GB2538256A

GB2538256A - Optical data insertion device

Info

Publication number: GB2538256A
Application number: GB1508076.5A
Authority: GB
Inventors: Cairnduff Bruce
Original assignee: Thermoteknix Systems Ltd
Current assignee: Thermoteknix Systems Ltd
Priority date: 2015-05-12
Filing date: 2015-05-12
Publication date: 2016-11-16
Anticipated expiration: 2035-05-12
Also published as: GB2538256B; GB201508076D0

Abstract

An optical data insertion device 20 is operable to insert additional optical data into an existing primary image received from a primary optical system 11 so as to provide a combined image. A primary aperture 21 is operable to receive incident light from the primary optical system 11 comprising said primary image. A secondary aperture 22 through which light comprising a combined image passes; and a partially transparent screen 23 are provided between the primary aperture 21 and the secondary aperture 22. The screen 23 is operable in response to control signals to selectively emit light corresponding to said additional optical data or to selectively block the passage of light corresponding to said additional optical data. The additional data comprises a difference image generated by subtracting the output values of pixels in each captured image from the output values of the corresponding pixels in the subsequent captured image.

Description

Optical Data Insertion Device Technical Field of the Invention The present invention relates to an optical data insertion device. In particular, the present invention relates to an optical data insertion device operable to insert additional optical data into an existing primary image received from a primary optical system so as to provide a combined image.

Background to the Invention

In certain circumstances it may be desirable to combine image information from two or more sources to provide a composite image. One such occasion is where it is desirable to provide text data (such as range or similar) over an image. Another such occasion is where it may be desirable to combine image data from an image intensifier (12) with image data obtained from a thermal imager. An image intensifier amplifies visible light and near infra red light (say 400nm-900nm in wavelength); whilst a thermal imager operates in a further portion of the infra red light spectrum (say 7000nm- 14000nm in wavelength). This is advantageous as the longer wavelengths are generally less attenuated by smoke and dust, although image intensifiers generally have better resolution than thermal imagers.

Current night vision systems using image intensification benefit from higher resolution and more natural imaging in comparison to imaging in the far infrared.

However, 12 systems are limited in so far as they do need at least some ambient light to operate. A typical intensifier tube becomes noise limited at around 100p.lux which corresponds to a moonless overcast night sky. At this point and at lower light levels effective night vision requires infrared systems.

Thermal imaging also offers advantages over 12 in detecting targets concealed by camouflage. Addressing I2 limitations by including a thermal imaging capability improves overall night vision performance but at the expense of complexity and weight. Hand held systems are easy to interchange when each system is self contained with its own optics, display and power supply. On the other hand helmet or system mounted image intensifiers cannot be easily swapped over.

An example of an apparatus that provides this image combination is disclosed in US2008/0302966. In this system, a conventional image intensifier s provided with a clip on attachment comprising a thermal imager, a projector operable to project a visible image captured by the thermal imager and a light turning element which turns light from the projector into the aperture of the image intensifier. In this manner light from the thermal imager and the image intensifier may be combined to provide a single image.

This apparatus does however have drawbacks in that the light turning element obstructs the field of view of the image intensifier. Additionally, the contrast from the projected light may reduce the sensitivity of the image intensifier because obstruction of the intensifier collection aperture allows less visible light to enter the intensifier tube. Furthermore, some of the projected light may be reflected from the collection aperture of the image intensifier, drawing attention to a user who may wish to remain covert.

Another issue is that the impact of the projected light on the combined image is limited by the optical properties of the image intensifier, and thus for generating a monochrome combined image.

A further fundamental problem with such devices is that inserting light into the collection aperture of the image intensifier necessitates an external attachment of the projector increasing the size and bulk of the combined apparatus. It is also necessary for the projector to be provided with a separate power supply which also adds to the bulk of the combined apparatus. This is particularly true when considering the relative power requirements for an image intensifier and an IR sensing array and projector. Whilst a typical image intensifier can operate for tens of hours on the power output by a standard AA battery, an IR sensing array and projector each require considerably more power. In the event that the sensing array output is processed so as to improve the image or select particular aspects of the image for output by the projector, the power requirements increase still further. In consequence, providing sufficient additional battery capacity for the IR sensing array and projector adds significant weight and bulk to the combined apparatus.

