WO2005119571A1

WO2005119571A1 - Imaging apparatus and method for vehicle occupant determination

Info

Publication number: WO2005119571A1
Application number: PCT/GB2005/002202
Authority: WO
Inventors: Leon Mario Lobo; John Raymond Tyrer
Original assignee: Laser Optical Engineering Limited
Priority date: 2004-06-04
Filing date: 2005-06-03
Publication date: 2005-12-15
Also published as: GB2414790A; GB0412505D0

Abstract

Imaging apparatus (10) for determining the number of occupants in a vehicle (12) comprises an infrared camera (14) arranged to capture an infrared image and a visible camera (16) arranged to capture a visible image. The apparatus (10) includes an optical arrangement (18) which is adapted to provide a common view (20) of the interior (13) of the vehicle (12) to both the infrared and visible cameras (14, 16) to enable the infrared and visible cameras (14, 16) to capture infrared and visible images respectively of the common view (20) of the interior (13) of the vehicle (12), and a processor (22) which is operable to analyse the captured infrared and visible images of the common view (20) of the interior (13) of the vehicle (12) and operable to determine the number of occupants in the vehicle (12) based on the image analysis.

Description

Imaging Apparatus and Method for Vehicle Occupant Determination

Embodiments of the present invention relate to imaging apparatus for determining the number of occupants in a vehicle and/or a method for determining the number of occupants in a vehicle.

It can be desirable to determine the number of occupants in a vehicle in a variety of situations. One such situation is where high occupancy vehicle lanes are employed so that penalties can be imposed on vehicles travelling in such lanes which have less than a predetermined number of occupants, for example less than two occupants. Other such situations are where toll-based charging or congestion charging is employed and is based on the number of vehicle occupants, at the entrances/exits of high occupancy car parks, shopping centre car parks and high security areas.

It will of course be appreciated that the above examples are not exhaustive and that there may be numerous other situations in which it may be desirable to determine the number of occupants in a vehicle.

One method for determining the number of occupants in a vehicle is for an observer to view a vehicle and count the number of occupants on board. However, manual observation is generally regarded as being time consuming and inaccurate.

Due to the difficulties and drawbacks associated with manual observation techniques, apparatus for automatically detecting the number of occupants in a vehicle has been developed. However, existing apparatus does not enable an accurate determination of the number of occupants in a vehicle. According to a first aspect of the present invention, there is provided imaging apparatus for determining the number of occupants in a vehicle, the apparatus comprising an infrared image capture means arranged to capture an infrared image, a visible image capture means arranged to capture a visible image, an optical arrangement adapted to provide a common view of the interior of the vehicle to both the infrared and visible image capture means to enable the infrared and visible image capture means to capture infrared and visible images respectively of the common view of the interior of the vehicle, and a processor operable to analyse the captured infrared and visible images of the common view of the interior of the vehicle and operable to determine the number of occupants in the vehicle based on the image analysis.

The optical arrangement may include a lens arrangement, and the lens arrangement may comprise a single lens.

The infrared image capture means may be operable to capture an infrared image in which the wavelength of the infrared radiation may be in the infrared range of the electromagnetic spectrum between approximately 1400nm and approximately 1600nm. The infrared image capture means may be operable to capture an infrared image in which the wavelength of the infrared radiation is approximately 1550nm.

The apparatus may include a filter device for filtering infrared radiation received from the optical arrangement to provide infrared radiation having a predetermined wavelength to the infrared image capture means. The filter device may be adapted to filter infrared radiation received from the optical arrangement to provide infrared radiation having a predetermined wavelength of approximately 1550nm.

The visible image capture means may be operable to capture a visible image in which the wavelength of the visible radiation is in the visible range of the electromagnetic spectrum between approximately 400nm and approximately 700nm. The visible image capture means may be operable to capture a visible image in which the wavelength of the visible radiation is in the red portion of the visible range between approximately 600nm and approximately 700nm.

The optical arrangement may include a beam splitter device. The beam splitter device may be located between the lens arrangement and the infrared and visible image capture means. The beam splitter device may be adapted to direct infrared and visible radiation from the lens arrangement to the infrared and visible image capture means, respectively. The beam splitter device may be adapted to direct infrared radiation from the lens arrangement to the infrared image capture means by transmitting the infrared radiation through the beam splitter device. The beam splitter device may be adapted to direct visible radiation from the lens arrangement to the visible image capture means by reflecting the infrared radiation.

The apparatus may include an infrared illumination means to provide infrared illumination to the interior of the vehicle. The infrared illumination means may be adapted to provide infrared illumination in which the wavelength of the infrared radiation may be in the infrared range of the electromagnetic spectrum between approximately 1400nm and approximately 1600nm. The wavelength of the infrared radiation may be approximately 1550nm.

