JP2014174282A - Device and method for detecting focus, and image capturing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable accurate focus detection even when focusing on an ultra-bright object.SOLUTION: A focus detection device includes; characteristic value detection means which cycles through and monitors a plurality of line sensors, each of which generates a pair of image signals having parallax therebetween, and detects a characteristic value signal of a pair of image signals generated by a line sensor being monitored; control means which provides control such that, if the detected characteristic value signal is no less than a predetermined accumulation halt level but less than a saturation detection level, the line sensor being monitored halts charge accumulation and, if the detected characteristic value signal is no less than the saturation detection level, either the line sensor being monitored starts a re-accumulation process and halts the charge accumulation when the characteristic value signal obtained after the re-accumulation process reaches the accumulation halt level, or the line sensor being monitored is kept monitored until a predetermined single monitoring period is over; and focus detection means which detects focal condition using the pair of image signals read from a line sensor that has halted the charge accumulation.

Description

  The present invention relates to a focus detection apparatus and method, and an imaging apparatus equipped with the focus detection apparatus.

  Conventionally, a phase difference detection method is generally well known as an automatic focus detection method for a camera. In the phase difference detection method, a light beam from a subject that has passed through different exit pupil regions of the photographing lens is imaged on a pair of line sensors of a focus detection photoelectric conversion device (AF sensor). Then, by calculating the relative position of a pair of subject images obtained by photoelectric conversion by the pair of line sensors (hereinafter referred to as “phase difference calculation”), the focus state of the photographing lens is detected. Recently, various AF sensors in which a plurality of line sensors are arranged so as to detect the focus state of a plurality of points (hereinafter referred to as “AF frames”) in the screen have been proposed.

  For example, the photoelectric conversion element is divided into AF frame areas, the accumulation time is controlled for each of the areas 1 to n while sequentially cycling from the area 1 to the area n, and the amplification factor (gain) at the time of reading the pixel signal for each area A technique for appropriately controlling the above is disclosed in Patent Document 1 (FIG. 1). By performing an appropriate charge accumulation operation for each region, it is possible to read pixel signals with an appropriate gain even for a subject having various luminance levels.

Japanese Patent No. 3854704

  However, in the focus detection device using the photoelectric conversion device described in Patent Document 1, the cycle for circulating the region becomes long, and the accumulation end timing may be delayed. In particular, when the subject has extremely high brightness, the signal of another area exceeds a predetermined value while circulating the signal of one area, and as a result, the image signal of the other area is converted into a photoelectric conversion element. In some cases, the focus detection accuracy deteriorates because the dynamic range of the AD converter is exceeded.

  The present invention has been made in view of the above problems, and an object of the present invention is to make it possible to perform focus detection with high accuracy even for an extremely bright subject.

  In order to achieve the above object, the focus detection apparatus of the present invention accumulates charges obtained by photoelectrically converting a light beam from an incident subject, and outputs a plurality of pairs of image signals each having a parallax. A line sensor, a feature quantity detection means for monitoring the plurality of line sensors while circulating, and detecting a feature quantity signal of the pair of image signals output from the line sensor in the monitor; and the feature quantity detection means When the detected feature value signal is larger than a predetermined accumulation stop level and smaller than the saturation detection level, a charge accumulation stop process is performed to stop charge accumulation of the line sensor being monitored, and When the quantity signal is equal to or higher than the saturation detection level, the charge accumulated in the line sensor being monitored is reset to perform a charge re-accumulation operation. The line sensor is monitored until the feature signal reaches the accumulation stop level to stop the charge accumulation of the line sensor being monitored, or until a predetermined single monitoring period elapses. Continued control means for performing control so as to perform single monitor processing, and focus detection means for detecting a focus state based on a pair of image signals read from the line sensor that stopped the charge accumulation.

  According to the present invention, it is possible to perform focus detection with high accuracy even for an extremely bright subject.

1 is a block diagram showing a detailed circuit configuration of an AF sensor according to an embodiment of the present invention. 1 is a block diagram showing a schematic configuration of a camera body according to an embodiment of the present invention. The figure which shows the structure concerning the optical system of a camera. The figure which shows the detailed structure of a focus detection optical system among the optical systems shown in FIG. The figure which shows arrangement | positioning of the line sensor concerning embodiment. The figure which shows the relationship between arrangement | positioning of the line sensor and AF frame concerning embodiment. The figure which shows accumulation time, Peak signal level, accumulation stop level, and saturation detection level. The flowchart of AF sensor operation | movement in 1st Embodiment. The time chart for demonstrating an example of the single monitor process in 1st Embodiment. 6 is a time chart for explaining an example of a single monitor process when subject luminance differs in the first embodiment. The flowchart of AF sensor operation | movement in 2nd Embodiment. The time chart for demonstrating the problem of the single monitor process of 1st Embodiment. The figure for demonstrating the re-accumulation start timing in 2nd Embodiment. The time chart for demonstrating an example of the single monitor process in 2nd Embodiment. The time chart for demonstrating an example of the single monitor process in case the to-be-photographed object brightness | luminances differ in 2nd Embodiment. The figure for demonstrating the operation time of AF sensor with respect to several different subject brightness | luminance in 2nd Embodiment.

