JP5417773B2 - On-vehicle camera and optical device - Google Patents

Description

  The present invention relates to a vehicle-mounted camera and an optical device having the vehicle-mounted camera.

Recently, various on-vehicle cameras that are mounted on a vehicle and photograph the driving environment in front (or rear) of the vehicle have been proposed. When shooting, there was a problem that the dashboard and the like reflected on the front window shield and lowered the contrast of the image. As means for solving this problem, there has been proposed a method of installing a polarizing filter in front of the camera (see, for example, Patent Document 1).
JP-A-11-78737

  However, the method of installing a polarizing filter on the front of the camera is certainly simple and effective, but at the same time, when photographing the driving environment in front of the vehicle, the light intensity is attenuated, and further, it is in the outside scene. When the polarization component is included, there is a problem that a drawing different from human vision occurs, for example, an object to be photographed is not photographed.

  The present invention has been made in view of such a problem, and when photographing the outside of the vehicle, the dashboard or the like is used for the front window shield and the like so that the necessary scenery can be reliably captured without causing attenuation of the light amount. It is an object of the present invention to provide a vehicle mounted camera and an optical device having the vehicle mounted camera which are configured to prevent only the image reflected on the camera from passing through the rear window shield.

  In order to solve the above-described problem, a vehicle-mounted camera according to the present invention includes an imaging lens that images the outside of the vehicle through a window shield, and a linear polarization filter disposed outside the field of view of the imaging lens. Configured.

In such a vehicle-mounted camera, the linear polarizing filter is disposed at a position where a light beam reflected by the window shield and incident on the imaging lens is transmitted before being reflected by the window shield .

  In such a vehicle-mounted camera, it is preferable that the linear polarization filter is disposed below the imaging lens.

  In such a vehicle-mounted camera, it is preferable that the linear polarization filter is disposed on the side of the imaging lens.

  Moreover, in such a vehicle-mounted camera, it is preferable that the linear polarization filter is attached in a direction that blocks at least the S-polarized component of the light rays incident on the imaging lens.

  In such a vehicle-mounted camera, it is preferable that the linear polarization filter is disposed to be inclined from the optical axis of the imaging lens.

  Moreover, in such a vehicle-mounted camera, it is preferable that the linear polarization filter is disposed so as to cover the front periphery of the imaging lens.

  Further, such a vehicle-mounted camera further includes a second linear polarizing filter arranged so that light rays that pass through the linear polarizing filter and enter the imaging lens are transmitted before entering the linear polarizing filter. The second linear polarizing filter is preferably arranged so that the polarization axis thereof is substantially orthogonal to the polarization axis of the linear polarizing filter.

  An optical device according to the present invention includes any one of the above-described vehicle-mounted cameras.

  When the vehicle-mounted camera and the optical device having the vehicle-mounted camera according to the present invention are configured as described above, it is possible to effectively remove an image such as a dashboard reflected by the window shield and reflected.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a vehicle-mounted camera K that is mounted on a vehicle and photographs the front through a front window shield W, and shows a case where this camera K is attached to the back (front side) of a room mirror R, for example. Yes. A light ray group (for example, direct light from the sun) L falling on the dashboard D of the vehicle is diffusely reflected by the dashboard D and scattered in all directions. A part of the light beam L ′ is reflected by the front window shield W (reflected light L ″) and reflected in the camera K, thereby reducing the contrast of the image photographed by the camera K. Therefore, the following description will be given. Now, attention is focused on the reflection angle of the light beam reflected on the surface of the front window shield W.

  FIG. 2 is a calculation of the reflectance of light incident on glass having a refractive index of 1.55 from the air (see, for example, “Applied Chemistry”, Zen Iwanami, Hiroshi Kubota, pp 146-152). In FIG. 2, the horizontal axis represents the incident angle (degrees), the vertical axis represents the intensity of the reflected light, and the reflection intensity of the reflected light with respect to the incident angle is graphed. Considering the (incident plane) and a plane perpendicular thereto, the polarization component in the incident plane is defined as a P-polarized component and the P component of the reflection intensity is defined as Ip. In addition, a polarization component perpendicular to the incident surface is an S polarization component, and an S component of reflection intensity is Is. Although the reflectivity varies depending on the incident angle, the difference in polarization characteristics is particularly significant. Particularly, the vicinity of the incident angle of 60 degrees is called the Brewster angle, and the reflected light becomes zero in the P component. Under this condition, the reflected light intensity of the S component reaches as high as 20%, so that the reflectance is quite high, but the reflected light can be extinguished through a linear polarizing filter that removes this. In other words, the vehicle-mounted camera described below is intended to utilize the above-mentioned properties with respect to the surface reflection of glass, and mainly attempts to remove the S-polarized light component with a linear polarization filter.

