JP4085720B2 - Digital camera - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a digital camera.
[0002]
[Prior art]
Conventional AF methods used in digital cameras include a contrast detection method and a phase difference method. There is also a method for detecting the distance from the camera to the subject by attaching an external AF module. The contrast detection method performs a focusing operation based on the contrast of the 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 photographic lens to the imaging optical system is guided to the AF sensor, and whether the aerial image of the photographic lens is in front of or behind the film surface is determined from the spatial phase shift of the image. Investigate.
[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 drawback that the time required for focusing is longer than that of other methods. Further, the phase difference method has a problem that it is difficult to obtain accuracy because a sufficient base line length cannot be obtained with a digital camera having a small lens system. 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, and there is a risk that the focus will not be achieved at all. there were.
[0004]
An object of the present invention is to provide a digital camera that can quickly perform an accurate AF operation by performing distance measurement using parallax.
[0005]
[Means for Solving the Problems]
(1) A digital camera according to a first aspect of the present invention is a photographic image pickup device that picks up a photographic subject image formed by a photographic optical system , and has a smaller number of pixels than the photographic image pickup device, and an AF optical system. Subject distance calculation that calculates the subject distance using parallax based on the AF imaging element that captures the formed AF subject image, the imaging data of the imaging sensor and the imaging data of the AF imaging element A focus evaluation value calculating means for calculating a focus evaluation value of a photographic subject image based on imaging data of a photographic imaging element, and a focus lens of the photographic optical system, the focus lens including a plurality of divided movement ranges a moving means for moving the movable range, after moving the focus lens on the basis of the calculation result of the subject distance calculating means, including the position of the focus lens after the movement That within the moving range, and control means on the basis of the focus evaluation value that is repeatedly calculated at a predetermined timing to perform the focusing operation by moving the focus lens by the evaluation value computing means while scanning moving the focus lens, if Adjusting means for adjusting the degree of blur of the shooting subject at the start of the focusing operation to be substantially equal to the degree of blur of the AF subject image .
(2) The invention of claim 2 is the digital camera according to claim 1, wherein the adjusting means adjusts the degree of blur by a diaphragm mechanism that adjusts the amount of light of the subject light beam.
(3) The invention of claim 3 is the digital camera according to claim 1 or 2, wherein the AF optical system includes a part of a finder optical system of the digital camera.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below 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 the 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 baseline length. The subject light L2 that has passed through the imaging lens 5 of the finder optical system 4 is split into a light beam L21 and a light beam L22 by the half mirror 6.
[0007]
The light beam L21 passes through the half mirror 6 and enters the viewfinder 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 imaged on the image pickup surface. That is, the CCD image pickup device 3 picks up the subject image formed by the photographing optical system 2, and the CCD image pickup device 8 picks up the subject image formed by the image forming lens 5 of the finder optical system 4. Since the CCD image pickup device 8 is used for AF instead of shooting, the number of pixels may be smaller than that of the CCD image pickup device 3 for shooting. For example, even when a CCD with 3 million pixels is used for the photographing CCD image sensor 3, the same 3 million pixels are not necessarily required for the AF CCD image sensor 8, and about 300,000 pixels are sufficient. In the present embodiment, a CCD type imaging device is used, but it 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 drive mechanism that drives the focusing lens and a drive circuit thereof. A diaphragm 11 is provided between the photographing optical system 2 and the CCD image pickup device 3, and the diaphragm 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 related to the CCD image pickup device 3 that controls the drive of the CCD image pickup device 3 via the driver 15 and performs various image processing based on the image pickup signal of the CCD image pickup device 3. The captured image data after the image processing is recorded on the recording medium 16. On the other hand, 17 is a CPU related to the CCD image pickup device 8, which controls the drive of the CCD image pickup device 8 via the driver 18 and performs various image processing based on the image pickup signal of the CCD image pickup 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 image displacement, and a second AF calculation unit 132 that performs 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 using the contrast detection method, only 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 imaging signals.
[0011]
The evaluation value calculation unit 133 is provided with a bandpass filter (not shown) that extracts a high-frequency component of a predetermined band from the imaging signal. The high-frequency component extraction in the evaluation value calculation unit 133 is performed on the imaging signal in the 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. The The AF calculation unit 132 calculates the peak position of the focus evaluation value as will be 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, the AF operation in the digital camera 1 of the present embodiment will be described. In this 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 by the triangulation. A case will be described in which both AF operations by the contrast detection method using the calculation result are used.
[0013]
First, before explaining the AF operation example of the present embodiment, the AF operation by the triangulation and the AF operation by the contrast detection method will be individually explained.
(AF operation by triangulation)
A method for calculating the 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 subject image shift amount d. In order to simplify the explanation, it is assumed that the focal length f2 of the photographing optical system 2 is equal to the focal length f5 of the imaging lens 5, and the value is assumed to be f. Actually, f2 ≠ f5, and the subject image on the CCD image pickup device 3 and the subject image on the CCD image pickup device 8 are different in size. However, if the sizes of both images are made equal in terms of software, f2 = This is the same as assuming f5 = f.
