JP2004037732A - Digital camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital camera in which an accurate automatic focusing (AF) is quickly performed by measuring a distance by making use of a parallax. <P>SOLUTION: A charged coupled device (CCD) imaging device 8 for AF is provided in addition to a CCD imaging device for image shooting. A deviation of an image taken with the CCD device 8 with respect to an image taken with the CCD device 3 is calculated in an AF calculation part 131, and the distance of an object is calculated on the basis of the deviation. Further, an AF action is performed on the basis of the distance of the object. Further, a peak position of a focal point estimation value is calculated in an AF calculation part 132, and an AF motion by a contrast detection method may be used together. As a result, the AF action is sped up while keeping the AF accuracy. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a digital camera.
[0002]
[Prior art]
Conventionally, AF methods used for digital cameras include a contrast detection method and a phase difference method. There is also a method of detecting a distance from a camera to a subject by attaching an external AF module. The contrast detection method performs a focusing operation based on the contrast of an output image, and moves the focus lens little by little to position the lens at a position where the contrast reaches a peak. In the phase difference method, a part of the light beam guided from the photographing lens to the imaging optical system is guided to the AF sensor, and whether the aerial image of the photographing lens is before or after the film surface is determined from the spatial phase shift of the image. Find out.
[0003]
[Problems to be solved by the invention]
However, the contrast detection method is a method of searching for a position where the contrast reaches a peak while moving the focus lens little by little, and thus has a disadvantage that the time required for focusing is longer than other methods. Further, in the phase difference method, there is a problem that a digital camera having a small lens system cannot obtain a sufficient base line length, so that accuracy is hardly obtained. Further, in the method using the external AF module, the subject image formed on the image sensor of the camera and the subject image for focusing captured by the AF module do not always match, so that there is a possibility that the focus may not be achieved at all. there were.
[0004]
An object of the present invention is to provide a digital camera capable of quickly performing an accurate AF operation by performing distance measurement using parallax.
[0005]
[Means for Solving the Problems]
(1) A digital camera according to the first aspect of the present invention includes a photographing image sensor for photographing a photographing subject image formed by a photographing optical system, and an AF for photographing an AF subject image formed by an AF optical system. An image pickup device for photographing, a subject distance calculating unit for calculating a subject distance using parallax based on image data of the image pickup device for photographing and image data of the image pickup device for AF, and a calculation result of the object distance calculating unit. Control means for moving the focus lens of the photographing optical system to perform a focusing operation to achieve the above object.
(2) A digital camera according to a second aspect of the present invention includes a photographing image sensor for photographing a photographing subject image formed by a photographing optical system, and an AF for photographing an AF subject image formed by an AF optical system. Object distance calculating means for calculating the object distance using parallax based on the imaging data of the imaging element for imaging and the imaging data of the imaging element for AF, based on the imaging data of the imaging element for imaging Evaluation value calculating means for calculating the focus evaluation value of the photographic subject image, moving means for moving the focus lens of the photographic optical system, and evaluation value after moving the focus lens based on the calculation result of the subject distance calculation means. The above-mentioned object is achieved by providing a control means for performing a focusing operation by moving a focus lens based on a focus evaluation value calculated by the calculation means.
(3) In the digital camera according to the second aspect of the present invention, after the focus lens is moved within a predetermined range including a focus lens position at which the subject at the calculated subject distance is focused, the evaluation value is calculated. The focus lens is moved based on the focus evaluation value calculated by the means to perform a focusing operation.
(4) In the digital camera according to any one of the first to third aspects, the degree of blur of the photographing subject image at the start of the focusing operation is substantially the same as the degree of blur of the AF subject image. An adjusting means for adjusting the values so as to be provided is provided.
(5) According to a fifth aspect of the present invention, in the digital camera according to the fourth aspect, the degree of blur is adjusted by an aperture mechanism that adjusts the light amount of the subject light flux.