  The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings.

<First Embodiment>
FIG. 2 is a block diagram illustrating a schematic configuration of a camera body including the AF sensor according to the first embodiment of the present invention.

  The camera microcomputer (CPU) 100 includes a signal input circuit 204 for detecting a switch group 214 for various camera operations, an image sensor (image sensor) 206 including a CMOS sensor and a CCD, and an AE sensor 207. Is connected. A shutter control circuit 208 for controlling the shutter magnets 218a and 218b and the AF sensor 101 are also connected. In addition, a signal 215 is transmitted to the photographing lens 300 shown in FIG. 3 to be described later via the lens communication circuit 205 to control the focal position and the aperture. The operation of the camera is determined by the setting of the switch group 214.

  The AF sensor 101 includes a pair of line sensors, and by controlling the AF sensor 101 by the CPU 100, a focus state is detected from a phase difference between a pair of image signals having parallax obtained from the pair of line sensors, and a photographing lens 300 focus positions are controlled.

  Further, the CPU 100 controls the AE sensor 207 to detect the luminance of the subject and determines the aperture value and shutter speed of the photographing lens 300. Then, the aperture value of the photographing lens 300 is controlled via the lens communication circuit 205, the shutter speed is controlled by adjusting the energization time of the magnets 218a and 218b via the shutter control circuit 208, and the image sensor 206 is further controlled. The shooting operation is performed.

  In the CPU 100, there is a storage circuit 209 such as a ROM storing a program for controlling the camera operation, a RAM for storing variables, and an EEPROM (electrical erasing and writable memory) for storing various parameters. Built in.

  Next, the configuration of the optical system of the camera will be described with reference to FIG. Most of the light beam from the subject incident through the photographing lens 300 is reflected upward by the quick return mirror 305 and formed on the finder screen 303 as a subject image. The user of the camera can observe this image through the pentaprism 301 and the eyepiece lens 302. Further, a part of the light flux from the subject passes through the quick return mirror 305, is bent downward by the rear submirror 306, passes through the field mask 307, the field lens 311, the stop 308, and the secondary imaging lens 309, and then the AF sensor. 101 is imaged. The focus state of the photographic lens 300 can be detected by processing an image signal obtained by photoelectrically converting this image. Further, when photographing, the quick return mirror 305 and the sub mirror 306 jump up and retreat from the optical path, so that the total incident light beam is imaged on the image sensor 206 and the subject image is exposed.

  In FIG. 3, the focus detection method by the focus detection apparatus of the present embodiment, which includes the optical system from the field mask 307 to the secondary imaging lens 309 and the AF sensor 101, is a known phase difference detection method. Then, it is possible to detect the focus state of a plurality of different areas in the screen.

  FIG. 4 shows a detailed configuration of an optical system related to focus detection. The light beam from the subject that has passed through the photographing lens 300 (shown by one lens for convenience in FIG. 4) is reflected by the sub mirror 306 as described with reference to FIG. Once formed in the vicinity of the field mask 307 in FIG. In FIG. 4, the optical path reflected by the sub-mirror 306 and turned back is shown expanded. The field mask 307 is a member for shielding extra light outside the focus detection area (or “AF frame”) in the screen.

  The field lens 311 has an effect of forming each aperture of the diaphragm 308 in the vicinity of the exit pupil of the photographing lens 300. A secondary imaging lens 309 is disposed behind the stop 308 and is composed of a pair of two lenses. Each lens corresponds to each opening of the stop 308. Each light beam that has passed through the field mask 307, the field lens 311, the stop 308, and the secondary imaging lens 309 forms an image on the line sensor on the AF sensor 101. In FIG. 4, only one pair of line sensors is shown on the AF sensor 101, but a plurality of pairs of line sensors are arranged as will be described later.

  Next, the relationship between the line sensor on the AF sensor 101 and the AF frame in the shooting screen will be described with reference to FIGS.

  FIG. 5 is a diagram showing the arrangement of line sensor pairs on the AF sensor 101. Each of the line sensor pairs 102-1 to 102-5 is composed of a pair of two line sensors, and detects a focus state based on a phase difference between a pair of signals obtained from the line sensor pair. Each line sensor pair is projected onto substantially the same area (AF area) on the subject by a focus detection optical system such as the secondary imaging lens 309 and detects the phase difference between the two images output from these line sensor pairs. Thus, the focus state can be detected.

  FIG. 6 is a diagram showing the arrangement of AF frames displayed in the viewfinder and the AF field of view of each line sensor pair on the AF sensor 101. In the first embodiment, there are a total of five AF frames, and line sensor pairs 102-1 to 102-5 correspond to the AF frames 1 to 5, respectively.

  Next, a detailed circuit configuration of the AF sensor 101 will be described with reference to the block diagram of FIG. The control unit 103 is connected to the CPU 100 and controls each block of the AF sensor 101 based on a communication command from the CPU 100. It also has a plurality of flag registers, setting registers, storage circuits, and timers for various controls (not shown). Further, accumulation stop information, accumulation time information, and the like of the AF sensor 101 are transmitted to the CPU 100.

