JP2003319238A - Electronic camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To minimize a time lag up to photographing by omitting unneeded focus adjustment operation while adopting a contrast method with high focus accuracy. <P>SOLUTION: An electronic camera comprises: an image pickup element for receiving transmitted light of a photographing optical system including a focusing lens; a calculation means for calculating a focus evaluation value changing in accordance with the adjusted focus state of the focusing lens on the basis of an image pickup signal; a focus adjustment means for operating the calculation means while moving the focusing lens in the direction of an optical axis in accordance with focus adjustment start operation, detecting a focal position on the basis of a calculation output of the calculation means and driving the focusing lens to the detected focal position; a clock means for starting clocking at photographing start operation or after photographing; and a determination means for determining whether to operate the focus adjustment means on the basis of a time clocked by the clock means when focus adjustment start operation is performed at the next photographing start after the photographing. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic camera that performs automatic focusing (AF) using a contrast method.

[0002]

2. Description of the Related Art Conventionally, there is a so-called contrast method as an automatic focus adjusting method for electronic cameras. this is,
The subject is imaged by an image pickup device such as a CCD, and the in-focus position is obtained using an image pickup signal in a predetermined focus detection area. Specifically, a focus evaluation value is calculated by extracting a component of a predetermined spatial frequency band from the image pickup signal in the focus detection area using a bandpass filter and integrating the absolute value of the component. This focus evaluation value is an amount corresponding to the contrast of the focus detection area, and the higher the contrast, the higher the value. In view of the fact that the image contrast becomes higher as the focusing lens is closer to the in-focus position, the position where the focus evaluation value reaches a peak (hereinafter referred to as the peak position) is found, and the in-focus position is determined. Drive the focusing lens.

[0003]

A so-called hill-climbing control is used to detect the peak position in the contrast method. In this method, focus evaluation values are calculated for each predetermined movement pitch while moving the focusing lens along the optical axis, and the focus evaluation values are analyzed to find the peak position. In this method, generally, a highly accurate focusing result is obtained, but it takes time to find the focusing position, and there is a risk of missing a photo opportunity.

It is an object of the present invention to provide an electronic camera which adopts a cost-last method with high focusing accuracy and which has a high possibility of taking a photo opportunity by omitting an unnecessary focus adjusting operation. .

[0005]

SUMMARY OF THE INVENTION An electronic camera according to the present invention includes an image pickup device which receives transmitted light of a photographing optical system including a focusing lens and outputs an image pickup signal, and a focusing lens based on the image pickup signal. A calculation means for calculating a focus evaluation value that changes according to the focus adjustment state, and the calculation means is operated while moving the focusing lens in the optical axis direction in accordance with the focus adjustment start operation,
The focus position is detected based on the calculation output, and the focus adjusting means drives the focus lens to the detected focus position, the time measuring means for starting the time measurement with the shooting start operation or after the shooting, and the after shooting When a focus adjustment start operation is performed at the start of the next photographing, a determination means for determining whether to activate the focus adjustment means based on the time measured by the time measurement means is provided, thereby solving the above problems. . According to the second aspect of the invention, the operation of the focus adjusting means is prohibited when the time measuring time of the time measuring means is within a predetermined time. According to a third aspect of the present invention, a determination unit that determines the difference between the focus evaluation value at the focus position detected immediately before shooting and the focus evaluation value at the same lens position detected along with the focus adjustment start operation immediately after shooting. Further, the operation of the focus adjusting means is prohibited when the time measured by the time measuring means is within a predetermined time and the difference is determined to be less than or equal to a predetermined value. According to the invention of claim 4, timekeeping is started in association with the shooting start operation. According to the invention of claim 5, the timing is started with the end of the photographing. According to a sixth aspect of the present invention, there is further provided image pickup / recording means for performing image pickup by the image pickup element in response to the image pickup start operation and writing the image pickup signal output from the picked-up image element to the temporary storage medium, and to the temporary storage medium. The clock is started at the end of writing. According to a seventh aspect of the present invention, there is further provided image pickup / recording means for performing image pickup by the image pickup device in response to an image pickup start operation and writing the image pickup signal output from the image pickup device into a long-term storage storage medium. The clock is started when the writing to the storage medium is completed. According to the invention of claim 8, as the storage medium for long-term storage, an external storage medium which can be inserted into and removed from the camera is used.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a functional block diagram of the electronic camera of this embodiment. The subject light flux that has passed through the photographing optical system 101 passes through the diaphragm 102 and is imaged on the light receiving surface of the image sensor 103. The image pickup element 103 is a photoelectric conversion image pickup element that outputs an electric signal according to the light intensity of the subject image formed on the light receiving surface, and a CCD type or MOS type solid state image pickup element is used. The image pickup signal output from the solid-state image pickup element 103 is input to the analog signal processing circuit 104, where processing such as correlated double sampling processing (CDS processing) is performed.