  FIG. 3 shows an optical system of the vehicle-mounted camera 1 configured to monitor the front through a front windshield (windshield) W of the car. The imaging lens 2 and the linear polarizing filter 3 are shown in FIG. Have. In this case, the imaging lens 2 has a field of view of the vertical viewing angle ω1 and can image the front. As the outside of the front window shield W becomes relatively darker than the inside, the internal structures such as the light of the dashboard D and the instrument panel M are reflected by the air interfaces W1 and W2 of the front window shield W and a ghost image is formed. It becomes noticeable and this is very detrimental for forward monitoring. As an example, FIG. 3 illustrates an optical path in which the dashboard D creates a harmful image by superimposing it on the image of the field of view.

  Lights L1, L2, and L3 are rays from the outside sky or indoors. As described above, these rays are diffused on the surface of the dashboard D and diffusely reflected in all directions. Among them, the specularly reflected light that is specularly reflected by the dashboard D, further specularly reflected by the air interfaces W1 and W2 of the front window shield W, passes through the entrance pupil 2a of the imaging lens 2 and reaches the imaging surface I is a ray. L1 ', L2', and L3 'are shown. These light rays L1 ′ to L3 ′ pass through the center of the entrance pupil 2a of the imaging lens 2 and can be incident from any direction around the rotation axis with a virtual axis Q1 perpendicular to the front window shield W as a rotation axis. A part thereof is detected by an image pickup device (not shown) arranged on the image pickup surface I. Light rays L1 to L3 from the outside sky or the room are usually natural light and non-polarized light.

  However, the incident angle when reflected by the front window shield W of the car is considerably large, and as a result of the reflection, polarized light is generated as described with reference to FIG. For example, if the front window shield W of a passenger car has an inclination of about 30 degrees from the horizontal, and the imaging lens 2 faces in the horizontal direction in order to photograph the front of the vehicle, the light beam L1 ′ is incident on the front window shield W. Incident light is incident at θ1 = 60 degrees. As a result, a light beam having a small P-polarized component and a large S-polarized component is incident on the imaging lens 2 (the same applies to the reflected lights L2 ′ and L3 ′). As described above, in order to reduce the ghost image by the reflected lights L1 ′ to L3 ′, it is effective to reduce the S-polarized light component having a relatively large light quantity among these reflected lights L1 ′ to L3 ′. It is effective to insert at least the polarizing filter 3 that reduces the transmission of the S-polarized component of the light beams L1 ′ to L3 ′.

  In FIG. 3, the polarizing filter 3 is arranged so as to block the S-polarized components of the light beams L1 ′ to L3 ′ reflected by the dashboard D or the like, and the center of the entrance pupil 2a of the imaging lens 2 is a spherical center. It is formed in a spherical shape. Actually, the rotation angle of the polarization filter 3 that maximizes the extinction effect may be determined by rotating the polarization filter 3 around the rotation axis Q2 passing through the entrance pupil 2a. In addition, the position where the polarizing filter 3 that reduces the transmission of the S-polarized component is inserted may be anywhere in the optical path, but the front side is a place that does not affect the captured image of the imaging lens 2 that monitors the front and the driver's field of view. It is appropriate to dispose the polarizing filter 3 at a position where it does not enter the field of view of the imaging lens 2 immediately before the light rays L1 ′ to L3 ′ are reflected by the window shield W, that is, at a position shown in FIG. 3 (below the imaging lens 2). . At that time, the polarizing filter 3 may be arranged in any manner so long as it does not reach the field of view of the imaging lens 2, but the surface reflection of the polarizing filter 3 itself may be strong. It is desirable to arrange so that the surface reflected light does not enter the entrance pupil 2a of the imaging lens 2. For example, as shown in FIG. 3, by installing a polarizing filter 3 having the center of the entrance pupil 2a of the imaging lens 2 as a spherical center, reflections other than light rays that pass through the entrance pupil 2a are reflected on the surface of the polarization filter 3. The light can be prevented from passing through the entrance pupil 2a, and the light rays parallel to the light rays L1 and L2 are not regularly incident on the entrance pupil 2a of the imaging lens 2 after being regularly reflected by the surface of the polarizing filter 3.