Another problem with respect to power consumption is the processing of the captured infrared images before projection into the intensifier. Firstly, one needs to choose either a cooled infrared sensing array or to conduct significant processing on the raw images to deal with the unbalanced pixel outputs generated by an uncooled array. Either of these requirements increases the complexity and power requirement of the device.

It is therefore an object of the present invention to provide an optical data insertion device that at least partly overcomes or alleviates the above problems.

Summary of the Invention

According to a first aspect of the present invention there is provided an optical data insertion device operable to insert additional optical data into an existing primary image received from a primary optical system so as to provide a combined image, the device comprising: a primary aperture operable to receive incident light from the primary optical system comprising said primary image; a secondary aperture through which light comprising a combined image passes; and a partially transparent screen provided between the primary aperture and the secondary aperture, the screen operable in response to control signals to selectively emit light corresponding to said additional optical data or to selectively block the passage of light corresponding to said additional optical data.

In this manner the optical data insertion device of the present invention provides for the optical insertion of additional image information between an existing primary optical system and a viewer rather than into the collection aperture of the existing primary optical system. This arrangement eliminates problems from blocking the collection aperture or reflection of light projected into the collection aperture. This also enables the optical insertion device to use a small screen thereby providing for reduced power consumption and hence facilitating the use of smaller, lighter batteries. It also allows the optical insertion device to have a relatively compact arrangement which in combination with the reduction in power requirements reduces the size and weight of the apparatus as a whole. An additional benefit is that the inserted information is not restricted by the capabilities of the primary optical system.

Where the screen is operable to selectively emit light, the screen may be operable to emit monochrome light. Alternatively, the screen may be operable to emit light of different colours. This can enable coloured information to be overlaid on a monochrome primary image, providing intuitive contrast with the data from the primary optical system. Where the screen is operable to emit light of different colours, the screen may be adapted to emit coloured light corresponding to all the inserted optical data, and/or the screen may be operable to emit coloured light in respect of only some of the inserted optical data and/or the screen may be operable to emit different coloured light in response to the particular nature of the inserted optical data.

Where the screen is operable to selectively emit light, the screen may be an LED screen or an OLED screen. Where the screen is operable to selectively block light, the screen may be an LCD screen.

The transmissivity of the screen is preferably of the order of 40% or greater.

The primary aperture may be provided with a mounting arrangement for attachment to the primary optical system. The device may comprise further optical elements. In particular, the device may be provided with an eyepiece. The eyepiece may comprise a flexible rim or shield and a focussing arrangement. The focussing arrangement may comprise one or more lenses or mirrors and may be adjustable.

The primary optical system may comprise a mirror and/or lens arrangement operable to direct light to an exit aperture. The mirror and/or lens arrangement may comprise a telescope, sight, or similar. In such circumstances, the exit aperture may be provided adjacent to or abutting the primary aperture of the optical data insertion device. In alternative embodiments, the primary optical system may comprise an output screen operable to emit light. In such circumstances, the output screen may be provided adjacent to or abutting the primary aperture of the optical data insertion device. The output screen may be operable to output light in response to a light sensing system. The light sensing system may be an image intensifier, imaging array, magnifying arrangement or the like. In one preferred embodiment, the light sensing system is an image intensifier.

The inserted optical data may include, but is not limited to text (including alphanumeric characters and symbols), icons, images or any mixture of the foregoing.

In particular, the inserted optical data may comprise or relate to the output of a secondary system such as a communication device, ranging device or navigation device. The secondary system may be mounted to or alongside the primary optical system or the optical data insertion device. In some embodiments, the secondary system may be mounted separately to or remotely from the primary optical system or the optical data insertion device.

Preferably, the inserted optical data comprises or relates to the output of a secondary optical system. The secondary optical system may comprise a light sensing system such as an image intensifier, imaging array or the like. In one preferred embodiment, the secondary optical system is an infrared sensing array.

