mode in which the imaging signal is recorded, the image signal stored in the SDRAM 229 is recorded on the recording medium 228 by the recording medium control unit 227.

  The ROM 230 stores a control program executed by the camera control unit 232 and various data necessary for the control. The flash ROM 231 stores various setting information related to the operation of the camera body 20 such as user setting information. Yes.

  The AF signal processing unit 224 sets and arranges a focus detection area for performing focus detection in the imaging screen as described later, based on information from the camera control unit 232 and information from the AF signal readout control unit 233. . Then, among the pair of AF signals output from the CDS / AGC / AD circuit 222, a known correlation calculation is performed based on the pair of AF signals included in the set focus detection area, and the image shift amount and reliability are determined. Calculate information. The reliability information includes, for example, two-image coincidence, two-image steepness, contrast information, saturation information, scratch information, and the like. Then, the calculated image shift amount and reliability information are output to the camera control unit 232.

  The camera control unit 232 is configured by, for example, one or more programmable processors and the like, and implements the operation of the entire camera system including the lens unit 10 by executing a control program stored in the ROM 230, for example. First, the camera control unit 232 performs control by exchanging information with each configuration in the camera body 20. In addition to the processing in the camera body 20, the power ON / OFF, the setting change, and the recording are controlled according to the input from the camera operation unit 234 operated by the user. Furthermore, various functions corresponding to user operations such as switching between auto focus (AF) / manual focus (MF) control, confirmation of a recorded image, and designation of a focus detection area are executed. As will be described later, the camera control unit 232 determines and controls a row from which the image sensor 221 reads an AF signal.

  Further, as described above, information is exchanged with the lens control unit 106 in the lens unit 10, a control command and control information for the photographing optical system are transmitted, and information in the lens unit 10 is acquired. As one of the controls, the camera control unit 232 drives the focus lens 103 via the lens control unit 106 based on the correlation calculation result of the focus detection area acquired from the AF signal processing unit 224.

  In the present embodiment, the user designates the focus detection area via the camera operation unit 234, but the present invention is not limited to this method. For example, when a configuration is provided in which a specific subject is detected from the imaging screen, the focus detection area may be designated based on the subject detection result.

  In addition, the camera control unit 232 sends parameter information necessary for setting the AF signal readout range, such as control information of the camera body 20 and the state of the lens unit 10, and information on the designated focus detection area to the AF signal. The read control unit 233 is notified. The AF signal read control unit 233 uses the information acquired from the camera control unit 232 to set a range for reading the AF signal to the image sensor 221.

Configuration of Image Sensor Next, the configuration of the image sensor 221 in the first embodiment will be described with reference to FIGS. 2 and 3. The image sensor 221 in the first embodiment is, for example, a CMOS image sensor that employs an XY address type scanning method.

  FIG. 2 is a diagram illustrating a schematic configuration of the image sensor 221 in the present embodiment. As illustrated in FIG. 2, the image sensor 221 includes a pixel unit 205 in which a plurality of pixels are two-dimensionally arranged, a vertical scanning circuit 206, a reading circuit 207, a horizontal scanning circuit 208, and an output circuit 209. . The pixel unit 205 is covered with a color filter composed of a plurality of colors. In this embodiment, R (red), G (green), and B (blue) filters are two-dimensionally arranged in a mosaic pattern. The color filter is assumed to be a Bayer array.

  The vertical scanning circuit 206 selects and drives an arbitrary pixel row in the pixel unit 205 based on control signals from the AF signal readout control unit 233 and the timing generator 235. The readout circuit 207 reads out signals output from the pixels in the row selected by the vertical scanning circuit 206 and transfers the readout signals to the output circuit 209 according to the control of the horizontal scanning circuit 208. Thereby, scanning in the main scanning direction (horizontal direction) is performed. Further, the vertical scanning circuit 206 shifts the pixel row to be selected in the sub-scanning direction (vertical direction), so that a signal can be read from the entire pixel unit 205. The read signal is transmitted to the outside of the image sensor 221 via the output circuit 209.

  FIG. 3A is a conceptual diagram illustrating a configuration example of one pixel included in the pixel unit 205, and FIG. 3B is a circuit diagram illustrating a configuration example of the pixel 201. As shown in FIG. 3A, the pixel 201 includes one microlens 202 and two photodiodes of a first photodiode (PD) 203 and a second photodiode (PD) 204. The first PD 203 and the second PD 204 are photoelectric conversion units that receive light that has passed through the same microlens 202 and generate signal charges according to the amount of light received. As shown in FIG. 3B, the first PD 203 and the second PD 204 are controlled by the transfer pulse signals PTXA and PTXB from the vertical scanning circuit 206. Transfer switches 214 are connected to each other. The first transfer switch 213 and the second transfer switch 214 transfer the charges generated in the first PD 203 and the second PD 204 to the common floating diffusion region (FD) 215 when each is ON.