  The subject image formed by the secondary imaging lens 309 is photoelectrically converted by the line sensor group 102 including the line sensor pairs 102-1 to 102-5 and accumulated as electric charges. The accumulated charge is output as a voltage by the amplifier circuit. The line sensor selection circuit 104 selects one line sensor pair from the plurality of line sensor pairs in the line sensor group 102. Then, it has a function of outputting the signal of the selected line sensor pair to the maximum value detection circuit 105 (feature amount detection means) and the output circuit 108 for monitoring the feature amount (here, the maximum value) of the signal of the line sensor pair. .

  The maximum value detection circuit 105 stores a maximum value signal (Peak signal), which is the largest signal among the pixel signals of the line sensor pair being monitored selected by the line sensor selection circuit 104, and a saturation detection circuit. To 109. The Peak signal is one of feature quantity signals indicating the feature quantity of the pixel signal. On the other hand, by driving the shift register 107, the pixel signal is output from the output circuit 108 to the CPU 100 pixel by pixel.

  FIG. 7 is a diagram showing the relationship between the signal amount of the Peak signal that is an output signal from the maximum value detection circuit 105, the accumulation time, the accumulation stop determination, and the saturation detection. The accumulation time 0 is the accumulation start timing, and the Peak signal increases as time elapses. The accumulation stop determination circuit 106 compares and determines the Peak signal and the accumulation stop level Vref. The accumulation stop level Vref is set so that the signal level of the line sensor pair being monitored does not exceed the input / output allowable range of each unit such as the photoelectric conversion unit, the amplifier (not shown), and the output circuit of the line sensor pair. Yes. When the Peak signal becomes greater than the accumulation stop level Vref, the accumulation stop determination circuit 106 outputs an accumulation stop determination signal to the control unit 103.

  A contrast detection circuit (feature amount) for detecting a contrast (difference signal) of a subject as a feature amount using a minimum value detection circuit (not shown) of a signal of the line sensor pair, a maximum value detection circuit 105, and a subtraction circuit (not shown). Detection means) may be configured. In that case, the accumulation stop determination may be performed using the contrast signal obtained therefrom. Also in this case, the accumulation stop determination circuit 106 makes a comparison with a predetermined accumulation stop level. For example, the accumulation stop level is set so that the signal amplified by the output circuit 108 does not exceed the input allowable range of the CPU 100. Alternatively, accumulation stop may be determined by detecting both the Peak signal and the contrast signal as the feature amount signal.

  Then, the control unit 103 outputs an accumulation stop signal to the line sensor group 102 in order to stop accumulation of the line sensor pair under monitoring selected by the line sensor selection circuit 104. Further, an accumulation end signal and line information for which accumulation has been completed are output to the CPU 100 (charge accumulation stop process). If the Peak signal does not reach the target value within a predetermined time (maximum accumulation time), the CPU 100 transmits an accumulation stop command to the AF sensor 101 to forcibly stop accumulation, and the control unit 103 Outputs an accumulation stop signal to the line sensor group 102.

  When the saturation detection circuit 109 detects that the Peak signal is equal to or higher than the saturation detection level, the saturation detection circuit 109 outputs a saturation detection signal to the control unit 103. The saturation detection level is set higher than the accumulation stop level, and the signal level of the line sensor pair is within the input / output allowable range even if any one of the photoelectric conversion unit, amplifier (not shown), output circuit, etc. of the line sensor pair is used. It is set so that it can be detected when there is a risk of exceeding. When saturation is detected, the operation of the AF sensor 101 is controlled by the control unit 103 based on a flowchart described later.

  As described above, the pixel signals accumulated in the line sensor group 102 are output to the output circuit 108 via the line sensor selection circuit 104. A control command for pixel readout is transmitted from the CPU 100, and the shift register 107 is driven to output a pixel signal for each pixel from the output circuit 108 to an A / D converter (not shown) of the CPU 100. At this time, the output circuit 108 performs processing such as extracting and amplifying the contrast component from the pixel signal.

  The operation of the focus detection apparatus configured as described above will be described in detail based on the flowchart of FIG. 8 and FIGS. 9 and 10. Here, it is assumed that only the subject image projected onto the line sensor pair 102-3 is bright and the subject image projected onto the line sensor pair other than the line sensor pair 102-3 is sufficiently dark. In addition, accumulation of all line sensors (line sensor pairs 102-1 to 102-5) is permitted.

  Steps S800 to S803 are operations from the initial setting operation of the AF sensor 101 and the circuit reset operation to the start of accumulation. In S800, various settings in the AF sensor 101 are performed based on commands from the CPU 100. The setting performed here includes a setting (accumulation permission setting) as to whether or not accumulation of each line sensor pair is permitted.

  In step S801, the charges of the photoelectric conversion units of all line sensor pairs are reset, and charge accumulation is started. Here, in the line sensor pair 102-n (n = 1 to 5) for which accumulation permission is not set in S800, the photoelectric conversion unit remains fixed at the reset potential even after the accumulation is started, and the corresponding accumulation end flag end [ n] (n = 1-5) is set to 1. The accumulation end flag end [n] (n = 1 to 5) will be described later.