The image pickup signal processed by the analog signal processing circuit 104 is converted into digital image data by the A / D converter 135 and then temporarily stored in the buffer memory 105. The buffer memory 105 is a frame memory capable of storing image data for a plurality of frames, but this is only for temporarily storing image data.
Image data is not stored in the long term. The data stored in the buffer memory 105 is read out to the digital signal processing circuit 106, where various image processing such as contour compensation and gamma correction is performed. The digital signal processing circuit 106 includes various signal processing circuits such as a gain control circuit, a luminance signal generation circuit, and a color difference signal generation circuit, which are controlled by an instruction from the CPU 112.

The image data after digital processing is stored again in the buffer memory 105 and then recorded in the image storage medium 111 via the recording / reproducing signal processing circuit 110.
As the image storage medium 111, an external storage medium such as a memory card that can be inserted into and removed from the camera is generally used.

When recording image data in the storage medium 111, data compression is generally performed in a predetermined compression format, for example, the JPEG system. Recording / reproducing signal processing circuit 110
Performs data compression (for example, JPEG compression) when recording the image data in the storage medium 111, and data decompression processing when reading the compressed image data from the storage medium 111. The recording / reproducing signal processing circuit 110 includes a storage medium 11
1 also includes an interface for data communication.

The monitor 109 is a liquid crystal display device for displaying picked-up image data, and is also used for reproducing and displaying the image data recorded in the storage medium 111.
When displaying an image on the monitor 109, the image data stored in the buffer memory 105 is read, the D / A converter 108 converts the digital image data into an analog video signal, and the analog video signal is used to monitor the monitor 10.
The image is displayed at 9.

There are two display modes of the subject image captured by the image sensor 103 on the monitor 109. One is the display form when the release operation is not performed,
This is a display form called a through image in which subject images repeatedly captured by the image sensor 103 are sequentially updated and displayed. The other is a display form called a freeze image in which the subject image captured by the image sensor 103 is displayed for a predetermined time after the release operation of the camera.

The CPU 112 is an AE calculation unit 112 that performs automatic exposure calculation based on the image signal from the image sensor 103.
1 and an AWB calculation unit 1122 that calculates a white balance adjustment coefficient, and a focus detection unit that includes a bandpass filter (hereinafter, BPF) 1124, an evaluation value calculation unit 1125, and an AF calculation unit 1126. . The BPF 1124 extracts a high frequency component in a predetermined band from the image pickup signal in the focus detection area provided in the image pickup area. In addition, when a plurality of focus detection areas are set, the signals in each area are sequentially read, and the extraction processing in each area is performed by the bandpass filter 1124. In the following, a case where there is one focus detection area will be described as an example.

The output of the BPF 1124 is the evaluation value calculation unit 11
25, the focus evaluation value is calculated by integrating the absolute value of the high frequency component in the evaluation value calculation unit 1125. The AF calculation unit 1126 determines that A based on the focus evaluation value.
F calculation is performed to recognize the in-focus position. Details of this AF calculation will be described later. Based on the calculation result of the AF calculation unit 1126, the CPU 112 drives a stepping motor (not shown) for focusing through the driver 113, and directs the focusing lens forming the photographing optical system 101 to the focusing position along the optical axis. Drive. The timer 1127 counts time for determining whether or not AF restart is necessary, and details thereof will be described later.

