JP2001230964A - Image pickup device, focusing control method and storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem where exact AF cannot be performed due to low electric charges, when AF operation is tried with low luminance. SOLUTION: This image pickup device has an image pickup area for performing electro-optical conversion, a drive circuit for changing charge storage time in the image pickup area, changing and reading a range to read signals out of the image pickup area, and a focusing control circuit for performing focusing control on the basis of signals read from of the image pickup area.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging device such as an electronic still camera.

[0002]

2. Description of the Related Art In an image pickup apparatus having a two-dimensional image pickup area, such as an electronic still camera, the sharpness of a screen is detected from a video signal of a subject image, and the position of a focus lens is controlled so that the sharpness is maximized. There is a known method of bringing the subject into focus.

In general, the sharpness is evaluated based on 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 differentiating circuit or the like. Used.
This is the focus when shooting a normal subject
When the object is out of focus, the value is small. When the object is in focus, the value becomes large. When the object is completely in focus, the maximum value is reached. Therefore, the control of the focus lens, when the sharpness is small, move as soon as possible in the direction to increase,
As it gets bigger, it moves slowly so that the focus lens stops accurately at the top of the mountain, that is, comes into focus. In addition, such an autofocus method is generally called a hill-climbing autofocus (hereinafter, abbreviated as hill-climbing AF).

Further, by accurately detecting the focus lens position, storing the focus lens position when the sharpness signal is at the maximum value, and returning to the stored focus lens position when the sharpness signal falls by a predetermined value. The focus lens is stopped at the peak of the peak of the sharpness signal.

Further, after the focus lens is stopped at the peak value of the sharpness signal and the focus signal is focused, if the sharpness signal changes to some extent from the peak value, it is determined that the subject has changed, and the focus lens is driven. Find the peak value of the sharpness signal of the subject. This operation is called restart.

Further, in performing the hill-climbing AF, in order to determine whether the focus lens should be driven to infinity or close-up, the focus lens is finely driven with a predetermined pulse to the close-up or infinity side, and the sharpness at that time is determined. A degree signal is detected, and hill-climbing AF is started in a direction in which the sharpness signal is large. This operation is called wobbling.

A video signal of a subject for performing AF is often near the center of the image sensor, and its range is limited to some extent. Therefore, it is desirable that the video signal for performing AF is not over the entire surface of the image sensor, but is within a range where the subject can be extracted. If the signal of the entire surface is extracted, a phenomenon called a near-far conflict, in which the background is focused, will occur. Therefore, the AF measurement frame often has a range as shown in FIGS. 2B and 2C. In some cases, the photographer can select an arbitrary place.
The range as shown in FIG.

[0008]

Conventionally, however, the charge accumulation time in the image pickup area is the same regardless of whether the subject has high luminance or low luminance. for that reason,
When trying to perform the AF operation at a low luminance, there is a problem that accurate AF cannot be performed due to a small amount of electric charge or the like.

[0009]

In order to solve the above-mentioned problems, according to the present invention, the charge accumulation time in the imaging area for performing photoelectric conversion and the brightness of a subject are changed, and the charge accumulation time in the imaging area is changed. There is provided an imaging apparatus comprising: a driving unit that changes a range of reading a signal from an area and reads the signal; and a focus adjustment unit that performs focus adjustment based on the signal read from the imaging area.

[0010] Further, an imaging area for performing photoelectric conversion, focus adjusting means for performing focus adjustment based on a signal from the imaging area, and the imaging area in parallel with the focus adjustment operation according to the brightness of a subject. And a control means for controlling a mode for displaying an image based on a signal from the camera and a mode for not displaying an image in parallel with the focus adjustment operation. .

According to the brightness of the subject, the charge accumulation time in the imaging region where the photoelectric conversion is performed is changed, and the signal reading range from the imaging region is changed and read. Provided is a focus adjustment method for performing focus adjustment based on the focus adjustment.

[0012] Still further, according to the brightness of the subject, the charge accumulation time in the imaging region where the photoelectric conversion is performed is changed, and a signal reading range is changed and read out from the imaging region. And a computer-readable storage medium storing a procedure for performing focus adjustment based on a signal to be read.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG.
1 is an overall configuration diagram of an imaging device according to an embodiment.

In FIG. 1, 101, 102, 103, 1
Reference numerals 04 denote constituent elements of the lens system, which are a fixed front lens group, a second lens group having a focusing function, an aperture, and a fixed third lens group, respectively. The image light transmitted through this lens system forms an image on the surface of the image sensor 105 including the image pickup area where photoelectric conversion is performed, and is converted into a video signal by photoelectric conversion. The image sensor according to the present embodiment is an X-ray sensor such as a CMOS image sensor.
It is a Y-address type, and signals in only a predetermined area can be read from the image sensor. 106 is an A / D conversion circuit,
Reference numeral 107 denotes a camera signal processing circuit. The video signal processed here is converted into an analog signal by a 108 D / A conversion circuit, processed by an LCD display circuit 109 serving as a video display unit, and then processed by an LCD (display unit). Liquid cry
The captured image is displayed by a “strat display” 110.