The processor may be operable to analyse the captured infrared and visible images of the common view of the vehicle interior by comparing the respective captured images to detect differences therebetween. The processor may be operable to compare the captured infrared and visible images of the vehicle interior by comparing the greyscale values of corresponding individual pixels in the respective images. The processor may be operable to mathematically process the greyscale values of corresponding individual pixels in the respective images to obtain a processed composite image. The processor may be operable to subtract the greyscale values of corresponding individual pixels in the respective images to obtain a processed composite image. The processor may be operable to determine the presence of dark and light areas defined by groups of pixels in the processed composite image and may be operable to perform an analysis of the dark and light areas to determine the number of occupants in the vehicle.

According to a second aspect of the present invention, there is provided a method for determining the number of occupants in a vehicle, the method comprising: providing a common view of an interior of a vehicle to both infrared and visible image capture means; capturing infrared and visible images of the common view of the interior of the vehicle using the infrared and visible image capture means respectively; analysing the captured infrared and visible images of the common view of the interior of the vehicle to detect the presence of persons in the captured images; and determining the number of occupants in the vehicle based on the image analysis.

The method may comprise illuminating the interior of the vehicle with infrared illumination to enable an infrared image to be captured using the infrared image capture means. The method may comprise the use of a laser to illuminate the interior of the vehicle with infrared illumination. The method may comprise illuminating the interior of the vehicle with infrared radiation having a predetermined wavelength, and the step of capturing an infrared image may comprise capturing an infrared image comprising infrared radiation at the predetermined wavelength. The method may comprise filtering the infrared radiation provided to the infrared image capture means so that it is at the predetermined wavelength. The method may comprise illuminating the interior of the vehicle with infrared radiation having a predetermined wavelength in the infrared range of the electromagnetic spectrum between approximately 1400nm and approximately 1600nm. The method may comprise illuminating the interior of the vehicle with infrared radiation having a predetermined wavelength of approximately 1550nm.

The step of capturing an infrared image of the common view of the interior of the vehicle may comprise capturing an infrared image in which the infrared radiation has a wavelength in the infrared range of the electromagnetic spectrum between approximately 1400nm and approximately 1600nm. The step of capturing an infrared image of the common view of the interior of the vehicle may comprise capturing an infrared image in which the infrared radiation has a wavelength of approximately 1550nm.

The step of capturing a visible image of the common view of the interior of the vehicle may comprise capturing a visible image in which^' the visible radiation has a wavelength in the visible range of the electromagnetic spectrum between approximately 400nm and approximately 700nm. The step of capturing a visible image of the common view of the interior of the vehicle may comprise capturing a visible image in which the visible radiation has a wavelength in the red portion of the visible range between approximately 600nm and approximately 700nm.

The step of providing a common view of an interior of a vehicle to both the infrared and visible image capture means may comprise the use of an optical arrangement. The optical arrangement may include a lens arrangement. The lens arrangement may comprise a single lens.

The optical arrangement may include a beam splitter device and the step of providing a common view of an interior of a vehicle to both the infrared and visible image capture means may comprise transmitting infrared radiation from the lens arrangement through the beam splitter device into the infrared image capture means. The step of providing a common view of an interior of a vehicle to both the infrared and visible image capture means may comprise reflecting visible radiation from the lens arrangement, using the beam splitter device, into the visible image capture means.

The step of analysing the captured infrared and visible images of the common view of the interior of the vehicle may comprise comparing the captured images to detect differences between the captured images. The step of comparing the captured infrared and visible images to detect differences between the captured images may comprise comparing greyscale values of corresponding individual pixels in the respective images. The step of comparing the captured infrared and visible images to detect differences between the captured images may comprise mathematically processing the greyscale values of corresponding individual pixels in the respective images to obtain a processed composite image. The step of comparing the captured infrared and visible images to detect differences between the captured images may comprise subtracting greyscale values of corresponding individual pixels in the respective images to obtain a processed composite image. The step of comparing the captured infrared and visible images to detect differences between the captured images may comprise subtracting greyscale values of individual pixels in the captured infrared image from greyscale values of corresponding individual pixels in the captured visible image to obtain a processed composite image. The method may comprise inverting the greyscale values of pixels in the processed composite image to provide an inverted processed composite image. The step of determining the presence of persons in the vehicle based on any detected differences between the compared images may comprise analysing the processed composite image or the inverted processed composite image to detect the presence of dark and light areas in the image, the dark areas being representative of exposed skin.

The step of determining the presence of persons in the vehicle may comprise analysing the detected dark areas to identify the dark areas which correspond to an exposed human face. The step of determining the presence of persons in the vehicle may comprise counting the identified dark areas corresponding to an exposed human face to determine the number of persons present in the vehicle.