  In addition, when it is difficult to install the spherical polarizing filter 3, the polarizing filter 3 having a parallel plane shape may be used as shown in FIG. 4, and it is arranged strictly in the direction perpendicular to the entrance pupil 2a. (In FIG. 4, the same components as those in FIG. 3 are denoted by the same reference numerals, and detailed description thereof is omitted). As shown in FIG. 4, it is desirable to use a lens hood 4 in combination with the imaging lens 2 that is normally used.

  FIG. 5 is a schematic view of the car as viewed from above. Reflected light L4 ′ and L5 ′ from the side of the imaging lens 2 having a field of view with a horizontal viewing angle ω2 is incident on the entrance pupil of the imaging lens 2. It is the figure which showed a mode that it passed and reached | attained an image surface. As described with reference to FIG. 3 described above, rays such as the reflected lights L1 ′ to L3 ′ pass through the center of the entrance pupil 2a of the imaging lens 2 and have a virtual axis Q1 perpendicular to the front window shield W as a rotation axis. 5, the reflected lights L4 'and L5' shown in FIG. 5 can be rotated by one of the reflected lights L1 'to L3' described above and the like with the virtual axis Q1 shown in FIG. As rotated. Therefore, the incident angle when reflected by the front window shield W is not different from the incident angle of the above-mentioned light beam. Therefore, these light rays L4 'and L5' are also polarized, and linear polarizing filters 3b and 3c are arranged on the side of the imaging lens 2 of the vehicle-mounted camera 1 in order to reduce the reflected light. The linearly polarizing filters 3b and 3c in FIG. 5 are arranged in a parallel plane shape so as to be inclined, but other shapes may be used. Further, as shown in FIG. 5, it may be a part of a linear polarizing filter 3a corresponding to reflected light from below (in the following description, the lower linear polarizing filter is 3a). In FIG. 5, left and right linear polarizing filters 3 b and 3 c are provided so as to extend upward from the left and right side portions of the linear polarizing filter 3 a disposed below the imaging lens 2 to cover the front periphery of the imaging lens 2. The case where it arrange | positions is shown.

  In FIG. 5, the on-vehicle camera 1 ′ is arranged to be viewed backward through the rear window shield W ′ by the imaging lens 2 ′ having a field of view with a horizontal viewing angle ω3. The rear window shield W ′ is also inclined in the same manner as the front window shield W described above, and reflection ghost is often a problem. Also in this case, the ghost can be reduced by providing the linear polarization filter 3 ′ as shown in FIG. 5 (the configuration and the like are the same as those of the vehicle-mounted camera 1 for forward monitoring).

  By the way, as shown in FIG. 6, when the instrument panel M on the dashboard D is turned on, the light from the instrument panel M is reflected by the front window shield W and incident on the imaging lens 2 to generate a ghost. I will let you. In such a case, if the instrument panel M is self-luminous and is not polarized, a second linear polarizing filter 5 having a polarization axis substantially perpendicular to the linear polarizing filter 3 is disposed immediately before the instrument panel M. That's fine. Then, due to the combination of the linear polarizing filter 3 and the second linear polarizing filter 5 whose polarization axis is substantially perpendicular, most of the reflected light L2 ′ reflected by the instrument panel M of the dashboard D is not transmitted, and the front The ghost of the instrument panel M is completely extinguished by the reflection at the window shield W. The portions other than the instrument panel M, for example, the reflected light from the dashboard D are omitted because they overlap with the description of FIG. 3 described above, but in the configuration of FIG. L1 ′ is held at an inclination so as to enter substantially perpendicularly. In the case of such a configuration, light rays from the sky like the light rays L1 and L2 can pass through the entrance pupil 2a of the imaging lens 2 after being reflected by the surface of the filter 3, but are out of the field of view. It is possible to prevent ghost and flare by devising the shield.