In embodiments where the inserted data comprises or relates to the output of a secondary optical system, images captured by the secondary optical system may be processed before insertion. The processing may be undertaken by the secondary optical system or by the optical data insertion device.

In one implementation, the processing may comprise the enhancement of edges in the images output by the secondary optical system by use of an edge detection algorithm. In a preferred implementation, the secondary optical system is operable to capture a series of secondary images, each secondary image comprising an array of pixels, each pixel having an output value related to the detected light intensity in the portion of the captured image represented by the pixel. In such implementations, the processing preferably comprises the generation of difference images by subtracting the output values of pixels in each captured image from the output values of the corresponding pixels in the subsequent captured image. This enables edge enhancement using relatively little processing power, thus reducing demands on power and complexity. It also avoids the requirement for calibration of the imaging array, further reducing cost and complexity. Furthermore, this technique provides particularly good results when the secondary optical system is unstably mounted, such as when helmet mounted.

The inserted data may be of constant brightness or may vary in brightness. Varying the intensity of the inserted data can reduce the possibility that the inserted data swamps the primary image or vice versa. Additionally or alternatively, it can help to differentiate between the primary image and the inserted data.

The variation may be automatically controlled by a variation control unit. This frees a user of the device from attending to this control thus making the device easier to use and more likely to select an optimum intensity level. In some embodiments, the variation control unit may further comprise a user operable intensity control input.

The automatic variation control may be responsive to specified parameters.

Suitable parameters may include, but are not limited to: the intensity of the primary image, settings or sensors on the primary optical system, ambient light levels or the like. In this manner, the variation control unit may reduce the projector intensity in response to low ambient light levels or a low intensity of the primary image.

The automatic variation control may be responsive to a timer input. In particular, the timer input may be a periodic or pulsed timer nput. The periodic or pulsed input can have any suitable form and any suitable frequency. In this manner, the inserted optical data can vary in intensity on a periodic or pulsed basis. This enables a human observer to readily identify that part of a composite image that is provided by projected light.

According to a second aspect of the present invention there is provided an imaging apparatus operable to provide a combined output image, the imaging apparatus comprising: a primary optical system operable to provide an primary image; a secondary system operable to provide additional data for insertion into the primary image; and an optical data insertion device according to the first aspect of the present invention adapted to insert the additional data into the primary image to generate the combined image.

The apparatus of the second aspect of the present invention may incorporate any or all features of the first aspect of the present invention as are desired or as are appropriate.

The apparatus may be adapted to be mounted on another article. In particular, the apparatus or article may be adapted to be worn by, mounted on or carried by a user. In a preferred embodiment, the article may be a helmet or a set of goggles. In other embodiments, the article may be a weapon or other equipment.

The apparatus may comprise a power source. Typically the power source comprises one or more batteries.

According to a third aspect of the present invention there is provided a method of processing captured secondary image data for insertion into a primary image, the method comprising the steps of: capturing a series of secondary images, each secondary image comprising an array of pixels, each pixel having an output value related to the detected light intensity in the portion of the captured image represented by the pixel; subtracting the output values of pixels in each captured image from the output values of the corresponding pixels in the subsequent captured image to thereby generate a difference image; outputting the successive difference images to an optical data insertion device for insertion into the primary image.

According to a fourth aspect of the present invention, there is provided an imaging apparatus operable to provide a combined output image, the imaging apparatus comprising: a primary optical system operable to provide an primary image; a secondary imaging system operable to capture additional data for insertion into the primary image; and an optical data insertion device adapted to insert the additional data into the primary image to generate the combined image wherein the additional data comprises a difference image generated by subtracting the output values of pixels in each captured image from the output values of the corresponding pixels in the subsequent captured image In this manner edge enhancement may be provided using relatively little processing power, thus reducing demands on power and complexity. It also avoids the requirement for calibration of the imaging array, further reducing cost and complexity. Furthermore, this technique provides particularly good results when the secondary optical system is unstably mounted, such as when helmet mounted.