(6) The invention of claim 6 is the digital camera according to any one of claims 1 to 5, wherein the AF optical system includes a part of a finder optical system of the digital camera.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of a digital camera 1 according to the present invention. The photographing optical system 2 forms an image of the subject light L1 on a CCD image pickup device 3 for photographing. On the other hand, 4 is a finder optical system, and the optical axis of the photographing optical system 2 and the optical axis of the finder optical system 4 are separated by a distance a. This distance a is the base line length. The subject light L2 that has passed through the imaging lens 5 of the finder optical system 4 is split by the half mirror 6 into a light beam L21 and a light beam L22.
[0007]
The light beam L21 passes through the half mirror 6 and enters the finder eyepiece 7. On the other hand, the light beam L22 reflected by the half mirror 6 is guided to the AF CCD image pickup device 8 and is imaged on its image pickup surface. That is, the CCD imaging device 3 captures the subject image formed by the imaging optical system 2, and the CCD imaging device 8 captures the subject image formed by the imaging lens 5 of the finder optical system 4. Since the CCD image sensor 8 is used not for photographing but for AF, the number of pixels may be smaller than that of the photographing CCD image sensor 3. For example, even when a CCD having 3 million pixels is used as the imaging CCD imaging device 3, the same 3,000,000 pixels are not necessarily required for the AF CCD imaging device 8, and about 300,000 pixels is sufficient. In this embodiment, a CCD type image pickup device is used, but the present invention is not limited to the CCD type and can be used.
[0008]
FIG. 2 is a functional block diagram of the digital camera 1 shown in FIG. A focusing lens (not shown) of the photographing optical system 2 is driven by a driver 10. The driver 10 includes a driving mechanism for driving the focusing lens and a driving circuit for the driving mechanism. An aperture 11 is provided between the imaging optical system 2 and the CCD image sensor 3, and the aperture 11 is driven by a driver 12. Each of the drivers 10 and 12 is controlled by the main CPU 13.
[0009]
Reference numeral 14 denotes a CPU relating to the CCD imaging device 3, which controls the driving of the CCD imaging device 3 via a driver 15 and performs various image processing based on the imaging signals of the CCD imaging device 3. The photographed image data after the image processing is recorded on the recording medium 16. On the other hand, reference numeral 17 denotes a CPU relating to the CCD imaging device 8, which controls the driving of the CCD imaging device 8 via the driver 18 and performs various image processing based on the imaging signals of the CCD imaging device 8.
[0010]
The main CPU 13 is provided with a first AF calculation unit 131 that calculates a subject distance by a triangulation method based on an image shift, and a second AF calculation unit 132 that performs an AF calculation by a contrast detection method. . Both the image data based on the imaging signal of the CCD imaging device 3 and the image data based on the imaging signal of the CCD imaging device 8 are input to the AF calculation unit 131. On the other hand, when performing the AF calculation by the contrast detection method, only the image data based on the imaging signal of the CCD image sensor 3 is input to the evaluation value calculation unit 133, and the calculation result is input to the AF calculation unit 132. Hereinafter, these image data are also referred to as image pickup signals.
[0011]
The evaluation value calculation unit 133 is provided with a band-pass filter (not shown) for extracting a high-frequency component of a predetermined band from the image signal. The extraction of the high-frequency component in the evaluation value calculation unit 133 is performed on the imaging signal in a predetermined AF area within the imaging range, and the focus evaluation value is calculated by integrating the absolute value of the extracted high-frequency component in the AF area. You. The AF calculation unit 132 calculates the peak position of the focus evaluation value as described later. The subject distance calculated by the AF calculation unit 131, the focus evaluation value calculated by the evaluation value calculation unit 133, and the peak position calculated by the AF calculation unit 132 are stored in the storage unit 134. The focus evaluation value is stored in pairs with the focus lens position.
[0012]
<< Explanation of AF operation >>
Next, an AF operation in the digital camera 1 according to the present embodiment will be described. In the present embodiment, (1) the AF operation using the calculation result of the AF calculation unit 131, that is, the AF operation using only the subject distance by the triangulation, and (2) the AF operation and the AF calculation unit 132 using the triangulation. The case where both of the AF operations by the contrast detection method using the calculation result of the above are used will be described.
