JP2656143B2 - Omnidirectional imaging device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an omnidirectional photographing apparatus capable of photographing all directions at the same resolution.

[Related Art] In recent years, research on autonomous travel to a destination using an intelligent mobile robot has been actively conducted.

The intelligent mobile robot is required to recognize the road, move without departing from the road, avoid obstacles, and reach the destination.

In order to satisfy this demand, the intelligent mobile robot must be equipped with an image input device capable of simultaneously inputting omnidirectional images.

As the above-mentioned conventional image input devices, two types of image input devices have been proposed.

One type of image input device is one in which a television camera combined with a fish-eye lens is arranged vertically, for example, "Guidance of a Mobile Robot Using an Omnidirectional Vision Navigation. System ”(Guidance of a Mobi
le Robot Using an Omnidirectional Vision Navigatio
n System), S.J.Oh, SJOh and ELHall, S.P.I.E. (S
PIE) Vol.852, Mobile Robots II
(1987).

In this image input device, the camera can capture images in all directions using the fisheye lens.

However, since an image of the ceiling, the sky, or the like that does not need to be observed is taken, there is a shortage of an actually necessary horizontal image.

As a supplement to the above-mentioned drawbacks of the image input device, another
Two types of image input devices have been proposed.

The image input device is a conical mirror, an industrial television camera [(Industrial TV camera)
Hereinafter, referred to as an ITV camera] and an image processing device, and are described in, for example, "Yagi, Kawato: Omnidirectional Environment Recognition by Conical Projection", PRU89-46, (1989).

Configuration of conventional image input device using conical mirror
Shown in the figure.

In the figure, the conical mirror 111 is disposed vertically downward, and the viewing area reflected by the conical mirror 111 is 360 degrees on the horizontal plane around the vertical axis.

The image reflected by the conical mirror 111 is
According to 2, as shown in FIG. 12, the horizontal angle of the visual field is represented by the angle θ in polar coordinates, and the vertical direction (vertical direction) of the visual field is represented by the radius r.

For example, as shown in FIG. 13, a character when "copy" is arranged horizontally theta ₁ and the vertical direction, the character vertical distance Δr corresponds to the length of the "copy", the characters "copy" The horizontal length corresponds to the angle Δθ.

Here, the ITV camera 112 operates in a rectangular coordinate system,
The image of the character “sha” captured by the V camera 112 is
As shown in the figure, the image becomes a fan shape, and the image is in a polar coordinate system.

The image processing device 113 cuts the image captured by the ITV camera 112 into a fan shape as shown in FIG. 14, converts the coordinate system from the polar coordinate system to the orthogonal coordinate system for the cut portion, and The image is corrected as shown in FIG.

According to the above-described method, the image of the ceiling, the sky, or the like, which is not originally required to be observed, is removed by the conical mirror 111, and only the actually required horizontal image is captured in all directions.

Examples of the omnidirectional photographing apparatus using the polar coordinate photographing apparatus include, for example, “Ariga, Yoshino, Kogo, Mizote, Terakawa: Examination of Polar CCD Line CCD Camera, IEEJ Transactions on Electronics Vol.109
-C, No. 5, pp. 394-399 (May, 1989) ".

[Problems to be Solved by the Invention] However, in the above-described conventional omnidirectional photographing device using a conical mirror, the image captured by the ITV camera is cut into a fan shape, so that the number of pixels in the angular direction increases from the outer periphery toward the center. However, there is a problem in that the resolution becomes worse from the outer periphery toward the center, and the sampling rate in the angular direction becomes coarser from the outer periphery toward the center.

Further, in a conventional omnidirectional imaging apparatus in which the center pixel is interpolated by interpolation or the like so that the number of pixels at the outer periphery and the center is equal, the method of interpolation or the like is equivalent to a filter for a low frequency region (low-pass filter). There is a problem that the spatial resolution on the center side is deteriorated.

Furthermore, in the conventional omnidirectional photographing apparatus, there is a problem that the image processing apparatus performs complicated processing at a high speed, so that the apparatus becomes large and it is difficult to incorporate the image processing apparatus into a moving body such as a robot.

SUMMARY OF THE INVENTION An object of the present invention is to provide a miniaturized omnidirectional photographing apparatus which has clear spatial resolution over all pixels and does not require image processing, in view of the above-mentioned problems of the conventional omnidirectional photographing apparatus.