The method of the third aspect of the present invention and the apparatus of the fourth aspect of the present invention may incorporate any or all features of the first two aspects of the present invention as desired or as appropriate. In particular, the method of the third aspect of the present invention and the apparatus of the fourth aspect of the present invention may incorporate an optical data insertion device according to the first aspect of the present invention.

In alternative embodiments, the optical data insertion device may comprise: a light source operable to emit light corresponding to the additional optical data; and a light guiding device for receiving light from the light source and directing it to collection aperture of the primary optical system. The light guiding device may comprise an arrangement of mirrors and/or lenses and or prisms. In one embodiment, the light guiding device comprises: an elongate light transmitting solid body, the body tapering from a wider end to a narrower end, the wider end adapted to provide a receiving surface for receiving incident light and the narrower end adapted to provide an exit surface for said incident light; and a reflector provided adjacent to the narrower end, the reflector adapted to receive said incident light from the exit surface and reflect said incident light away from the device into the collection aperture of the primary optical system. A device of this type is disclosed in GB2472516.

The optical data insertion device may comprise an optical bypass device comprising: a pair of prisms having separated collection apertures and adjacent exit apertures; and a projector provided between the prisms and operable to project light through an opening provided between the exit apertures of the prisms. Such an optical data insertion device may be fitted such that the exit apertures of the prisms and the opening there between are positioned over the collection aperture of the primary optical system. A device of this type is disclosed in GB2468948.

Detailed Description of the Invention

In order that the invention may be more clearly understood an 5 embodiment/embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a schematic illustration of an imaging apparatus operable to insert infrared images into an image intensifier according to the prior art; Figure 2 is a schematic illustration of a maging apparatus according to the present invention; Figure 3 is a schematic illustration of an optical data insertion device according to the present invention; and Figure 4 is a comparative illustration of an image generated by an image intensifier with and without inserting data corresponding to infrared images.

Turing now to figure 1, an imaging apparatus 0 comprises an image intensifier 1 and an infrared imaging array 2. The image intensifier 1 is operable to capture light incident on collection aperture 3 and generate an output image at eyepiece 4. The infrared imaging array is operable to capture incident light through collection aperture 5 and to output a corresponding image via a projector 6. The light output by the projector 6 is captured by a light guiding device 7 which is operable to guide this light into the collection aperture 3 of the image intensifier 1. Accordingly, a composite image can be viewed at eyepiece 4. The eyepiece 4 may incorporate a focussing arrangement and is provided with a flexible shield rim 8 which may substantially enclose a user's eye area in use. This has the effect of both shielding the user's eye from external incident light and shielding external reflection of light from the composite image.

Whilst apparatus 0 provides good performance, it does have some drawbacks including: the light guiding device 7 obstructs collection aperture 3 of the image intensifier 1; the contrast from the projected light may reduce the sensitivity of the image intensifier 1, projected light may be reflected from the collection aperture 3 of the image intensifier 1; and external attachment of the projector 6 increases the size and bulk of the apparatus 0.

Turning now to figure 2, a schematic illustration of an imaging apparatus 10 according to the present invention is provided. The imaging apparatus 10 comprises a primary optical system 11 and a secondary system 12. The primary optical system 11 is operable to capture light incident on collection aperture 13 and generate an output image at exit aperture 19. Typically, the primary optical system 11 may be an image intensifier or a telescopic sight or similar.

The secondary system 12 is operable to provide additional optical data which is combined with the optical data from the primary optical system 11 by way of an optical data insertion device 20. Typically, the secondary system 12 might be an optical system such as an infrared imaging array operable to output an image corresponding to infrared light incident upon collection aperture 15. In alternative embodiments, the secondary system 12 can comprise an alternative optical system or an alternative device such as a range finder, navigation unit or communication unit. In some embodiments, two or more different devices may be combined into the secondary system 12.