  The FD 215 functions as a charge-voltage converter that temporarily holds the charges transferred from the first PD 203 and the second PD 204 and converts the held charges into a voltage signal. The amplifying unit 216 is a source follower MOS transistor, amplifies a voltage signal based on the charge held in the FD 215, and outputs it as a pixel signal. The selection switch 218 is controlled by the control signal PSEL from the vertical scanning circuit 206 and outputs the pixel signal amplified by the amplification unit 216 to the vertical output line 220 when selected.

  The reset switch 217 is controlled by the reset pulse signal PRES from the vertical scanning circuit 206, and resets the potential of the FD 215 to the reference potential VDD. Further, by simultaneously turning on the reset switch 217, the first transfer switch 213, and the second transfer switch 214, the potentials of the first PD 203 and the second PD 204 can be reset to the reference potential VDD.

  In the pixel 201 having the above configuration, when only the recording / display signal (A + B signal) is read, first, both the first transfer switch 213 and the second transfer switch 214 are turned ON. Then, the charges generated in the first PD 203 and the second PD 204 are transferred to the FD 215 and read. By performing the above control with the control signal PSEL while the selection switch 218 is ON, a recording / display signal (A + B signal, addition signal) can be obtained. Hereinafter, this reading method is referred to as “addition reading” (second reading).

  On the other hand, when a pair of AF signals for phase difference detection AF is obtained, readout control is performed as follows. First, the charge generated in the first PD 203 or the second PD 204 is transferred to the FD 215 by turning on the first transfer switch 213 or the second transfer switch 214 by the transfer pulse signal PTXA or PTXB. Then, one of the pair of AF signals (A signal) is obtained by reading this while the selection switch 218 is ON by the control signal PSEL. Next, both the first transfer switch 213 and the second transfer switch 214 are turned on, so that the charges generated in the first PD 203 and the second PD 204 are transferred to the FD 215. Then, by reading this while the selection switch 218 is turned on by the control signal PSEL, a recording / display signal (A + B signal, addition signal) can be obtained. Then, the other AF signal (B signal) can be obtained by subtracting one of the pair of AF signals (A signal) read out first from the recording / display signal (A + B signal). A pair of AF signals (A signal, B signal) may be read out and added to obtain a recording / display signal (A + B signal, addition signal). Hereinafter, the above-described reading method is referred to as “divided reading” (first reading).

  In the present embodiment, the image sensor 221 having the above configuration can be controlled by addition reading or division reading in units of rows to read signals. Then, the AF signal processing unit 224 calculates the phase difference between the pair of AF signals obtained by the divided readout, so that focus detection by the phase difference detection method can be performed. Further, a normal image for one screen can be obtained by an addition signal obtained by addition reading and division reading.

  2 and 3 show the pixel configuration in which two photodiodes divided in the horizontal direction with respect to one microlens 202 are shown, the present invention is not limited to this. For example, even if it is divided in the vertical direction, three or more photoelectric conversion units may be arranged for one microlens. As described above, the imaging element may be any one in which pixels that can receive light beams that have passed through different pupil regions are two-dimensionally arranged.

Next, the operation of the camera body 20 in the first embodiment will be described with reference to FIGS. FIG. 4 is a flowchart showing the procedure of the photographing process of the camera body 20. First, in S101, the camera control unit 232 performs initialization processing such as camera settings. In next step S102, the camera control unit 232 determines whether the shooting mode of the camera body 20 is the moving image shooting mode or the still image shooting mode. If the shooting mode is the moving image shooting mode, the process proceeds to S103 to perform the moving image shooting process. move on. On the other hand, if it is the still image shooting mode in S102, the process proceeds to S104 to perform still image shooting processing, and the process proceeds to S105. Note that the present invention can be applied to both moving image and still image shooting modes, but in the first embodiment, control in the still image shooting process of S104 will be described later.

  In S105, the camera control unit 232 determines whether or not the shooting process has been stopped. If the shooting process has not been stopped, the camera control unit 232 advances the process to S106, and if stopped, ends the shooting process. Note that when the shooting process is stopped, the camera body 20 is turned off through the camera operation unit 234, the user setting process of the camera, the playback process for checking the captured image / movie, etc. Is performed. In S106, the camera control unit 232 determines whether or not the shooting mode has been changed. If the shooting mode has not been changed, the process returns to S102, and the camera control unit 232 continues to process the current shooting mode. On the other hand, if changed, the process returns to S101, the initialization process is performed, and the process of the changed shooting mode is performed.

