WO2005043890A1

WO2005043890A1 - Imaging device

Info

Publication number: WO2005043890A1
Application number: PCT/GB2004/003636
Authority: WO
Inventors: Charles Nicolas Granville Charlesworth
Original assignee: Stereonics Limited
Priority date: 2003-10-09
Filing date: 2004-08-26
Publication date: 2005-05-12
Also published as: GB0323624D0

Abstract

A camera imaging device including one or more lens and/or sensors for viewing and/or capturing images, one or more ambient light level detectors, illumination means to provide infra-red and/or visible light, and switching means to enable the active lens and/or sensors to be changed and/or adjusted in response to the ambient light levels detected to allow effective image viewing and/or capture.

Description

Imaging Device

This invention relates to an imaging device for use in viewing and /or recording images and/ or video in varying light conditions

Although the following description refers in detail to use of an imaging device for recording video images, it will be appreciated by persons skilled in the art that the present invention can be used in one embodiment to view and/or record moving images and also still images. Typically the viewing can occur in ambient light levels ranging from zero to high.

Cameras, whether for still or moving images conventionally include a lens, sensor and a viewfinder which allow the user to place and point the camera at a particular object and when content with the image, the camera can be triggered to capture and/or record the said video image, either by recording the image in a digital data memory, or alternatively by recording the same on a photo sensitive image film, or by simply displaying the image via the device. A common problem is that if the ambient light level is relatively low then if a colour lens or sensor is provided in the camera, the resultant recorded image is at best dark or at worst indistinguishable.

The core parts of electronic digital colour and black and white sensors and lenses are the same. Generally with respect to colour sensors an infra-red filter is added typically between the lens and the sensor to remove the non-visible infra-red light. The sensors are typically most sensitive to infra-red light and if this is not filtered out, it is difficult to obtain true colour images. Typically the lens is surface coated with a suitable material to act as the filter. Alternatively a small piece of glass that has been suitably coated can be placed in the light path, typically between the lens and sensor.

With respect to sensors, the colour sensor is typically a converted black and white sensor with the pixels coated with red green or blue filters, the combination of which produces colour images.

For moving images, cameras are typically based on charge- coupled devices (CCD) or CMOS sensors which are effective in capturing video under normal visible light conditions, and a large number of devices are available to both the professional and home user. However, under low visible light conditions, or in the absence of visible light, colour information is poor, such that the resulting video is of lower quality, often being too dark if no gain is used or too noisy if colour gain extrapolates the poor data.

Low light cameras, as used in security devices and other devices such as night vision goggles, utilise a sensor device sensitive to light in the infra-red range of the electromagnetic spectrum rather than that in the visible light range. However, such devices are not suitable for use in normal or high light conditions, as the sensor can overload, resulting in whiteout, if not compensated for. In addition, such devices may only produce greyscale video, which is not necessarily suitable for a user's requirements. In addition, such cameras still produce poor results when there is no source of illumination, or as the ambient light level approaches the sensors lower limit of light detection.

There have been attempts to create devices that produce good results in both normal and low light conditions, typically using a system of filters, but the results are generally compromised, often with the colours being distorted under normal light conditions or the sensitivity being reduced with respect to low light conditions.

It is therefore an aim of the present invention to provide a camera imaging device for use in viewing and/ or recording video images and which is adaptive to varying light conditions which overcomes the abovementioned problems.

According to a first aspect of the present invention there is provided camera imaging device including at least one sensing means for detecting the ambient light level, at least one or more imaging means for viewing and/or capturing still and/or moving images, and switching means, characterised in that in response to the ambient light level detected, the switching means is controlled to selectively operate said one or more imaging means and/or an indication is generated as to the imaging means or imaging means mode of operation which should be used for capturing said images at that instant of use.

Thus in one embodiment there is provided a camera imaging device including at least one sensing means for detecting the ambient light level, at least one imaging means for viewing and/or capturing still and/or moving images, and switching means, such that in response to the ambient light level detected, one or more imaging means are rendered operable by actuation of said switching means or are indicated as being the imaging means which should be used for capturing still and/or moving images at that instant of use.

In one embodiment the sensing means includes a first sensor, said sensor set to a predetermined trigger level and if the light level is above said level a first, colour viewing lens and sensor is used and if the light level is below said level a second, black and white and/or infra red viewing lens and sensor is used. In one embodiment the same or a further sensor is used to detect light level with respect to a second, typically lower predetermined light trigger level and in this case the second viewing lens and sensor is used but if the light level drops below said second trigger level, a light source on the device or connected thereto is illuminated.

