Illumination device for a monitoring camera

The present application claims the benefit of previously filed co-pending German Patent Application, Appl. No. 103 60 761.7, filed Dec. 23, 2003, and incorporates by reference the contents therein.

The present invention relates to radiation emitting devices. In particular, the invention relates to an illumination device for a monitoring camera.

Monitoring cameras that are sensitive to radiation in the infrared range and/or light in the visible range are used to monitor security-relevant areas in passenger aircraft. Such monitoring cameras are used, for example, to monitor cockpit doors, passenger doors, as well as the interior space of passenger aircraft. In complete darkness, as occurs, for example, during night flights, it is also necessary to additionally illuminate the monitoring region during use of monitoring cameras that are sensitive mostly to infrared light. For this purpose, illumination devices are used with light devices that emit radiation in the near-infrared range or in the visible light range. Infrared-emitting diodes or simple light-emitting diodes that emit light in the visible range are widely used as light devices in this context.

In traditional variants of illumination devices for monitoring cameras according to the prior art, a parallel arrangement of the camera optics and the illumination device is common. In order to achieve effective illumination of the monitoring area or the monitoring space in front of the monitoring camera, the infrared-emitting diodes (IRED) or the light-emitting diodes (LED) are arranged either with the camera optics behind a cover panel or the diodes are situated separately arranged on the housing front. The direction of emission of such illumination devices is determined mostly by the emission angle of the diodes as a result of the arrangement of the infrared-emitting diodes or light-emitting diodes parallel to the camera optics.

The already known variants of illumination devices often lead to overexposure of the image center of the image obtained with the monitoring camera, because the main radiation intensity of the diodes points in the direction of the camera optics and therefore to the center of the surveyed object. A higher contrast difference between image information in the image center and the edge regions of the image results from this, so that, for example, automatic evaluation of the image contents by appropriate image processing algorithms for image recognition, for recognition of access authorization and the like is hampered. In addition, security-relevant objects cannot be reliably identified precisely in the edge region of the image, because the image center is overexposed.

There may be a need to improve the already known illumination devices for monitoring cameras, so that uniform illumination of the monitoring area or monitoring space monitored with the monitoring camera and the image obtained from it may be achieved by establishing high contrast over the entire image surface as a result.

According to an exemplary embodiment of the present invention, an illumination device is provided with a plurality of light devices, each having a light device axis. The light device axes intersect an optical axis of the monitoring camera, i.e., the light device axes of the light devices do not run parallel to the optical axis of the monitoring camera. Uniform illumination of the monitoring area or monitoring space in front of the monitoring camera is achieved by the illumination device on this account. Undesired overexposure of the surveyed object in the direction of the optical axis may be avoided. The contrast of the image obtained by the illumination device of the invention may be uniform over the entire image surface and, in addition, well suited for evaluation by automated image processing algorithms. Any security-relevant objects and details in the edge region of the image may be readily recognized.

Further exemplary embodiments and advantages are apparent from the following detailed description of the exemplary embodiment illumination device of the invention.

FIG. 1 shows a top view of the illumination device;

FIG. 2 shows a side view of the illumination device of FIG. 1 ;

FIG. 3 shows a schematic view of the radiation distribution of the illumination device;

FIG. 4 shows a test picture with an ordinary illumination device; and

FIG. 5 shows a test picture with the illumination device of the invention.

FIG. 1 shows an exemplary embodiment of an illumination device 1 in a view from above. The illumination device 1 encloses a monitoring camera with objective 3 . The objective 3 is provided with an aperture 4 , in order to largely avoid blinding of the monitoring camera 2 by the illumination device 1 . The monitoring camera 2 has a vertical optical axis O perpendicular to the plane of the drawing or to a light device plate E spanning an x-and y-axis. The arrow on the optical axis O points in the direction of a surveyed object situated in front of the monitoring camera 2 in the monitoring space monitoring area, not further shown in the drawing in the interest of better clarity. As depicted the illumination device 1 of the invention, the objective 3 , as well as the aperture 4 , are positioned rotationally symmetric with reference to optical axis O. Deviating from this depicted arrangement, other positionings, for example, eccentric arrangement of the monitoring camera 2 , aperture 4 and illumination device 1 , are also possible. The illumination device may comprise a plurality of light devices 5 , which emit light.

