JP4365973B2 - Imaging apparatus, focus adjustment apparatus, and focus adjustment method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an imaging apparatus such as an electronic still camera, a focus adjustment apparatus, and a focus adjustment method.
[0002]
[Prior art]
In an imaging apparatus having a two-dimensional imaging area, such as an electronic still camera, a method of detecting the sharpness of the screen from the video signal of the subject image and controlling the focus lens position so that it becomes the maximum, thereby bringing the camera into focus It has been known.
[0003]
For the evaluation of the sharpness, in general, the intensity of a high frequency component of a video signal extracted by a band pass filter (hereinafter abbreviated as BPF) or the blur width detection intensity of a video signal extracted by a differentiation circuit or the like is used. When a normal subject is photographed, this is small when the focus is in focus, increases as the focus is achieved, and reaches a maximum value when the subject is completely in focus. Therefore, when controlling the focus lens, when the sharpness is small, the focus lens is moved as fast as possible in the direction of increase, and slowly as it increases, so that the focus lens is stopped at the top of the mountain with high accuracy, that is, the focus is adjusted. Let them be. In general, such an autofocus method is called hill-climbing autofocus (hereinafter abbreviated as hill-climbing AF).
[0004]
In addition, the focus lens position is accurately detected, the focus lens position when the sharpness signal is the maximum value is stored, and when the sharpness signal falls to a predetermined value, the focus lens position is returned to the stored focus lens position. Is stopped at the peak of the peak of the sharpness signal.
[0005]
After the focus lens is stopped at the peak value of the sharpness signal and brought into focus, if the sharpness signal changes to some extent from the peak value, it is determined that the subject has changed, the focus lens is driven, and the next subject Find the peak value of the sharpness signal. This operation is called restart.
[0006]
In addition, when performing hill-climbing AF, in order to determine whether the focus lens should be driven infinitely or in close proximity, the focus lens is driven minutely by a predetermined pulse to the closest or infinite side, and the sharpness signal at that time is output. It is detected and hill-climbing AF is started in the direction in which the sharpness signal is large. This operation is called wobbling.
[0007]
In many cases, the video signal of the subject for AF is near the center of the image sensor, and the range is limited to some extent. Therefore, it is desirable that the video signal for performing AF is not the entire surface of the image sensor, but the range in which the subject can be extracted. If the signal of the entire surface is extracted, a phenomenon of focusing on the background, which is called perspective conflict, will occur. Therefore, the AF range finder frame often has a range as shown in FIGS. In addition, there is a camera that allows the photographer to select an arbitrary place, in which case the range shown in FIG. 2A may be taken.
[0008]
[Problems to be solved by the invention]
However, conventionally, the charge accumulation time in the imaging region is the same regardless of whether the subject has high luminance or low luminance. For this reason, when an AF operation is performed at a low luminance, there is a problem that accurate AF cannot be performed due to a small amount of charge.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, an imaging unit that performs photoelectric conversion in an imaging region, an accumulation control unit that changes a charge accumulation time for performing photoelectric conversion in the imaging region according to the brightness of a subject, and the imaging When the signal is read from the area, the signal reading area is set wider when the brightness of the subject is the second illuminance lower than the first illuminance than when the brightness of the subject is the first illuminance. Area setting means for controlling to read out, and focus adjustment means for performing focus adjustment based on a signal in a predetermined area in accordance with a distance measuring frame among signals read from the area set by the area setting means In the case of the first illuminance, a signal photoelectrically converted in the set area is not displayed on the video display means, and in the case of the second illuminance, photoelectric conversion is performed in the set area. Display the recorded signal Providing focusing device being characterized in that a control means for controlling to display on the stage.
[0010]
Further, the step of changing the charge accumulation time for performing photoelectric conversion in the imaging region according to the brightness of the subject, and when reading the signal from the imaging region, compared to the case where the subject brightness is the first illuminance In the case where the second illuminance is lower than the first illuminance, a step of setting a wider area for reading the signal and reading the signal, and ranging of the signals read from the set area A step of performing focus adjustment based on a signal of a predetermined area aligned with the frame; and in the case of the first illuminance, the photoelectric conversion signal in the set area is not displayed on the video display means, In the case of the second illuminance, there is provided a focus adjustment method including a step of controlling to display a signal photoelectrically converted in the set area on the image display means .
