Autofocus control device, imaging device, autofocus control method, and program

Abstract

To provide an autofocus control device that enables more accurate focus detection at a higher speed than conventional devices upon performing an autofocus using a contrast detection method.SOLUTION: An autofocus control device, which controls a focus drive unit driving a focus lens group serving as at least a part of an imaging optical system on the basis of contrast information obtained from an image-pickup element in which a plurality of photoelectric conversion units including a light reception unit converting light incident from the imaging optical system into a voltage pulse, and a count unit counting the number of pulses of the voltage pulse is arranged in a two-dimensional plane, has a control unit that causes the focus drive unit to reciprocally drive the focus lens group while continuing an exposure of the image-pickup element, and controls the focus drive unit on the basis of the contrast information on each of a plurality of images to be generated from the number of pulses of the voltage pulse generating within an exposure period of the exposure.SELECTED DRAWING: Figure 2

Description

Technical Field

[0005]

[0001] The present invention relates to an autofocus control device.

Background Art

[0002] When performing autofocus using contrast information, the focus lens group is reciprocally driven in a minute range to determine the direction in which the focus lens group is moved. In the case of this contrast detection method, unlike the active method of irradiating a subject with auxiliary light, there is an advantage that focus can be achieved without being noticed by a subject such as an animal. However, since the contrast of an image is used, the focus speed is slower than the method using triangulation. Further, in a conventional camera equipped with a CMOS or a CCD, it is difficult to obtain a contrast difference in a dark place, and the focusing accuracy is not high.

[0003] In recent years, a light detection element capable of detecting weak light at a single photon level has attracted attention. As an example thereof, an avalanche photodiode (hereinafter, APD) can be mentioned.

[0004] Patent Document 1 discloses an autofocus control device that aims to increase the focus control speed by changing the frame rate of a photoelectric conversion means according to the subject luminance.

Prior Art Documents

Patent Documents

[0007] The present invention provides an autofocus control device that enables faster and more accurate focus detection than conventional methods when performing autofocus using a contrast detection method. [Means for solving the problem]

[0008] An autofocus control device as one aspect of the present invention is an autofocus control device that controls a focus drive unit which drives a focus lens group, which is at least a part of the imaging optical system, based on contrast information obtained from an image sensor arranged in a two-dimensional plane, wherein the focus drive unit drives the focus lens group back and forth while the exposure of the image sensor continues, and controls the focus drive unit based on the contrast information of each of a plurality of images generated from the number of pulses of the voltage pulses that occur during the exposure period.

[0009] Other objects and features of the present invention are described in the following embodiments. [Effects of the Invention]

[0010] According to the present invention, an autofocus control device is provided that enables faster and more accurate focus detection than conventional methods when performing autofocus using a contrast detection method. [Brief explanation of the drawing]

[0011] [Figure 1] This block diagram shows the configuration of an imaging device using a conventional autofocus control device. [Figure 2] This block diagram shows the configuration of an imaging device using the autofocus control device of each embodiment. [Figure 3] (A) A circuit diagram showing the configuration of the imaging pixels in each embodiment, and (B) A diagram explaining the operating principle of the image sensor. [Figure 4] This is a flowchart illustrating the operation of a conventional imaging device. [Figure 5] This is a flowchart showing the operation of the imaging device according to each embodiment. [Figure 6] This is a timing chart showing the operation of conventional contrast AF. [Figure 7] This is a timing chart showing the operation of contrast AF in Embodiment 1. [Figure 8] This is a timing chart showing the operation of contrast AF in Embodiment 2. [Modes for carrying out the invention]

[0012] The following describes in detail an imaging apparatus using an autofocus device according to an embodiment of the present invention, with reference to the drawings. In each figure, the same reference numerals are used for the same components, and redundant explanations are omitted.

[0013] Figure 1 is a block diagram showing the configuration of a conventional imaging device 1. The imaging device 1 includes an imaging optical system 100, an image sensor 101, an A / D conversion unit 102, an image processing unit 103, a memory 104, a focus drive unit 106, a control unit 107, a contrast determination unit 108, a recording medium 109, an operation unit 110, and a display unit 111. The image processing unit 103, memory 104, control unit 107, and contrast determination unit 108 constitute an autofocus control device 10.

