JP2003315665A - Camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make AF (automatic focusing) fast while employing a contrast system with high focusing accuracy. <P>SOLUTION: A camera is provided with: an imaging element which receives transmitted light of a photography optical system including a focusing lens and outputs an imaging signal; an arithmetic means which computes a focus evaluated value varying with the focus adjustment state of the focusing lens on the basis of the imaging signal; and a focus adjusting means which places the arithmetic means in operation while moving the focusing lens along the optical axis within a specified lens movement object range, detects a focusing position on the basis of the arithmetic output and drives the focusing lens to the detected focusing position. When a 1st photographic mode is set, the lens movement object range for the focusing position detection by the focus adjusting means is set to a 1st range E1 up to a specified distance from a near end to before an infinite distance end and when a 2nd photographic mode is set by a mode setting means, the lens movement object range is set to a 2nd range E2 up to a prescribed distance form the infinite-distance end to before the near end. <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 a camera for performing automatic focusing (AF) using a contrast method.

[0002]

2. Description of the Related Art Conventionally, there is a method called a contrast method as an automatic focus adjusting method for a camera. In this method, an image of a subject is picked up by an image pickup device such as a CCD, and an 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. This method generally provides a highly accurate focus result, but it may take time to find the focus position.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a camera in which the AF speed is increased while adopting the cost last method with high focusing accuracy.

[0005]

The camera according to the present invention comprises:
An image pickup element that receives transmitted light of a photographing optical system including a focusing lens and outputs an image pickup signal, and a calculation unit that calculates a focus evaluation value that changes according to a focus adjustment state of the focusing lens based on the image pickup signal. Then, while operating the focusing lens in the optical axis direction within the predetermined lens movement target range, the calculation means is operated,
A focus adjustment unit that detects a focus position based on the calculation output and drives the focus lens to the detected focus position, a mode setting unit that sets a shooting mode, and a first shooting mode by the mode setting unit. Is set, the lens movement target range for detecting the in-focus position by the focus adjusting means is set to the first range from the close end to a predetermined distance not reaching the infinity end, and the mode setting means sets the first range. When the shooting mode of No. 2 is set, there is provided range setting means for setting the lens movement target range to a second range from the infinity end to the close end up to a predetermined distance, which causes the above problems. To solve. According to a second aspect of the present invention, the first shooting mode includes a person shooting mode, and the second shooting mode includes any of a sports shooting mode, a landscape shooting mode, and a night view mode. In the invention of claim 3, the first range is a range from the closest end to a distance of 3 m, and the second range is a range from the infinite end to a distance of 1 m.

[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 a digital still camera according to this embodiment. Shooting optical system 101
The subject light flux that has passed through the aperture passes through the diaphragm 102 and is imaged on the light receiving surface of the image sensor 103. The image pickup device 103 is a photoelectric conversion image pickup device that outputs an electric signal according to the light intensity of the subject image formed on the light receiving surface, and is of a CCD type or a MOS type.
Type solid-state imaging device 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 that can store image data for a plurality of frames. 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, but a memory fixedly provided in the camera may be 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 1123 that includes a bandpass filter (hereinafter, BPF) 1124, an evaluation value calculation unit 1125, and an AF calculation unit 1126. There is. 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 is generally called a half-press timer, and starts counting when the half-press operation of the release button is released and after the first focusing after the power is turned on.

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.

The operation unit 116 connected to the CPU 112 includes a power switch 1161 for turning on / off the power of the camera, a half-push switch 1163 that is turned on by half-pressing the release button, and a full-press operation of the release button. A full-press switch 1162 that is turned on by and a setting button 1164 for selecting a shooting mode and the like are provided.
The shooting modes set by the setting button 1164 include a normal shooting mode, a landscape mode, a portrait shooting mode, a sports shooting mode, a close-up mode, a night view mode, etc., and a method of determining an exposure value differs depending on each mode. C
The PU 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 a lens position where the focus evaluation value reaches a peak (hereinafter referred to as a peak position), an AF calculation method called hill climbing control has been conventionally used. this is,
While moving the focusing lens, the focus evaluation value is obtained at a predetermined sampling cycle, and each time it is compared with the previous evaluation value to sequentially grasp the fluctuation of the evaluation value, and finally the peak position of the evaluation value, that is, the peak value. It is to find the summit. Then, the peak position is determined to be the in-focus position.

By the way, the approximate position of the peak of the focus evaluation value is determined to some extent by the above-mentioned photographing mode. For example, the person photographing mode is a mode for photographing a subject (person) at a relatively short distance, and therefore, a peak is overwhelmingly overwhelmed at the short distance side. On the contrary, the landscape shooting mode and the night view mode are modes for shooting a subject at a long distance, and therefore often have a peak at the long distance side. Therefore,
In detecting the peak position, it is not always necessary to set the entire range from the infinity end to the close end to the detection target range (lens movement target range), and the target range may be limited according to the shooting mode. .

Therefore, in the present embodiment, the lens movement target range for detecting the peak position is defined as follows according to the photographing mode. (1) Portrait shooting mode The lens movement target range is from the closest end to 3 m (see FIG. 2).
The range E1) is restricted to. That is, if the focusing lens is not within the range E1, the peak position detection is started after moving the focusing lens into the range E1, and if the peak position is found, the position is recognized as the focusing position. If the peak position is not found within the range E1, the predetermined lens position is recognized as the in-focus position. (2) Landscape shooting mode, night view mode The lens movement target range is limited to the range from the end of infinity to 1 m (range E2 in FIG. 2). Focusing lens is in this range E2
If the peak position is not found within the range E2, the peak position detection is started, and if the peak position is found, the position is recognized as the in-focus position. If the peak position is not found within the range E2, the predetermined lens position is recognized as the in-focus position. (3) Other modes (including normal shooting mode) The lens movement target range is the entire range from infinity to the close range. In other words, in the modes other than the above, it cannot be generally stated at what distance the subject is located, so the peak position detection is performed over the entire region without setting a limit.

