JP4226235B2 - Imaging device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an imaging apparatus capable of obtaining a deeper depth of field.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a pinhole camera is known as a camera that focuses on a subject at a wide objective distance and captures an image. However, the pinhole camera has a drawback that only a bright subject can be imaged because the amount of incident light to the imaging device is small. In addition, a camera that uses a wide-angle lens and has a depth of field as deep as possible has been proposed. However, in the case of such a camera, the surrounding geometric distortion becomes too large.
[0003]
As another imaging apparatus that can obtain a deep depth of field, an imaging apparatus described in Japanese Patent Laid-Open No. 9-116807 is known. In this imaging apparatus, the optical path of the imaging lens is divided into two optical paths, and an imaging element is arranged in each optical path, and the arrangement distances of these imaging elements from the principal point of the imaging lens are slightly different from each other. Then, a high-frequency filtering process is performed on the video signal output from one imaging device, and an unfiltered video signal output from the other imaging apparatus and a high-frequency filtering video signal are added. . In this known imaging device, since the unfiltered video signal and the high-frequency filtered video signal are added, the depth of field as the imaging device is substantially increased, and a deeper depth of field. The imaging device is realized.
[0004]
[Problems to be solved by the invention]
In the above-described known imaging device, if the distance between the imaging devices is too small, the overlapping range of the depth of field of both imaging devices increases, and the expanded range of the depth of field of the finally obtained video signal is small. On the other hand, if the shift distance is too large, there is a drawback in that the depth-of-field regions of both image sensors are not continuous and a continuous wide range of depth of field cannot be obtained. Furthermore, since the video signal obtained from one image sensor is subjected to high-pass filter processing and addition processing is performed with the video signal obtained from the other image sensor, the image obtained from one image sensor has an unclear image portion. In such a case, there is a drawback that the sharpness of the video that is finally output is lowered only by adding a clear image.
[0005]
Accordingly, an object of the present invention is to realize an imaging apparatus that can focus on a wide range of subjects even when imaging is performed with an arbitrary aperture value using an imaging lens having an arbitrary focal length.
[0006]
[Means for solving the problems]
An imaging apparatus according to the present invention includes an imaging lens that captures an image of a subject, an optical path dividing unit that divides an optical path of light that has passed through the imaging lens into a plurality of optical paths, and is disposed on each of the divided optical paths. An image sensor that generates a video signal by imaging the image sensor, an image sensor driving device that moves each image sensor along the optical axis direction, and an optical axis of each image sensor according to the lens parameters of the input imaging lens. An arithmetic processing device for determining the position of the image processing device, and an image synthesis device for synthesizing the video signal output from each imaging device,
When b is the distance along the optical axis from the principal point of the imaging lens to the position where the imaging element is arranged, f is the focal length of the imaging lens, F is the F number of the lens diaphragm, and δ is the allowable confusion circle diameter The arithmetic processing unit is
The distance in the optical axis direction of one image sensor from the principal point of the imaging lens is set so as to satisfy the formula b = f ² / (f−δF),
The distance in the optical axis direction from the principal point of the imaging lens of the other imaging element is set so as to satisfy the formula b = f ² / (f−3δF).
[0007]
If the distance from the principal point of the imaging lens of at least two imaging elements is set so as to satisfy the above equation, the range of the objective distance focused by the imaging apparatus is from infinity to H / 4 with respect to the hyperfocal distance H described later. The focusing range of the imaging apparatus can be greatly expanded. Moreover, the two depth-of-field regions can be continued without overlapping. As a result, it is possible to realize an imaging apparatus having a greatly improved depth of field. Furthermore, since each image sensor can move freely in the direction of its optical axis, a wider range of focusing can be obtained by using an imaging lens having an arbitrary focal length or imaging with an arbitrary aperture value. Obtainable.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a diagram showing a configuration of a first embodiment of an imaging apparatus according to the present invention. Light from the far-field subject 1 and the near-field subject 2 passes through the imaging lens 3 and enters the prism 4 which is an optical path dividing unit. Although the imaging lens 3 is illustrated as a single lens, it can be an imaging lens system including a plurality of lens sets. The prism 4 has a half mirror structure, and divides incident light into two light paths. The first image sensor 5 is disposed on one optical path, and the second image sensor 6 is disposed on the other optical path. The first and second imaging elements are two-dimensional imaging elements in which a large number of light receiving elements, that is, pixels are arranged in a two-dimensional matrix.
