Patent Application
20110267467
This application is based on and incorporates herein by reference Japanese Patent Application No. 2010-103822 filed on Apr. 28, 2010.
1. Field of Application
The present invention relates to a camera apparatus for installation on a host vehicle, enabling reliable discrimination between a red-color light source consisting of a tail lamp of a preceding vehicle and an orange-color light source consisting of a headlamp or a reflector of another vehicle.
In particular, the invention relates to such an apparatus, whereby a tail lamp of a preceding vehicle can be reliably identified within a captured image even when the preceding vehicle is substantially distant from the host vehicle.
2. Description of Related Art
A system referred to as an AHB (Automatic High-Beam) system is known, which automatically switches the headlamps of a vehicle between the high-beam condition and the low-beam condition. This form of automatic headlamp control is sometimes referred to as Hi-Lo control.
Such an AHB system utilizes an in-vehicle camera apparatus (where “camera apparatus” is used herein to refer to electronic types of image-capture apparatus in general) installed in a host vehicle, which discriminates between headlamps and tail lamps of other vehicles, appearing within images captured by the camera apparatus. The camera apparatus generally utilizes a type of image sensor, having a Bayer array of pixels sensors that are variously sensitive to R (red), G (green) and B (blue) components of incident light. Such pixel sensors, are referred to herein simply as “pixels” for brevity. The color at any position within a captured image is obtained based on demosaicing processing (e.g., averaging) of respective color values derived by a set of R, G and B pixels at that position, such as a 2×2 block (RGGB block) of the RGB pixels. An image of the external scene ahead of the host vehicle is focused on the image sensor by a lens assembly of the camera apparatus. When another vehicle is relatively close to the host vehicle and is a preceding vehicle, a tail lamp of the other vehicle can be identified as a red-color region within an image captured by the in-vehicle camera apparatus, while a headlamp or reflector of another vehicle can be identified as an orange-color region. Hence it is possible to reliably distinguish between tail lamps and headlamps or reflectors of other vehicles when these are relatively close. Such an apparatus is described for example in Japanese patent application publication No. 2004-189229.
However problems arises with utilizing a Bayer type of image sensor in is such an application. When light is received from a source which is substantially distant and hence appears as a point source, the size of a resultant light spot which falls on the image sensor may be smaller than a RGGB pixel block of the Bayer array. In particular, the light spot may fall on only a single pixel. In that case, if for example the color of the point light source is orange, and this falls only on a R (red-sensitive) pixel, the color will be detected as being red. Hence, orange-color light that is transmitted from a reflector or headlamp of a distant vehicle may be erroneously detected as arriving from a tail lamp. This is referred to as the “false color” effect.
Thus with such a prior art type of apparatus, reliable discrimination between tail lamps and reflectors (or headlamps) of other vehicles can only be achieved when these vehicles are not distant from the host vehicle.
To attempt to overcome this false color problem, it is possible to defocus the optical image which is formed by the camera lens on the image sensor. The size of a light spot (corresponding to a point light source) formed as on the surface of the image sensor can thereby be increased. However this results in blurring of the image that is captured by the camera apparatus, and a lowering of the signal/noise ratio, so that tail lamps of other vehicles cannot be reliably identified from the captured image.
It is an objective of the present invention to overcome the above problem, by providing an in-vehicle camera apparatus employing a Bayer type of image sensor, which can reliably distinguish between orange-color light sources and red-color light sources (such as tail lamps of preceding vehicles) even when these are of small size and located at a substantial distance from a host vehicle of the camera apparatus.
To achieve this the invention provides an in-vehicle camera apparatus having an image sensor, a lens assembly, an infra-red blocking filter and a beam-splitting optical filter. The image sensor comprises a RGB Bayer array of is pixels (sensor elements) which respectively detect the R (red), G (green) and B (blue) components of light. The lens assembly focuses a beam of external incident light upon the RGB Bayer array. When light is received from a distant small source such as a tail lamp of a distant preceding vehicle, the beam-splitting optical filter splits the corresponding beam of focused light into a plurality of light beams which become incident on respectively different ones of the RGB pixels of the RGB Bayer array.
Thus for example when the incident light entering the lens assembly 20 is orange light from a reflector or headlamp of a distant vehicle, so that a resultant plurality of orange-color beams fall upon respective RGB pixels, the orange color will be detected based on levels of color components that are respectively detected by R, G and B pixels. Hence the orange color can be reliably distinguished from red color. In the case of red light from a tail lamp of a distant vehicle, only the red component will be detected, by the R pixels, so that the tail lamp will be reliably identified.
Since external incident light becomes focused on the RGB Bayer array, a higher S/N ratio can be achieved than is possible with a method whereby a defocused light beam falls upon the RGB Bayer array, to increase the size of a resultant light spot as described hereinabove.