According to a third aspect of the present invention, there is provided an imaging system for detecting the presence of humans and other animals by detecting the presence of skin in a target area, the imaging system comprising an infrared camera arranged to capture an infrared image of the target area, a visible camera arranged to capture a visible image of the target area, an optical arrangement adapted to provide a common view of the target area to both the infrared and visible cameras to enable the infrared and visible cameras to capture infrared and visible images respectively of the common view of the target area, and an analysis system operable to analyse the infrared and visible images captured by the infrared and visible cameras respectively to identify the presence of skin in the images.

An embodiment of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:-

Fig. 1 is a diagrammatic view of imaging apparatus for determining the number of occupants in a vehicle, in use;

Fig. 2 is a detailed view of the imaging apparatus of Fig. 1; and

Fig. 3 shows examples of images obtained using the imaging apparatus of Fig. 2. Referring to Fig. 1, there is shown generally imaging apparatus 10 for determining the number of occupants in a vehicle 12. The imaging apparatus 10 may be mounted in use on a suitable post 11 , gantry, bridge, or using any other suitable mounting arrangement.

Referring to Fig. 2, the imaging apparatus 10 comprises an infrared image capture means, for example an infrared camera 14, which is arranged to capture an infrared image, and a visible image capture means, for example a visible camera 16, which is arranged to capture a visible image.

The imaging apparatus 10 includes an optical arrangement 18 which is adapted to provide a common view 20 of the interior 13 of the vehicle 12 to both the infrared and visible cameras 14, 16 to enable the infrared and visible cameras 14, 16 to capture infrared and visible images respectively of the common view 20. For clarity purposes, the interior of the vehicle 13 is represented schematically in Fig. 2 by the cross-hatched area.

The imaging apparatus 10 includes a processor 22 which is operable to analyse the captured infrared and visible images of the common view 20 of the vehicle interior 13 to determine the number of occupants in the vehicle 12, based on the image analysis.

In more detail, the infrared camera 14 is adapted to capture an infrared image of the common view 20 of the vehicle interior 13 in which the wavelength of the infrared radiation is approximately 1550nm. In order to ensure that the infrared camera 14 receives infrared radiation at this predetermined wavelength only, the imaging apparatus 10 includes a filter device 24, for example a notch filter or band pass filter, which filters the infrared radiation provided by the optical arrangement 18 to the infrared camera 14. The imaging apparatus 10 also includes an infrared illumination means, such as a laser 26. The laser 26 provides infrared illumination having a predetermined wavelength of approximately 1550nm to the vehicle interior 13, thereby supplementing naturally occurring infrared radiation provided by natural daylight. The provision of radiation at a wavelength of 1550nm using the laser 26 is advantageous since, at this wavelength, there is no risk of retinal damage to the vehicle occupants.

A suitable beam spreading device (not shown), for example a telescope, spreads out the emitted laser beam so that substantially the entire vehicle interior 13 is illuminated by the infrared illumination.

An infrared image is captured by activating the laser 26 to provide infrared illumination to the vehicle interior 13 and activating the infrared camera 14 to capture an infrared image of the vehicle interior 13. The resultant captured infrared image will be a greyscale image comprising dark and light areas, defined by individual pixels in the image. The level of greyscale, that is the greyscale value, of each pixel will depend upon the reflectance characteristics of objects present in the common view 20 of the vehicle interior 13.

In particular, the exposed skin of any occupants in the vehicle 12 will appear as dark areas, defined by groups of adjacent dark or black pixels, in the captured infrared image due to the fact that human skin absorbs a substantial amount of infrared radiation at the predetermined wavelength of 1550nm. Human skin absorbs, rather than reflects, infrared radiation at this wavelength because it consists of a substantial amount of water, the spectral characteristics of water being such that it absorbs infrared radiation at the predetermined wavelength of 1550nm. It will of course be appreciated that water and, therefore, human skin absorbs infrared radiation over a range of wavelengths. The use of infrared radiation having a predetermined wavelength of 1550nm is, however, advantageous for the reasons discussed above and for further reasons which will be explained later.

Other materials inside the vehicle 12, including hair and artificial materials such as clothing and upholstery, will appear as lighter areas in the captured infrared image since these materials will reflect significantly more of the infrared radiation at the predetermined wavelength of 1550nm than human skin. The individual pixels of the infrared image defining these lighter areas will have different greyscale values according to the different reflectance characteristics of the particular materials.

In one embodiment, the imaging apparatus 10 utilises greyscale values in the range 0 to 255, a greyscale value of 0 corresponding to a black pixel, and a greyscale value of 255 corresponding to a white pixel. It will of course be appreciated by those skilled in the art that the imaging apparatus 10 could utilise any suitable range of greyscale values.