On the other hand, the video signal subjected to the signal processing in 107 is converted into an AWB evaluation value processing circuit 111 as white balance adjustment means and an AE evaluation value processing circuit 1 as exposure adjustment means.
12. It is sent to the AF evaluation value processing circuit 113 which is a focus adjusting means.

An automatic white balance (AW) in the microcomputer 123 based on the data from the AWB evaluation value processing circuit 111.
The calculation for B) is performed, and the result is fed back to the camera signal processing circuit 107 to perform white balance.

According to the video signal input level from the AE evaluation value processing circuit 112, the microcomputer 123 as a control means drives the IG driver 118 and the IG meter 119,
The diaphragm 103 is controlled to adjust the amount of light, and at the same time, the shutter speed, which is the exposure time, is set from the microcomputer 123 to the timing generator (TG) 115 as the driving means.

The AF evaluation value processing circuit 113 extracts and processes only the high-frequency components of the video signal in the ranging frame according to the gate signal from the ranging frame generating circuit 114. 1
Reference numeral 23 denotes a microcomputer, which performs lens drive control and distance measurement frame control for changing a distance measurement area in accordance with the AF evaluation signal strength.

Reference numeral 121 denotes a release switch, which stores a video signal in a recording memory 122 in accordance with the operation of the switch. This release switch is a two-stage type, and the first release switch (SW1) which is the first switch means is turned on.
If N, the focus position is fixed after the AF operation, and the data is recorded in the recording memory 122 when the second release switch (SW2) as the second switch means is turned on.

Reference numeral 119 denotes a driver for outputting driving energy to a lens driving motor in accordance with the driving command 102 output from 123, and 120 denotes a motor for driving 102.

Assuming that the motor for driving the lens is a stepping motor, a method of driving the motor will be described below.

The microcomputer 123 determines the driving speed of the zoom motor and the focus motor by the program processing,
It is sent to the driver 119 for driving the focus motor 120 as a rotation frequency signal of each stepping motor. Further, a drive / stop command of the motor 120 and a rotation direction command of each motor are sent to the driver 119. The drive / stop signal and the rotation direction signal correspond to a drive command determined by processing in the microcomputer 123 at the time of AF for the focus motor. The motor driver sets the phase of the four-phase motor excitation phase to the forward rotation and reverse rotation phases according to the rotation direction signal, and according to the received rotation frequency signal,
By outputting while changing the applied voltages (or currents) of the four motor excitation phases, while controlling the rotation direction and rotation frequency of the motor, the output to the motor is turned ON / OFF in response to the drive / stop command. It is off.

FIG. 3 is a control flow for operating the image pickup apparatus according to the present embodiment, which is processed in the microcomputer 123.

Reference numeral 301 denotes the start of processing. 302
To control the aperture and shutter speed (charge accumulation period of a photoelectric conversion unit such as a photodiode) optimal for the subject at that time. At 302, a timing generator (TG) 115 is set so that the shutter speed determined at 301 is attained. At 304, it is determined whether the first release switch (SW1) has been pressed. If it has not been pressed, the process returns to step 302 and the AE operation is repeated. By this operation, the photographer can always see the subject with the optimal exposure on the LCD. If SW1 is pressed at 304, the process proceeds to 305. In 305, A performed in 302
From the result of the E processing, it is determined whether or not the shooting condition at that time is low illuminance. When the illuminance is low, the shutter speed (exposure time) increases, and when the illuminance is low, the shutter speed increases. If it is determined in 305 that the illuminance is low, the process proceeds to 306 and 30
In step 6, video signals are read from the entire range of the imaging area in which photoelectric conversion is performed in the imaging device.

FIG. 4 shows the timing of reading the video signal from the image sensor. 1 to 6 are timing charts at the time of all read processing. 1 is a 1/30 second cycle when a still picture is taken out by a vertical synchronizing signal. Reference numeral 2 denotes a read pulse for extracting a video signal from the image sensor, and the video signal can be read at the timing of this pulse. Reference numeral 3 denotes an exposure period, and it is desirable to perform exposure as long as possible at low illuminance. In this case, exposure is performed at a shutter speed of 1/30 second. 4 ~
Reference numeral 6 denotes the timing when the gate signal is gated by the gate circuit 114 in accordance with the AF distance measurement frame when all the video signals have been read (4 is FIG. 2A and 5 is FIG. 2C). 6
(B)). That is, of all the ranges in the imaging region,
AF processing is performed using signals in a predetermined area (hatched portions in FIGS. 2A to 2C).