  In step S802, the line sensor pair having the smallest line sensor number among the line sensor pairs for which accumulation permission is set in step S800 is set as a monitor start line sensor. Here, assuming that all line sensor pairs are permitted to accumulate, monitoring is started from the line sensor pair 102-1 with n = 1. When starting the monitoring, the timer timer built in the control unit 103 is reset in S803 and then counting is started, and measurement of the elapsed time of charge accumulation is started.

  S804 to S811 are cyclic monitoring operations in which each line sensor pair is selected and monitored while circulating at a predetermined cycle. In step S <b> 804, the timer timer_monitor built in the control unit 103 is reset and then counting is started, and measurement of the elapsed time of the monitoring period is started. In S805, the line sensor selection circuit 104 selects one of the line sensor pairs 102-n (n = 1 to 5), and the signal of the line sensor pair 102-n being monitored is output to the maximum value detection circuit 105. The

  In step S <b> 806, the accumulation stop determination circuit 106 determines accumulation stop based on the Peak signal of the line sensor pair 102-n being monitored output from the maximum value detection circuit 105. In S807, the value of the timer timer_monitor is compared with the monitor cycle time period_monitor of one line sensor pair, and it is determined whether or not the monitor period has reached the monitor cycle time. S806 and S807 are repeated, and if the accumulation stop determination is made before the monitoring period reaches the monitoring cycle time, the process proceeds to S812. When the monitoring period reaches the monitoring cycle time without determining whether or not to stop accumulation, the monitoring period ends, and the process proceeds to S808 to shift to an operation for determining a line sensor pair to be monitored next.

  In S808 to S811, a line sensor pair to be monitored next is determined. In S808, it is determined whether n is the maximum value (here, 5). If n is the maximum value, n is initialized to 1 in S801, and if it is not the maximum value, n is incremented in S809. In S811, based on the accumulation end flag end [n] of the next monitoring target candidate line sensor pair, it is determined whether the line sensor pair has completed accumulation. If the accumulation end flag end [n] = 1, the accumulation of the licensor pair has been completed.

  If the accumulation has been completed, the process returns to S808, and further determination is made for the next line sensor pair. On the other hand, if the accumulation has not ended, the process returns to S804 to start the monitoring operation of the line sensor pair.

  An example of the monitoring operation of S804 to S811 described above will be specifically described with reference to FIG. In the first round of monitoring, S804 to S811 are repeated without determining that all line sensor pairs stop accumulating, and the line sensor pairs 102-1 to 102-5 are sequentially monitored by the monitor cycle period period_monitor. In FIG. 9, the solid line portion of the line sensor Peak signal is a period during which the line sensor pair 102-3 is selected and monitored, and the broken line portion is selected and monitored other than the line sensor pair 102-3. It is a period. When the monitoring of the line sensor pair 102-5 ends, the line sensor pair 102-1 is monitored again.

  Returning to FIG. 8, when it is determined in S806 that accumulation is stopped during the monitoring period, the process proceeds to S812 to perform accumulation stop processing. In step S812, the accumulation of the line sensor pair 102-n is stopped to hold the pixel signal, and the value of the timer timer is stored in the storage unit time_acc [n] built in the control unit 103 as the accumulation time. If it is a stop determination after re-accumulation, the elapsed time timer_reacc from the reset is stored. The timer_reacc will be described later.

  In S813, the saturation detection circuit 109 detects saturation based on the maximum value signal (Peak signal) of the line sensor pair 102-n output from the maximum value detection circuit 105. If saturation is detected, the process proceeds to S816. If saturation is not detected, the process proceeds to S814.

  In S814, the accumulation end flag end [n] = 1 is set, and the fact that the accumulation of the line sensor pair 102-n has been completed is stored. In S815, it is determined whether or not all line sensor pairs have been accumulated. If the accumulation end flags end [n] (n = 1 to 5) are all 1, it is determined that the accumulation of all the line sensor pairs is completed, and the AF sensor operation is terminated. On the other hand, if any one of the accumulation end flags end [n] (n = 1 to 5) is not 1, it is determined that there are remaining line sensor pairs that have not been accumulated, and the process proceeds to S808, where AF Continue sensor operation.

If saturation is detected in S813, the process proceeds to S816, and processing for re-reset and re-accumulation (single monitor process) is performed in S816 to S821 in order to obtain a signal without saturation. In S816, when the line sensor pair 102-n is reaccumulated, a period for monitoring the line sensor pair 102-n alone is calculated. Here, as an example of the calculation of the single monitor period period_reacc [n], it is calculated as follows.
period_reacc [n] = time_acc [n] + α,
(N = 1-5)
Here, it is assumed that the single monitor period period_reacc [n] is obtained by adding an arbitrary margin time α to the accumulation time time_acc when the previous saturation occurred.

  If the position and brightness of the subject are the same as when accumulated when saturated, the Peak signal of the line sensor n should reach the accumulation stop level Vref within the single monitor period period_reacc [n]. In consideration of the stop control error, a margin time α is added thereto. For example, the margin time α is the monitor time period_monitor. By providing the single monitor period period_reacc [n] in this way, it is possible to prevent an increase in the single monitor period due to a decrease in the amount of light due to the movement of the subject or a change in luminance of the image projected on the line sensor.