The photographing optical system 101 also includes a zoom lens, and the driver 113 also drives the zoom. In addition, the driver 114 responds to a command from the CPU 112 to stop the aperture 1
02, and the driver 115 controls the timing of signal extraction from the image sensor 103.

An operation unit 116 connected to the CPU 112
Is a power switch 1161 for turning on / off the power of the camera, a half-press switch 1163 that is turned on by half-pressing the release button, a full-press switch 1162 that is turned on by fully-pressing the release button, a shooting mode, etc. A setting button 1164 for selecting is provided.
The shooting modes set by the setting button 1164 include a normal shooting mode, a landscape shooting mode, a portrait shooting mode, a sports shooting mode, a close-up shooting mode, a night view mode, and the like, and a method of determining an exposure value differs depending on each mode. . The CPU 112 sets one of the modes according to the operation of the setting button 1164.

Next, the contrast A in this embodiment
The F control will be described in detail. The contrast method focuses on the fact that there is a correlation between the degree of blurring of an image and the contrast, and the fact that the contrast of the image becomes maximum when the image is in focus is used for focusing. The size of the contrast can be evaluated by the size of the high frequency component of the image pickup signal. That is, the BPF 1124 extracts the high frequency component of the image pickup signal, and the evaluation value calculation unit 1125 integrates the absolute value of the high frequency component to obtain the focus evaluation value.
This focus evaluation value is an amount that changes according to the contrast of the image, in other words, the focus adjustment state of the focusing lens, and becomes the maximum value (peak value) when the contrast is maximized by focusing.

In order to obtain the lens position where the focus evaluation value reaches a peak (hereinafter referred to as the peak position), an AF calculation method called hill climbing control is conventionally known. This is to obtain the focus evaluation value at a predetermined sampling period while moving the focusing lens, and to grasp the variation of the evaluation value each time by comparing it with the previous evaluation value each time, finally the peak position of the evaluation value, In other words, it is to find the top of the mountain. And
The peak position is determined to be the in-focus position. AF like this
The calculation is usually started with a half-press operation of the release button (focus adjustment start operation).

FIG. 2 is a time chart showing the procedure of the operation related to the first exposure. When the peak position is found by the AF calculation (FIG. 2A), the focusing lens is driven to that position. As a result, the focusing lens focuses on the subject (FIG. 2B). Shooting is started along with the full-press operation of the release button (shooting start operation: FIG. 2C) (FIG. 2D). The photography here is an operation performed immediately before the exposure and an operation including the exposure itself. For example, in the case of a single-lens reflex type electronic camera, photographing is performed by raising a mirror, narrowing down, and subsequently opening and closing a shutter. Further, the exposure refers to an operation in which the image sensor 103 receives a subject light flux for a time (exposure time) corresponding to a shutter speed and generates an image signal corresponding thereto.

The image pickup signal of the image pickup element 103 is read out after the image pickup is completed, and the analog signal processing circuit 1 responds to the signal
At 04, a correlated double sampling process (CDS process) or the like is performed, and the A / D converter 135 further performs A / D conversion. The converted digital image data is temporarily stored in the buffer memory 105 (FIG. 2E), and then recording processing such as compression for recording the image data in the storage medium 111 is performed (FIG. 2F). ), And then the image data is written to the storage medium 111 (FIG. 2).
(G)).

By the way, after the AF calculation and the lens driving, the first shot is taken, and then the half-press operation is performed to take the next shot (FIG. 2 (h)), the AF is restarted (the AF calculation is performed again). Is usually done). However, in the case of taking a next shot at a relatively short time interval from the end of shooting, there are many cases where the same subject as the previous one is shot at the same subject distance. In this case, the focusing lens has already focused on the subject, and it is not necessary to restart AF. Therefore, in the present embodiment, timing is started after the release button is fully pressed, and if the release button is pressed halfway before the timed time reaches the predetermined time, the AF is not restarted. . As a result, unnecessary focus adjustment operations can be omitted and the next shot can be taken quickly.