[0014] The focus drive unit 106 adjusts the focus of the imaging optical system 100 by driving the focus lens group, which is at least a part of the imaging optical system 100, in the optical axis direction. The image sensor 101 acquires an optical image of the subject formed by the imaging optical system 100. Conventional image sensors 101 are, for example, CMOS sensors or CCD sensors. The A / D conversion unit 102 converts the optical image acquired by the image sensor 101 into digital data. The converted digital data is processed by the image processing unit 103 and stored in the memory 104. The contrast determination unit 108 uses the digital data processed by the image processing unit 103 and stored in the memory 104 to determine the driving direction of the focus lens group. Based on the result of the contrast determination unit 108, the control unit 107 controls the focus drive unit 106 to move the focus lens group.

[0015] In conventional systems, multiple images are acquired for autofocus determination, and the contrast determination unit 108 performs contrast determination. However, the image for focus determination is acquired by reading analog data from the image sensor 101, and then the A / D conversion unit 102 converts the analog data into digital data. At this time, the image sensor 101 temporarily stops exposure. Therefore, in order to acquire the next image for focus determination, the image sensor 101 needs to start exposure again. Thus, in order to determine the contrast by comparing the contrast values ​​(contrast information) and drive the focus lens group, time is required for A / D conversion of multiple data points and re-exposure.

[0016] The control unit 107 comprehensively controls the operations of the imaging device 1. The control unit 107 includes a CPU and executes a program for controlling each part of the imaging device 1. Also, the control unit 107 controls the focus drive unit 106 using the result of the correlation operation output from the image processing unit 103 to adjust the focus of the imaging optical system 100. The operation unit 110 is an operation member for the shutter operation and exposure control operation of the imaging device 1. The display unit 111 displays the captured still images and moving images. Also, the display unit 111 displays a menu screen and the like. The recording medium 109 is a detachable recording medium for recording still image data and moving image data.

[0017] FIG. 2 is a block diagram showing the configuration of the imaging device 2 according to each embodiment. The imaging device 2 includes an imaging optical system 200, an imaging element 201, a photon counting unit 202, and a storage unit 203. Further, the imaging device 2 includes an image generation unit 204, an imaging element control unit 205, a focus drive unit 206, a control unit 207, a contrast determination unit 208, a recording medium 209, an operation unit 210, and a display unit 211. In each embodiment, the photon counting unit 202, the storage unit 203, the image generation unit 204, the control unit 207, and the contrast determination unit 208 constitute the autofocus control device 20.

[0018] The focus drive unit 206 adjusts the focus of the imaging optical system 200 by driving at least a part of the imaging optical system 200, that is, the focus lens group, in the optical axis direction. The storage unit 203 and the photon counting unit 202 may be provided inside the imaging element 201.

[0019] The imaging device 2 of each embodiment is an imaging device in which a lens device including the imaging optical system 200 and a camera body are integrally configured, but each embodiment is not limited to this. The imaging device 2 may be configured to be able to detachably attach a lens device (interchangeable lens). At this time, the focus drive unit 206 may be provided on the lens device side.

[0020] The image sensor 201 acquires an optical image of the subject formed by the imaging optical system 200. The photon counting unit 202 counts the voltage pulse output from each pixel of the image sensor 201 each time a photon is incident on that pixel (hereinafter referred to as photon counting). The number of counted photons, along with the time when the photons were counted, is recorded in the storage unit 203. The image generation unit 204 generates an image using the voltage pulses output from the image sensor 201. The image sensor 202 is controlled by the image sensor control unit 205. In each embodiment, the image sensor 202 is a so-called photon counting type image sensor equipped with pixels that utilize the avalanche effect (multiplication). For example, it is a SPAD (Single Photon Avalanche Diode) with an avalanche photodiode in which each pixel is driven in Geiger mode. The image sensor 201 also includes a pixel array in which multiple pixels are arranged in the matrix direction (a two-dimensional plane in the row and column directions), and outputs image data from the pixels by sequentially scanning each row.