[0014]
The base line length a is the distance between the optical axis of the photographing optical system 2 and the optical axis of the imaging lens 5. If the optical axes do not coincide with each other, parallax (parallax) occurs. Reference numeral 20A denotes 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 imaged 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 with respect to the imaging lens 5, the subject image 20 </ b> B is imaged at a position away from the center of the CCD image sensor 8 by a distance d. At this time, the relationship of the following equation (1) is established between the subject distance D and the base line length a.
[Expression 1]
D = f · a / d (1)
[0015]
4A shows an image 21 imaged by the CCD image sensor 3, and FIG. 4B shows an image 22 imaged by the CCD image sensor 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. 3 is at the center of the image 21. In the case of the image 22, the subject 20 is shifted by a distance d ′ to the right of the center. This deviation d ′ corresponds to the deviation 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 so far away that the subject distance can be regarded as infinite, 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 in which the top and bottom and the left and right sides of the subject 20 are inverted are formed on the CCD image pickup devices 3 and 8, the image 20B is shifted to the left from the center.
[0016]
The AF calculation unit 131 calculates the shift amount d in FIG. 3 based on the image pickup signals of the CCD image pickup device 3 and the CCD image pickup device 8, and calculates the subject distance D from the shift amount d and the equation (1). The focal length f2 of the photographing 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 for the conventional triangulation, and the outline of the principle will be 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 in focus. In other words, the image pickup signal corresponding to the subject in the AF area 25 in the image pickup signal output from the CCD image pickup device 3 is used for calculating the subject distance D.
[0018]
On the other hand, in the case of the CCD image pickup device 8, the image pickup signal of the band-like region 26 extending to the right side including the region at the same position as the AF region 25 is used for AF calculation. Thus, the reason why the long region 26 is set on the right side is that the subject image formed on the CCD image sensor 8 is always more than the subject image captured on the CCD image sensor 3 as shown in FIG. This is because it shifts to the right.
[0019]
FIG. 5 schematically shows the imaging signal of the AF area 25 and the imaging 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 diagonal lines. Further, the area 26 is divided into 12 divided areas B1 to B12 in the left-right direction, and the magnitude of the signal is represented by diagonal lines similar to the AF area 25. 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, it is determined that the subject image formed in the divided regions B4 to B7 and the subject image formed in the divided regions A1 to A4 are the same subject.
[0020]
If the amount of deviation of one divided area of the divided areas B1 to B12 is g, the amount of deviation in the area 26 of the subject image captured in the AF area 25 is 3 g. This deviation amount 3g is equal to the deviation amount d in FIG. From the relationship of 3g = d and the equation (1), the subject distance D is calculated by the following equation (2).
[Expression 2]
D = f · a / 3g (2)
[0021]
In the present embodiment, since the triangulation is performed using the subject images picked up by the two image pickup systems provided separately, the base line length a can be set to a sufficient distance, and the accuracy is high. Triangular distance measurement can be performed. Moreover, since the imaging lens 9 of the finder optical system 4 is also used as the imaging optical system of the AF CCD image pickup device 8, it is possible to suppress cost increase and enlargement of the camera as much as possible.
[0022]
(AF operation by contrast detection method)
Next, an AF operation using the contrast detection method will be described. FIG. 6 is a diagram illustrating an example of the focus evaluation value. The horizontal axis represents the lens position of the focus lens, and the vertical axis represents 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 infinite 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 is maximized at the lens position P. That is, the subject is in focus. Thus, 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]
For the detection of the peak position, a method generally called “mountain climbing focusing operation” is used. x3 is a focusing lens position at the start of mountain 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 by a predetermined amount to the close side, 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 at which the focus evaluation value reaches a peak is closer to the lens position x4. Is determined to be on the side. When it is determined that the lens is in the close side, the focusing lens is further moved to the close side by a predetermined amount, and the focus evaluation value y5 at the lens position x5 after the movement is calculated. Thereafter, the focus evaluation value y4 and the focus evaluation value y5 are compared.
[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 infinite side with respect to the lens position x5. Therefore, an interpolation calculation based on the data (x3, y3), (x4, y4), (x5, y5) is performed to calculate the peak position P of the focus evaluation value, 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, so that the focusing lens has a peak position P of the focus evaluation value. Move to. When moving the lens, 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 it is repeated many times. Therefore, the AF operation of the contrast detection method has a drawback that it takes time.
[0026]
<< Description of specific AF operation example >>
Next, the two types of AF operations (1) and (2) described above will be described.