  Next, the still image shooting process performed in S104 of FIG. 4 will be described with reference to FIG. In step S201, the camera control unit 232 performs focus state detection processing for detecting a focus state. The focus state detection process performed in S201 is for imaging plane phase difference AF in which AF is performed using a signal obtained from the image sensor 221 by the camera control unit 232, the AF signal processing unit 224, and the AF signal readout control unit 233. To obtain defocus information and reliability information. Details of the processing performed here will be described later with reference to FIGS.

  In step S <b> 202, the camera control unit 232 determines whether an AF instruction is given by the camera operation unit 234. In the present embodiment, the AF instruction represents, for example, a state where the shutter button is half-pressed or a case where an AFON button for performing AF is pressed. Of course, a configuration in which the AF instruction is given by other means may be used. If an AF instruction has been issued, the process proceeds to S203, and the camera control unit 232 performs a known AF process using a phase difference method using the defocus information and reliability information obtained in S201, and FIG. Return to the process.

  On the other hand, if the AF instruction has not been performed, the process proceeds to S204, and the camera control unit 232 determines whether the camera operation unit 234 has issued a shooting instruction. In the present embodiment, the shooting instruction represents a state where the shutter button is fully pressed. Of course, a configuration in which a shooting instruction is given by other means may be used. If no shooting instruction has been issued, the process directly returns to the process of FIG. On the other hand, if a shooting instruction has been issued, the process proceeds to S205, and the camera control unit 232 determines whether the in-focus state is present as a result of the in-focus state detection in S201. If it is not in the in-focus state, the process proceeds to S203, and the in-focus control is performed by starting or continuing the AF process. On the other hand, if it is in the in-focus state, the process proceeds to S206, and the camera control unit 232 performs a shooting process of reading by addition reading from the entire area of the pixel unit 205, and shooting on the recording medium 228 via the recording medium control unit 227. The image is saved and the process returns to the process of FIG.

  Next, the focus state detection process performed in S201 of FIG. 5 will be described with reference to FIG. First, in S301, the camera control unit 232 acquires shooting parameter information used for AF that the camera body 20 or the lens unit 10 has, and advances the process to S302. The imaging parameter information acquired here is information including the aperture information of the aperture 102 in the lens unit 10, the sensor gain applied to the image sensor 221 in the camera body 20, and the like. Acquire necessary information according to The camera control unit 232 provides the acquired shooting parameter information to the AF signal processing unit 224 and the AF signal readout control unit 233. Next, in S302, a focus detection area for detecting the focus state is designated in the imaging screen. For example, if the user can operate the camera operation unit 234 to set an arbitrary region or any of a plurality of predetermined focus detection regions, or the subject can be detected, the focus detection region can be designated. For example, an area where a face is detected may be designated as the focus detection area. Information on the designated focus detection area is sent from the camera control unit 232 to the AF signal processing unit 224 and the AF signal readout control unit 233.

  Next, in S303, the AF signal readout control unit 233 determines a range to be divided and read from the imaging screen based on the information provided from the camera control unit 232, and advances the process to S304. Here, with reference to FIG. 7, the divided read range setting process performed in S303 will be described.

  In S401, the AF signal readout control unit 233 obtains the center position of the designated focus detection area, and sets the position of the obtained center position in the sub-scanning direction as the center position of the divided readout range. This is performed in order to align the center position of the designated focus detection area in the sub-scanning direction and the center position of the sub-scanning direction range (divided reading range) in which the divided reading is performed to obtain a pair of AF signals.

  Next, in S402, the AF signal readout control unit 233 determines whether the sensor gain (gain value) applied to the image sensor 221 is equal to or less than the first threshold Th1 based on the imaging parameter information provided from the camera control unit 232. Judge whether. If it is less than or equal to the first threshold Th1, the process proceeds to S403, and if it is greater than the first threshold Th1, the process proceeds to S409.

  In S403, the AF signal readout control unit 233 determines whether the conversion coefficient to be applied to convert the image shift amount calculated in S307, which will be described later, into the defocus amount in S309 is equal to or less than the second threshold Th2. If it is equal to or smaller than the second threshold Th2, the process proceeds to S404. If it is greater than the second threshold Th2, the process proceeds to S409.

  In S404, the AF signal read control unit 233 determines whether or not an AF signal has been generated so far in the process performed in S305, which will be described later, and if not, the process proceeds to S408. If it has been generated, the process proceeds to S405. As described above, whether or not the determination from S405 to S407 is performed is divided depending on whether or not the processing after S305 in FIG. 6 has not been performed yet.