In order to realize the above control, it is necessary to have a time measuring means for measuring the time until the next half-press operation, and the timer 1127 is used as the time measuring means. Timer 112
There are several cases in which timing 7 should be started, and these cases are shown in FIGS. 2 (i) to (l). Hereinafter, they will be described in order.

FIG. 3 shows a timer 1127 in response to the full-press operation.
Is started, which corresponds to FIG. 2 (i). This program is executed by the CPU 112 when the power is turned on. First, in steps S1 and S2, either the AF start operation (for example, half-press operation) or the power off operation is waited for. When the power-off operation is performed, the process ends, and when the AF start operation is performed, the AF process by the hill climbing control described above is performed in steps S3 to S6. That is AF
When the focusing lens is driven to the peak position by repeating the calculation and the movement of the focusing lens by a predetermined pitch alternately, the focusing lens is determined to be in focus and the focusing lens is stopped. There is also a device that starts the AF process when the power is turned on.

In step S7, the timer 1127 is reset, and in steps S8 and S9, the full-push operation or the half-push operation is released. When the half-push operation is released, step S1
Returning to step S10, when the full press operation is performed, the process proceeds to step S10. In step S10, the timer 1127 is started,
Start timing. In FIG. 2 (i), t1 indicates the time when the timer starts.

After that, the processing of steps S11 to S14 and the processing of step S15 and subsequent steps are performed in parallel. In steps S11 to S14, photographing, image pickup signal reading, A / D conversion, buffer writing, recording processing described in FIG.
Writing to the storage medium is sequentially performed to complete the process. On the other hand, in the flow after step S15, a half-press operation or a power-off operation is waited for in steps S15 and S16, and the process is terminated when the power is turned off. When the half-push operation is confirmed in step S15, the elapsed time T from the timer start is compared with the predetermined time T1 (FIG. 2 (i)) in step S17. If T ≦ T1, that is, if the half-press operation is performed within a predetermined time T1 from the full-press operation, the same subject as in the front is photographed from the same distance, that is, the subject is already in focus. The determination is made, and the process returns to step S8 without restarting the AF. On the other hand, if T> T1, it is determined that the focus state has collapsed because the composition has been changed or the subject has moved, and the process returns to step S3 to restart the AF.

Here, the predetermined time T1 used in the determination in step S17 is a time obtained by adding a predetermined time α to the time (reference) required from the start of photographing to the end of writing the storage medium, as shown in FIG. 2 (i). Is set. However, since the time required for each operation after full-press operation can vary under various conditions,
Time T1 during any one of steps S11 to S14
May pass. Therefore, for example, the longer the exposure time is, the higher the possibility of restarting.

FIG. 4 shows another example, in which the timer 1127 is started at the end of photographing, and FIG.
Corresponding to. 3 is different from FIG. 3 in that the timer start time point (t2 in FIG. 2 (j)) is after the processing of step S11, and thereafter, the processing of steps S12 to S14 and the processing of step S15 and thereafter are performed in parallel. And the point at which the elapsed time T is determined to be the predetermined time T2 (step S
17-2). The predetermined time T2 is set as a time obtained by adding a predetermined time α to the time (reference) required from the end of shooting to the end of writing the storage medium, as shown in FIG. 2 (j).
In this way, when the timing is started after the end of the photographing, the exposure time is short and the restart is not affected. However,
If the time taken for the processing performed after shooting is long, the possibility of restarting becomes high.