[0013]
First, before describing an AF operation example of the present embodiment, an AF operation by triangulation and an AF operation by a contrast detection method will be individually described.
(AF operation by triangulation)
A method of calculating a subject distance by triangulation will be described. FIG. 3 is a diagram showing the relationship between the subject distance D, the base line length a, and the displacement amount d of the subject image. For the sake of simplicity, the focal length f2 of the imaging optical system 2 is assumed to be equal to the focal length f5 of the imaging lens 5, and the value is set to f. Actually, f2 ≠ f5, and the size of the subject image on the CCD image sensor 3 and the size of the subject image on the CCD image sensor 8 are different. However, if the size of both images is equalized by software, f2 = This is the same as assuming that f5 = f.
[0014]
The base line length a is a distance between the optical axis of the imaging optical system 2 and the optical axis of the imaging lens 5, and if the optical axes do not match, parallax (parallax) occurs. 20A is an image of the subject 20 formed on the CCD image pickup device 3 by the photographing optical system 2. On the other hand, 20B is an image of the subject 20 formed on the CCD image sensor 8 by the imaging lens 5. In FIG. 3, the subject 20 is substantially on the optical axis of the photographing optical system 2, and the subject image 20 </ b> A is formed at the center of the CCD image sensor 3. On the other hand, since the subject 20 is outside the optical axis of the imaging lens 5, the subject image 20B is formed at a position separated by a distance d from the center of the CCD imaging device 8. At this time, a relationship represented by the following equation (1) is established between the subject distance D and the base line length a.
(Equation 1)
D = f · a / d (1)
[0015]
FIG. 4A illustrates an image 21 captured by the CCD imaging device 3, and FIG. 4B illustrates an image 22 captured by the CCD imaging device 8. In FIG. 4, the images 21 and 22 are displayed in the same size. In the case of the image 21, the subject 20 in FIG. In the case of the image 22, the subject 20 is shifted to the right from the center by a distance d '. This shift amount d ′ corresponds to the shift amount d in FIG. 3, and can be expressed as d ′ = k · d using the proportionality constant k. On the other hand, in the case of the subjects 23 and 24 that are far enough that the subject distance can be regarded as infinity, the position in the image 21 and the position in the image 22 are the same. In FIG. 3, since the images 20A and 20B of the subject 20 inverted upside down and left and right are formed on the CCD image pickup devices 3 and 8, the image 20B is shifted leftward from the center.
[0016]
The AF calculation unit 131 calculates the shift amount d in FIG. 3 based on the respective imaging signals of the CCD image sensor 3 and the CCD image sensor 8, and calculates the subject distance D from the shift amount d and Expression (1). The focal length f2 of the imaging optical system 2 is used for f in Expression (1). The focal lengths f2 and f5 and the base line length a are stored in the storage unit 134 in advance. The main CPU 13 moves the focus lens of the photographing optical system 2 based on the subject distance D calculated by the AF calculation unit 131.
[0017]
The method of calculating the shift amount d based on the image pickup signals of the CCD image pickup devices 3 and 8 is the same as the method used in the conventional triangulation, and the principle thereof will be briefly described below. An area 25 shown in FIG. 4A represents an AF area, and an AF operation is performed so that a subject in the AF area 25 is focused. That is, of the imaging signals output from the CCD imaging device 3, the imaging signal corresponding to the subject in the AF area 25 is used for calculating the subject distance D.
[0018]
On the other hand, in the case of the CCD imaging device 8, an imaging signal of the band-like region 26 extending to the right including the region at the same position as the AF region 25 is used for the AF calculation. As described above, the reason for setting the long region 26 on the right side is that the subject image formed on the CCD imaging device 8 is always smaller than the subject image captured on the CCD imaging device 3 as shown in FIG. This is because it shifts to the right.