  In S405, the AF signal read control unit 233 determines whether the signal level of the AF signal generated last time is equal to or higher than the third threshold Th3. If it is greater than or equal to the third threshold Th3, the process proceeds to S406, and if it is smaller than the third threshold Th3, the process proceeds to S409.

  In S406, the AF signal readout control unit 233 determines whether the difference between the maximum value and the minimum value of the signal level of the AF signal generated last time is equal to or greater than the fourth threshold Th4. If it is greater than or equal to the fourth threshold Th4, the process proceeds to S407, and if it is less than the fourth threshold Th4, the process proceeds to S409.

  In S407, the AF signal read control unit 233 determines whether or not the reliability of the defocus amount calculated from the previously generated AF signal is equal to or greater than the fifth threshold Th5. If it is greater than or equal to the fifth threshold Th5, the process proceeds to S408, and if it is lower than the fifth threshold Th5, the process proceeds to S409. As the fifth threshold Th5 set here, for example, if the defocus amount or the defocus direction is reliable, the process proceeds to S408, and if the defocus direction is also unreliable, the process proceeds to S409. The threshold value is set such that the process proceeds.

As described above, if YES is determined in S402 and S403 and YES is determined in S404 or NO is determined in S404, but YES is determined in S405, S406, and S407, the process proceeds to S408. . In S408, the AF signal readout control unit 233 sets the number of divided readout lines to α (first range), and proceeds to S410. Further, as described above, when it is determined NO in any of S402, S403, S405, S406, and S407, in S409, the AF signal readout control unit 233 sets the number of divided readout lines to β (second Range) and the process proceeds to S410. In the present embodiment, the set values α and β of the number of divided readout lines have the following relationship.
α <β

  That is, if the conditions from S402 to S409 are such that the accuracy of the imaging plane phase difference AF is sufficient, α is a condition that makes it difficult to obtain the accuracy of the imaging plane phase difference AF. If you want to use β, use β. This is because the processing load can be reduced or reduced by unnecessarily increasing the number of divided readout lines rather than unnecessarily increasing the number of divided readout lines if the imaging surface phase difference AF is sufficiently accurate. This is because heat generation can be suppressed. Further, in the condition where the accuracy of the imaging plane phase difference AF is difficult to be obtained, although the processing load is increased, the number of divided readout lines is set to be larger in order to further improve the accuracy.

  Here, the relationship between the determination from S402 to S409 and the number of divided readout lines will be specifically described.

  Whether the sensor gain is equal to or smaller than the first threshold Th1 in S402 is determined for the following reason. That is, since the noise component increases as the sensor gain increases, the AF accuracy may decrease. Therefore, if the sensor gain is large and greater than the first threshold Th1, the number of divided readout lines is set to β in S409, and the readout signal for AF used for focus state detection is performed by performing divided readout in more rows. Acquire more and improve the S / N ratio. By doing so, an AF signal with as little noise as possible can be obtained.

  The reason why it is determined in S403 whether the conversion coefficient for converting the image shift amount into the defocus amount is equal to or smaller than the second threshold Th2 is as follows. That is, the larger the conversion coefficient, the greater the variation in accuracy of the defocus amount, making it difficult to calculate the correct defocus amount. Therefore, if the conversion coefficient is larger than the second threshold Th2, the number of divided readout lines is set to β in S409, and a large number of AF signals are obtained by performing divided readout in more rows, and S / The N ratio is improved and the calculation accuracy of the image shift amount is increased as much as possible.

  Whether the AF signal has been generated before in S404 is determined for the following reason. That is, since the AF signal has not yet been generated in the first divided readout range setting process, the determination cannot be performed using the AF signal and the result calculated based on the AF signal. Therefore, if no AF signal has been generated, the processing from S405 to S407 is not performed.

  Whether the signal level of the AF signal generated last time in S405 is equal to or higher than the third threshold Th3 is determined for the following reason. That is, it can be determined that the higher the signal level of the AF signal, the higher the possibility that the subject is bright. Conversely, if the signal level of the AF signal is low, it can be determined that the subject is likely to be dark, and if the subject is dark, there is a concern that the noise component is large. Therefore, when the signal level of the AF signal is smaller than the third threshold Th3, the number of divided readout lines is set to β, and a large number of AF signals are obtained by performing divided readout in more rows, and the S / N The ratio is improved so that an image signal with as little noise as possible can be obtained.