  In S817, only the line sensor pair 102-n that detects saturation is reset (re-reset). In S818, the timer timer_reacc [n] is started, and the process proceeds to S819, where the re-accumulation operation of the line sensor pair 102-n is performed. Do. Therefore, the timer timer_reacc [n] measures the reaccumulation time of the line sensor pair 102-n.

  In S819, the accumulation stop determination is performed in the same manner as in S806. If the storage stop determination circuit 106 does not determine stop, the process proceeds to S820. In S820, the value of the re-accumulation time timer_reacc [n] is compared with the single monitor period period_reacc [n] calculated in S811, and it is determined whether or not the re-accumulation time has reached the single monitor period.

  S819 and S820 are repeated, and if the accumulation stop determination is made before the re-accumulation time reaches the single monitor period period_reacc [n], the process proceeds to S821 to perform the accumulation stop process. If the re-accumulation time reaches the single monitoring period without determining whether to stop accumulation, the process proceeds to S808, and the single monitoring period ends.

  In S821, the accumulation of the line sensor pair 102-n is stopped and the pixel signal is held, and the value of the timer timer_reacc [n] is stored as the accumulation time in the storage unit time_acc [n] built in the control unit 103.

  The operation of the AF sensor including the re-accumulation operation of S804 to S821 will be specifically described with reference to FIGS. In FIG. 9, the second round of monitoring is entered, and the line sensor pairs 102-1 to 102-3 are successively monitored again. In the second round of the line sensor pair 102-3, since the Peak signal of the line sensor pair 102-3 has reached the accumulation stop level Vref, accumulation stop processing is performed (S812).

  Next, it is determined that the Peak signal of the line sensor 102-3 is saturated because the saturation signal is equal to or higher than the saturation detection level Vsat (YES in S813). Next, the single monitor period period_reacc [3] is calculated (S816). Thereafter, the re-accumulation operation of the line sensor pair 102-3 is performed (S817, S818).

  After the re-accumulation operation, it is a single monitoring period in which only the line sensor pair 102-3 is monitored (S819, S820). In FIG. 9, accumulation stop processing (S821) is performed during this period, and the accumulation end flag end [n] = 1 is set.

  FIG. 10 shows a case where the accumulation stop determination is not made during the single monitor period (after the start of re-accumulation) due to the movement of the subject or the luminance change. As shown in FIG. 10, when the accumulation stop determination is not made during the single monitor period, the line sensor pair 102-3 is continuously monitored until the single monitor period ends, and the normal cyclic operation is started. At this time, since the accumulation end flag end [n] = 1 is not set, the cyclic operation including the line sensor pair 102-3 is performed.

  These operations are repeated, and when the accumulation end flags end [n] (n = 1 to 5) of all the line sensor pairs are all 1, the AF sensor operation is terminated. The CPU 100 appropriately reads the signal of the line sensor pair, and performs focus detection calculation using this signal.

  Although not explicitly shown in the figure, when a forced accumulation stop command is transmitted from the CPU 100, the process forcibly proceeds to S812 in S806 to perform a stop process, and the process proceeds to S814 in S813 forcibly. The end flag end [n] = 1. Even when a forced accumulation stop command is transmitted from the CPU 100 during the single monitor period, the process is forcibly shifted from S819 to S821 to perform the stop process.

  As described above, according to the first embodiment, only a saturated line sensor pair is reset and re-accumulated, and the accumulation control is performed by providing a single monitor period for monitoring only the line sensor pair. As a result, it is possible to accumulate the signal of the pair of line sensors in which the projected subject is extremely bright without saturating, while accumulating the plurality of line sensor pairs in which the projected subject is dark in parallel. By using the signal obtained in this way, it is possible to detect the focus state of a subject in a wide luminance range projected onto a plurality of AF frames.

<Second Embodiment>
Next, a second embodiment of the present invention will be described. In addition, since the structure of the camera in 2nd Embodiment is the same as that of what was demonstrated with reference to FIGS. 1-6 in 1st Embodiment, description is abbreviate | omitted here. Hereinafter, the operation flow of the focus detection apparatus according to the second embodiment of the present invention will be described with reference to FIG. In addition, the same step number is attached | subjected to the process similar to FIG. 8 mentioned above, and description is abbreviate | omitted suitably.

  In S800 to S811, processing for sequentially monitoring the line sensor pairs 102-1 to 102-5 is performed as in the processing described with reference to FIG. If it is determined in S811 that the accumulation end flag end [n] = 1 of the next monitor target candidate line sensor pair is not set, the process proceeds to S1112. In S1112, based on a saturation flag sat [n] to be described later, it is determined whether or not the next monitor target candidate line sensor is waiting for re-accumulation after saturation detection. If the saturation flag sat [n] = 1, the line sensor pair is waiting for re-accumulation. If the line sensor is not waiting for re-accumulation, the process returns to S1104 to continue the patrol monitoring operation.

  On the other hand, if sat [n] = 1 and the line sensor pair 102-n is on standby for re-accumulation, the process proceeds to S1120, and it is determined whether or not the time is the re-accumulation timing. In S1120, the time indicated by the timer started in S803 is compared with a re-accumulation timing time_restart calculated in S1119 described later.