[0009]
Each of the image sensors 5 and 6 is attached to the driving devices 7 and 8 and can freely move in the optical axis direction. Therefore, the distance from the principal point of the imaging lens 3 of each imaging element can be freely set according to the focal length of the imaging lens to be used and the condition of the diaphragm. The image pickup devices 5 and 6 are read out in synchronization with each other under the control of the controller, supplied to the image composition device 12, and a video signal obtained by image composition is output.
[0010]
The lens parameters of the imaging lens 3, such as the focal length and aperture value of the lens, are input to the arithmetic processing device 10, and the arithmetic processing device allows the imaging elements 5 and 6 from the imaging lens 3 to respond to the characteristics of the imaging lens to be used. Calculate the distance. These calculated values are supplied to the drive circuits 10 and 11, respectively, and drive signals for the drive devices 7 and 8 are formed. The first and second image sensors are arranged at positions corresponding to the lens parameters.
[0011]
Next, the contents of the arithmetic processing in the arithmetic processing device will be described with reference to FIG. FIG. 2 shows the relationship between the focal length f of the imaging lens 3, the distance l from the principal point of the imaging lens to the subject, the imaging distance b, the rear depth of field d1, the forward depth of field d2, and the allowable circle of confusion δ. Indicates. When a subject with a depth is imaged, it appears in focus within the focal depth before and after the focal point. This is because when the image blur is smaller than the allowable circle of confusion, the blur cannot be detected. This in-focus range is referred to as the depth of field. Further, when focusing on an objective distance l that is a distance from the principal point of the imaging lens to the subject, a focusing range farther than the objective distance l is referred to as a rear depth of field d1, and the lens is positioned beyond the objective distance. The in-focus range closer to is referred to as the forward depth of field d2.
[0012]
When the focal length of the imaging lens is f, the F number of the lens aperture is F, the allowable circle of confusion is δ, and the objective distance is l, the depth of field can be obtained by the following equation.
Back depth of field: d1 = δ · F · l ² / (f ² −δ · F · l) Equation (1)
Forward depth of field: d2 = δ · F · l ² / (f ² + δ · F · l) Equation (2)
Hyperfocal distance: H = f ² / δ · F Equation (3)
[0013]
Here, the hyperfocal distance H is the value of the objective distance l when the far point of the rear depth of field is set to infinity. When focusing on this distance, the hyperfocal distance H is ½ of the hyperfocal distance. Focus to the distance.
[0014]
Further, when the objective distance measured from the lens principal point is l and the imaging distance is b, the following imaging formula is established.
1 / l + 1 / b = 1 / f Equation (4)
Here, the imaging distance b with respect to the objective distance l is obtained. First, when l = infinity, b = f from equation (4)
It becomes. In other words, the imaging distance coincides with the focal distance.
Next, when l = hyperfocal distance H, from equations (3) and (4), δF / f ² + 1 / b = 1 / f
Therefore, b = f ² / (f−δF) Equation (5)
Therefore, when the first image sensor 5 is arranged in the arithmetic processing unit 9 according to the imaging distance calculated from the equation (5), an image focused from infinity to 1 / 2H can be obtained by the first image sensor. Therefore, the first image sensor is disposed at the image formation position when the subject is located at the hyperfocal distance H of the imaging lens.
[0015]
Next, the arrangement position of the second image sensor 6 will be described. Let L be an objective distance such that the rear focal point of the second image sensor 6 becomes equal to the front focal point of the first image sensor 5, that is, 1 / 2H. FIG. 3 shows the depth of field of the image sensors 1 and 2. The rear depth of field of the image sensor 1 is d _2L , the front depth of field is d _2H , the rear depth of field of the second image sensor 6 is d _1L , and the front depth of field is d _2L . At this time, the objective distance is
L = H / 2−d _1L
It can be expressed.
D _1L is obtained from the equation (1), H is substituted from the equation (3), and L = f ² / (3δF) Equation (6)
Therefore, when l = L,
3δF / f ² + 1 / b = 1 / f
Therefore, b = f ² / (f + 3δF) Equation (7)
It becomes.
At this time, the shortest focusing distance L ′ in focus is
L ′ = L−d _2L
When d _2L is obtained from Equation (2), L is substituted from Equation (6), and calculated,
L ′ = f ² / 4δf = H / 4 Formula (8)
[0016]
Therefore, when the second image sensor 6 is arranged according to the imaging distance calculated from the expression (7) in the arithmetic processing unit, the objective distance is focused from 1 / 2H to L ′, that is, from 1 / 2H to 1 / 4H. Video is obtained.