Although the use of infrared radiation having a predetermined wavelength of 1550nm is preferred, infrared radiation having a predetermined wavelength of between 1400nm and 1600nm could be emitted by the laser 26 and captured by the infrared camera 14 to provide the captured infrared image. This is because most modern vehicle windscreens employ materials, such as coatings or layers, which prevent the transmission of infrared radiation through the windscreen into the vehicle interior 13. These materials are generally provided to prevent the vehicle interior from heating up in sunny conditions, but may also prevent the operation of imaging apparatus which relies on the use of infrared radiation to capture infrared images.

The applicant has, however, appreciated that the transmission of infrared radiation having a wavelength within the range of approximately

1400nm to approximately 1600nm is not prevented by such materials and, hence, an accurate infrared image of the vehicle interior 13 can be captured using the imaging apparatus 10 according to the invention which utilises infrared radiation within this range.

It is possible that objects inside the vehicle 12, other than human skin, may contain water and therefore absorb infrared radiation at the predetermined wavelength. For example, natural vegetation such as a cabbage may contain water and, therefore, appear as a dark area in the captured infrared image. Since such objects which appear as dark areas in the captured infrared image may be of a size similar to a human head, it is undesirable to rely solely on the captured infrared image to determine the number of occupants in the vehicle 12 since it would be possible to easily fool the apparatus 10 and, for example, avoid the imposition of penalties in situations such as those where the apparatus 10 is used to determine the number of occupants in vehicles using high occupancy vehicle lanes.

In view of the above, in order to improve the accuracy of occupant detection using the imaging apparatus 10, as indicated above a visible image of the common view 20 of the vehicle interior 13 is also captured using the visible camera 16. In a preferred embodiment of the invention, a visible image in which the wavelength of the visible radiation is in the red portion of the visible range of the electromagnetic spectrum, between approximately 600nm and 700nm, is captured using the visible camera 16.

The applicant has appreciated that restriction of the wavelength of visible radiation to the red portion of the visible range in the captured visible image is advantageous because all skin reflects radiation in the red portion, irrespective of skin type or colour. This is believed to be due to the presence of haemoglobin in the human body. The use of visible radiation in the red portion of the visible spectrum provides a captured visible greyscale image comprising dark and light areas, having different greyscale values, defined by individual pixels in the visible image. Areas of the captured visible image in which exposed skin is present may appear darker or lighter than areas in which no exposed skin is present due to the fact that the surrounding artificial materials and objects may reflect the incident visible radiation to a greater or lesser extent than exposed skin.

Due to the fact that exposed skin reflects incident visible radiation in the red portion of the visible range, it will always appear lighter in the captured visible image than in the captured infrared image.

However, areas of the captured visible image in which no exposed skin is present will, in most cases, have a similar appearance to corresponding areas of the captured infrared image in which no exposed skin is present. This is because objects inside the vehicle 12, for example hair and artificial materials such as clothing and upholstery, will generally reflect incident visible radiation having a wavelength in the range of 600 to 700nm, and incident infrared radiation having a wavelength of approximately 1550nm, in a similar way.

Furthermore, in order to maximise the similarity of the appearance of corresponding areas of the captured infrared and visible images in which no exposed skin is present, the processor 22 is operable to continuously monitor the greyscale values of pixels defining one or more selected predetermined areas in each of the infrared and visible images in which no exposed skin is present, and to adjust or calibrate the greyscale values of these predetermined areas so that they are substantially the same in both the infrared and visible images. The processor 22 is operable to adjust the greyscale values in these corresponding predetermined areas by continuously adjusting the shutter speeds, and hence lighting levels, of the infrared and visible cameras 14, 16. Continuous monitoring of the shutter speed of the visible camera 14 is particularly important since the image quality will be dependent upon the level of daylight provided to the vehicle interior 13. This is because the imaging apparatus 10 does not use artificial visible lighting to illuminate the vehicle interior 13.

The predetermined areas are selected to ensure it is unlikely that there will be any exposed skin present in those areas. In one embodiment, the greyscale values of corresponding pixels defining corresponding predetermined areas at each corner of the infrared and visible images are monitored. There is unlikely to be any exposed skin present in the infrared and visible images of these corresponding predetermined areas since they are at the extremities of the common view 20 of the vehicle interior 13.

The greyscale values of corresponding individual pixels in the captured infrared and visible images will therefore in general be similar in corresponding areas in which no exposed skin is present, whilst the greyscale values of individual pixels defining areas of the captured visible image in which exposed skin is present will be much greater than the corresponding pixels defining corresponding areas in which exposed skin is present in the captured infrared image.