Preferably at least one light source is provided to provide visible and/ or infra-red light in the environment of the imaging device when the ambient light level falls below the predefined second trigger level.

Thus, when the user is operating the camera under good light conditions, the first lens and sensor is used to provide a still and/ or video image in colour. However, if the light level drops below the first trigger level an indication is provided to the user and/or the camera can automatically switch to the second lens and sensor allowing the still and/or video image to be in black and white with better clarity than would be the case with the colour lens. If the light level improves to above the first trigger level, the camera may be switched back either manually or automatically to use the colour sensor.

In one embodiment the device can illuminate the surrounding environment especially when ambient light level decreases below a second trigger level.

In one embodiment if the light source is a visible light source, this may also allow the user to record the image in colour even at the lower ambient light level when the visible light source is illuminated. Preferably one or two photo- sensitive detectors are incorporated to monitor the light level, such that when the ambient light level reaches a predefined trigger level, the sensor from which the data is recorded or the image captured on film is changed.

In one embodiment of the invention, the device switches automatically between the sensors in response to the detected light level.

In another embodiment of the invention, the lens and sensor arrangement used is switched manually by the user in response to an indication generated by the device or at the discretion of the user.

An advantage of using an infra-red light source, such as that provided by an infra-red LED operating at 880nm, is that it allows the area to be covertly illuminated with respect to normal human sight, which may be useful in a device designed for security functions amongst others where it can be beneficial to prevent the alert to the presence of such a device.

In a further advantage of the invention the imaging device in accordance with the invention can be utilised to provide a security or monitoring function even when the light in the environment being monitored varies. For example, if the environment is a baby in a cot, the imaging device can continue to monitor by changing the lens and sensor used and if necessary providing the illumination of the surrounding environment as the light in the environment decreases.

The external light source can be operated automatically or manually by a user Preferably the device includes a switch, said switch being provided to prevent automatic illumination at a specified ambient light level.

An advantage of the present invention is that it allows a user to continue recording uninterrupted if preferred whilst maintaining a reasonable quality of image output when light conditions change.

In a further embodiment, filtering means are provided, wherein in response to the ambient light levels detected, the imaging means is rendered operable by actuation of the switching means to adjust the filtering means.

In this embodiment the imaging means comprises one or more colour viewing lenses and/or sensors, preferably in the form of CCDs or CMOS.

Typically the filtering means is an infra-red (IR) filter and may be moved between at least two positions; a first position wherein the filter is placed in the light-path of the imaging means, and a second position where it is not in the light-path of the imaging means.

Preferably the switching means allows the filter to be moved between first and second positions. The switching means may be automatic according to the ambient light levels detected, or may be manually operated.

Thus under normal or high light conditions, the colour sensors, which are typically much more sensitive to infra-red light than visible light, operate with the IR filter placed in the light path of the same, thereby preventing infra-red light from overloading the colour signal and distorting the colour balance of the generated image. Under low light conditions, the IR filter is removed from the light path of the sensors, such that infra-red light forms the main signal captured.

Typically, three colour CCDs or filters covering individual sensor elements (typically Red, Green, Blue) are required to form a single colour pixel of the resulting image at a given resolution. A further advantage of this arrangement is that when the device is used under low light conditions without the IR filter, each of the three aforementioned colour pixels may be viewed as individual black and white pixels thereby tripling the number of pixels, or a single individual pixel formed from the said three pixel units may be combined thereby increasing the brightness of the single pixel. Thus the resolution of the image formed therefrom and/or the sensitivity of the device is improved.

Embodiments of the present invention will now be described with reference to the accompanying figures wherein:

Figure 1 is a perspective view of an imaging device according to one embodiment of the present invention.

Figures 2a-b describes two possible operating modes of an imaging device according to one embodiment of the present invention.

Figure 3 is a perspective view of an imaging device according a further embodiment of the invention.

Referring firstly to figure 1, there is illustrated a camera imaging device 2 comprising a housing 14, a colour lens and sensor arrangement 4, and a black and white and/ or infra red lens and sensor arrangement 6. In this embodiment the sensors are CCDs connected to output means which may allow the display and/or recording of moving images or still images in response to a user selection.