AF operation (1)
In the AF operation (1), only the AF operation by triangulation is performed. That is, the FA calculation unit 131 in FIG. 2 detects the amount of deviation 3g in FIG. 5 and calculates the subject distance D by Expression (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 shortened as compared with the conventional AF operation using only the contrast detection method using the “mountain 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 for explaining a first example and a second example of the AF operation (2). In the first example, the subject distance D is first calculated by triangulation, and the lens position x7 based on the subject distance D is calculated. Then, the focus lens is moved to the lens position x7 calculated from the lens position x6 at the start of AF. Up to this point, the operation is the same as the AF operation (1). Thereafter, a hill-climbing focusing operation is performed from the lens position x7 by the contrast detection method, and the focus lens is moved to the peak position P. In the case of this AF operation, 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 and may be any number. First, the subject distance D is calculated by triangulation, and it is determined whether the corresponding lens position is included in the range H1, H2, or H3. The example of FIG. 8 is a case where the lens position obtained by the triangulation is included in the range H2, and in this case, the focus lens is moved to the infinite side boundary position x8 of the range H2. Thereafter, the focus lens is moved from the lens position x8 to the lens position x9, and during the movement, the focus evaluation value calculation by the evaluation value calculation unit 133 is repeatedly performed at a predetermined timing. 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. If the peak position P is obtained, the focus lens is moved to the peak position. In this way, the AF operation is completed. In the case of this second example, a rough lens movement is performed by triangulation with a high operating speed, and then the focus lens is scanned within the range H2 to detect the peak position of the focus evaluation value. The focus lens was 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]
Further, in the triangulation in the case of the second example, it is only necessary to know whether the peak position P is in the range H1, H2, or H3. Simplification can be achieved. Also, the contrast detection AF operation is not the “mountain climbing focusing operation”, but the focus evaluation value in the range H2 is sampled by scanning movement and then the peak position P is searched. I can plan.
[0031]
Although the scan start position is the boundary position x8 on the infinity side, it may be the boundary position x9 on the closest side. Further, the lens movable range may be divided into a large number, and the “mountain climbing focusing operation” may be performed instead of the “scanning focusing operation”. In this case, the hill-climbing focusing operation may be started from either boundary of the divided range, or may be performed from, for example, the center position of the divided range.
[0032]
In the embodiment described above, the photographing optical system 2 is not a zoom optical system, but the present invention can be similarly applied even when the photographing optical system 2 is a zoom optical system. In that case, a magnifying lens that is 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 and the imaging range of the CCD imaging device 8 are matched. By the way, 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, since the subject image on the finder side is small in blur, it is preferable to narrow down the diaphragm 11 on the CCD image sensor 8 side during the AF operation. Thereby, the AF accuracy can be further improved.
[0033]
In correspondence between the embodiment described above and the elements of 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 optical devices. The first AF calculation unit 131 adjusts the subject distance calculation means, the main CPU 13 and the driver 10 adjust the control means and 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 system. Each means is configured.
[0034]
【The invention's effect】
As described above, according to the present invention, an AF imaging element and an AF optical system are provided separately from the imaging optical system and imaging imaging element for capturing a captured image, and the subject imaged by each imaging element. There rows calculated by focusing operation of the object distance by using the parallax image, further, since to perform the focusing operation based on the focus evaluation value, it is possible to perform the AF operation accurately and quickly.
[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 between a subject distance D, a baseline length a, and a subject image shift amount d;
4A and 4B are diagrams illustrating captured images, where FIG. 4A is an image captured by the CCD image sensor 3 and FIG. 4B is an image captured by the CCD image sensor 8;
FIG. 5 schematically shows imaging signals in 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 an AF operation (2).
FIG. 8 is a diagram illustrating a second example of AF operation (2).
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Digital camera 2 Shooting optical system 3, 8 CCD image pick-up element 4 Finder optical system 5 Imaging lens 6 Half mirror 7 Finder eyepiece 10, 12, 15, 18 Driver 11 Aperture 13, 14, 17 CPU
16 Recording medium 20 Subject 25 AF area 26 Band-like area 131 First AF calculation unit 132 Second AF calculation unit 133 Evaluation value calculation unit 134 Storage unit

Claims (3)

A photographic image sensor for capturing a photographic subject image formed by the photographic optical system;
An AF imaging element that captures an AF subject image formed by an AF optical system with a smaller number of pixels than the imaging imaging element;
Subject distance calculation means for calculating a subject distance using parallax based on imaging data of the imaging sensor for imaging and imaging data of the AF imaging element;
Evaluation value calculation means for calculating a focus evaluation value of the shooting subject image based on imaging data of the shooting imaging element;
Moving means for moving the focus lens of the photographing optical system within a movable range of the focus lens composed of a plurality of divided movement ranges ;
After the focus lens is moved based on the calculation result of the subject distance calculation means, the evaluation value calculation means performs predetermined movement while moving the focus lens within a moving range including the position of the focus lens after the movement. based on the focus evaluation value that is repeatedly calculated at a timing and control means for causing the moving focusing operation of the focusing lens,
A digital camera comprising: adjusting means for adjusting a blur condition of the photographing subject image at the start of the focusing operation so as to be substantially equal to a blur condition of the AF subject image . The digital camera according to claim 1, wherein
The digital camera according to claim 1, wherein the adjusting means adjusts a degree of blur by a diaphragm mechanism that adjusts a light amount of a subject light beam . The digital camera according to claim 1 or 2,
The digital camera characterized in that the AF optical system includes a part of a finder optical system of the digital camera.

Images