[0021] The control unit 207 comprehensively controls the operation of the imaging device 2. The control unit 207 includes a CPU and executes programs to control each part of the imaging device 2. The contrast determination unit 208 calculates the contrast value (contrast information) of each image based on the image output from the image generation unit 204. Based on the result of the contrast value of each image, the control unit 207 controls the focus drive unit 206 to adjust the focus of the imaging optical system 200. The recording medium 209 is a removable recording medium for recording still image data and video data. The operation unit 210 is an operating member for the shutter operation and exposure control operation of the imaging device 2. The display unit 211 displays captured still images and video images. The display unit 211 also displays menu screens, etc.

[0022] Next, the configuration of the image sensor 201 will be explained in detail using Figure 3(A). Figure 3(A) is a circuit diagram showing the configuration of the imaging pixels of the image sensor 201. The imaging pixel circuit (photoelectric conversion unit) 300 of each pixel of the image sensor 201 consists of an avalanche photodiode (hereinafter referred to as APD) 301, a quench resistor 302, a waveform shaping circuit 303, and a counter 304. The APD 301 can amplify the signal charge excited by a photon by several times to about a million times by utilizing the avalanche multiplication phenomenon generated by a strong electric field induced at the pn junction of the semiconductor. By utilizing the high gain of this avalanche multiplication phenomenon, the APD 301 can greatly amplify weak light signals, improve the signal-to-noise ratio with respect to readout noise generated in the readout circuit, and achieve single-photon level brightness resolution.

[0023] APD301 is connected to the reverse bias voltage VAPD via a quench resistor 302, and when a photon is incident on it, it generates charge through avalanche multiplication. The generated charge is discharged through the quench resistor 302. In other words, the generation of charge through avalanche multiplication and the discharge of charge through the quench resistor 302 are repeated depending on the number of photons incident on APD301. If we look at the cathode voltage of APD301 as a reference, when no photons are incident it is approximately the same voltage value as the reverse bias voltage VAPD, and this voltage decreases as the charge generated by the incidence of photons on APD301 occurs.

[0024] The waveform shaping circuit 303 generates a voltage pulse by amplifying and detecting the edge of the voltage change on the cathode side of the APD301 caused by the generation and discharge of charge in response to the incidence of photons. In each embodiment, the APD301 corresponds to a light receiving unit that converts light (light beam) incident from the exit pupil of the imaging optical system 200 into a voltage pulse based on the avalanche effect.

[0025] The counter 304, acting as a counter unit, counts the number of voltage pulses (pulse count) output by the waveform shaping circuit 303 for a predetermined period of time and outputs the count result as a digital value to the photon count unit 202 outside the pixel. In each embodiment, the counter 304 corresponds to a count unit that counts the number of voltage pulses generated within the exposure time.

[0026] The digital value resulting from the count is stored in an externally provided storage unit 203 via the photon count unit 202. By acquiring the count from multiple imaging pixel circuits 300 in a predetermined area on the pixel array, it is possible to generate an image for autofocus determination, an image for one frame, or the final image. In each embodiment, A / D conversion is not required when acquiring the image for autofocus determination. When acquiring multiple images for focus determination, the photon count information (count information), which includes the number of photons (number of pulses) obtained from the image sensor 201 and the time information associated with that count, is stored in the storage unit 203. By adding or subtracting the photon count at any timing while exposure continues, it is possible to acquire an image for autofocus determination at any timing during the exposure period. For example, by taking the difference between the count at time t1 and the count at time t2 (>t1), an image for autofocus determination at the time corresponding to time t2 can be acquired. The image used for autofocus determination at time t3 (>t2) may be obtained by the difference between the count at time t2 and the count at time t3. Alternatively, the image used for autofocus determination at time t3 may be obtained by adding or subtracting the count at time t2 to the difference between the count at time t1 and the count at time t3. Therefore, compared to conventional examples, the time required for A / D conversion and the time required to reacquire the image for autofocus determination are eliminated, and each embodiment can achieve faster autofocus. Furthermore, by using SPAD, high-precision autofocus can be achieved even in dark places without irradiating with active light.