The device is illustrated with light detection means in the form of a photo-sensitive detector such as a photodiode 8 to monitor the ambient light level.

The device is illustrated with a light source 10 to provide visible and/or infra-red light externally when the ambient light level falls below a trigger level.

The device is illustrated with a viewfinder 12 which aids the user in framing the desired image.

Referring to figure 2a- b, there is illustrated two examples of how the device would operate given different lighting conditions and system configuration.

In figure 2a, under normal or 'HIGH' light conditions, the colour lens and sensor is operated and captures image data which is passed to memory means. However, when the light level falls below a trigger level, indicated as 'LOW, the lens and/or sensor which is used is switched to the black and white lens and/or sensor and th.e image data used is taken from that lens and/or sensor. If the ambient light level is then detected as falling below a second trigger level indicated as 'VERY LOW, a light source, in this example an infra-red light, is switched on to illuminate the area of interest and improve the clarity of the image data. In addition it should be noted that the infra red light source and sensor arrangement will operate successfully in conditions where ambient light is negligible or absent completely ('ZERO'). In an alternative arrangement shown in Figure 2b , in normal light conditions, the colour lens provides the capture of data for the image. However, should the detected light level fall below the first trigger level, the light source is switched on to illuminate the area of interest.

Referring to Figure 3, there is illustrated a further embodiment of the device which includes a colour lens and sensor arrangement 4 only, without the black and white and/ or infra red lens and sensor arrangement as hereinbefore described.

In this embodiment, the device includes an infra-red filter 18 which may be moved over the lens/sensor arrangement 4 thereby filtering out the infra-red light. In this example the filter can be slid along rails 16, although it could be moveably mounted in a number of alternative ways, for example via pivoting means.

Colour sensors are typically five times more sensitive to infrared light than they are to visible light, so when the filter is positioned so that it is not filtering the light reaching the sensor, the image data captured is predominantly infra-red. When the filter is moved so that it filters the light reaching the sensor, colour image data is captured.

When the camera is used under normal or high light conditions, the filter 18 is positioned in front of the sensor 4, thereby allowing the camera to capture colour images. However, when the light level falls to a low level, the filter 18 may be moved away from the sensor 4, either manually by the user in response to an indication of the light level sensed by the photodiode 8, or automatically by switching means connected to the same. The light under these conditions is no longer filtered, such that the camera receives a predominantly infra-red signal and thus captures black-and-white images. If the ambient light level falls further, an infra-red light source 10, may be switched on to illuminate the area of interest and improve the signal received by the camera.

Claims

1 A camera imaging device including at least one sensing means for detecting the ambient light level, at least one or more imaging means for viewing and/or capturing still and/or moving images, and switching means, characterised in that in response to the ambient light level detected, the switching means is controlled to selectively operate said one or more imaging means and/ or an indication is generated as to the imaging means or imaging means mode of operation which should be used for capturing said images at that instant of use.

2 A camera imaging device according to claim 1 characterised in that said switching means switches operability between a first imaging means and a second imaging means.

3 A camera imaging device according to claim 2 characterised in that said first imaging means is one or more colour lenses and/or sensors.

4 A camera imaging device according to claim 2 characterised in that said second imaging means is one or more black- and-white or infra-red lenses and/ or sensors.

5 A camera imaging device according to claim 1 characterised in that said sensing means includes one or more photosensitive detectors.

6 A camera imaging device according to claim 1 characterised in that when a pre- etermined ambient light level is reached, said sensing means indicates the same and/or activates the switching means. A camera imaging device according to claim 1 characterised in that illumination means are provided in the form of visible and/or infra-red light, and are controlled manually or by said sensing means and/or switching means.

A camera imaging device according to claim 1 characterised in that said imaging means comprises one or more colour lenses and/or sensors, and filtering means are provided and are controlled manually or by said sensing means and/or switching means to be selectively positionable with respect to the imaging means.

A camera imaging device according to claim 8 characterised in that the filtering means are in the form of an infra-red filter.

A camera imaging device according to claim 8 characterised in that the filtering means is moveable by the switching means between at least two positions, with respect to the imaging means, depending on the light level detected by the sensing means.

A camera imaging device according to claim 10 characterised in that the filtering means is moveable between a first position where light is filtered through the filtering means before reaching the imaging means, and a second position where light reaches the imaging means without being filtered.