FIG. 5 shows still another example, in which the timer 1127 is started when the writing of the image signal into the buffer memory is completed, and corresponds to FIG. 2 (k). The difference from FIG. 3 is that when the timer is started (see FIG.
(T) of (k) is after the processing of steps S11 and S12, that the processing of steps S13 and S14 and the processing of step S15 and thereafter are performed in parallel, and the determination target of the elapsed time T is predetermined. This is the point at time T3 (step S17-3). The predetermined time T3 is set as a time obtained by adding a predetermined time α to the time (reference) required from the end of writing the buffer to the end of writing the storage medium, as shown in FIG. In this case, the time until the end of the buffer writing (including the exposure time) does not affect the presence or absence of restart. However, if the processing performed after writing the buffer takes a long time, the possibility of rebooting increases.

FIG. 6 shows still another example, in which the timer 1127 is started at the time when writing to the storage medium is completed, and corresponds to FIG. 2 (l). 3 is different from that in FIG. 3 in that the timer start time point (t4 in FIG. 2 (l)) is after the processing in steps S11 to S14, the processing in step S15 and subsequent steps are performed, and the elapsed time T The point where the determination target is the predetermined time T4 (step S17-
4). As the predetermined time T4, the predetermined time α is set as shown in FIG. In this case, each processing time from the start of shooting to the writing of the recording medium does not affect the presence or absence of restart.

In each of the examples shown in FIGS. 3 to 6, the necessity of restarting is determined based on only the elapsed time T, but the presence or absence of restarting is also determined by taking into consideration the fluctuation of the focus evaluation value. Good. FIG. 7 shows an example thereof, in which step S18 is added after step S17 in FIG. Step S17
If it is determined that the elapsed time T is within the predetermined time T1, the fluctuation of the peak value of the focus evaluation value is determined in step S18.
Specifically, the peak value of the focus evaluation value obtained by the AF calculation in step S3 (peak value immediately before shooting) and step S1
The difference with the same peak value obtained when 7 is affirmed (the peak value obtained with half-pressing immediately after shooting) is determined, and it is determined whether the difference exceeds a predetermined value. If the difference is less than or equal to the predetermined value, it is determined that the focusing lens is at the focusing position and the process returns to step S8 without restarting. If it exceeds the predetermined value, the focusing lens is not at the focusing position. Then, the process returns to step S3 to restart. In this way, by also taking into consideration the fluctuation of the focus evaluation value, it is possible to more accurately determine whether or not the focus is achieved when the shutter button is half-pressed again, and more appropriate treatment can be performed.
The above step S18 may be added to the processing of FIGS.

In the above-described embodiment, the CPU 112 computing means, clocking means, determining means, and determining means, the buffer memory 105 as a temporary storage medium, and the image storage medium 111.
Constitutes a storage medium for long-term storage and an external storage medium, respectively.

In the above, the hill climbing control is shown as the AF calculation method, but a method called whole area scanning may be used. This is, for example, the focusing lens from the infinity end to the close-up end, or vice versa, is scan-driven, and during the scan driving, the focus evaluation value is obtained each time the focusing lens moves by a predetermined movement pitch, The obtained focus evaluation values are sequentially stored. After the scan drive is completed, the stored focus evaluation values are analyzed to determine the peak position.

As the storage medium for long-term storage, an external storage medium (for example, a memory card) that can be inserted into and removed from the camera was used, but this is a memory fixed to the camera (a memory different from the buffer memory). May be Further, an electronic camera of a type that does not have a temporary storage medium such as a buffer memory and directly writes data to a storage medium for long-term storage may be used. Further, an electronic camera of a type in which only a temporary storage medium is used and a long-term storage storage medium is not used may be used.

[0033]

According to the present invention, when the photographing start operation or the timing after the photographing is started and the focus adjustment start operation for the next photographing after the photographing is performed, the focus adjusting means is based on the time measured by the time measuring means. Since it is determined whether or not to operate, the unnecessary focus adjustment operation can be omitted, and the possibility that the shutter chance can be realized can be increased.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing a control system of an electronic camera according to an embodiment of the present invention.

FIG. 2 is a time chart showing a procedure of operations related to shooting.

FIG. 3 is a flowchart showing an example of an operation in the embodiment.

FIG. 4 is a flowchart showing another example of the operation, in which the timer start timing is different from that in FIG.