Means for Solving the Problems The above-mentioned object of the present invention is to provide a reflection means for reflecting an omnidirectional image in a predetermined direction, and a reflection means which is gradually arranged from a central axis toward an outer end, and An image pickup device having an image pickup device including a plurality of pixels configured to increase toward the outer end portion, and an image pickup device for picking up the image reflected by the reflection unit with the image pickup device. The means scans the image sensor in the rotational direction and the radial direction of the central axis with respect to the central axis of the reflecting means so that the resolution in the rotational direction and the radial direction is constant. Achieved by the imaging device.

[Operation] The reflection unit reflects the omnidirectional image in a predetermined direction different from the direction in which the image was input, and the imaging unit includes a plurality of images arranged gradually from the first end to the second end. Is scanned in the rotational direction and the radial direction of the central axis of the reflection means, and an omnidirectional image reflected by the reflection means is taken at a clear resolution.

Hereinafter, embodiments of the omnidirectional photographing apparatus according to the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view showing a configuration of an omnidirectional photographing apparatus according to a first embodiment of the present invention, and FIG. 2 is a schematic diagram showing a configuration of the embodiment apparatus of FIG.

The omnidirectional photographing device shown in FIGS. 1 and 2 is a stepping motor 15 having a reflecting mirror 11 as a reflecting means, a polar coordinate type photographing device 12 as an imaging means, a condenser lens 13, and a rotating shaft 14 as a central axis. , Fan-shaped image sensor 16 as an element
It consists of.

 Next, the operation of the omnidirectional photographing apparatus according to the present embodiment will be described.

The reflecting mirror 11 has a conical shape and is arranged vertically downward, that is, in the −z-axis direction when the z-axis direction is the vertical direction.

In the present embodiment, the reflecting mirror 11 is conical, but may be a polygonal pyramid having a reflecting surface on the side surface or a hemispherical shape.

The image reflected by the reflection mirror 11 is displayed by a radial distance r and a horizontal angle θ in the polar coordinate system (see FIG. 12).

In the vertical optical path reflected by the reflection mirror 11,
A polar coordinate type imaging device 12 is provided.

The image photographed by the polar coordinate photographing device 12 is directly output to a television camera or the like without passing through an image processing device.

 FIG. 3 shows the configuration of the polar coordinate type photographing apparatus 12 described above.

The polar coordinate type photographing apparatus 12 includes a condenser lens 13, a stepping motor 15 having a rotating shaft 14, and a sector-shaped image pickup device 16 attached to the rotating shaft 14 so as to extend in the radial direction.

 FIG. 4 shows the configuration of the fan-shaped imaging device 16 described above.

As shown in FIG. 4, the fan image pickup device 16 has a plurality of pixels that are gradually arranged outward from the center of the rotation shaft 14 of the stepping motor 15.

The first end of the fan-shaped image sensor 16 represents the end located on the center side of the rotating shaft 14, and the second end represents the end extending radially from the center.

The longer the pixels are arranged in the radial direction from the center of the rotation shaft 14, the longer the length in the angular direction (θ direction).

Therefore, the area of each pixel is arranged such that the larger the pixel is arranged in the radial direction from the center of the rotation shaft 14, and the width of each pixel in the radial direction is constant.

In this embodiment, as a pixel, a charge-coupled device (hereinafter, referred to as a pixel)
CCD).

 Next, the operation of the above-described polar coordinate type photographing apparatus 12 will be described.

Each time the sector image sensor 16 scans in the radial direction of the rotating shaft 14 of the motor 15, the motor 15 moves the sector image sensor 16 in the angular direction (θ
Direction).

As shown in FIG. 4, since the area of the pixel of the fan-shaped imaging device 16 is configured to increase from the center to the outside, the image captured by the fan-shaped imaging device 16 is, as shown in FIG. The angular resolution and the radial resolution are the same.

In this case, an image represented by a polar coordinate system is converted into an image of a rectangular coordinate system by extracting an electric signal captured by the fan-shaped image sensor 16 with a slip ring, a rotary transformer, or the like. Absent.

When the image is taken by the polar coordinate type photographing device 12, a sample grid is generated in a polar coordinate shape on the photographing surface of the sector image pickup device 16.

Hereinafter, how the generated sample grid samples the actual field of view will be described. The operation of the sample grating will be described in terms of both the sample rate and the aperture ratio.

 First, the radial direction of the photographing surface will be described.

The distance from the center of the photographing plane (that is, the center of the rotating shaft 14 of the motor 15) is proportional to the vertical (vertical) angle in the actual visual field.