[0027] Figure 3(B) is a diagram illustrating the operating principle of the image sensor 201 according to this embodiment. In Figure 3(B), the horizontal axis represents time, and it shows the relationship between the pulse waveform of the output voltage due to avalanche multiplication output from the APD301 when a photon is incident, and the threshold Vth for determining the incidence of the photon. Figure 3(B) shows the case where a potential is supplied to the APD301 that allows a reverse bias voltage exceeding the breakdown voltage to be applied. For each of the photons A (time tA) and photons B (time tB) incident on the APD301, avalanche multiplication occurs to such an extent that a pulse waveform that changes beyond the counter threshold Vth is output, and each pulse is time-resolved. Therefore, it becomes possible to count the incident photons over time.

[0028] Figure 4 shows a flowchart illustrating the operation of a conventional imaging device 1 from image acquisition to contrast determination and driving of the focus lens group. First, in step S401, the control unit 107 starts exposure of the image sensor 102 to acquire an image for autofocus determination. Then, in step S402, the control unit 107 temporarily ends the exposure of the image sensor 102 and slightly drives the focus lens group to acquire the next image. In step S403, the control unit 107 causes the A / D conversion unit 103 to read analog data from the image sensor 102. In step S404, the control unit 107 causes the A / D conversion unit 103 to convert the analog data into digital data. In step S405, the control unit 107 causes the image processing unit 103 to generate an image. In step S406, the control unit 107 saves the generated image to the memory 104. In step S407, the control unit 107 causes the contrast determination unit 108 to calculate the contrast value from the image stored in the memory 104. The operations from step S401 to step S407 are performed multiple times, and in step S408, the control unit 107 causes the contrast determination unit 108 to compare contrast values ​​from multiple images. In step S409, the control unit 107 controls the focus drive unit 106 to drive the focus lens group in the direction of increasing the contrast value.

[0029] Figure 6 shows the timing chart of a conventional imaging device 1. Exposure is started to acquire an image for autofocus determination. After that, exposure ends, analog data is read from the image sensor, and an image for autofocus determination is generated by A / D conversion, and the contrast value of this image is calculated. Once exposure ends, the focus lens group is driven slightly, and when the initial analog data is read out, exposure starts again to acquire the next image for autofocus determination. This operation is repeated multiple times to calculate the contrast values ​​of multiple images. By comparing the contrast values, the focus lens group is driven in the direction of the higher contrast value. For live view display on the screen and for capturing unit frames of video or still images, exposure is performed for a predetermined exposure time after the focus lens group has moved, and a final in-focus image is output.