When the all reading process is completed in 306,
Using the video signal read out in 307, processing of auto white balance (AWB), AE, and AF is performed. Then, in 308, it is determined whether or not all the processes of AWB, AE, and AF have been completed.
A series of operations from 06 to 308 are performed. Here, a series of operations 306 to 308 are performed in synchronization with the vertical synchronization signal shown in FIG. Thus, the subject can always be projected on the LCD in an optimal state 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.

At step 309, it is confirmed whether or not the switch SW1 has been pressed. If so, it is checked 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,
At 311 a capture operation is performed. The capture operation is to store the video signal at that time in the 122 recording memory. Then, at 312, the process waits for the end of the capture, and when it is completed, returns to 302 and repeats a series of operations. The above is the flow of shooting at low illuminance. During this time, the image of the subject is always displayed on the LCD in real time, and the photographer can press the SW2 with confidence.

Next, the operation when the illuminance is not low will be described. If it is determined in 305 that the illuminance is not low, the process proceeds to 313. At 313, as a readout of a video signal from the image sensor, a block readout process for AF (AF
The image sensor reads out the signal of only the area used for

4 to 6 in FIG. 4, when the light amount is sufficient and bright, the timing of the gate for the AF distance measurement frame is completed only for extracting the video signal for AF. Immediately after the next exposure is started, the sampling frequency of the evaluation value from the AF video signal is increased, and A
It can be seen that high-speed F operation can be realized. From this, when the illuminance is not low, according to the AF ranging frame,
Read out only the necessary parts, increase the shutter speed, shorten the exposure time, speed up the sampling cycle,
The speed of the AF operation is increased. Timing charts at that time are shown in FIGS. 313
7 indicates a vertical synchronizing signal, and sets 115TG so as to increase the frequency of the vertical synchronizing signal in accordance with the reading of the block for AF. Then, the shutter speed is increased to match the block reading for AF, and 115TG is set. Then, the timing for performing block reading is set to 115TG so that only the portion corresponding to the AF ranging frame is read from the image sensor. By this block reading, it is possible to quickly accumulate and extract necessary video signals at any location regardless of the location of the AF ranging frame. Then, in accordance with the signal, the hill-climbing AF is performed, and it is determined whether the AF process has been completed in 314, and the process returns to 313 if not completed, and proceeds to 315 if completed.

In step 315, as in step 313, an AE block read process is performed to read a video signal from the image sensor. Then, AE is performed according to the signal, and it is determined at 316 whether the AE process has been completed. If not completed, the process returns to 315, and if completed, the process proceeds to 317.

In step 317, similarly to step 313, an AWB block reading process is performed as reading of a video signal from the image sensor. Then, according to the signal, AW
B, it is determined whether the 318 AWB process has been completed, and if not completed, the process returns to 317;
Proceed to.

A series of AF, AE, and AWB operations are completed as described above. During this period, an image of a subject cannot be displayed on the LCD as in the case of low illuminance, but the series of operations is ended early. be able to.

As described above, at the time of low illuminance, the reading of the video signal from the image sensor is set to the full reading mode,
The subject can be drawn on D in real time, and the reading of the video signal from the image sensor is performed except during low illuminance.
By setting the block read mode according to the function,
The AF operation becomes faster, and the preparation time for capture by SW1 becomes shorter.

That is, in other words, the following effects can be obtained.

Since the charge accumulation time does not need to be extended except at the time of low illuminance, the signal read time from the image sensor is not negligible with respect to the charge accumulation time. For this reason, it is possible to shorten the time required for AF by reducing the readout range in the image pickup area and thereby reducing the amount of signal readout from the image pickup device.

At low illuminance, it is necessary to lengthen the charge accumulation time. Therefore, the signal read time from the image pickup device is relatively shorter than the charge accumulation time, and the read range in the image pickup area is reduced. At least, even if the entire area is read, the charge accumulation time is negligible. Therefore, at low illuminance, signals in the entire range of the imaging region are read out, and an image is displayed on the LCD in parallel with the AF operation.

As described above, it is possible to perform an appropriate AF operation according to the brightness of the subject.

(Second Embodiment) In the first embodiment, regarding the setting of 115TG in 313, 115TG is set so as to increase the frequency of the vertical synchronization signal in accordance with reading of the block for AF. Then, the shutter speed is set to 115 TG, which is faster than the block reading for AF, and the timing at which block reading is performed is set to 115 TG so that only the portion corresponding to the AF ranging frame is read from the image sensor. ". Here, since the XY address type image pickup device can perform block reading, it is possible to accumulate and read only the portion to be read from the portion to be read regardless of the position of the AF ranging frame. For example, as shown in FIG. 5, the photographer is going to shoot the image of FIG. 5A, and assuming that the AF distance measurement frame is 50 frames of FIG. Can be read as follows. Assuming that the AF distance measuring frame is slightly larger and is the 51 frame shown in FIG. 5A, when the block is read out by the image sensor, it can be read out as shown in FIG. 5C. Therefore. A
By setting the exposure time and the vertical synchronization period in accordance with the shutter speed at which a video signal capable of AF can be extracted in accordance with the size of the distance measuring frame of F, a more optimal AF operation can be performed.