  The reason why it is determined whether or not the difference between the maximum value and the minimum value of the signal level of the AF signal generated last time in S406 is greater than or equal to the fourth threshold Th4 is as follows. That is, when the value is smaller than the fourth threshold Th4, the subject is expected to have low contrast. When the subject has low contrast, the calculation accuracy of the image shift amount is rough, and there is a concern that the accuracy may be reduced. Therefore, by setting the number of divided readout lines to β, divided readout is performed in more rows, and the amount of image shift is calculated using more AF signals, thereby improving the focus detection accuracy.

  The reason why it is determined whether or not the reliability calculated from the previously generated AF signal in S407 is equal to or greater than the fifth threshold Th5 is as follows. In other words, when the reliability is low, that is, as described above, even the defocus direction is not reliable, there is a possibility that the subject is not captured in the focus detection area. It is expected that the subject captured at least in the focus detection area is greatly blurred. Therefore, in order to focus on the subject quickly, when the reliability is lower than the fifth threshold Th5, the focus detection is performed by calculating the defocus amount in a wider range by setting the number of divided readout lines to β. Control to make it easier to catch the subject in the area.

  In the first embodiment described above, two types of α and β are set as the number of divided readout lines. However, three or more types of values may be set. Further, although α and β are described as being fixed values, for example, they may be changed according to the above-described conditions, or may be changed according to the size of the designated focus detection area. In addition, although conditions for properly using the number of divided readout lines are provided in S402 to S407, the conditions are not limited to the above-described conditions as long as the conditions are in accordance with the spirit of the invention.

  After setting the number of divided read lines, in S410, the AF signal read control unit 233 sets the divided read range from the center position of the divided read range determined in S401 and the number of divided read lines set in S408 or S409. To finish the process.

  FIG. 8 is a diagram showing the relationship between the designated focus detection area 800 and the set divided readout range 801. FIG. 8A shows the number of divided readout lines α, and FIG. The case where the number of divided readout lines is β is shown. A region between the dotted lines in FIG. 8 is a divided readout range 801. 8A shows a case where the width of the focus detection region 800 in the sub-scanning direction and the number of divided readout lines α are the same, but may not be the same if α <β.

  An area 802 above the divided reading range 801 is read by addition reading, the divided reading range 801 is read by divided reading, and an area 803 below the divided reading range 801 is read by addition reading. By reading in this way, the time and load required for reading can be reduced and the heat generated by the reading can be suppressed as compared with the case where the entire area is read by divided reading.

  When the divided readout range 801 is set as shown in FIG. 8, the signals obtained by the readout are the A + B signal for one screen and the A signal and B of the divided readout range 801 as shown on the right side of the figure. Signal. When the divided readout range 801 is set as shown in FIG. 8B, the A signal and the B signal can be obtained in a wider area, although it takes time to read out compared to the case of FIG. 8A.

  When the number of divided read lines is an odd number (for example, 7 lines), the divided read range 801 is set as shown in FIG. 9A, and when the number is an even number (for example, 8 lines), the line is changed to FIG. 9B. As shown, a divided readout range 801 is set. Reference numeral 901 denotes the center position of the divided reading range 801. When the number of divided read lines is an even number, the center position 901 of the divided read range 801 may be the position of the fifth line instead of the position of the fourth line as shown in FIG. 9B.

  When the setting of the divided readout range is completed in S303, the process returns to the processing in FIG. 6, and in S304, the AF signal processing unit 224 resets the focus detection area based on the divided readout range set by the readout control unit 233. . Here, the range in the sub-scanning direction of the focus detection area set in S302 is changed to be the same as the number of divided readout lines α or β set in S408 or S409 of FIG. To do. FIG. 10 is a schematic diagram illustrating an example of the focus detection area before and after the change. FIG. 10A is a diagram illustrating a case where the number of rows in the focus detection area 800 specified in S302 is larger than the number of divided readout lines α set in S408. In this case, since the AF signal can be obtained only from the rows corresponding to the divided readout line number α in the designated focus detection area 800, the number of lines is reduced to α and changed to the focus detection area 810. Conversely, when the number of rows in the focus detection area 800 designated in S302 is smaller than the divided readout line number β, the number of rows is increased to β and changed to the focus detection region 810 in order to increase focus detection accuracy. As in the example shown in FIG. 8A, when the number of rows in the focus detection area 800 and the number of divided readout lines α are the same, there is no need to change.

  Next, in S305, the AF signal processing unit 224 extracts an AF signal included in the focus detection area set in S304 from the AF signals obtained in the divided readout range. Next, in S306, the AF signal processing unit 224 calculates the correlation amount using the extracted AF signal. Subsequently, in S307, the AF signal processing unit 224 calculates an image shift amount from the correlation amount. In S308, the AF signal processing unit 224 calculates the reliability indicating how reliable the image shift amount is. In step S309, the AF signal processing unit 224 multiplies the image shift amount calculated in step S307 by a conversion coefficient to convert it into a defocus amount, and ends the focus state detection process. Note that the processing from S306 to S309 is performed for each row of the focus detection area set in S304, and the finally obtained values may be averaged, for example, or the AF signal in the focus detection area may be vertically It is also possible to carry out using the added value after adding to.