[0030] Figure 5 is a flowchart illustrating the determination of the contrast value and autofocus operation during the exposure time of a unit frame of the imaging device 2 according to this embodiment. First, in step S501, the control unit 207 starts the exposure of the image sensor 201. Then, in step S502, the control unit 207 causes the photon count unit 202 to count the number of photons incident on each pixel and records the counted number of photons together with the time in the storage unit 203. In step S503, the control unit 207 causes the image generation unit 204 to generate an image for autofocus determination from the photon count information stored in the storage unit 203, which includes the number of photons and the time at which the count was acquired. Here, the image generation unit 204 can generate an image for autofocus determination at any timing during the exposure period by appropriately adding or subtracting the photon count information at any timing. In step S504, the control unit 207 causes the contrast determination unit 208 to calculate the contrast value from the generated image for autofocus determination. In step S505, the control unit 207 controls the focus drive unit 206 to drive the focus lens group toward a higher contrast value. In step S506, the control unit 207 determines whether the time is within the exposure time of a unit frame, and if it is, repeats the process from step S501 to step S505. In step S507, the control unit 207 terminates the exposure of the image sensor 201. (Embodiment 1) Figure 7 is a timing chart for video recording using the imaging device 2 according to Embodiment 1. Embodiment 1 assumes video recording that keeps the camera in focus on a predetermined subject while constantly driving the focus lens group back and forth in the optical axis direction. First, exposure is started to acquire an image of one frame of the video. Simultaneously, photon counting is started to count the number of photons, and the number of photons is recorded in the storage unit 203. While driving the focus lens group back and forth (reciprocating drive), an image for autofocus determination is created at an arbitrary timing based on the number of photons, and the contrast value of the image is calculated. The focus lens group is driven in the direction of a higher contrast value. Exposure continues throughout the operation of one frame. After the operation of one frame is completed, exposure is temporarily stopped, the photon counter is reset, and exposure is started again to acquire the image of the next frame. As shown in Figure 7, Embodiment 1 can continuously acquire determination images for autofocus. This makes it possible to constantly track the subject and perform high-precision video recording. (Embodiment 2) Figure 8 is a timing chart for still image capture using the imaging device 2 according to Embodiment 2. Embodiment 2 assumes that autofocus control is started when the shutter button of the imaging device 2 is half-pressed by the user (S1), and then the shutter button is further pressed to a fully pressed state (S2) to acquire a still image. First, exposure starts simultaneously with the half-pressing of the shutter button of the imaging device 2, and photon counting, which counts the number of photons, is started and the number of photons is recorded in the storage unit 203. While the focus lens group is driven back and forth in the optical axis direction (reciprocating drive), an image for autofocus determination is created at an arbitrary timing based on the number of photons, and the contrast value of the image is calculated. The focus lens group is driven in the direction of the higher contrast value, and finally the focus lens group is driven to the position where the contrast value is maximum. Then, when the shutter button is fully pressed (S2), exposure is performed for a predetermined exposure time based on the number of photons stored in the storage unit 203, and a still image, which is a final in-focus image, is generated. For still image generation, the number of voltage pulses (photon count) generated during the still image exposure period, excluding the exposure period used to generate the image for autofocus determination, is used. Alternatively, still images may be generated by adding or subtracting images created based on the photon count acquired during the still image shooting exposure period. Exposure continues throughout this series of operations.

[0031] In each embodiment, it is preferable that the following condition (1) is satisfied.

[0032] 0.0 <m / fT<1.0 ···(1) Here, m is the average number of incident photons per pixel of the image sensor 201. fT is the clock speed of the image sensor 201. Condition (1) defines the average number of incident photons m per pixel for the clock speed fT.

[0033] Here, we will explain the relationship between the count number n per pixel and the average number of incident photons m per pixel. The count number n per pixel is defined by the following equation, using the average number of incident photons m and the clock speed fT.

[0034] n = fT × (1 - Exp(-m / fT)) Here, the average number of incident photons m per pixel is defined by the following formula.

[0035] m = S × Lf × t Lf = (R × T / 4F^2) × Le Here, S is the sensor sensitivity, Lf is the sensor surface illuminance, t is the exposure time, R is the reflectance of the subject, T is the lens transmittance, and F is the lens's Fno. From condition (1), the smaller the value of the average number of incident photons per pixel m relative to the number of clocks fT, the more likely linearity is to be satisfied.

[0036] If the value exceeds the upper limit of condition (1), the relationship between the number of incident photons m and the counted value becomes nonlinear, which is undesirable. If it falls below the lower limit of condition (1), the measurement error increases due to the influence of noise components, which is also undesirable. Note that the criteria for determining linearity may be based not only on the count of photons, but also on the subject illumination and the image brightness value.

[0037] Furthermore, it is more preferable that the numerical range of conditional expression (1) be within the range of conditional expression (1a) below.

[0038] 0.01 <m / fT<0.80 ···(1a) Furthermore, it is even more preferable that the numerical range of conditional expression (3a) be within the range of conditional expression (3b).

[0039] 0.05 <m / fT<0.50 ···(1b) (Other examples) The present invention can also be realized by supplying a program that implements one or more of the functions of the above-described embodiments to a system or device via a network or storage medium, and by having one or more processors in the computer of that system or device read and execute the program. It can also be realized by a circuit (e.g., an ASIC) that implements one or more functions.

[0040] Each embodiment of the disclosure includes the following configuration and method.