[0013]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
FIG. 1 is an overall configuration diagram of the imaging apparatus according to the first embodiment.
[0014]
In FIG. 1, reference numerals 101, 102, 103, and 104 denote elements constituting the lens system, respectively, a fixed front lens group, a second lens group having a focusing function, a diaphragm, and a fixed third lens. A group. The image light transmitted through this lens system forms an image on the surface of the image sensor 105 including an image pickup region for photoelectric conversion, and is converted into a video signal by photoelectric conversion. The image sensor in this embodiment is an XY address type such as a CMOS image sensor, and can read signals from only a predetermined area from the image sensor. Reference numeral 106 denotes an A / D conversion circuit, and reference numeral 107 denotes a camera signal processing circuit. The video signal processed here is converted into an analog signal by the 108 D / A conversion circuit and processed by the LCD display circuit 109 which is a video display means. Thereafter, the captured image is displayed on an LCD (Liquid crystal display) 110 which is a display unit.
[0015]
On the other hand, the video signal signal-processed at 107 is sent to an AWB evaluation value processing circuit 111 as white balance adjustment means, an AE evaluation value processing circuit 112 as exposure adjustment means, and an AF evaluation value processing circuit 113 as focus adjustment means. It is done.
[0016]
Calculation for auto white balance (AWB) is performed in the microcomputer 123 using the data from the AWB evaluation value processing circuit 111, and the result is fed back to the camera signal processing circuit 107 to perform white balance.
[0017]
In accordance with the video signal input level from the AE evaluation value processing circuit 112, the microcomputer 123, which is a control means, drives the IG driver 118 and the IG meter 119 to control the aperture 103, adjust the light quantity, and simultaneously adjust the exposure time. A certain shutter speed is also set from the microcomputer 123 to the timing generator (TG) 115 which is a driving means.
[0018]
The AF evaluation value processing circuit 113 extracts and processes only the high frequency component of the video signal in the distance measurement frame in accordance with the gate signal from the distance measurement frame generation circuit 114. Reference numeral 123 denotes a microcomputer that performs lens drive control and distance measurement frame control for changing the distance measurement area in accordance with the AF evaluation signal intensity.
[0019]
Reference numeral 121 denotes a release switch, which stores a video signal in a 122 recording memory in accordance with the operation of this switch. This release switch is a two-stage type. When the first release switch (SW1), which is the first switch means, is turned on, the in-focus position is fixed after the AF operation, and the second release means, which is the second switch means. When the switch (SW2) is turned on, it is recorded in the recording memory 122.
[0020]
Reference numeral 119 denotes a driver for outputting driving energy to the lens driving motor in accordance with the driving instruction 102 outputted from 123, and 120 denotes a motor for driving 102.
[0021]
Assuming that the lens driving motor is a stepping motor, a motor driving method will be described below.
[0022]
The microcomputer 123 determines the driving speeds of the zoom motor and the focus motor by program processing and sends them to the driver 119 for driving the focus motor 120 as the rotation frequency signal of each stepping motor. In addition, a drive / stop command for the motor 120 and a rotation direction command for each motor are sent to the driver 119. The drive / stop signal and the rotation direction signal correspond to the drive command determined by the processing in the microcomputer 123 during AF for the focus motor. The motor driver sets the phases of the four motor excitation phases to forward and reverse rotation phases according to the rotation direction signal, and applies the applied voltages (four motor excitation phases) according to the received rotation frequency signal. In addition, the output to the motor is turned ON / OFF according to the drive / stop command while controlling the rotation direction and the rotation frequency of the motor by outputting while changing the current).
[0023]
FIG. 3 is a control flow for operating the imaging apparatus of the present embodiment, and is processed in the microcomputer 123.