  As described above, the imaging apparatus according to the present embodiment changes the number of divided readout lines for performing the imaging plane phase difference AF depending on whether or not the imaging plane phase difference AF is difficult to obtain. When the imaging conditions are such that the imaging surface phase difference AF is sufficiently accurate, the number of divided readout lines is reduced to reduce the processing load while maintaining the AF accuracy and reduce the heat generated by the processing. Can be suppressed. On the other hand, when the imaging surface phase difference AF is difficult to obtain, the AF accuracy can be improved by increasing the number of divided readout lines. Further, by aligning the center position of the divided readout range with the center position of the designated focus detection area in the sub-scanning direction, the number of divided readout lines can be minimized.

<Second Embodiment>
Next, a second embodiment of the present invention will be described. The second embodiment has a configuration capable of further subject detection in addition to the first embodiment. In the state where the subject detection is detected, control is performed so as to set a large number of divided readout lines. Since the detected subject has a movement, the subject can be easily captured by setting a large number of divided readout lines.

  FIG. 11 is a block diagram illustrating a schematic configuration of an imaging system according to the second embodiment of the present invention. The camera body 30 shown in FIG. 11 is different from that shown in FIG. 1 in that it further includes a subject detection unit 236 and a follow-up signal processing unit 237. Other than that, the configuration is the same as in FIG. 1, and thus the same reference numerals are given and description thereof is omitted.

  The follow-up signal processing unit 237 receives the tracking image signal from the SDRAM 229 in accordance with a command from the camera control unit 232, and generates a feature amount including a color information histogram and a luminance information histogram from the tracking image signal.

  On the other hand, the image pickup signal and AF signal read out from the image pickup element 221 are input to the CDS / AGC / AD circuit 222, and correlated double sampling for removing reset noise, gain adjustment, and signal digitization are performed. Do. Then, the CDS / AGC / AD circuit 222 outputs the processed imaging signal to the image signal processing unit 223 and the subject detection unit 236, and outputs the AF signal to the AF signal processing unit 224.

  The subject detection unit 236 performs subject search processing that follows the feature amount generated by the tracking signal processing unit 237 with respect to the addition signal output from the CDS / AGC / AD circuit 222 and follows the shooting screen. Whether there is a subject corresponding to the subject to be identified. If there is a subject to follow, the subject region is determined based on the position coordinates where the subject is present, and the result is transmitted to the camera control unit 232. The camera control unit 232 sets the subject area as a focus detection area or as an area for performing AE. Also, the position coordinates where the subject exists are held in the SDRAM 229, and can be used for detecting the subject area from the next time on, thereby limiting the area where the subject search process is performed. When the subject area is specified, whenever the position coordinates of the subject area are updated, the position coordinates held in the SDRAM 229 are also updated. The subject detection unit 236 detects a subject that exists mainly in the face or an area designated by the user via the camera operation unit 234.

  In the imaging system having the above configuration, the method for setting the divided readout range performed in S303 of FIG. 6 is different from the processing described with reference to FIG. 7 in the first embodiment. Other than that, the operation is the same as that described in the first embodiment, and this point will be described below with reference to FIG.

  First, in S501, the AF signal readout control unit 233 obtains the center position of the designated focus detection area, and sets the position of the obtained center position in the sub-scanning direction as the center position of the divided readout range. Note that the designated focus detection area in the second embodiment is an area designated by the user via the camera operation unit 234 or a subject area detected by the subject detection unit 236 as described above.

  In S402 to S407, the same processing as in FIG. 7 described above is performed. Thereafter, in S <b> 502, the AF signal readout control unit 233 acquires information from the camera control unit 232 as to whether or not the subject detection unit 236 is detecting a subject. If the subject is not detected, the process proceeds to S408, and if the subject is detected, the process proceeds to S409. When a subject is detected, the focus detection area may be updated according to the movement of the subject. At this time, if the number of divided readout lines is small, that is, if the range for performing imaging plane phase difference AF is narrow, there is a high possibility that an AF signal corresponding to the detected subject will be missed. Therefore, during the detection of the subject, control is performed so that the subject is easily focused by setting a larger number of divided readout lines.

  As described above, according to the second embodiment, when the subject is being detected, the number of divided readout lines is set to be large, and the range in which the imaging plane phase difference AF can be performed is set wide. . Accordingly, it is possible to prevent the AF signal corresponding to the detected subject from being missed, and to focus on the subject even when the subject is moving.