Preferably, the focused light beam from the lens assembly 20 is split into a plurality of light beams which are mutually parallel and spaced apart (horizontally and vertically) from one another by a distance substantially equal to the pitch (i.e., pixel height and width dimension) of the RGB sensor array. With a preferred embodiment, four of such light beams are formed, which become incident on respective adjacent pixels of the RGB Bayer array.
Preferably, the beam-splitting optical filter comprises a successively stacked combination of a first polarizing beam splitter, a ¼-wave plate, and a second polarizing beam splitter. The first polarizing beam splitter is oriented (i.e., has an optic axis oriented) such as to split an incident light beam into a first is linearly polarized beam and a second linearly polarized beam, having respective axes which are vertically displaced from one another, and having respective polarization directions which differ by 90 degrees. The second polarizing beam splitter is oriented such as to split the first linearly polarized beam into a third linearly polarized beam and a fourth linearly polarized beam, which are horizontally displaced from one another and have respective polarization directions which differ by 90 degrees. The second polarizing beam splitter further splits the second linearly polarized beam into a fifth linearly polarized beam and a sixth linearly polarized beam, which are horizontally displaced from one another and have respective polarization directions which differ by 90 degrees.
Furthermore preferably, the beam-splitting optical filter is configured such that the first and second linearly polarized beams are mutually parallel, and vertically separated by a predetermined distance that is substantially equal to the pixel pitch of the Bayer array, the third and fourth linearly polarized beams are mutually parallel and horizontally separated by that predetermined distance, and the fifth and sixth linearly polarized beams are mutually parallel and horizontally separated by the predetermined distance.
From another aspect, such an in-vehicle camera apparatus preferably comprises an infra-red blocking filter, for blocking an infra-red component of an externally incident light beam from passing to the RGB Bayer array. Such an infra-red blocking filter can be readily provided as a coating of magnesium fluoride, formed on a surface of a lens of the lens assembly.
Furthermore the lens assembly of such an in-vehicle camera apparatus is preferably configured to effect chrominance aberration compensation whereby respective levels of chrominance aberration of a green component and a red component of externally incident light are made substantially equal.
The lens assembly preferably includes a lens having an anti-reflection coating formed on a surface of the lens, for suppressing reflection of a red component of externally incident light.
As shown in
An anti-reflection coating 26 of a material such as MgF2 or quartz is formed (by vacuum evaporative deposition or by sputtering) on the face of the biconcave lens 22 which opposes the plano-convex lens 21. This coating 26 acts to reduce the extent of reflection of the R component of incident light, relative to the extent of reflection of each of the G and B components of the incident light.
The infra-red blocking filter 30 acts to block infra-red rays which enter the lens assembly 20. With this embodiment the infra-red blocking filter 30 consists of a thin film, formed on the opposite face of the beam-splitting optical filter 40 from the RGB Bayer array 18. The infra-red blocking filter 30 is preferably formed by evaporative deposition of a material such as SiO2 or TiO2, to constitute a reflective type of infra-red blocking filter. However it would be equally possible to form the infra-red blocking filter 30 from glass containing an additive material such as AlO2 or Cu.
The beam-splitting optical filter 40 is disposed between the image sensor 10 and the lens assembly 20, and serves to split an incident light beam (passed through the lens assembly 20 and infra-red blocking filter 30) into four light beams which become incident on the RGB Bayer array 18 of the image sensor 10. The configuration of the beam-splitting optical filter 40 is basically as illustrated in
The first polarizing beam splitter 41 is formed of a plate of quartz crystal, having an optic axis oriented at an angle of 44.83° from the direction of thickness t of the plate, i.e., displaced by that angle from a direction normal to the main planar surfaces of the plate. The first polarizing beam splitter 41 splits a randomly polarized incident light beam into an undeviated light beam and a is deviated light beam.
The vertical separation amount d is determined by the thickness t of the first polarizing beam splitter 41, and is substantially equal to the size (width and height dimension) of each pixel of the Bayer array 18, i.e., is substantially equal to the sensor pitch.
The ¼-wave plate 43 is also formed as a quartz crystal plate, having a thickness that is ¼ of the average wavelength of the light that is to be detected. When the rays of the undeviated light beam and the deviated light beam emitted from the first polarizing beam splitter 41 pass through the ¼-wave plate 43, each of the resultant pair of emitted beams from ¼-wave plate 43 is circularly polarized, i.e., is a combination of two orthogonal linearly polarized waves which differ in phase by ¼ wavelength)(90°).