[0024]
301 indicates the start of processing. In step 302, AE processing is performed, and an optimum aperture and shutter speed (charge accumulation period of a photoelectric conversion unit such as a photodiode) for the subject at that time are controlled. In 302, 115 timing generators (TG) are set so that the shutter speed determined in 301 is obtained. In 304, it is determined whether or not the first release switch (SW1) is pressed. If not pressed, the process returns to 302 and the AE operation is repeated. By this operation, the photographer can always see the subject with the optimum exposure on the LCD. If SW1 is pressed in 304, the process proceeds to 305. In 305, based on the result of the AE process performed in 302, it is determined whether the shooting condition at that time is low illuminance. When the illuminance is low, the shutter speed (exposure time) is long. When the illuminance is not low, the shutter speed is high. If it is determined that the illuminance is low at 305, the process proceeds to 306, and at 306, video signals are read from the entire imaging area where photoelectric conversion is performed in the imaging device.
[0025]
Here, FIG. 4 shows the readout timing of the video signal from the image sensor. 1 to 6 are timing charts at the time of all reading processing. 1 is a 1/30 second cycle when a still image is taken out by a vertical synchronizing signal. Reference numeral 2 denotes a readout pulse when the video signal is taken out from the image sensor, and the video signal can be read out at the timing of this pulse. Reference numeral 3 represents an exposure period, and it is desirable to expose as long as possible at low illuminance. Here, exposure is performed at a shutter speed of 1/30 seconds. 4 to 6 indicate the timing at which the gate circuit 114 is gated in accordance with the AF range frame when all the video signals are read out (4 is FIG. 2 (a) and 5 is (c). ) 6 is (b)). That is, AF processing is performed using signals in a predetermined area (shaded area in FIGS. 2A to 2C) within the entire imaging area.
[0026]
When the all reading process is completed in 306, the auto white balance (AWB), AE, and AF processes are performed using the video signal read in 307. Then, in 308, it is determined whether all the processes of AWB, AE, and AF are completed. If not completed, the process returns to 306, and a series of operations from 306 to 308 are performed. Here, 306 to 308 perform a series of operations in synchronization with the vertical synchronization signal shown in FIG. As a result, the subject can always be displayed in an optimal state on the LCD even during the operation of AF or the like. When all the processes of AWB, AE, and AF are completed in 308, the process proceeds to 309.
[0027]
In 309 SW1 is confirmed whether the pressed, returns to 302 when I already release. If it has been pressed, it is confirmed at 310 whether the second release switch (SW2) has been pressed. If not, the process returns to 309 and waits for SW2 to be pressed. When SW2 is pressed, a capture operation is performed at 311. The capture operation is to store the video signal at that time in 122 recording memory. Then, in 312, the end of the capture is waited. When the capture is completed, the process returns to 302 to repeat a series of operations. The above is the flow of shooting at low illumination. During this time, the subject image is always displayed in real time on the LCD, and the photographer can press SW2 with peace of mind.
[0028]
Next, the operation when the illumination is not low will be described. If it is determined in 305 that the illumination is not low, the process proceeds to 313. In 313, as a video signal read from the image sensor, an AF block read process (the image sensor reads a signal only in an area used for AF in the imaging area) is performed.
[0029]
Here, from 1 to 6 in FIG. 4, when the amount of light is sufficient and bright, the timing immediately after the timing of the gate for the AF distance measurement frame is completed only for taking out the video signal for AF. When the exposure is started, the sampling frequency of the evaluation value from the AF video signal is increased, and it can be understood that the AF operation can be speeded up. For this reason, when the illumination is not low, only the necessary parts are read out according to the AF distance measurement frame, the shutter speed is increased, the exposure time is shortened, the sampling cycle is accelerated, and the AF operation is performed at high speed. Try to make it easier. The timing chart at that time is shown as 7 to 10 in FIG. In 313, 7 indicates a vertical synchronization signal, and 115TG is set so as to increase the frequency of the vertical synchronization signal in accordance with the block reading for AF. The shutter speed is also increased in accordance with AF block reading and 115 TG is set. Then, the block reading timing is set to 115TG so that only the portion corresponding to the AF distance measurement frame is read from the image sensor. By this block readout, it is possible to quickly accumulate and take out a necessary video signal regardless of the location of the AF distance measurement frame. Then, hill-climbing AF is performed in accordance with the signal, and it is determined in 314 whether the AF process has been completed. If not completed, the process returns to 313, and if completed, the process proceeds to 315.