  The second embodiment can also be used at the time of reading in moving image shooting. In that case, for example, for each frame of the moving image, subject detection and readout control of divided readout and addition readout may be performed, or may be performed every plural frames.

<Third Embodiment>
Next, a third embodiment of the present invention will be described. In the first embodiment and the second embodiment, one focus detection area is designated as the focus detection area in the imaging screen, and the divided readout range is set around the center position. In contrast, in the third embodiment, a method for setting the divided readout range when two or more focus detection areas are designated as the focus detection area in the imaging screen will be described.

  As the imaging system in the third embodiment, the one used in the first embodiment or the second embodiment can be used, and the description thereof is omitted. The third embodiment differs from the processing described with reference to FIG. 7 in the first embodiment in the method of setting the divided readout range performed in S303 of FIG. Other than that, the operation is the same as that described in the first embodiment, and this point will be described below with reference to FIG. However, in the third embodiment, it is assumed that a plurality of focus detection areas are designated as shown in FIG. 14 in S302 of FIG.

  In S701 of FIG. 13, the AF signal readout control unit 233 has the smallest (uppermost in the imaging screen) Y coordinate and the largest among the Y coordinates of the center positions of the plurality of focus detection areas set in S302. The Y coordinate (lowermost in the imaging screen) is extracted. Here, the smallest Y coordinate is Y1, and the largest Y coordinate is Y2. In step S <b> 702, the AF signal readout control unit 233 sets the range from Y1−coordinate with the predetermined number of lines γ to Y2 + coordinate with the predetermined number of lines γ as the divided readout range, and ends the process. Here, as a value to be set to γ, for example, a value that has a certain range with respect to the focus detection region position such as α / 2 and β / 2 is set. At this time, γ may be determined as described in S402 to S409 in FIG. 7, or may be set so as to include the entire focus detection region.

  FIG. 14 shows an example when a plurality of focus detection areas are set. For example, in the multipoint focus detection mode, the divided readout range is set as shown in FIG. 14 so that the defocus amount can be detected for all of the plurality of set focus detection areas.

  As described above, according to the third embodiment, when a plurality of focus detection areas are set, the divided readout range is set so that the defocus amount can be detected in all of the set focus detection areas. . As a result, it is possible to slightly reduce the reading load by performing addition reading for a portion where no focus detection area is set while detecting the defocus amounts of all the set focus detection areas.

  In each of the above-described embodiments, the case where the present invention is applied to a digital camera has been described as an example. However, this is not limited to this example. That is, the present invention may be applied to any device with an image sensor. That is, the present invention can be applied to any device capable of capturing an image, such as a mobile phone terminal, a portable image viewer, a television set equipped with a camera, a digital photo frame, a music player, a game machine, and an electronic book reader.

  DESCRIPTION OF SYMBOLS 10: Lens unit, 103: Focus lens, 105: Focus lens drive part, 106: Lens control part, 107: Lens operation part, 20, 30: Camera main body, 201: Pixel, 202: Micro lens, 203: 1st Photodiode (PD), 204: Second photodiode (PD), 205: Pixel unit, 206: Vertical scanning circuit, 207: Reading circuit, 208: Horizontal scanning circuit, 221: Image sensor, 223: Image signal processing unit 224: AF signal processing unit, 232: Camera control unit, 233: AF signal readout control unit, 235: Timing generator, 236: Subject detection unit, 237: Tracking signal processing unit

Claims (16)