  If timer <time_restart, the process returns to S1108, and it is further determined whether or not the next line sensor pair is to be monitored. The re-accumulation timing and the re-accumulation operation performed in S1121 to S1127 will be described later.

  On the other hand, the processing of S812 to S815 performed after the stop determination is made in S806 is the same as in FIG. When saturation is detected by the saturation detection circuit 109 in S813,

The process proceeds to S1117. In S1117, the saturation flag sat [n] = 1 is set, the line sensor pair 102-n is stored as saturated, and the process proceeds to S1118. In S1118, similar to S816, the period for monitoring the line sensor pair 102-n alone is calculated when the line sensor pair 102-n is re-accumulated. In S1119, the timing time_restart [n] for performing the reset and re-accumulation of the line sensor pair 102-n is determined.
Here, the reaccumulation timing time_restart [n] will be described. In the first embodiment, the re-reset and re-accumulation operations of the saturated line sensor are performed immediately after detecting the saturation. In this case, during the single monitoring period, the other line sensor pairs are not monitored and may be saturated. As a result, the operation is such that line sensor pairs are accumulated one by one, and the operation responsiveness of the AF sensor may deteriorate.

  FIG. 12 shows a specific example for explaining the above-described problem that may occur due to the processing described in the first embodiment. Here, it is assumed that accumulation of the line sensor pairs 102-1 to 102-3 is permitted.

  In the second round of the monitor, the saturation of the line sensor pair 102-1 is detected, and the line sensor pair 102-1 is immediately reset and stored again. In the example shown in FIG. 12, the line sensor pair 102-2 is saturated during the single monitoring period of the line sensor pair 102-1. Here, according to the flowchart of FIG. 8, when the re-accumulation and re-accumulation operations of the line sensor pair 102-2 are performed after the re-accumulation of the line sensor pair 102-1, the line sensor pair 102-3 further includes the line sensor It becomes saturated during the single monitoring period of the pair 102-2. In this example, the operation until the signal level of the line sensor pair 102-3 becomes equal to or higher than the accumulation stop determination level Vref is performed twice before the operation of the AF sensor 101 ends, and time is wasted.

  Therefore, in the second embodiment, the line sensor pair whose saturation is detected is not immediately re-accumulated, and is set in a standby state. Thereafter, by controlling the line sensor pair to be reset again and stored again at a timing at which the other line sensor pair is not saturated during the single monitoring period of the saturated line sensor pair, The operation of the AF sensor can be shortened with respect to the operation of the embodiment. A specific example of this effect will be described later.

Here, as an example of the calculation of the re-accumulation timing time_restart [n] (standby time) obtained in S1119, the following calculation is performed.
time_restart [n]
= Period_reacc [n] × Vref / (Vsat−Vref) + β

  Here, the first term of the above formula will be described with reference to FIG. The relationship between the above equations is shown in FIG. 13A. In this figure, m ≠ n. The brightness of the object projected on the line sensor pair 102-m is a brightness that causes the Peak signal of the line sensor pair 102-m to grow by Vsat-Vref during the single monitor period period_reacc [n] of the line sensor pair 102-n. That's it.

  As shown in FIG. 13B, if the subject brightness projected on the pair of line sensors 102-m is brighter than the subject brightness in FIG. 13A, the accumulation is stopped by time_restart [n]. It never saturates inside.

  Conversely, as shown in FIG. 13C, when the subject brightness projected on the line sensor pair 102-m is darker than the subject brightness in FIG. That is, the saturation detection level Vsat is not reached even if it is not monitored during the single monitoring period period_reacc [n] of the line sensor pair 102-n, and the signal level that is not saturated when the line sensor pair 102-m is monitored. The accumulation stop determination is made at.

Here, in consideration of monitoring periods of a plurality of line sensor pairs, an arbitrary margin time β is added to the value calculated in the first term of the above formula. For example, the margin time β is calculated as follows.
β = period_monitor × l
Here, l is the number of licensor pairs that have not been accumulated at the timing for obtaining the reaccumulation timing. That is, in addition to the single monitor period, the monitor period is not saturated during the normal cyclic operation.

  If another line sensor pair (line sensor pair 102-i) is waiting for the re-accumulation at the timing for obtaining the re-accumulation timing, the re-accumulation timing is also taken into account in consideration of the single monitor period of the line sensor pair 102-i To decide. The same applies when there are a plurality of line sensor pairs waiting for re-accumulation.

  As another example of obtaining the reaccumulation timing time_restart [n], signal monitor information of all line sensor pairs other than the line sensor pair 102-n can be used. For example, at the timing for obtaining the re-accumulation timing, the signal level (subject luminance information) of all the line sensor pairs is obtained by cyclically monitoring all the line sensor pairs while gradually decreasing the accumulation stop determination level Vref. ) Can be confirmed. The re-accumulation timing time_restart [n] is determined using this information.

  After the re-accumulation timing time_restart [n] of the line sensor pair 102-n is determined in S1119, the line sensor pair 102-n enters a re-accumulation standby state, and the process proceeds to S808 to determine the next monitored line sensor pair. The patrol monitoring operation is continued.