Once the infrared and visible images of the common view 20 have been captured, the processor 22 is operable to analyse the captured images by comparing the images to detect differences between the images. Based on the detected differences, the processor is then able to determine the number of occupants in the vehicle 12. The processor 22 analyses the captured infrared and visible images by mathematically processing the greyscale values of corresponding individual pixels in the captured infrared and visible images. In one embodiment of the invention, the processor 22 analyses the captured images by subtracting the greyscale values of individual pixels in the captured infrared image from the greyscale values of corresponding individual pixels in the captured visible image to provide a processed composite image of the common view 20 of the vehicle interior 13.

Referring to Fig. 3, as explained above, the greyscale values of individual pixels in the captured infrared image 31 of the common view 20 will be low in areas where exposed skin, such as the exposed skin of a human face 32, is present so that these areas will appear dark, and generally black. In the example of Fig. 3, the pixels defining the area of the captured infrared image 31 of the common view 20 in which the human face 32 is present have greyscale values of 20. This is due to the absorption of substantially all of the infrared radiation at the predetermined wavelength of 1550nm by the exposed skin.

In the captured visible image 34 of the common view 20, the greyscale values of the corresponding individual pixels defining the area in which the exposed skin of the human face 32 is present will always be greater due to the fact that the exposed skin reflects incident radiation in the red portion of the visible range, again as explained above. In the example of Fig. 3, the pixels defining the area of the captured visible image 34 of the common view 20 in which the human face 32 is present have greyscale values of 100. The average greyscale values of the corresponding pixels defining corresponding areas of the captured infrared and visible images 31 , 34 in which no exposed skin is present are similar, as explained in detail above. In the example shown, the average greyscale value of the pixels in the areas of the captured infrared 31 image in which no exposed skin is present is 78, whilst in the captured visible image 34 the average greyscale value of the corresponding pixels is 80. Subtraction of the greyscale values of individual pixels in the captured infrared image 31 from the greyscale values of the corresponding individual pixels in the captured visible image results in a processed composite image 36 in which the individual pixels defining the area of the common view 20 in which the human face 32 is present have greyscale values of 80, and in which the individual pixels defining the area of the common view 20 in which no exposed skin is present have an average greyscale value of 2. The area of the processed composite image 36 in which the human face 20 is present will therefore appear lighter than the other areas of the processed composite image 36 which will appear darker.

The processed composite image 36 is then inverted, for example the processor 22 may be operable to invert the image, so that the lighter area which corresponds to the human face 32 becomes darker, whilst the other areas of the processed composite image 36 become lighter. Areas of the inverted processed composite image 36 in which exposed skin is present will therefore appear much darker than the surrounding areas in which no exposed skin is present, thus enabling vehicle occupants to be readily distinguished from the background and readily identified in the processed composite image 36.

Due to possible slight variations between the greyscale values of corresponding individual pixels in different areas of the captured infrared and visible images, the areas of the inverted processed composite image in which no exposed skin is present may not appear completely white, and instead may comprise different levels of greyscale. However, the process described above performed by the apparatus 10 minimises the different levels of greyscale of these areas thereby minimising the dynamic range of these background areas. This results in a general loss of definition in areas of the inverted processed composite image in which no exposed skin is present, thereby enhancing the dynamic range of the areas of the inverted processed composite image in which exposed skin is present. Depending upon the reflectance characteristics of objects in the interior 13 of the vehicle 12, it is possible that the incident infrared and visible radiation may be reflected to different extents, resulting in corresponding pixels defining corresponding areas of the captured infrared and visible images of the common view 20 in which no exposed skin is present having different greyscale values.

By way of example, a blue item of clothing worn by a vehicle occupant would reflect the incident infrared radiation provided by the laser 26, and therefore appear very light grey in the captured infrared image, and would absorb the incident visible radiation in the red portion of the spectrum, and therefore appear dark grey in the captured visible image. Although subtraction of the greyscale values of the individual pixels defining this area in the infrared image from the greyscale values of the corresponding individual pixels in the visible image defining the corresponding area will result in an area in the processed composite image which is not as dark as other areas in the processed composite image in which visible radiation was reflected to substantially the same extent in the captured infrared and visible images, this area will nevertheless appear darker in the processed composite image than areas in which any exposed skin is present.

This is because there will always be a high level of contrast between the greyscale values of corresponding pixels in the respective captured infrared and visible images in areas in which exposed skin is present. This high level of contrast occurs because the wavelength of the infrared radiation used by the imaging apparatus 10 is predetermined so that there is maximum absorption of the infrared radiation by exposed skin, whilst the wavelength of the visible radiation is predetermined so that there is maximum reflection of the visible radiation by exposed skin. Accordingly, whenever the processed composite image is inverted in the manner described above, areas of the processed composite image in which exposed human skin is present will always appear much darker than surrounding areas in which no exposed skin is present.

As any single occupant in the vehicle 12 will have a number of body parts with exposed skin, for example face, hands, etc, the composite processed image is likely to comprise a plurality of darker areas corresponding to exposed skin.