[0030]
In 315, as in the case of 313, block readout processing for AE is performed as readout of the video signal from the image sensor. Then, AE is performed in accordance with the signal, and it is determined in 316 whether the AE process has been completed. If not completed, the process returns to 315, and if completed, the process proceeds to 317.
[0031]
In 317, similarly to 313, AWB block readout processing is performed as readout of the video signal from the image sensor. Then, AWB is performed according to the signal, and it is determined whether the 318 AWB process has been completed. If it has not been completed, the process returns to 317, and if it has been completed, the process proceeds to 309.
[0032]
Thus, a series of operations of AF, AE, and AWB ends. During this period, the subject image cannot be projected on the LCD as in the case of low illuminance, but the series of operations can be completed quickly. .
[0033]
As described above, the readout of the video signal from the image sensor can be set to the full readout mode when the illumination is low, and the subject can be drawn in real time on the LCD. The readout of the video signal from the imaging device is possible except when the illumination is low. By making the block read mode suitable for the function, the AF operation becomes faster and the capture preparation time in SW1 becomes shorter.
[0034]
In other words, the following effects can be obtained.
[0035]
Since it is not necessary to lengthen the charge accumulation time when the illumination is not low, the signal readout time from the image sensor is not negligible with respect to the charge accumulation time. For this reason, it is possible to reduce the time required for AF by reducing the amount of signal readout from the image sensor by reducing the readout range in the imaging region.
[0036]
In addition, since it is necessary to lengthen the charge accumulation time at low illuminance, the signal readout time from the image sensor is relatively less than the charge accumulation time, and the readout range in the imaging region is reduced. However, even if the entire region is read, the charge accumulation time is negligible. For this reason, at low illuminance, signals in the entire imaging area are read out and images are displayed on the LCD in parallel with the AF operation.
[0037]
In this way, it is possible to perform an appropriate AF operation according to the brightness of the subject.
[0038]
(Second Embodiment)
In the first embodiment, “with respect to the setting of 115TG in 313, 115TG is set so as to increase the frequency of the vertical synchronizing signal in accordance with the AF block reading. The shutter speed is also set to the AF block. 115TG is set to be faster in accordance with the readout, and the timing for performing the block readout is set to 115TG so that only the portion corresponding to the AF distance measurement frame is read out from the image sensor. Here, since the XY address type image sensor can perform block reading, only the portion to be read can be accumulated and read out from the portion to be read regardless of the position of the AF distance measurement frame. For example, as shown in FIG. 5, if the photographer is going to shoot the image of (a) and the AF distance measurement frame is the frame of 50 of (a), when the block reading is performed with the image sensor, (b) of FIG. Can be read as follows. Assuming that the AF distance measurement frame is slightly enlarged and is the frame 51 of (a), reading can be performed as shown in (c) of FIG. Therefore. By setting the exposure time and the vertical synchronization period in accordance with the shutter speed at which an AF-capable video signal can be extracted in accordance with the size of the AF distance measurement frame, a more optimal AF operation can be performed.
[0039]
(Third embodiment)
In the first embodiment, “in 315, as in 313, block reading processing for AE is performed as readout of a video signal from the image sensor. Then, AE is performed in accordance with the signal, and AE processing is performed in 316. If it is not completed, the process returns to 315. If completed, the process proceeds to 317. ”However, the photometry frame for AE differs depending on the shooting mode (program AE). A more optimal AE operation can be performed by determining a range in which block reading for AE is performed in accordance with the shooting mode at the time of shooting.
[0040]
In the above first to third embodiments, the XY address type image sensor has been described. However, a charge transfer type image sensor such as a CCD may be used. In other words, for example, block readout can be achieved by transferring the charges in unnecessary areas at high speed and then sweeping them out, or by sweeping out charges in unnecessary areas between the vertical CCD and horizontal CCD. Also good.