  If it is determined in S1112 that the next monitoring target candidate line sensor pair 102-n is on standby for re-accumulation (sat [n] = 1) while repeating the cyclic monitoring operation, the process proceeds to S1120 as described above. Then, it is determined whether the time is the re-accumulation timing of the line sensor pair.

  If the timer timer indicating the elapsed time has passed the re-accumulation timing time_restart [n], the process proceeds to S1121 because of the re-accumulation timing, and the re-accumulation operation is executed.

  S1121 to S1125 are re-accumulation operations similar to S817 to S821 in FIG. If the accumulation stop determination is not made during the single monitor period (YES in S1124), the single monitor period is ended, the saturation flag sat [n] = 0 is set in S1128, and the normal cyclic operation is started.

  On the other hand, when the accumulation stop determination is made during the single monitor period (YES in S1123), the single monitor period ends and the stop process of S1125 to S1127 is performed. Here, the same processing as S821, S814, and S815 of FIG. 8 is performed.

  Although not explicitly shown in the figure, if all line sensor pairs are either saturated and either waiting for re-reset or if accumulation is complete, re-reset timing has not been reached However, the reset operation and the re-accumulation operation of the line sensor pair in the standby state are performed. When there are a plurality of line sensor pairs in the standby state, the reset timing of each line sensor pair is determined from signal monitor information obtained from each single monitor period.

  Further, when a forced accumulation stop command is transmitted from the CPU 100, in S806, the process is forcibly shifted to S812 and the stop process is performed. In S813, the process is forcibly shifted to S814, and the accumulation end flag end [n] = 1. To do. Note that even when a forced accumulation stop command is transmitted from the CPU 100 during the single monitor period, the process is forcibly shifted from S1123 to S1125 to perform stop processing.

  An example of the operation of the AF sensor 101 according to the flowchart of FIG. 11 described above will be specifically described with reference to FIGS.

  Here, it is assumed that only the subject image projected onto the line sensor pair 102-3 is bright and the subject image projected onto the line sensor pair other than the line sensor pair 102-3 is sufficiently dark.

  The process up to the accumulation stop process of the line sensor pair 102-3 in the second round of the monitor is the same as in FIG. Next, it is determined that the Peak signal of the line sensor pair 102-3 is saturated because it exceeds the saturation determination level Vsat (S813), and the saturation flag sat [3] = 1 is set (S1117). Next, the single monitor period period_reacc [3] is calculated (S1118). Further, the re-accumulation start timing time_restart [3] is determined (S1119).

  Thereafter, the line sensor 102-3 enters a re-accumulation standby state, and monitors the second round of the line sensor pair 102-4 and the line sensor pair 102-5 according to the flowchart of FIG.

  In the monitoring operation after the third round, the monitoring operation of the line sensor pair 102-3 is not performed until the elapsed time reaches the re-accumulation start timing time_restart [3]. The line sensor pair 102-1, the line sensor pair 102-2, the line sensor pair 102-4, and the line sensor pair 102-5 are circulated and monitored.

  As time elapses and the re-accumulation start timing time_restart [3] is exceeded at time t1 (S1120), the re-accumulation operation of the line sensor pair 102-3 is performed (S1121, S1122). After the re-accumulation operation, it is a single monitoring period in which only the line sensor pair 102-3 is monitored (S1123, S1124). In FIG. 14, accumulation stop processing is performed during this period, and the accumulation end flag end [n] = 1 is set (S1125, S1126).

  FIG. 15 shows a case where the accumulation stop determination is not made during the single monitoring period (after the start of re-accumulation) due to the movement of the subject or the luminance change. As shown in FIG. 15, when the accumulation stop determination is not made during the single monitor period, the single monitor period is ended, and the normal cyclic operation is started. At this time, since the accumulation end flag end [n] = 1 is not set, the cyclic operation including the line sensor pair 102-3 is performed.

  These operations are repeated, and when the accumulation end flags end [n] (n = 1 to 5) of all the line sensor pairs are all 1, the AF sensor operation is terminated. The CPU 100 appropriately reads the signal of the line sensor pair, and performs focus detection calculation using this signal.

  The effect of the operation of the second embodiment on the operation of the first embodiment will be described with reference to FIG. In FIG. 16, it is assumed that the setting for permitting the accumulation of the line sensor pairs 102-1 to 102-3 is made as in FIG. The subject brightness projected on each line sensor pair is also the same as in FIG.

  In FIG. 16, the resetting of the line sensor pair 102-1 as shown in FIG. 12 is not started immediately but is in a standby state. During this standby period, the line sensor pairs 102-2 and 102-3 are subjected to accumulation stop processing without being saturated. Thereafter, since the accumulation of the line sensors other than the line sensor pair 102-1 is stopped, the re-reset timing has not been reached.

  The operation time of the AF sensor 101 is the time until the signal level of the line sensor pair 102-3 becomes equal to or higher than the accumulation stop determination level Vref, and until the signal level of the line sensor pair 102-1 becomes equal to or higher than the accumulation stop determination level Vref. It will be about the time added. Thus, the operation time is shortened compared to the example of FIG.