An image sensor that includes a plurality of photoelectric conversion units for each of a plurality of microlenses arranged in two dimensions and outputs an image signal corresponding to the amount of incident light;
A designation means for designating a focus detection area for performing focus detection;
Based on the focus detection area designated by the designation means and the imaging conditions, a pair of signals having parallax and signals of the plurality of photoelectric conversion units from the plurality of photoelectric conversion units corresponding to the respective microlenses. Determining means for determining a readout range in the sub-scanning direction in the image sensor, performing first readout capable of obtaining an addition signal obtained by adding
A signal is read out by the first reading from the photoelectric conversion unit in the reading range determined by the determining unit, and an addition signal is obtained without obtaining a pair of signals from the photoelectric conversion unit excluding the reading range. Control means for controlling to read a signal by reading;
An imaging device comprising:   The size in the sub-scanning direction of the focus detection area designated by the designation means is changed to be the same as the readout range determined by the determination means, and obtained from the changed focus detection area The imaging apparatus according to claim 1, further comprising a focus detection unit that performs phase difference type focus detection based on the pair of signals.   The determination unit sets the reading range so that a center position of the designated focus detection region in the sub-scanning direction matches a center position of the reading range in the sub-scanning direction. 2. The imaging device according to 2.   The determination unit sets a first range as the readout range when the shooting condition is a shooting condition in which the accuracy of focus detection by the focus detection unit is likely to be higher, and the accuracy of the focus detection is A second range that is wider than the first range is set as the readout range when the imaging condition is such that the focus detection accuracy is likely to be lower than the imaging condition that tends to be higher. The imaging apparatus according to claim 2 or 3.   The determination means sets the second range when a gain value used in the image sensor is larger than a first threshold as an imaging condition in which the accuracy of focus detection tends to be lower. Item 5. The imaging device according to Item 4. The focus detection unit obtains an image shift amount by correlation calculation based on the pair of signals, converts the obtained image shift amount into a defocus amount using a conversion coefficient,
6. The determination unit according to claim 4, wherein the determination unit sets the second range when the conversion coefficient is larger than a second threshold as an imaging condition in which the accuracy of focus detection is likely to be lower. The imaging device described.   The deciding means, as an imaging condition in which the accuracy of focus detection is likely to be lower, is obtained when the signal level of a pair of signals obtained by the first reading performed last time is smaller than a third threshold value. The range of 2 is set, The imaging device of any one of Claims 4 thru | or 6 characterized by the above-mentioned.   The determination means has a difference between a maximum value and a minimum value among signal levels of a pair of signals obtained by the first reading performed last time as an imaging condition in which the accuracy of focus detection is likely to be lower. The imaging apparatus according to any one of claims 4 to 7, wherein the second range is set when it is smaller than a fourth threshold value. The focus detection means calculates reliability information of the focus detection;
The determination unit is configured to detect the second range when the reliability indicated by the reliability information obtained in the previous focus detection is lower than a fifth threshold as an imaging condition in which the accuracy of the focus detection is likely to be lower. The imaging apparatus according to claim 4, wherein the imaging device is set. In the image represented by the addition signal, the image processing apparatus further includes detection means for detecting a subject.
8. The imaging according to claim 2, wherein the determination unit sets the second range as the reading range when an object is detected by the detection unit. 9. apparatus. Based on the pair of signals corresponding to the focus detection area, further comprising a focus detection means for performing phase difference type focus detection,
When the plurality of focus detection areas are designated by the designation means, the determination means is configured to obtain the pair of signals corresponding to each of the plurality of focus detection areas designated by the designation means. The imaging apparatus according to claim 1, wherein the reading range in which the first reading is performed is determined. A control method of an imaging apparatus having an imaging element that includes a plurality of photoelectric conversion units for each of a plurality of microlenses arranged in two dimensions and outputs an image signal corresponding to an incident light amount,
A designation step for designating a focus detection area for performing focus detection;
Based on the focus detection area designated in the designation step and the imaging condition, a determining unit receives a pair of signals having parallax and the plurality of photoelectric signals from the plurality of photoelectric conversion units corresponding to the microlenses. A determination step of determining a reading range in the sub-scanning direction of the image sensor, performing a first reading capable of obtaining an addition signal obtained by adding the signals of the conversion unit;
The control means reads a signal by the first reading from the photoelectric conversion unit in the reading range determined in the determination step, and outputs an addition signal without obtaining a pair of signals from the photoelectric conversion unit excluding the reading range. A control step of controlling the signal to be read by the second reading obtained;
A control method characterized by comprising:   The focus detection unit changes the size of the focus detection area designated in the designation step so as to be the same as the readout range determined in the determination step, and the focus detection after the change The control method according to claim 12, further comprising a focus detection step of performing phase difference type focus detection based on the pair of signals obtained from a region.   In the determination step, when the photographing condition is a photographing condition in which the accuracy of focus detection in the focus detection step is likely to be higher, a first range is set as the reading range, and the accuracy of the focus detection is A second range that is wider than the first range is set as the readout range when the imaging condition is such that the focus detection accuracy is likely to be lower than the imaging condition that tends to be higher. The control method according to claim 13. The detection means further includes a detection step of detecting a subject from the image represented by the addition signal,
The control method according to claim 13 or 14, wherein, in the determination step, the second range is set as the readout range when a subject is detected in the detection step. The focus detection unit further includes a focus detection step of performing phase difference type focus detection based on the pair of signals corresponding to the focus detection region,
In the designating step, when a plurality of the focus detection areas are designated, in the determination process, the pair of signals corresponding to the plurality of focus detection areas designated in the designation process are obtained. The control method according to claim 12, wherein the reading range in which the first reading is performed is determined.

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