[0019]
FIG. 5 schematically shows an image signal of the AF area 25 and an image signal of the area 26. The AF area 25 is divided into four divided areas A1 to A4 in the left-right direction, and the magnitude of the signal is indicated by oblique lines. The area 26 is divided into twelve divided areas B <b> 1 to B <b> 12 in the left-right direction. In the example shown in FIG. 5, the signal patterns of the divided areas B4 to B7 and the signal patterns of the divided areas A1 to A4 are substantially the same. That is, the subject image formed on the divided areas B4 to B7 and the subject image formed on the divided areas A1 to A4 are determined to be the same subject.
[0020]
Assuming that the shift amount of one of the divided areas B1 to B12 is g, the shift amount of the subject image captured in the AF area 25 in the area 26 is 3 g. This shift amount 3g is equal to the shift amount d in FIG. From the relationship of 3g = d and Expression (1), the subject distance D is calculated by the following Expression (2).
(Equation 2)
D = fa / 3g (2)
[0021]
In the present embodiment, since triangulation is performed using subject images captured by two individually provided imaging systems, the base line length a can be set to a sufficient distance, and the accuracy can be improved. Triangulation can be performed. Further, since the imaging optical system of the AF CCD imaging device 8 is also used as the imaging lens 9 of the finder optical system 4, it is possible to minimize cost increase and enlargement of the camera.
[0022]
(AF operation by contrast detection method)
Next, the AF operation by the contrast detection method will be described. FIG. 6 is a diagram illustrating an example of the focus evaluation value. The horizontal axis indicates the lens position of the focus lens, and the vertical axis indicates the magnitude of the focus evaluation value. A curve L indicates a focus evaluation value obtained when the focus lens is moved from the closest side to the infinity side with respect to the subject in the AF area 25 in FIG. The curve L has a peak at the lens position P, and the contrast of the subject image becomes maximum at the lens position P. That is, the subject is in focus. As described above, in the contrast detection method, focusing is performed by moving the focus lens to a position where the focus evaluation value reaches a peak.
[0023]
To detect the peak position, a method generally called a “hill-climbing focusing operation” is used. x3 is the focusing lens position at the start of hill climbing, and the focus evaluation value at that time is y3. The lens position x3 and the focus evaluation value y3 are stored in the storage unit 134 in FIG. When the focusing operation is started, for example, the focus lens is moved to the close side by a predetermined amount, and the focus evaluation value y4 at the moved position x4 is calculated.
[0024]
Next, the calculated focus evaluation value y4 is compared with the focus evaluation value y3 at the start of movement stored in the storage unit 134. In the case of FIG. 6, since the obtained focus evaluation value y4 is larger than the focus evaluation value y3, the focus evaluation value tends to increase in the moving direction, and the lens position P where the focus evaluation value peaks is closer to the lens position x4. Is determined to be on the side. When it is determined that the lens is on the closest side, the focusing lens is further moved to the closest side by a predetermined amount, and the focus evaluation value y5 at the moved lens position x5 is calculated. Thereafter, the focus evaluation value y4 is compared with the focus evaluation value y5.
[0025]
In the second movement, it is determined that the focus evaluation value y5 at the lens position x5 is smaller than the focus evaluation value y4 at the lens position x4. That is, it is determined that the peak position P is on the infinity side of the lens position x5. Therefore, the peak position P of the focus evaluation value is calculated by performing an interpolation operation based on the data (x3, y3), (x4, y4), (x5, y5), and the focusing lens is moved to the peak position P. As described above, in the hill-climbing focusing operation, a series of processes of “lens movement” → “calculation of focus evaluation value” → “comparison of focus evaluation value” is repeatedly performed to move the focusing lens to the peak position P of the focus evaluation value. Go to When the lens is moved, the moving direction is determined by comparing the focus evaluation value at the current position with the focus evaluation value obtained last time. By the way, when the lens position x3 at the start of the operation is far away from the peak position P, the peak position P cannot be detected unless the repetition is performed many times. Therefore, the AF operation of the contrast detection method has a disadvantage that it takes time.
[0026]
<< Description of Specific AF Operation Example >>
Next, the two types of AF operations (1) and (2) will be described.