The second polarizing beam splitter 42 is formed as a quartz crystal plate, configured as for the first polarizing beam splitter 41, but with the optic axis of the second polarizing beam splitter 42 rotated by 90° from the optic axis of the first polarizing beam splitter 41. The second polarizing beam splitter 42 acts to split each of the two circularly polarized light beams from the ¼-wave plate 43 into an undeviated light beam and a deviated light beam (as defined above), which are orthogonally linearly polarized and are mutually parallel and separated horizontally by the aforementioned distance d, i.e., by an amount substantially equal to the pixel pitch of the RGB Bayer array 18.
Four beams light beams thereby emerge from the second polarizing beam splitter 42, with their axes spaced apart by the distance d in a horizontal direction (at right angles to the optical axis of the lens assembly) and vertical direction, as illustrated conceptually in
The diameter of each of the four resultant light spots which are thereby focused on the RGB Bayer array 18 is determined by the lens assembly 20 and beam-splitting optical filter 40. Preferable, when the focused light has been received from a tail lamp of a distant vehicle (with the tail lamp thereby approximating to a point source of light), the light spot diameter will not exceed the width of each of the pixels 12, 14, 16 of the RGB Bayer array 18.
In that way, as can be understood from
The above advantages of the first embodiment will be further described referring to
With a prior art type of apparatus, when incident light is received from a distant source, the resultant focused light spot on the RGB Bayer array 18 will be extremely small, and so cannot cover all of a 2×2 block (RGGB block) of pixels of the RGB Bayer array 18. This is illustrated in
In that case, if orange-colored light from a vehicle reflector falls as a light spot on a R pixel, the false-color problem will arise. That is, the average value of the output signal levels from that R pixel and from a set of immediately adjacent B and G pixels will be derived, and that value will be interpreted as corresponding to the red color. Hence the color of the light source will be erroneously detected as being red.
It would be possible to avoid this by increasing the size of the light spot corresponding to a distant light source, by adjusting the lens assembly 20 to defocus the light spot at the plane of the RGB Bayer array 18. However in that case the size of the light spot will be increased, for example such as to cover all of the area of the RGB Bayer array 18, as illustrated in
However with the first embodiment described above, when a light beam originating from a point source (such as a tail lamp of a distant vehicle) passes through the lens assembly 20, the light beam becomes split into two pairs in the vertical direction and two pairs in the horizontal direction. Thus a corresponding set of four light spots are formed on the RGB Bayer array 18, as illustrated in
In addition, the respective optical characteristics of the lenses 21, 22, 23, 24 of the lens assembly 20 are predetermined such that the amount of chrominance aberration of the G component of incident light is identical to the amount of chrominance aberration of the R component of the light. The effects of chrominance aberration of the R and G components are thereby minimized. Hence the respective levels of the R and G components can be accurately detected. This further serves to ensure that orange light from a reflector (or headlamp) and red light from the tail lamp of another vehicle can be distinguished with reliability.
Furthermore the coating 26, formed on the lens assembly 20, suppresses reflection of the R component of the RGB components of incident light, and thereby prevents reddish-color ghost images from being produced by the lens assembly 20. Erroneous detection of apparent red light from tail lamps can thereby be avoided.
The infra-red blocking filter 30 can be readily formed, as a thin film on a surface of the beam-splitting optical filter 40, by evaporative deposition of magnesium fluoride.
The first embodiment has been described above for the case of light received from a source which is sufficiently distant to effectively constitute a point source. However in the case of a light beam received from a source other than a point source, the area covered by each of the split beams may be greater than the area of a R, G or B pixel of the RGB Bayer array 18. Hence it will be understood that in the general case, the respective axes of the light beams which emerge from the beam-splitting optical filter 40 become incident on respectively separate ones of the RGB pixels of the RGB Bayer array 18.
Similarly, it will be understood that with the first embodiment, respective axes of the pair of light beams emerging from the first polarizing beam splitter 41 are vertically separated by the distance d, while respective axes of a first pair of light beams emerging from the second polarizing beam splitter 42 are horizontally separated by the distance d, as are also the respective axes of the second pair of light beams which emerge from the second polarizing beam splitter 42.
A second embodiment will be described referring to
As shown in
With the in-vehicle camera apparatus 7 of this embodiment, as for the first embodiment, an incident light beam which enters the first polarizing beam splitter 41 emerges as an undeviated light beam and a deviated light beam, i.e., as two parallel linearly polarized beams having polarization planes which differ by 90d, separated by the vertical displacement d. The second polarizing beam splitter 42 splits each of the undeviated beam and deviated beam from the first polarizing beam splitter 41 into a corresponding beam pair, with the beams of each pair being separated horizontally by the distance d. Thus as illustrated in
Hence with the second embodiment, as illustrated in
An embodiment of a headlamp control apparatus 100, for executing automatic control of switching between the high-beam and low-beam conditions of vehicle headlamps, will be described referring first to the overall configuration shown in
(A) Acquire an image from the in-vehicle camera apparatus 5
(B) Extract an image region expressing a tail lamp of another vehicle, from the acquired image.