(Third Embodiment) In the first embodiment, as in the case of 313, as in 313, an AE block read process is performed to read a video signal from the image sensor. Perform AE according to
At 316, it is determined whether the AE process has been completed. If not completed, the process returns to 315, and if completed, the process proceeds to 317. "
However, since the photometric frame for the AE differs depending on the shooting mode (program AE), a more optimal AE operation can be performed by determining the range in which the AE block is read out according to the shooting mode at the time of shooting. Becomes possible.

In the first to third embodiments, XY
Although the address type image sensor has been described, a charge transfer type image sensor such as a CCD may be used. That is, for example, after the charges in the unnecessary areas are transferred at a high speed, they are swept away or the charges in the unnecessary areas are transferred to the vertical CCD and the horizontal CCD.
Block reading may be achieved by using a structure of sweeping between CDs.

(Other Embodiments) According to the present invention, a storage medium storing a program code of software for realizing the functions of the above-described embodiments is supplied to a system or an apparatus, and a computer (or a computer) of the system or apparatus is provided. It is needless to say that the present invention is also achieved when the CPU or the MPU reads and executes the program code stored in the storage medium.

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.

As a storage medium for supplying the program code, for example, a floppy disk, hard disk, optical disk, magneto-optical disk, CD-ROM, C
DR, magnetic tape nonvolatile memory card, ROM, and the like can be used.

When the computer executes the readout program code, the functions of the above-described embodiment are realized. In addition, based on the instructions of the program code, the OS running on the computer performs actual processing. The functions of the above-described embodiment can be realized by performing a part or all of the above.

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, based on the instructions of the program code, A CPU or the like provided in the function expansion board or the function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments can also be realized by the processing.

The present invention is also applicable to a case where the program is transferred from a storage medium storing a program code of software for realizing the functions of the above-described embodiments to a requester via a communication line such as a personal computer communication. It goes without saying that it can be applied.

[0047]

According to the present invention, the focus can be adjusted by an optimal operation such as displaying or not displaying an image during the focus adjustment operation, according to 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 ranging 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 showing an AF ranging frame;

[Explanation of symbols]

 101, 104 Fixed lens 102 Focus lens 103 Aperture 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 measuring 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 (9)

[Claims] An imaging region for performing photoelectric conversion; a driving unit that changes a charge reading time in the imaging region according to brightness of a subject and changes and reads a signal reading range from the imaging region; An imaging apparatus, comprising: a focus adjustment unit that performs focus adjustment based on a signal read from the imaging area. 2. The method according to claim 1, wherein, when the subject has low illuminance, the charge accumulation time is longer than the low illuminance, and a range in which a signal is read from the imaging area is smaller than the low illuminance. The imaging device according to claim 1, wherein the size is increased. 3. The imaging apparatus according to claim 2, further comprising a video display unit that displays a video based on a signal read by the driving unit in parallel with the focus adjustment. 4. The driving unit, when the object is other than the low illuminance, makes the charge accumulation time longer than the case of the low illuminance, and when the brightness of the object is other than the low illuminance. 4. The imaging apparatus according to claim 1, wherein a signal is read from an area smaller than the imaging area. 5. The image pickup apparatus according to claim 4, wherein, when the subject is other than low illuminance, exposure adjustment and white balance adjustment are performed in time series after the focus adjustment operation is completed. . 6. An image pickup area for performing photoelectric conversion, focus adjustment means for adjusting focus based on a signal from the image pickup area, and the image pickup area in parallel with the focus adjustment operation according to brightness of a subject. An image pickup apparatus comprising: a mode for displaying an image based on a signal from the control unit; and control means for controlling a mode for not displaying an image in parallel with the focus adjustment operation. 7. A recording unit for recording a video signal, a first switch unit for performing the focus adjustment, and a second unit for controlling a timing at which the recording unit records a video signal based on a signal from the imaging area. The imaging device according to claim 6, further comprising: switch means. 8. A method according to claim 1, wherein a charge accumulation time in an imaging region where photoelectric conversion is performed is changed according to a brightness of a subject, and a signal reading range is changed and read out from the imaging region. A focus adjustment method for performing focus adjustment based on this. 9. A procedure for changing a charge accumulation time in an imaging region where photoelectric conversion is performed according to brightness of a subject, changing a range in which a signal is read from the imaging region, and reading the signal, and reading the signal from the imaging region. A computer-readable storage medium storing a procedure for performing focus adjustment based on a signal;