・ AF operation (1)
In the AF operation (1), only the AF operation based on triangulation is performed. That is, the shift amount 3g in FIG. 5 is detected by the FA calculation unit 131 in FIG. 2, and the subject distance D is calculated by equation (2). Then, the focus lens of the photographing optical system 2 is moved by a distance corresponding to the calculated subject distance D. Therefore, the FA operation time can be reduced as compared with the conventional AF operation using only the contrast detection method using the “hill-climbing focusing operation”.
[0027]
・ AF operation (2)
In the AF operation (2), both the triangulation and the contrast detection method are used. 7 and 8 are diagrams illustrating a first example and a second example of the AF operation (2). In the first example, first, a subject distance D is calculated by triangulation, and a lens position x7 based on the subject distance D is calculated. Then, the focus lens is moved from the lens position x6 at the start of AF to the calculated lens position x7. Up to this point, the operation is the same as the AF operation (1). Thereafter, a hill-climbing focusing operation by the contrast detection method is performed from the lens position x7, and the focus lens is moved to the peak position P. In the case of this AF operation, an accurate AF operation can be performed even when a deviation occurs between the lens position x7 and the peak position P by triangulation.
[0028]
On the other hand, in the second example shown in FIG. 8, the movable range of the focus lens is divided into three ranges H1, H2, and H3. The number of divisions is not limited to three, but may be any number. First, the subject distance D is calculated by triangulation, and it is determined which of the ranges H1, H2, and H3 the corresponding lens position is included in. The example of FIG. 8 is a case where the lens position obtained by the triangulation is included in the range H2. In this case, the focus lens is moved to the infinite side boundary position x8 of the range H2. After that, the focus lens is moved from the lens position x8 to the lens position x9, and the focus evaluation value calculation by the evaluation value calculation unit 133 is repeatedly performed at a predetermined timing during the movement. The plurality of focus evaluation values sampled in this way are stored in the storage unit 134 in pairs with the lens positions at the time of each sampling.
[0029]
The AF calculation unit 132 calculates the peak position P based on the sampled focus evaluation value. When the peak position P is obtained, the focus lens is moved to the peak position. Thus, the AF operation is completed. In the case of the second example, rough lens movement is performed by triangulation with a high operation speed, and then the focus lens is scanned and moved within the range H2 to detect the peak position of the focus evaluation value. The focus lens is moved to the peak position. As a result, it is possible to increase the speed of the AF operation while maintaining the AF accuracy.
[0030]
In addition, in the triangular ranging in the second example, it is only necessary to know which of the ranges H1, H2, and H3 the peak position P is in. Therefore, it is not necessary to perform exact ranging, and the triangular ranging calculation can be performed. Simplification can be achieved. Further, in the AF operation of the contrast detection method, the focus evaluation value within the range H2 is sampled by the scanning movement and the peak position P is searched for instead of the “hill-climbing focusing operation”. I can do it.
[0031]
Note that the scan start position is set to the boundary position x8 on the infinity side, but may be set to the boundary position x9 on the closest side. Further, the movable range of the lens may be divided into a large number, and the “focusing operation on a hill” may be performed instead of the “scanning operation”. In this case, the hill-climbing focusing operation may be started from either boundary of the divided range, or may be started from, for example, the center position of the divided range.
[0032]
In the above-described embodiment, the photographing optical system 2 is not a zoom optical system. However, the present invention can be similarly applied to a case where the photographing optical system 2 is a zoom optical system. In that case, a variable power lens driven in conjunction with the zoom is provided in the finder optical system 4 so that the imaging range of the CCD imaging device 3 matches the imaging range of the CCD imaging device 8. Incidentally, it is preferable that the images picked up by the two CCD image pickup devices 3 and 8 have the same degree of blur. In general, the subject image on the finder side is less blurred, so it is preferable to stop down the aperture 11 on the CCD image sensor 8 side during the AF operation. Thereby, the AF accuracy can be further improved.