(C) Based on the intra-image position of the extracted tail lamp, judge whether the distance of the other vehicle from the host vehicle exceeds a predetermined distance.
(D) Output the judgement results obtained in step (C), to the headlamp switching section 90.
Based on the judgement results thus obtained from the image processing section 80, the headlamp switching section 90 performs changeover between the high-beam and low-beam conditions of the headlamps of the host vehicle.
The above processing executed by the image processing section 80 will be described in more detail referring to the flow diagram of
Next (step S110), for each of these objects which are possible tail lamp, the corresponding color information is judged. If the corresponding color is red, then the object is judged to be an actual tail lamp. In that case, the position of the tail lamp within the image is obtained,
Next in step S115, based on the intra-image position of the tail lamp, a decision is made as to whether the distance of the tail lamp from the host vehicle (i.e., distance of a preceding vehicle carrying that tail lamp) exceeds a predetermined value.
Since methods are known whereby the distance of an object captured in an image can be estimated based upon the position of the object within the image and various parameters of the camera apparatus, detailed description is omitted. For example the distance may be calculated based upon the relationship between the vertical position of a tail lamp within the image and the estimated vertical position (within the image) of a ground-based point light source that is infinitely distant. The latter position can be estimated based on known parameters of the camera apparatus, such as the orientation and height of the camera with respect to the ground surface, etc. This distance calculation is performed for each acquired image in which a tail lamp is detected.
Next (step S120), the judgement results obtained in step S115 are outputted to the headlamp switching section 90. Operation then returns to step S100, and the above image processing steps are repeated for a succeeding acquired image.
In that way, the headlamp control apparatus 100 extracts light sources from within an image that is obtained by the in-vehicle camera apparatus 5, and uses color information in the extracted information to identify light sources which correspond to tail lamps of other (preceding) vehicles, and thereby judge respective distances of such other vehicles, based upon positions at which these tail lamps appear within the acquired image.
With the present invention, it becomes possible to reliably discriminate between a light source which is a tail lamp and a light source which is a reflector of another vehicle, since the invention enables reliable discrimination between a red-color light source and an orange-color light source, even if the light source is a tail lamp which is located at a long distance from the host vehicle and so becomes effectively a point light source. This accurate discrimination between red and orange colors is achieves by eliminating the false-color effect, as described above. It thus becomes possible to reliably judge whether another vehicle is located at more than a predetermined distance from the host vehicle, by identifying a tail lamp of such a vehicle, and utilizing the position of the tail lamp within an acquired image to estimate the distance of the corresponding vehicle.
With the first embodiment as shown in
With the first embodiment, a 2×2 set of four light spots (e.g., corresponding to a light beam originating from a distant tail lamp) are formed on respective adjacent RGB pixels of the RGB Bayer array 18. With that embodiment, the plane of the RGB Bayer array 18 is at right angles to the horizontal direction (at right angles to the optical axis of the lens assembly 20). This condition is illustrated in section (a) of
The invention has been described hereinabove referring to embodiments whereby an incident light ray is split into parallel rays which are mutually separated in the vertical and horizontal directions by the amount d. However it should be understood that the scope of the invention is not limited to a condition of strict beam parallelism. Basically it is only necessary to configure the beam-splitting optical filter and its separation from the RGB Bayer sensor such that, with a plurality of light beams emerging from the beam-splitting optical filter and travelling along respective directions to attain the RGB Bayer array at respective positions thereon, the centers of these positions are separated from one another by an amount substantially equal to the pixel pitch of the array.
With the present invention, as described above, an incident light ray is split into a plurality of light rays which can attain respectively separate ones of a set of mutually adjacent RGB pixels of a Bayer image sensor. It is thereby ensured that light which originates from a point source (such as a tail lamp of a distant vehicle), and which is focused on a Bayer image sensor, will become incident on a plurality of RGB pixels rather than on a single pixel. The above-described false-color problem can thereby be eliminated.
As described hereinabove, the expressions “horizontal” and “horizontally” are used in the above description and in the appended claims to refer to a direction within a plane that is parallel to a specific array direction (horizontal array direction) of the RGB Bayer array and to the optical axis of the lens assembly of the camera apparatus, while the expressions “vertical” and “vertically” refer to a direction at right angles to such a horizontal plane.
It is to be understood that the above embodiments are illustrative of the invention but are not to be taken in a limiting sense, and that various modifications of these or alternative embodiments may be envisaged, which fall within the scope claimed for the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-103822 | Apr 2010 | JP | national |