Therefore, the sample in the vertical angle direction in the viewing area is CC
Determined by the arrangement of D pixels.

By the way, the arrangement of the CCD pixels is determined by the mechanical constants of the CCD and is uniform.

Therefore, since the fan-shaped image sensor 16 operates so that the sample grid is uniform with respect to the actual visual field, the sample rate and the aperture ratio are the same at each location.

The sample rate in the angular direction is constant on the photographing surface because it corresponds to the unit rotation angle of the step motor 15. Since the image is also projected in polar coordinates, it operates so as to sample in equal steps in the horizontal direction with respect to the actual field of view, so that it is the same at each location.

Furthermore, since the area of a CCD pixel increases as it is arranged from the center toward the outer periphery, the angle from each pixel to the center of the CCD is also constant. That is, the aperture opening ratio of the sample in the angular direction is also the same from the center of the CCD toward the outer periphery. As a result, as shown in FIG. 5, the fan-shaped image sensor 16 operates so as to generate a sample grid so as to generate a sample pattern 17 having the same aperture opening ratio at the top and bottom of the screen.

According to the above-described embodiment, the sampling rate and the aperture ratio of the polar coordinate type imaging device 12 are constant in both the radial direction and the angular direction of the imaging surface. Therefore,
The amplitude characteristics [Modulation Trans Function
fer Function), hereinafter referred to as MTF].

FIG. 6 shows the configuration of a second embodiment of the polar coordinate type photographing apparatus of the present invention.

In FIG. 6, the optical path of the reflecting mirror 11 similar to that of the first embodiment shown in FIGS. 1 and 2 is provided with a filter 18 as an optical means for compensating for spatial resolution and a polar coordinate type as a photographing means. An imaging device 19 is provided.

The filter 18 is configured such that the amplitude characteristic (MTF) decreases as the distance from the center increases, as shown in FIG. As the filter 18, a commercially available optical filter can be used. In addition, instead of a commercially available optical filter,
Small projections, dents, irregularities, etc. may be added to the glass plate or plastic plate, etc.
13 (see FIG. 3) may be subjected to the same processing.

The polar coordinate type photographing apparatus 19 shown in FIG. 8 has a condensing lens 13 shown in FIG. 3, a stepping motor 15 having a rotating shaft 14 as a central axis, and a radius of the rotating shaft 14 instead of the sector image pickup device 16. It has a line-type image sensor 20 extending in the direction.

The line type image pickup device 20 is a fan type image pickup device 16 shown in FIG.
Similarly, a plurality of pixels are sequentially arranged from the end closer to the center of the rotary shaft 14 as the first end to the end farthest from the center in the radial direction as the second end. doing.

However, in the line-type imaging device 20, the area of each pixel is
It is the same from the center to the outside, and the length in the radial direction is also constant.

The output signal of the line-type imaging device 20 is ignored for a central region where pixels overlap during rotation.

When the image is captured by the polar imaging device 19, a sample grid in the form of a polar coordinate is generated on the imaging surface of the line imaging device 20, similarly to the sector imaging device 16 shown in FIG.

Hereinafter, how the generated sample grid samples the actual field of view will be described. The operation of the sample grating will be described in terms of both the sample rate and the aperture ratio.

 First, the radial direction of the photographing surface will be described.

The distance from the center of the photographing surface is proportional to the vertical angle (vertical direction) in the actual visual field.

Therefore, the sample in the vertical angle direction in the viewing area is CC
Determined by the arrangement of D pixels.

By the way, since the arrangement of CCD pixels is determined by the mechanical constants of the CCD and is uniform, a line type image sensor is used to generate a sample grid so that both the sample rate and aperture aperture are uniform with respect to the actual field of view. 20 works.

The sampling rate in the angular direction is equivalent to the unit rotation angle of the step motor 15 on the photographing surface and is constant.

Since the image is also projected in the form of polar coordinates, the line-type imaging device 20 operates so as to sample the actual field of view at equal steps in the horizontal direction. The sample is therefore uniform everywhere.

On the other hand, since the size of the CCD pixel is constant, the angle from the pixel to the center changes between the center and the outer periphery of the CCD. That is, the aperture opening ratio of the sample in the angular direction is
The central part and the peripheral part of the CCD are different. As a result,
As shown in FIG. 9, the line-type imaging device 20 operates so as to generate sample patterns 21, 22, and 23 having different aperture opening ratios at the top and bottom of the screen.