[0033]
In the correspondence between the embodiment described above and the elements described in the claims, the CCD image pickup device 3 is a photographing image pickup device, the CCD image pickup device 8 is an AF image pickup device, and the imaging lens and the half mirror 6 are AF optics. The first AF calculation unit 131 controls the object distance calculation means, the main CPU 13 and the driver 10 control the control means and the moving means, the aperture 11 and the driver 12 adjust the aperture mechanism, and the aperture 11, the driver 12 and the main CPU 13 adjust the The respective means are configured.
[0034]
【The invention's effect】
As described above, according to the present invention, an AF image sensor and an AF optical system are provided separately from a photographing optical system and a photographing image sensor for photographing a photographed image, and a subject imaged by each image sensor is provided. The focusing operation is performed by calculating the subject distance using the parallax of the image. As a result, the base line length can be set to a sufficient distance, and the AF operation can be performed accurately and quickly.
Further, by using the focusing operation based on the focus evaluation value together, the AF accuracy can be further improved.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of a digital camera 1 according to the present invention.
FIG. 2 is a functional block diagram of the digital camera 1.
FIG. 3 is a diagram illustrating a relationship among a subject distance D, a base line length a, and a displacement amount d of a subject image.
4A and 4B are diagrams illustrating captured images, in which FIG. 4A is an image captured by a CCD imaging device 3, and FIG. 4B is an image captured by a CCD imaging device 8.
FIG. 5 schematically shows image pickup signals of an AF area 25 and an area 26.
FIG. 6 is a diagram illustrating an example of a focus evaluation value.
FIG. 7 is a diagram illustrating a first example of the AF operation (2).
FIG. 8 is a diagram illustrating a second example of the AF operation (2).
[Explanation of symbols]
Reference Signs List 1 digital camera 2 photographing optical system 3, 8 CCD image pickup device 4 finder optical system 5 imaging lens 6 half mirror 7 finder eyepieces 10, 12, 15, 18 driver 11 diaphragms 13, 14, 17 CPU
16 Recording medium 20 Subject 25 AF area 26 Strip area 131 First AF calculation unit 132 Second AF calculation unit 133 Evaluation value calculation unit 134 Storage unit

Claims (6)

A photographing image sensor for photographing a photographing subject image formed by a photographing optical system;
An AF image sensor that captures an AF object image formed by the AF optical system;
Subject distance calculating means for calculating a subject distance using parallax based on image data of the image sensor for imaging and image data of the image sensor for AF,
A digital camera comprising: a control unit that moves a focus lens of the photographing optical system based on a calculation result of the subject distance calculation unit to perform a focusing operation. A photographing image sensor for photographing a photographing subject image formed by a photographing optical system;
An AF image sensor that captures an AF object image formed by the AF optical system;
Subject distance calculating means for calculating a subject distance using parallax based on image data of the image sensor for imaging and image data of the image sensor for AF,
Evaluation value calculation means for calculating a focus evaluation value of the imaging subject image based on imaging data of the imaging image sensor;
Moving means for moving a focus lens of the photographing optical system;
After moving the focus lens based on the calculation result of the subject distance calculation means, control means for moving the focus lens based on the focus evaluation value calculated by the evaluation value calculation means to perform a focusing operation; and A digital camera comprising: The digital camera according to claim 2,
The control means moves the focus lens within a predetermined range including a focus lens position for focusing on the subject at the calculated subject distance, and then performs the focusing based on the focus evaluation value calculated by the evaluation value calculation means. A digital camera characterized by moving a lens to perform a focusing operation. The digital camera according to claim 1,
A digital camera, further comprising an adjusting unit that adjusts the degree of blur of the photographing subject image at the start of the focusing operation to be substantially the same as the degree of blur of the AF subject image. The digital camera according to claim 4,
2. The digital camera according to claim 1, wherein the adjusting unit adjusts the degree of blurring using an aperture mechanism that adjusts the amount of the subject light beam. The digital camera according to any one of claims 1 to 5,
A digital camera, wherein the AF optical system includes a part of a finder optical system of the digital camera.

Images