In order to determine the number of occupants in the vehicle, the processor 22 is operable to analyse the composite processed image to determine which of the darker areas in the processed composite image correspond to human faces. In particular, the processor 22 is operable to filter the darker areas in the composite processed image, for example based on the size of the areas, or the aspect ratios of the areas, both of which can be correlated with known sizes and aspect ratios for human faces, to identify the darker areas which correspond to human faces. The processor 22 is finally operable to count the number of darker areas identified as corresponding to human faces to determine the number of occupants in the vehicle 12.

Depending upon the situation in which the imaging apparatus 10 is employed, the output from the apparatus 10 may be used to trigger further apparatus. For example, if the processor 22 determines that there is only one occupant in a vehicle travelling in a high occupancy vehicle lane where the minimum number of permitted occupants is two, the imaging apparatus 10 may trigger further apparatus such as a standard enforcement camera to capture an image of the vehicle from which the driver and vehicle registration plates can be easily identified for subsequent enforcement purposes.

A particular advantage of the imaging apparatus 10 according to the present invention is that by employing the optical arrangement 18, a common view 20 of the vehicle interior 13 can be provided to both the infrared and visible cameras 14, 16. This ensures that the individual pixels in each of the captured infrared and visible images provide a view of an identical part of the vehicle interior 13. The pixels in the separate infrared and visible images are thus fully aligned such there is no parallax between them, which could arise if cameras 14, 16 with individual lenses were employed to capture images of the vehicle interior 13.

In order to further ensure that the infrared and visible cameras 14, 16 both capture an identical image of the common view 20 of the vehicle interior 13, the CCD sensors (also known as camera chips) within the two cameras are matched both pixel for pixel, and dimensionally. This ensures that the fields of view of the infrared and visible cameras 14, 16 are matched, regardless of the distance between each of the cameras 14, 16 and the focal plane of the common view 20. This also ensures that the magnification of the common view 20, provided by the infrared and visible cameras 14, 16, is exactly the same.

In a preferred embodiment of the imaging apparatus 10, the optical arrangement 18 includes a lens arrangement having a single lens 28 which is focussed on the vehicle interior 13. It may not be possible using the imaging apparatus 10 to obtain a complete view of the vehicle interior 13 due to the fact that some of the rear interior of the vehicle 12 may be obscured by the front seats and the roof. However, by directing the lens 28 towards the front and one side of the vehicle 12, a common view 20 of the front seats and part of the rear seats can be provided to the infrared and visible cameras 14, 16 which is considered to be sufficient for most situations. If a complete view of the vehicle interior 13 is required, it will generally be necessary to employ two suitably positioned lenses 28 and further infrared and visible cameras 14, 16.

In order to enable the lens 28 to transmit the common view 20 of the vehicle interior 13 to both the infrared and visible cameras 14, 16, the optical arrangement 18 also includes a beam splitter device 30. The beam splitter device 30, which may comprise coated glass, is adapted to allow the transmission therethrough of infrared radiation at the predetermined wavelength to direct the infrared radiation from the lens 28 into the infrared camera 14 to enable it to capture an infrared image of the common view 20. Visible radiation received from the lens 28 at a wavelength of between 600 and 700nm is reflected by the beam splitter device 30 into the visible camera 16 to enable the visible camera 16 to capture a visible image of the common view 20.

Although embodiments of the invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that various modifications to the examples given may be made without departing from the scope of the present invention, as claimed. For example, infrared and visible image capture means other than infrared and visible cameras 14, 16 may be used. An alternative optical arrangement 18 to a lens 28 or beam splitter device 30 may be used to convey the infrared and visible images of the common view 20 to the infrared and visible cameras 14, 16. The beam splitter device 30 may be arranged to direct infrared radiation received from the lens 28 into the infrared camera 14 by reflecting it into the infrared camera 14, and may be arranged to direct visible radiation received from the lens 28 into the visible camera 16 by allowing the transmission of the visible radiation through the beam splitter device 30 into the visible camera 16. The imaging apparatus 10 may utilise a range of greyscale values between 0 and 1023, although as mentioned above, any suitable range of greyscale values may be employed. The processor 22 may be operable to analyse or compare the captured infrared and visible images other than by subtracting the greyscale values of corresponding individual pixels in the respective images. For example, the processor 22 may be operable to mathematically process the greyscale values of corresponding individual pixels in the captured infrared and visible images. This mathematical processing could, for example, be by addition or multiplication of the greyscale values of corresponding individual pixels in the captured infrared and visible images.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance, it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings, whether or not particular emphasis has been placed thereon.