[0041]
(Other embodiments)
In addition, the present invention supplies a storage medium storing software program codes for realizing the functions of the above-described embodiments to a system or apparatus, and the computer (or CPU or MPU) of the system or apparatus stores it in the storage medium. Needless to say, this can also be achieved by reading and executing the programmed program code.
[0042]
In this case, the program code itself read from the storage medium realizes the novel function of the present invention, and the storage medium storing the program code constitutes the present invention.
[0043]
As a storage medium for supplying the program code, for example, a floppy disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a magnetic tape nonvolatile memory card, a ROM, or the like can be used.
[0044]
In addition to executing the program code read out by the computer, the functions of the above-described embodiments are realized, and an OS operating on the computer is part of the actual processing based on an instruction of the program code. Alternatively, the functions of the above-described embodiment can be realized by performing all of them and performing the processing.
[0045]
Further, after the program code read from the storage medium is written into a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. The CPU or the like provided in the board or the function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments can be realized by the processing.
[0046]
It should be noted that the present invention can also be applied to a case where the program is backed to a requester via a communication line such as a personal computer communication from a storage medium in which a program code of software realizing the functions of the above-described embodiments is recorded. Needless to say.
[0047]
【The invention's effect】
According to the present invention, it is possible to perform focus adjustment with an optimal operation such as performing or not displaying an image during the focus adjustment operation, depending on the brightness of the subject.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an overall configuration of an imaging apparatus.
FIG. 2 is a diagram illustrating an AF distance measurement frame.
FIG. 3 is a flowchart showing the operation of the imaging apparatus.
FIG. 4 is a diagram illustrating drive timing of the imaging apparatus.
FIG. 5 is a diagram illustrating an AF distance measurement frame.
[Explanation of symbols]
101, 104 Fixed lens 102 Focus lens 103 Diaphragm 105 Image sensor 106 A / D conversion circuit 107 Camera signal processing circuit 108 D / A conversion circuit 109 LCD display circuit 110 LCD
111 AWB evaluation value processing circuit 112 AE evaluation value processing circuit 113 AF evaluation value processing circuit 114 Distance measurement frame generation circuit 115 TG
116 Drive circuit 117 IG driver 118 IG meter 119 Drive driver 120 Focus motor 121 SW
122 Recording memory 123 Microcomputer

Claims (4)

Imaging means for performing photoelectric conversion in the imaging region;
Accumulation control means for changing the charge accumulation time for performing photoelectric conversion in the imaging region according to the brightness of the subject;
When reading a signal from the imaging area, the area for reading the signal is set wider when the brightness of the subject is the second illuminance lower than the first illuminance than when the brightness of the subject is the first illuminance. Area setting means for controlling to read the signal,
A focus adjusting means for performing focus adjustment based on a signal in a predetermined area in accordance with a range-finding frame among signals read out from the area set by the area setting means ;
In the case of the first illuminance, the signal photoelectrically converted in the set area is not displayed on the image display means, and in the case of the second illuminance, the signal is photoelectrically converted in the set area. And a control means for controlling the signal to be displayed on the video display means . 2. The focus adjustment apparatus according to claim 1, wherein the charge accumulation time is longer when the subject has the second illuminance lower than the first illuminance than when the subject has the first illuminance. . The exposure adjustment and the white balance adjustment are performed in time series after the focus adjustment operation is completed when the subject has the second illuminance. Focus adjustment device. Changing the charge accumulation time for performing photoelectric conversion in the imaging region according to the brightness of the subject; and
When reading a signal from the imaging area, the area for reading the signal is set wider when the brightness of the subject is the second illuminance lower than the first illuminance than when the brightness of the subject is the first illuminance. Reading the signal and
Performing a focus adjustment based on a signal in a predetermined area in accordance with a range-finding frame among signals read out from the set area ;
In the case of the first illuminance, the signal photoelectrically converted in the set area is not displayed on the image display means, and in the case of the second illuminance, the signal is photoelectrically converted in the set area. And a step of controlling to display the signal on the image display means .

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