As described above, in the present embodiment, the lens movement target range in the peak position detection is limited according to the photographing mode. Therefore, the time required to detect the peak position is longer than in the case where the entire range is always set as the target range. Can be shortened, and thus the AF speed can be increased.

FIG. 3 shows a flowchart for realizing the above control by software. This program is CPU1
It is executed in step 12, and is started, for example, in response to a half-press operation. First, in step S1, it is determined whether or not the person photographing mode is set. If the result in step S1 is affirmative, in step S2 the lens movement target range for peak position detection is set to the range E1 in FIG. 2, otherwise, either landscape photography mode or night view mode is set in step S3. It is determined whether or not there is. If step S3 is affirmed, the lens movement target range is set to the range E2 in FIG. 2 in step S4, and if not, step S3
In 5, the lens movement target range is set to the entire range.

Then, in step S6, it is determined whether or not the current lens position is within the lens movement target range set in any of steps S2, S4, and S5. If step S6 is affirmed, the process proceeds to step S8, and if not, the focusing lens is driven within the lens movement target range in step S7. The position to be driven is preferably within the target range and closest to the current lens position. For example, if E1 is set as the lens movement target range and the lens is located other than E1, the end portion (3 m) on the infinity side of E1 is set.
Position). After the movement, go to step S8.

In steps S8 to S13, the AF processing by the above-mentioned hill climbing control is performed. That is, the AF calculation and the movement of the focusing lens at a predetermined pitch are alternately repeated, and when the focusing lens is driven to the peak position, the focusing lens is determined to be in focus and the focusing lens is stopped to prepare for photographing. However, if the focusing lens deviates from the lens movement target range before focusing (no peak is found), step S10 is denied. In this case, the focusing lens is driven to a predetermined position determined in step S12. To prepare for shooting. This predetermined position is a distance position that is expected to be focused most frequently, and differs depending on the shooting mode. For example, 2 in portrait mode
m to 3 m, and in landscape photography mode, it may be determined in the range of 5 m to infinity.

Next, in steps S14 and S15, either the full-press operation or the power-off operation is awaited. When the power-off operation is performed, the process is terminated, and when the full-press operation is performed, the image is taken in step S16.

In the above embodiment, the CPU 112 controls the calculation means, the mode setting means and the range setting means by the CP.
The U 112 and the driver 113 respectively configure the focus adjusting means.

In the above, the peak position is detected by the hill climbing control, but a method called whole area scanning may be used. For example, the focusing lens is scan-driven from the infinity end to the close-up end or vice versa, the focus evaluation value is obtained at a predetermined sampling period during the scan drive, and the obtained focus evaluation values are sequentially stored. Do it. After the scan drive is completed, the stored focus evaluation values are analyzed to determine the peak position. This whole-area scan often takes more time to detect the peak position than the hill-climbing method, so the effect of applying the present invention is great.

The lens movement target range according to the photographing mode is not limited to that shown in FIG. In particular, in view of the fact that the photographing magnification changes depending on the focal length of the photographing optical system, the lens movement target range may be determined in consideration of the focal length. For example, even in the same person shooting mode, it is necessary to widen the lens movement target range toward infinity as the focal length of the lens becomes longer. Further, the photographing mode is not limited to the above-described one, and other modes may be set, and in this case, the lens movement target range may be set according to the mode.

[0028]

According to the present invention, when the first photographing mode is set, the lens movement target range for detecting the in-focus position is set to the predetermined distance from the closest end to the infinity end. When the second shooting mode is set by the mode setting means, the lens movement target range is set to the second range up to a predetermined distance from the infinity end to the close end. Therefore, the focus detection can be performed within the range according to the shooting mode, and the AF speed can be increased by quickly obtaining the focus position.

[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 diagram showing an example of a lens movement target range restriction.

3 is a flowchart showing a processing procedure for realizing the range restriction of FIG.

[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

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Toshiaki Maeda             Marunouchi 3 2-3 No. 3 shares, Chiyoda-ku, Tokyo             Ceremony Company Nikon (72) Inventor Masaru Ota             Tokyo Stock Exchange 1-325, Futaba 1-32             Company Nikon technical workshop F term (reference) 2H011 AA03 BA33 CA29 DA00                 2H051 AA00 BA47 DD17 EB20 FA38                 5C022 AA13 AB29 AB66 AC69 AC74

Claims (3)

[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. An operating unit that operates the operating unit while moving the focusing lens in the optical axis direction within a predetermined lens movement target range and an operating unit that operates an evaluation value, and detects and detects a focus position based on the output of the operation. A focus adjusting means for driving the focusing lens to the focused position, a mode setting means for setting a shooting mode, and a focus adjusting means for setting the first shooting mode by the mode setting means. The lens movement target range for detecting the in-focus position is set to a first range from a near end to a predetermined distance that does not reach an infinity end, and a second photographing mode is set by the mode setting means. It is when it is in the camera, characterized by comprising a range setting means for setting a second range of said lens movement target range from the infinite end to a predetermined distance that does not lead to the closest end. 2. The first photographing mode includes a person photographing mode, and the second photographing mode includes any one of a sports photographing mode, a landscape photographing mode, and a night view mode. The listed camera. 3. The first range is a distance of 3 m from the closest end.
3. The camera according to claim 1, wherein the second range is a range from the infinity end to a distance of 1 m.