  As described above, according to the second embodiment, the re-reset and re-accumulation operations of the line sensor pair are performed at a timing such that other lines are not saturated during the single monitoring period of the saturated line sensor pair. Control. As a result, it is possible to accumulate without saturating the signal of the line sensor pair in which the projected subject has extremely high brightness while maintaining the operation responsiveness of the AF sensor.

  In the above-described embodiment, the case where there are five line sensor pairs has been described. However, the number of line sensor pairs is not limited to this.

  Moreover, although the said embodiment showed the structure which outputs a pair of signals with a phase difference using two line sensors, this invention is not limited to this. For example, two long images that have passed through different exit pupils may be formed on one long line sensor.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

Claims (12)

A plurality of line sensors for accumulating electric charge obtained by photoelectrically converting a light beam from an incident subject and outputting a pair of image signals having parallax with each other;
A feature amount detection means for monitoring the plurality of line sensors while circulating, and detecting a feature amount signal of the pair of image signals output from the line sensors in the monitor;
Charge accumulation stop for stopping the charge accumulation of the line sensor being monitored when the feature amount signal detected by the feature amount detecting means is larger than a predetermined accumulation stop level and smaller than a saturation detection level. When the feature amount signal is equal to or higher than the saturation detection level, the charge accumulated in the line sensor being monitored is reset to perform a charge re-accumulation operation, and the characteristic obtained after the re-accumulation operation The monitoring of the line sensor being monitored is continued until the amount signal reaches the accumulation stop level and the charge accumulation of the line sensor being monitored is stopped, or a predetermined single monitoring period elapses. Control means for performing control so as to perform a single monitor process;
A focus detection device comprising: a focus detection unit that detects a focus state based on a pair of image signals read from the line sensor that stops the charge accumulation.   The feature quantity detection means monitors the plurality of line sensors while cycling around a predetermined time, and the control means, during the single monitor process, when the feature quantity signal is equal to or higher than the saturation detection level. The focus detection apparatus according to claim 1, wherein the focus detection apparatus is controlled to stop the patrol.   The single monitor period is a time obtained by adding an arbitrary margin time to the time from when charge accumulation of the plurality of line sensors is started until it is determined that the feature signal exceeds the saturation detection level. The focus detection apparatus according to claim 2, wherein the focus detection apparatus is provided.   4. The focus detection apparatus according to claim 1, wherein the feature amount detection unit detects a maximum value of a pair of image signals output from a line sensor in the monitor. 5.   5. The feature amount detecting unit according to claim 1, wherein the feature amount detecting unit detects a difference signal between a maximum value and a minimum value of a pair of image signals output from the line sensor in the monitor. The focus detection apparatus described.   The said control means performs the said single monitor process as soon as it is detected that the said feature-value signal is more than the said saturation detection level, The any one of Claim 1 thru | or 5 characterized by the above-mentioned. Focus detection device.   When the feature signal is equal to or higher than the saturation detection level, the control means sets a waiting time from when the line sensors in the monitor are started to when the single monitor process is performed after the accumulation of the plurality of line sensors is started. 6. The focus detection apparatus according to claim 1, wherein the single monitor process is executed when the line sensor is circulated and monitored after the standby time has elapsed.   The focus detection apparatus according to claim 7, wherein the standby time is a time obtained so that line sensors other than the line sensor being monitored are not saturated during the single monitoring period.   The waiting time is a time obtained by adding an arbitrary margin time to a period obtained by multiplying the single monitoring period by a ratio of the accumulation stop level to a difference between the saturation detection level and the accumulation stop level. The focus detection apparatus according to claim 8. For each of the plurality of line sensors, it further comprises permission means for setting whether to permit charge accumulation,
10. The feature quantity detection unit circulates and monitors line sensors other than the line sensor that stops the charge accumulation among the line sensors permitted by the permission unit. The focus detection apparatus according to item 1. Imaging means for photoelectrically converting a light beam from an incident subject and outputting an image signal constituting an image;
An imaging apparatus comprising: the focus detection apparatus according to claim 1. The feature amount detection means accumulates charges obtained by photoelectrically converting a light beam from an incident subject, and monitors a plurality of line sensors that respectively output a pair of image signals having parallax. A feature amount detection step of detecting a feature amount signal of the pair of image signals output from the line sensor being monitored;
When the feature amount signal detected by the feature amount detection unit is larger than a predetermined accumulation stop level and smaller than a saturation detection level, the control unit stops charge accumulation of the line sensor being monitored. A charge stop process for performing charge charge stop processing;
When the feature amount signal is equal to or higher than the saturation detection level, the control unit resets the charge accumulated in the line sensor being monitored and performs a charge re-accumulation operation, and is obtained after the re-accumulation operation. The monitoring of the line sensor being monitored is continued until the feature amount signal reaches the accumulation stop level and the charge accumulation of the line sensor being monitored is stopped or a predetermined single monitoring period elapses. A single monitor process for performing a single monitor process;
A focus detection method, comprising: a focus detection step for detecting a focus state based on a pair of image signals read from the line sensor that stops the charge accumulation.

Images