[0017]
The operation of the arithmetic processing unit is summarized as follows. The lens parameters are calculated according to the equation (5) to determine and control the arrangement position of the first image sensor 5, and are calculated according to the equation (7) to calculate the second image sensor 6. Determines and controls the placement position. By this control, a subject whose objective distance is between 1 / 4H and infinity is always focused and imaged by either the first or second image sensor 5 or 6.
[0018]
Of the images obtained from the first and second image sensors 5 and 6, a focused video region is selected for each subject by a method such as detection or arbitrary designation, and the video composition device synthesizes it on a two-dimensional plane. By doing so, a composite image in which the objective position is focused from 1 / 4H to infinity is obtained.
[0019]
As apparent from the above description, even when the lens parameter changes, the arithmetic processing unit calculates the distances from the lens principal points of the first and second imaging elements according to the equations (5) and (7). By driving the driving devices 7 and 8, the arrangement of the image pickup elements is appropriately moved, and by synthesizing the video signals obtained from the respective image pickup elements, a combined image having the widest depth of field is always obtained. It is done. FIG. 3 schematically shows how the depth of field of the composite image changes when the aperture value changes.
[0020]
FIG. 4 is a diagram showing a modification of the image synthesizing apparatus of the imaging apparatus according to the present invention. In this example, high-pass filters 21 and 22 are respectively connected to the subsequent stages of the first and second image sensors 5 and 6, and signals that have passed through these high-pass filters are supplied to an adder 23 to synthesize an image. . All subjects in the in-focus range of the two image sensors 5 and 6 are always focused and imaged by either image sensor and blurred by the other image sensors. Accordingly, by performing appropriate high-pass filter processing on both images, only the in-focus portions of the respective images are extracted, and by adding them with an adder, an overall focused image is obtained. For example, a two-dimensional digital filter can be used as the high-pass filter.
[0021]
FIG. 5 shows an example of a technique for selecting a focused video for each block area composed of a plurality of pixels and synthesizing the selected video. The video signals obtained from the two image pickup devices 5 and 6 are each divided into block regions including a plurality of pixels, high-frequency components are extracted by the high-pass filters 31 and 32 for each block region, and the high-frequency components are output by the comparator 33. The amounts of ingredients are compared. In accordance with the output from the comparator 33, the video signal from the video block having the higher video high frequency component is selected by the switch 34. As the video to be finally output, the video closer to the focus is selected and output for each block. The smaller the number of pixels constituting each block, the finer the focused image can be selected. On the other hand, if the number is too small, the comparison accuracy of the high-frequency component is lowered. If you are concerned about the minute difference in the connecting date of the blocks as a result of combining for each block, perform appropriate two-dimensional low-pass filter processing etc. on the combined output as necessary, and influence the block connection May be reduced.
[0022]
FIG. 6 shows an in-focus area detected by electrically defocusing an image obtained from one image sensor and comparing it with the other image that has not been defocused. An example of the technique is shown. A defocus filter 41 is connected to the second image sensor 6, and the video signal of the second image sensor 6 is electrically defocused to give the same blur as that caused by the lens. Then, the video signal that has been subjected to the defocus processing and the video signal that has not been subjected to the defocus processing of the first image sensor 5 are supplied to the comparator 42 for comparison. The subject in focus by the image sensor 6 matches the blurred image of the image by the image sensor 5 by the electrical defocusing process, so the portion where both images match is determined to be the focused area of the subject of the image sensor 2. it can. The switch is switched according to the output result from the comparator, and the focused image is selectively extracted to synthesize the image. As a result, an image in which the entire image is focused can be formed by the image composition method.
[0023]
In the above-described embodiments, the example in which the optical path of the imaging lens is divided into two and the video signals output from the two imaging elements are combined has been described. However, the principle when the optical path is divided into two or more is described. Needless to say that is the same.
[0024]
A second embodiment using the present invention will be described with reference to FIG. This is because even if the focus ranges of the images obtained from the two image sensors are not continuous, if each of the image sensors focuses on each subject to be imaged, the objective distance from one image sensor This is an example in which images focused on a plurality of different subjects are obtained at the same time, and it is expected that the production effect is enhanced in television studio recording or the like. FIG. 7 is a diagram assuming a scene in which a puppet theater is recorded in a studio as an example of close-up photography. A doll is placed in front of the background image, and the background image and the doll are measured for the objective distance from the camera lens by means such as a distance sensor such as an infrared distance measuring device or a potentiometer. Is input to the arithmetic processing unit as a parameter. For example, the distance sensor 50 such as an infrared distance measuring device is used to measure the distance from the imaging device to the subject for each subject, and the obtained distance information is supplied to the arithmetic processing device 9. The arithmetic processing unit 9 calculates the in-focus position of each image sensor based on the supplied distance information and supplies it to the drive circuit. Then, according to the obtained distance information, each image sensor is moved and positioned within the focusing range.