[0041] (Composition 1) An autofocus control device that controls a focus drive unit that drives a focus lens group, which is at least a part of the imaging optical system, based on contrast information obtained from an image sensor arranged in a two-dimensional plane, wherein each of a plurality of photoelectric conversion units, each comprising a light receiving unit that converts light incident from the imaging optical system into voltage pulses and a counting unit that counts the number of pulses of the voltage pulses, An autofocus control device characterized by having a control unit that drives the focus lens group back and forth in the focus drive unit while continuing to expose the image sensor, and controls the focus drive unit based on the contrast information of each of a plurality of images generated from the number of pulses of the voltage pulses that occur during the exposure period of the exposure. (Configuration 2) The autofocus control device according to configuration 1, characterized in that the light receiving unit is an avalanche photodiode driven in Geiger mode, provided at each pixel of the image sensor. (Composition 3) The autofocus control device according to configuration 1 or 2, further comprising a storage unit for storing the number of pulses of the voltage pulse that occur during the exposure period of the exposure. (Composition 4) An autofocus control device according to any one of configurations 1 to 3, further comprising an image generation unit that generates a plurality of images using the number of pulses of the voltage pulse that occurs during the exposure period of the exposure. (Composition 5) The autofocus control device according to configuration 4, characterized in that the image generation unit generates the plurality of images using count information which includes the number of voltage pulses that occur during the exposure period of the exposure and time information associated with the number of pulses. (Composition 6) The autofocus control device according to configuration 5, characterized in that the image generation unit generates the plurality of images by adding or subtracting the count information. (Composition 7) The autofocus control device according to any one of configurations 4 to 6, characterized in that the image generation unit generates a focused image exposed for a predetermined exposure time using the number of voltage pulses that occur during the exposure period of the exposure. (Composition 8) The autofocus control device according to configuration 7, characterized in that the image generation unit generates the focused image exposed for a predetermined exposure time using the number of voltage pulses that occur within the exposure period excluding the exposure period in which the plurality of images were generated from the exposure period of the exposure. (Composition 9) The autofocus control device according to configuration 7 or 8, characterized in that the exposure period for generating each of the plurality of images is shorter than the predetermined exposure time for generating the in-focus image. (Composition 10) The autofocus control device according to any one of configurations 4 to 9, characterized in that the image generation unit generates the plurality of images in succession. (Composition 11) When the average number of incident photons per pixel of the image sensor is m and the clock speed of the image sensor is fT, 0.0 <m / fT<1.0 An autofocus control device according to any one of configurations 1 to 10, characterized in that it satisfies the following conditional expression. (Composition 12) The autofocus control device according to any one of configurations 1 to 11, characterized in that the plurality of images are images for focus determination. (Composition 13) The autofocus control device according to any one of configurations 1 to 12, characterized in that the control unit adjusts the focus of the imaging optical system by controlling the focus drive unit. (Composition 14) An autofocus control device according to any one of configurations 1 to 13, further comprising a contrast determination unit that calculates the contrast information for each of the plurality of images. (Composition 15) The autofocus control device according to any one of configurations 1 to 14, characterized in that the light receiving unit converts light incident from the imaging optical system into the voltage pulse based on the avalanche effect. (Composition 16) An image sensor comprising a plurality of photoelectric conversion units arranged in a two-dimensional plane, each unit having a light-receiving unit that converts light incident from an imaging optical system into voltage pulses, and a counting unit that counts the number of pulses in the voltage pulses, An imaging device characterized by having an autofocus device as described in any of configurations 1 to 15. (Composition 17) The imaging apparatus according to configuration 16, further comprising a focus drive unit for driving the aforementioned focus lens group. (Method 1) An autofocus control method that controls a focus drive unit that drives a focus lens group, which is at least a part of the imaging optical system, based on contrast information obtained from an image sensor arranged in a two-dimensional plane, wherein each of a plurality of photoelectric conversion units, each comprising a light receiving unit that converts light incident from the imaging optical system into voltage pulses and a counting unit that counts the number of pulses of the voltage pulses, An autofocus control method characterized by having the steps of: driving the focus lens group back and forth in the focus drive unit while continuing exposure of the image sensor; and controlling the focus drive unit based on the contrast information of each of a plurality of images generated from the number of pulses of the voltage pulses that occur during the exposure period. (Composition 18) A program characterized by causing a computer to execute the autofocus control method described in Method 18.