This means that the MTF of the polar coordinate type imaging device 19 is different for each part of the image. Since the aperture opening ratio increases toward the bottom of the screen, the MTF decreases toward the bottom of the screen.
Note that the sample rate is constant.

If the filter 18 is not provided, as shown in FIG. 9, sample patterns having different aperture aperture ratios are generated above and below the photographing screen. However, since the filter 18 reversely corrects this amplitude characteristic (MTF), the field of view The amplitude characteristic (MTF) becomes constant in all the regions.

In the above two embodiments, the sector-shaped image sensor 16 or the line-type image sensor 20 is attached to the rotating shaft 14 of the motor 15 so as to extend from the rotating shaft 14 in the radial direction.

However, instead of the fan-shaped imaging device 16 or the line-type imaging device 20, a cross-shaped imaging device extending at right angles in the radial direction or an * -shaped imaging device extending in all directions in the radial direction may be used.

Further, the fan-shaped image sensor 16 or the line-type image sensor 20 may not be disposed at a right angle in the radial direction from the rotation axis 14 of the motor 15, for example, a cone, a polygonal pyramid reflecting mirror may be rotated at the same angle. May be arranged. Further, without rotating the sector image sensor 16 or the line image sensor 20, the tenth
As shown in the figure, a two-dimensional imaging device having a polar coordinate address may be used.

[Effects of the Invention] An omnidirectional photographing apparatus according to the present invention is characterized in that a reflecting means for reflecting an omnidirectional image in a predetermined direction is arranged gradually from a central axis toward an outer end, and from the central axis to the outer end. An image pickup unit having an image pickup device including a plurality of pixels configured to increase toward the unit, and an image pickup unit for picking up the image reflected by the reflection unit with the image pickup unit, wherein the image pickup unit includes: The image sensor is scanned with respect to the central axis of the reflection means in the rotational direction and the radial direction of the central axis so that the resolution in the rotational direction and the radial direction is constant. Therefore,
The resolution in the rotation direction and the resolution in the radial direction are the same, and the sampling rate and the aperture ratio of the imaging device are constant in both the radial direction and the angular direction, and the amplitude characteristic is constant over the entire visual field. can do. Further, an image processing device for converting an image captured in a specific coordinate system to another coordinate system is unnecessary, and the device can be downsized.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a schematic configuration of an omnidirectional photographing apparatus according to a first embodiment of the present invention, FIG. 2 is a schematic diagram showing a schematic configuration of the embodiment apparatus of FIG. 1, and FIG. FIG. 4 is a perspective view showing a schematic configuration of a polar coordinate type imaging device in the embodiment of FIG. 4, FIG. 4 is an explanatory view showing a schematic configuration of the sector image pickup device of FIG. 3, and FIG. FIG. 6 is a schematic diagram showing a schematic configuration of an omnidirectional photographing apparatus according to a second embodiment of the present invention, FIG. 7 is a graph showing characteristics of the filter in FIG. 6, and FIG. Is an explanatory diagram showing the configuration of a line-type image sensor of the polar coordinate type photographing apparatus of FIG. 6,
FIG. 9 is an explanatory view showing the resolution of the polar coordinate type photographing apparatus of FIG. 6 when there is no filter, FIG. 10 is an explanatory view showing the pixels of the two-dimensional image pickup device, and FIG. FIG. 12 is an explanatory diagram of each variable of a polar coordinate system in a polar coordinate type photographing apparatus, FIG. 13 is an explanatory diagram showing a reflection image of a conical mirror of FIG. 11, and FIG. 14 is an image of FIG. FIG. 15 is an explanatory diagram showing the operation of the processing device, and FIG. 15 is an explanatory diagram showing the resolution of the omnidirectional photographing device of FIG. 11… Reflection mirror, 12,19 …… Polar coordinate type imaging device, 13…
... Condenser lens, 14 ... Rotary axis, 15 ... Stepping motor, 16 ... Sectoral image sensor, 18 ... Filter, 20 ... Line type image sensor.

Claims (1)

(57) [Claims] 1. A reflecting means for reflecting an omnidirectional image in a predetermined direction, and arranged gradually from a central axis toward an outer end, so as to increase from the central axis toward the outer end. And an image pickup means for picking up the image reflected by the reflection means with the image pickup element, the image pickup means having an image pickup element including a plurality of pixels, and the image pickup means is provided with respect to a central axis of the reflection means. An omnidirectional photographing apparatus, wherein the image sensor is scanned in a rotational direction and a radial direction of the central axis so that resolutions in the rotational direction and the radial direction are constant.