  FIG. 7 shows an example of an optical device having the above-described vehicle-mounted cameras 1 and 1 ′, a vehicle imaging system 10 that monitors the front and rear of the vehicle, and an image captured by the vehicle imaging system 10. The structure of the control part 20 which analyzes this internal and external environment and controls this vehicle is shown. An imaging system 10 for a vehicle includes an imaging lens 2 and a linear polarization filter 3, an on-vehicle camera 1 that is disposed in the vehicle and images the front through a front window shield W, and an image formed by the imaging lens 2. A vehicle-mounted camera 1 ′ having an image pickup device 11 for detecting the image, an image pickup lens 2 ′, and a linear polarization filter 3 ′, which is disposed in the vehicle and picks up the rear image via the rear window shield W ′, and an image pickup lens 2 ′. An image sensor 12 that detects an image formed by the image sensor 12, an image processor 13 that processes signals from the image sensors 11 and 12 to generate image information (video signal), and an image obtained by photographing in the vehicle And a video storage device 14 for storing or recording the signal in a memory or a recording medium as required. The image processing unit 13 has a control system for driving the on-vehicle cameras 1 and 1 ′ and a circuit for amplifying and other signal processing of video signals obtained by the cameras. Further, the control unit 20 has a function of analyzing the environmental conditions inside and outside the vehicle together with the video signal and other information including information other than the camera and issuing a control signal. The linear polarization filters 3 and 3 'provided around the imaging lenses 2 and 2' are necessary to suppress generation of unnecessary ghost images and provide a faithful and high-quality forward view (rear view) image. Can be selected.

  As described above, when the vehicle-mounted camera 1, 1 'is configured as described above, an image such as the dashboard D reflected by the front or rear window shields W, W' can be effectively removed. As a result, the contrast of the images of the on-vehicle cameras 1 and 1 'is not lowered.

The structure near the front window shield of a vehicle is shown. It is a graph which shows the relationship between an incident angle when a light ray injects into the glass of refractive index 1.55 from the air, and the intensity | strength of reflected light. It is a cross-sectional view of a vehicle-mounted camera when the front is monitored through a front window shield. FIG. 4 is a cross-sectional view of the on-vehicle camera when the shape of the linear polarization filter is changed in FIG. 3. The structure of a vehicle-mounted camera when the car is viewed from above is shown. It is a cross-sectional view of a vehicle-mounted camera in which the reflection of the instrument panel is also removed. It is a block diagram which shows the structure of the imaging system for vehicles.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,1 'Car mounted camera 2,2' Imaging lens 3 (3a, 3b, 3c), 3 'Linear polarization filter 4 Lens hood 5 2nd linear polarization filter 10 Imaging system for vehicles (optical apparatus)
W Front window shield W 'Rear window shield

Claims (8)

An imaging lens for imaging the exterior of the vehicle through a window shield;
A linear polarizing filter disposed outside the field of view of the imaging lens,
The vehicle-mounted camera in which the linear polarization filter is disposed at a position where a light beam reflected by the window shield and incident on the imaging lens is transmitted before being reflected by the window shield .   The vehicle-mounted camera according to claim 1, wherein the linear polarization filter is disposed below the imaging lens.   The on-vehicle camera according to claim 1, wherein the linear polarization filter is disposed on a side of the imaging lens.   The vehicle-mounted camera according to any one of claims 1 to 3, wherein the linear polarization filter is attached in a direction that blocks at least an S-polarized component of light incident on the imaging lens.   The vehicle-mounted camera according to any one of claims 1 to 4, wherein the linear polarization filter is disposed to be inclined with respect to the optical axis of the imaging lens.   The vehicle-mounted camera according to claim 1, wherein the linear polarization filter is disposed so as to cover a front periphery of the imaging lens. A second linear polarizing filter disposed so that a light beam that passes through the linear polarizing filter and enters the imaging lens is transmitted before entering the linear polarizing filter;
The on-vehicle camera according to any one of claims 1 to 6, wherein the second linear polarization filter is disposed such that a polarization axis is substantially orthogonal to a polarization axis of the linear polarization filter.   The optical apparatus which has a vehicle-mounted camera as described in any one of Claims 1-7.

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