Claims

1. Imaging apparatus for determining the number of occupants in a vehicle, the apparatus comprising an infrared image capture means arranged to capture an infrared image, a visible image capture means arranged to capture a visible image, an optical arrangement adapted to provide a common view of an interior of a vehicle to both the infrared and visible image capture means to enable the infrared and visible image capture means to capture infrared and visible images respectively of the common view of the interior of the vehicle, and a processor operable to analyse the captured infrared and visible images of the common view of the interior of the vehicle and operable to determine the number of occupants in the vehicle based on the image analysis.

2. Imaging apparatus according to claim 1 , wherein the optical arrangement includes a lens arrangement.

3. Imaging apparatus according to claim 2, wherein the lens arrangement comprises a single lens.

4. Imaging apparatus according to any of the preceding claims, wherein the infrared image capture means is operable to capture an infrared image in which the wavelength of the infrared radiation is in the infrared range of the electromagnetic spectrum between approximately 1400nm and approximately 1600nm.

5. Imaging apparatus according to claim 4, wherein the infrared image capture means is operable to capture an infrared image in which the wavelength of the infrared radiation is approximately 1550nm.

6. Imaging apparatus according to any of the preceding claims, wherein the apparatus includes a filter device for filtering infrared radiation received from the optical arrangement to provide infrared radiation having a predetermined wavelength to the infrared image capture means.

7. Imaging apparatus according to claim 6, wherein the filter device is adapted to filter infrared radiation received from the optical arrangement to provide infrared radiation having a predetermined wavelength of approximately 1550nm.

8. Imaging apparatus according to any of the preceding claims, wherein the visible image capture means is operable to capture a visible image in which the wavelength of the visible radiation is in the visible range of the electromagnetic spectrum between approximately 400nm and approximately 700nm.

9. Imaging apparatus according to claim 8, wherein the visible image capture means is operable to capture a visible image in which the wavelength of the visible radiation is in the red portion of the visible range between approximately 600nm and approximately 700nm.

10. Imaging apparatus according to any of the preceding claims, wherein the optical arrangement includes a beam splitter device.

11. Imaging apparatus according to claim 10 when dependent on any of claims 2 to 9, wherein the beam splitter device is located between the lens arrangement and the infrared and visible image capture means.

12. Imaging apparatus according to claim 11 , wherein the beam splitter device is adapted to direct infrared and visible radiation from the lens arrangement to the infrared and visible image capture means, respectively.

13. Imaging apparatus according to claim 11 or claim 12, wherein the beam splitter device is adapted to direct infrared radiation from the lens arrangement to the infrared image capture means by transmitting the infrared radiation through the beam splitter device.

14. Imaging apparatus according to any of claims 11 to 13, wherein the beam splitter device is adapted to direct visible radiation from the lens arrangement to the visible image capture means by reflecting the infrared radiation.

15. Imaging apparatus according to any of the preceding claims, wherein the apparatus includes an infrared illumination means to provide infrared illumination to the interior of the vehicle.

16. Imaging apparatus according to claim 16, wherein the infrared illumination means is adapted to provide infrared illumination in which the wavelength of the infrared radiation is in the infrared range of the electromagnetic spectrum between approximately 1400nm and approximately 1600nm.

17. Imaging apparatus according to claim 16, wherein the wavelength of the infrared radiation is approximately 1550nm.

18. Imaging apparatus according to any of the preceding claims, wherein the processor is operable to analyse the captured infrared and visible images of the common view of the vehicle interior by comparing the respective captured images to detect differences therebetween.

19. Imaging apparatus according to claim 18, wherein the processor is operable to compare the captured infrared and visible images of the vehicle interior by comparing the greyscale values of corresponding individual pixels in the respective images.

20. Imaging apparatus according to claim 19, wherein the processor is operable to subtract the greyscale values of corresponding individual pixels in the respective images to obtain a processed composite image.

21. Imaging apparatus according to claim 20, wherein the processor is operable to determine the presence of dark and light areas defined by groups of pixels in the processed composite image and to perform an analysis of the dark and light areas to determine the number of occupants in the vehicle.

22. A method for determining the number of occupants in a vehicle, the method comprising: providing a common view of an interior of a vehicle to both infrared and visible image capture means; capturing infrared and visible images of the common view of the interior of the vehicle using the infrared and visible image capture means respectively; analysing the captured infrared and visible images of the common view of the interior of the vehicle to detect the presence of persons in the captured images; and determining the number of occupants in the vehicle based on the image analysis.

23. A method according to claim 22, wherein the method comprises illuminating the interior of the vehicle with infrared illumination to enable an infrared image to be captured using the infrared image capture means.

24. A method according to claim 23, wherein the method comprises the use of a laser to illuminate the interior of the vehicle with infrared illumination.

25. A method according to any of claims 22 to 24, wherein the method comprises illuminating the interior of the vehicle with infrared radiation having a predetermined wavelength, and the step of capturing an infrared image comprises capturing an infrared image comprising infrared radiation at the predetermined wavelength.