[0025]
If the objective distance of the background subject is l ₁ and the objective distance of the doll subject is l ₂ , the imaging distances b ₁ and b _{2 of the} respective subjects, that is, the focus positions from the imaging lenses of the first and second imaging elements. From equation (4)
b ₁ = l ₁ f / (l ₁ −f)
b ₂ = l ₂ f / (l ₂ −f) Equation (9)
Is required.
[0026]
By controlling the imaging position of the image sensor based on the calculation result of Equation (9), it is possible to obtain an image that is adaptively focused on an individual subject even in a subject with a narrow focus area such as close-up photography. it can. In addition, since shooting with such a divided video can be performed by focusing on a subject at each objective distance, there is a possibility that the production effect will be further widened, such as blurring an arbitrary subject by video processing in post-production.
[0027]
A distance sensor can be provided for each image sensor, or one distance sensor can be shared by a plurality of image sensors.
[0028]
【The invention's effect】
As described above, according to the present invention, in a television camera or the like, an object with a wide range of objective distance is focused even when an imaging lens having an arbitrary focal length is used to capture an image at an arbitrary aperture value. A pan focus image is obtained. In addition, for a subject with a narrow focus area such as a close-up of a puppet show, for example, it is possible to obtain a focused video that is adapted to an individual subject such as a doll or a background image. In addition, the doll and the background image can be simultaneously photographed, and an effect such as blurring an arbitrary subject by video processing in post-production can be achieved.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an imaging apparatus according to a first embodiment of the present invention.
FIG. 2 is a diagram for explaining optical parameters of the imaging apparatus according to the present invention.
FIG. 3 is a diagram showing a change corresponding to an aperture value in an in-focus area.
FIG. 4 is a diagram showing an image composition apparatus.
FIG. 5 is a diagram showing an image composition apparatus.
FIG. 6 is a diagram showing another embodiment of the image composition device.
FIG. 7 is a diagram showing a configuration of an image pickup apparatus according to a second embodiment of the present invention.
[Explanation of symbols]
1, 2 Subject 3 Imaging lens 4 Prism 5 First imaging device 6 Second imaging device 7 First spatial device 8 Second spatial device 9 Arithmetic processing device 10 First drive circuit 11 Second drive circuit 12 Image synthesizer

Claims (4)

An imaging lens that captures an image of a subject, an optical path dividing unit that divides an optical path of light that has passed through the imaging lens into a plurality of optical paths, and is arranged in each of the divided optical paths. An image sensor to be generated, an image sensor driving device that moves each image sensor along the optical axis direction, and an arithmetic process that determines the position of each image sensor on the optical axis according to the lens parameters of the input imaging lens A device, and an image synthesis device that synthesizes video signals output from the respective image sensors,
When b is the distance along the optical axis from the principal point of the imaging lens to the position where the imaging element is arranged, f is the focal length of the imaging lens, F is the F number of the lens diaphragm, and δ is the allowable confusion circle diameter The arithmetic processing unit is
The distance in the optical axis direction of one image sensor from the principal point of the imaging lens is set so as to satisfy the formula b = f ² / (f−δF),
An imaging apparatus, wherein a distance in the optical axis direction from a principal point of an imaging lens of another imaging element is set so as to satisfy a formula b = f ² / (f−3δF).   The imaging apparatus according to claim 1, wherein the image synthesizing apparatus includes a high-pass filter connected to an output unit of each imaging device, and an adder for adding outputs of the high-pass filters, An image pickup apparatus characterized in that a high frequency component of a signal is combined by an image combining apparatus.   The image sensor has a plurality of light receiving elements arranged in a two-dimensional matrix, and outputs an output signal of the image sensor in a unit of a pixel block including a plurality of pixels, and the video output of each pixel block is a high-pass signal respectively. The filter processing is performed, the amount of high-frequency components included in each pixel block is compared, and the video output of the pixel block having many high-frequency components is selectively extracted to synthesize an image. The imaging device described.   The video signal from one image sensor is subjected to electrical defocus processing, and the defocused video signal is compared with the video signal from another image sensor that has not been defocused. 2. The imaging according to claim 1, wherein the video signal and a video signal from another imaging element that has not been defocused are selected, the image signal that has been defocused is selected, and the image is synthesized. apparatus.

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