Turning to figure 3, the optical data insertion device 20 comprises a screen 23 mounted within a body 24. The body 24 supports the screen 23 and defines a primary aperture 21 operable to receive light from the exit aperture of the primary optical system 11 and a secondary aperture 22. The screen 23 is partially transparent and operable in response to control signals to selectively emit light corresponding to the additional optical data. Preferably, the screen has a transm ss vity of the order of 40%. This is sufficient to provide viable performance in most instances. In order to emit light, the screen 23 is provided with an array of OLEDs (organic light emitting diodes). By controlling the light output by the OLEDs of the screen 23, a combined image is formed viewable at the secondary aperture 22.

Whilst the present example is directed to a light emitting screen 23, the skilled man will appreciate that it is also possible to substitute a screen 23 operable to selectively block the passage of light from the primary image in order to generate a combined image. Typically, this might be achieved by use of an LCD screen.

Whilst a user can view the combined image directly at the secondary aperture, for improved performance, an eyepiece 14 may be provided. The eyepiece 14 may connect with the secondary aperture 22 and may be adapted to facilitate viewing by means of a focussing arrangement (not shown). The eyepiece 14 may further be provided with a flexible rim or shield (not shown).

In one preferred embodiment, the imaging apparatus 10 has an image intensifier as the primary optical system 11 and an infrared imaging array as the secondary system 12. In this manner, the optical data insertion device 20 may be operable to insert optical data corresponding to images captured by the imaging array 12 into the image at exit aperture 19 to generate a combined image at secondary aperture 22 and thus viewable by a user through eyepiece 14.

Providing the optical data insertion device 20 between the primary optical system 11 and the user means that the optical data insertion device 20 does not obstruct the collection aperture 13. Furthermore, the inserted light does not adversely impact on the image output by the primary optical system 11 nor does the inserted light potentially reflect from the primary optical system 11. It is also possible to make the apparatus 10 as a whole smaller and lighter than the prior art apparatus 0. Additionally, screen 23 can draw less power than projector 6 used the prior art, enabling the use of a smaller, lighter power source.

The impact of combining the images is illustrated by figure 4: figure 4a illustrates the image output by image intensifier 11 at exit aperture 19; and figure 4b illustrates a combined image at secondary aperture 22 comprising an infrared image overlaid on the image intensifier image. The combined image highlights a number of persons who are not clearly visible on the intensifier image.

To help a user distinguish between the intensifier image and the combined image, it is possibly that the intensity of the image output by the screen 23 can be varied.

Typically, this would be a periodic or pulsed variation. Colour may also be used to differentiate between the data channels. For instance, if the inserted optical data comprises an infrared image, the colour may indicate the temperature of objects within the infrared image. Additionally or alternatively, only items within the infrared image having temperatures within a predetermined temperature range result in the emission of coloured light, the screen 23 being operable to emit only monochrome light or no light at all in respect of other features of the infrared image. Where the predetermined temperature range corresponds to human body or skin temperature, this can provide particularly effective highlighting of humans within an infrared image.

To further aid a user, the infrared image can be processed before combination. In a preferred embodiment, the processing takes the form of edge enhancement. Typically this might be achieved by direct processing of each captured image by an edge detection algorithm. In a preferred embodiment this can alternatively be achieved by the generation of difference images by subtracting the output values of pixels in each captured image from the output values of the corresponding pixels in the subsequent captured image. If negative pixel values are not permitted, the pixel values in the difference images may comprise the modulus of the difference between successive pixel values in the captured images.

This provides an edge enhancement effect using relatively little processing power, thus reducing demands on power and complexity. It also avoids the requirement for calibration of the imaging array, further reducing cost and complexity.

The above method of processing image is particularly effective where the imaging array 12 moves slightly between captured images. This might occur where the apparatus 10 is held by a user, mounted on a wearable article such as a helmet or a pair of goggles or is mounted on an article carried by a user such as a weapon or viewing device.

Whilst the above description has concentrated on the insertion of infrared imaging information over a primary image, the skilled man will appreciate that the inserted optical data can additionally or alternatively comprise alphanumerical data, perhaps indicating time/date, range, inclination, altitude, orders or other relevant information. For instance, in embodiments where the secondary system 12 comprises a rangefinder, this can allow range textual information to be injected into a combined image.

The above embodiments are described by way of example only. Many variations are possible without departing from the scope of the invention as defined in the appended claims.