5 is a flowchart showing still another example of the operation, in which the timer start timing is different from that in FIGS. 3 and 4. FIG.

FIG. 6 is a flowchart showing still another example of the operation, in which the timer start timing is different from that in FIGS. 3 to 5.

FIG. 7 is a flowchart showing still another example of the operation, and a method of determining whether or not a restart is necessary is different from that in FIGS. 3 to 6.

[Explanation of symbols]

101 shooting lens 102 aperture 103 image sensor 104 Analog signal processing circuit 106 digital signal processing circuit 112 CPU 113-115, 118 driver 116 Operation part 119 battery 120 Voltage detector 135 A / D converter 1161 power switch 1162 full-press switch 1163 Half-press switch 1164 Setting button 1123 storage unit 1124 bandpass filter 1125 Evaluation value calculation unit 1126 AF calculation unit 1127 timer

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) // H04N 101: 00 G03B 3/00 A (72) Inventor Toshiaki Maeda 3-2 Marunouchi, Chiyoda-ku, Tokyo No. 3 In stock company Nikon (72) Inventor Hideomi Hibino 3 2-3 Marunouchi, Chiyoda-ku, Tokyo Inside stock company Nikon (72) Inventor Masa Ota 1-3 25 Futaba, Shinagawa-ku, Tokyo Stock fair F term in Nikon technology studio (reference) 2H011 AA03 BA31 BB04 CA19 CA21 DA00 2H051 AA00 BA47 CE14 DD17 EA05 EA08 EA25 EA30 EB18 FA38 FA48 GB12 5C022 AA13 AB28 AC31 AC42 AC51 AC69 5C024 AX01 BX01 CY29 HXY EX04 EX42

Claims (8)

[Claims] 1. An image pickup device which receives transmitted light of a photographing optical system including a focusing lens and outputs an image pickup signal, and a focus which changes according to a focus adjustment state of the focusing lens based on the image pickup signal. A calculation means for calculating an evaluation value, and the focus adjustment lens is moved in the optical axis direction in accordance with the focus adjustment start operation to activate the calculation means, and the focus position is detected based on the calculation output and detected. A focus adjusting means for driving the focusing lens to a focus position, a time measuring means for starting timekeeping with or after a shooting start operation, and a focus adjusting start operation for starting the next shooting after the shooting At this time, the electronic camera is provided with a deciding means for deciding whether or not to operate the focus adjusting means on the basis of the time measured by the time measuring means. 2. The determining means prohibits the operation of the focus adjusting means if the time measuring time of the time measuring means is within a predetermined time even if the focus adjusting start operation is performed. The electronic camera described in 1. 3. A determination unit that determines a difference between a focus evaluation value at the in-focus position detected immediately before shooting and a focus evaluation value at the same lens position detected along with a focus adjustment start operation immediately after shooting. Further provided, the determination means, even if the focus adjustment start operation is performed,
2. The electronic camera according to claim 1, wherein the operation of the focus adjusting means is prohibited when the time measured by the time measuring means is within a predetermined time and the difference is determined to be a predetermined value or less. 4. The electronic camera according to claim 1, wherein the time counting means starts time counting in accordance with the photographing start operation. 5. The electronic camera according to claim 1, wherein the time counting means starts time counting when the photographing is completed. 6. The image pickup device further comprises an image pickup / recording unit for taking an image by the image pickup device and writing an image pickup signal output from the image pickup device in a temporary storage medium in response to the image pickup start operation. 4. The time counting is started with the completion of writing to the temporary storage medium.
The electronic camera according to any one of 1. 7. An image pickup / recording unit for performing image pickup by the image pickup device and writing an image pickup signal output from the image pickup device into a long-term storage medium in response to the image pickup start operation, the timekeeping The electronic camera according to any one of claims 1 to 3, wherein the means starts timing with the end of writing to the long-term storage medium. 8. The storage medium for long-term storage is an external storage medium that can be inserted into and removed from a camera.
The electronic camera described in.