[0042] Although preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of its gist. [Explanation of symbols]

[0043] 301 Light receiving part 304 Count section 300 Photoelectric conversion unit 20 Autofocus control device 207 Control Unit

Claims

1. An autofocus control device that controls a focus drive unit that drives a focus lens group, which is at least a part of the imaging optical system, based on contrast information obtained from an image sensor arranged in a two-dimensional plane, the photoelectric conversion unit having a light receiving unit that converts light incident from the imaging optical system into voltage pulses and a counting unit that counts the number of pulses of the voltage pulses, An autofocus control device characterized by having a control unit that drives the focus lens group back and forth in the focus drive unit while continuing to expose the image sensor, and controls the focus drive unit based on the contrast information of each of a plurality of images generated from the number of pulses of the voltage pulses that occur during the exposure period of the exposure.

2. The autofocus control device according to claim 1, characterized in that the light receiving unit is an avalanche photodiode driven in Geiger mode, provided at each pixel of the image sensor.

3. The autofocus control device according to claim 1, further comprising a storage unit for storing the number of pulses of the voltage pulse that occur during the exposure period of the exposure.

4. The autofocus control device according to claim 1, further comprising an image generation unit that generates a plurality of images using the number of pulses of the voltage pulse that occurs within the exposure period of the exposure.

5. The autofocus control device according to claim 4, characterized in that the image generation unit generates the plurality of images using count information which includes the number of pulses of the voltage pulses that occur during the exposure period of the exposure and time information associated with the number of pulses.

6. The autofocus control device according to claim 5, characterized in that the image generation unit generates the plurality of images by adding or subtracting the count information.

7. The autofocus control device according to claim 4, characterized in that the image generation unit generates a focused image exposed for a predetermined exposure time using the number of voltage pulses that occur during the exposure period of the exposure.

8. The autofocus control device according to claim 7, characterized in that the image generation unit generates the focused image exposed for a predetermined exposure time using the number of voltage pulses that occur within the exposure period excluding the exposure period in which the plurality of images were generated from the exposure period of the exposure.

9. The autofocus control device according to claim 7, characterized in that the exposure period for generating each of the plurality of images is shorter than the predetermined exposure time for generating the in-focus image.

10. The autofocus control device according to claim 4, characterized in that the image generation unit generates the plurality of images in succession.

11. When m is the average number of incident photons per pixel of the image sensor, and fT is the clock speed of the image sensor, 0.0<m / fT<1.0 The autofocus control device according to claim 1, characterized in that it satisfies the following conditional expression.

12. The autofocus control device according to claim 1, characterized in that the plurality of images are images for focus determination.

13. The autofocus control device according to claim 1, characterized in that the control unit adjusts the focus of the imaging optical system by controlling the focus drive unit.

14. The autofocus control device according to claim 1, further comprising a contrast determination unit that calculates the contrast information for each of the plurality of images.

15. The autofocus control device according to claim 1, characterized in that the light receiving unit converts light incident from the imaging optical system into voltage pulses based on the avalanche effect.

16. An image sensor comprising a plurality of photoelectric conversion units arranged in a two-dimensional plane, each unit having a light-receiving unit that converts light incident from an imaging optical system into voltage pulses, and a counting unit that counts the number of pulses in the voltage pulses, An imaging device characterized by having an autofocus device according to any one of claims 1 to 15.

17. The imaging apparatus according to claim 16, further comprising a focus drive unit for driving the aforementioned focus lens group.

18. An autofocus control method that controls a focus drive unit that drives a focus lens group, which is at least a part of the imaging optical system, based on contrast information obtained from an image sensor arranged in a two-dimensional plane, wherein each of a plurality of photoelectric conversion units, each comprising a light receiving unit that converts light incident from the imaging optical system into voltage pulses and a counting unit that counts the number of pulses of the voltage pulses, An autofocus control method characterized by having the steps of: driving the focus lens group back and forth in the focus drive unit while continuing exposure of the image sensor; and controlling the focus drive unit based on the contrast information of each of a plurality of images generated from the number of pulses of the voltage pulses that occur during the exposure period.

19. A program characterized by causing a computer to execute the autofocus control method described in claim 18.

Images