26. A method according to claim 25, wherein the method comprises filtering the infrared radiation provided to the infrared image capture means so that it is at the predetermined wavelength.

27. A method according to any of claims 23 to 26, wherein the method comprises illuminating the interior of the vehicle with infrared radiation having a predetermined wavelength in the infrared range of the electromagnetic spectrum between approximately 1400nm and approximately 1600nm.

28. A method according to claim 27, wherein the method comprises illuminating the interior of the vehicle with infrared radiation having a predetermined wavelength of approximately 1550nm.

29. A method according to any of claims 22 to 28, wherein the step of capturing an infrared image of the common view of the interior of the vehicle comprises capturing an infrared image in which the infrared radiation has a wavelength in the infrared range of the electromagnetic spectrum between approximately 1400nm and approximately 1600nm.

30. A method according to claim 29, wherein the step of capturing an infrared image of the common view of the interior of the vehicle comprises capturing an infrared image in which the infrared radiation has a wavelength of approximately 1550nm.

31. A method according to any of claims 22 to 30, wherein the step of capturing a visible image of the common view of the interior of the vehicle comprises capturing a visible image in which the visible radiation has a wavelength in the visible range of the electromagnetic spectrum between approximately 400nm and approximately 700nm.

32. A method according to claim 31, wherein the step of capturing a visible image of the common view of the interior of the vehicle comprises capturing a visible image in which the visible radiation has a wavelength in the red portion of the visible range between approximately 600nm and approximately 700nm.

33. A method according to any of claims 22 to 32, wherein the step of providing a common view of an interior of a vehicle to both the infrared and visible image capture means comprises the use of an optical arrangement.

34. A method according to claim 33, wherein the optical arrangement includes a lens arrangement.

35. A method according to claim 34, wherein the lens arrangement comprises a single lens.

36. A method according to claim 34 or claim 35, wherein the optical arrangement includes a beam splitter device and the step of providing a common view of an interior of a vehicle to both the infrared and visible image capture means comprises transmitting infrared radiation from the lens arrangement through the beam splitter device into the infrared image capture means.

37. A method according to claim 36, wherein the step of providing a common view of an interior of a vehicle to both the infrared and visible image capture means comprises reflecting visible radiation from the lens arrangement, using the beam splitter device, into the visible image capture means.

38. A method according to any of claims 22 to 37, wherein the step of analysing the captured infrared and visible images of the common view of the interior of the vehicle comprises comparing the captured images to detect differences between the captured images.

39. A method according to claim 38, wherein the step of comparing the captured infrared and visible images to detect differences between the captured images comprises comparing greyscale values of corresponding individual pixels in the respective images.

40. A method according to claim 38 or claim 39, wherein the step of comparing the captured infrared and visible images to detect differences between the captured images comprises subtracting greyscale values of corresponding individual pixels in the respective images to obtain a processed composite image.

41. A method according to any of claims 38 to 40, wherein the step of comparing the captured infrared and visible images to detect differences between the captured images comprises subtracting greyscale values of individual pixels in the captured infrared image from greyscale values of corresponding individual pixels in the captured visible image to obtain a processed composite image.

42. A method according to claim 40 or claim 41 , wherein the step of determining the presence of persons in the vehicle based on any detected differences between the compared images comprises analysing the processed composite image to detect the presence of dark and light areas in the image, the dark areas being representative of exposed skin.

43. A method according to claim 42, wherein the step of determining the presence of persons in the vehicle comprises analysing the detected dark areas to identify the dark areas which correspond to an exposed human face.

44. A method according to claim 43, wherein the step of determining the presence of persons in the vehicle comprises counting the identified dark areas corresponding to an exposed human face to determine the number of persons present in the vehicle.

45. An imaging system for detecting the presence of humans and other animals by detecting the presence of skin in a target area, the imaging system comprising an infrared camera arranged to capture an infrared image of the target area, a visible camera arranged to capture a visible image of the target area, an optical arrangement adapted to provide a common view of the target area to both the infrared and visible cameras to enable the infrared and visible cameras to capture infrared and visible images respectively of the common view of the target area, and an analysis system operable to analyse the infrared and visible images captured by the infrared and visible cameras respectively to identify the presence of skin in the images.

46. Imaging apparatus for determining the number of occupants in a vehicle substantially as hereinbefore described and/or as shown in the accompanying drawings.

47. A method for determining the number of occupants in a vehicle substantially as hereinbefore described and/or as shown in the accompanying drawings.

48. An imaging system for detecting the presence of humans and other animals by detecting the presence of skin in a target area substantially as hereinbefore described and/or as shown in the accompanying drawings.

49. Any novel subject matter or combination including novel subject matter disclosed herein, whether or not within the scope of or relating to the same invention as any of the preceding claims.