The illumination device 1 as depicted in FIG. 1 comprises eight light devices Lm 1, . . . ,n , arranged along a circular arc 6 and lying in the light device plane E spanned by the x-and y-axis. Light devices Lm 1, . . . , n each have the same spacing to the adjacent light device Lm 1, . . . , n . The light devices Lm l, . . . , n each have a light device axis Lma 1, . . . , n and emit radiation in the near-infrared range or radiation in the visible range primarily in the direction of the arrow on the corresponding light device axis Lma 1, . . . , n . The orientation of the light device axis Lma 1, . . . , n therefore corresponds to the main emission direction of the corresponding light device Lm 1, . . . , n .

The arrangement of light devices Lm 1, . . . , n can also occur in a different way than the positioning shown in FIG. 1 . For example, alternative embodiments position the light devices Lm 1, . . . , n along the perimeter of a square, a rectangular, a polygon or an arc, such as the arc of an elipse around the monitoring camera 2 . A statistical arrangement, distributed over the surface of the light devices Lm 1, . . . , n , is also conceivable as an alterative. It is also not essential that the light devices Lm 1, . . . , n be arranged in a light device plane E. For example, it is conceivable that the light devices Lm 1, . . . , n have different height positions relative to the optical axis O and may be arranged in different planes running parallel to the light device plane E. The number of light devices Lm 1, . . . , n is also not restricted in number to eight light devices Lm 1, . . . , n but may be any plurality of light devices Lm 1, . . . , n that better distributes the resulting light on the surveyed object.

Infrared-emitting diodes (IRED) or light-emitting diodes (LED) that emit light mostly in the visible range are preferably used as light devices Lm 1, . . . , n , depending on the spectral sensitivity of the employed monitoring camera 2 . The light-emitting diodes or infrared-emitting diodes have the advantage of long lifetime and limited sensitivity to vibration. As a result, diodes are almost maintenance-free. Instead of diodes, other light devices Lm 1, . . . , n can be used, for example, infrared lasers, infrared laser diodes or incandescent lamps.

In FIG. 1 , the light device axis Lma 1 of the first light device Lm 1 forms an angle θ 1 of about 45° with an x-axis. The y-axis is arranged at right angles to the x-axis. The angle θ 2, . . . , n between the other light device axes Lma 2, . . . , n of the light devices Lm 2, . . . , n and the x-axis is increased preferably as a function of their position on the circular arc 6 in 45° steps, and therefore have values of about 90°, 135°, 180°, 225°, 270°, 315° and 360°. In principle, the angles θ 1, . . . , n can assume any value between 0° and 360°. The corresponding light device axis Lma 1, . . . , n ; however, should preferably be aligned, so that it does not point exclusively toward camera 2 or aperture 4 . This ensures that the main emission direction of each light device Lm 1, . . . , n is directed primarily outward from the monitoring camera 2 and the optical axis O. A uniform increase of angle θ, depicted in FIGS. 1 and 2 as a function of the position of light device Lm 1, . . . , n on circular arc 6 is not necessary.

The employed number of light devices Lm 1, . . . , n and their alignment is mostly dependent on their radiation intensity, the size and geometry of the monitoring area or monitoring space being monitored with the monitoring camera. Depending on these parameters, other values can be necessary for angle θ as a function of the arrangement of light devices Lm 1, . . . , n on circular line 6 , in order to achieve optimal reproduction of a surveyed object.

In experiments, a number of seven light devices Lm 1, . . . , n , arranged rotationally symmetric around the optical axis O, proved to be particularly advantageous for monitoring smaller monitoring spaces or monitoring areas. The experimental arrangement is not shown in the figures, in the interest of clarity. The seven light devices Lm 1, . . . ,7 are arranged at a spacing from each other uniformly, starting from a “12 o'clock position” on a circular line. “12 o'clock position” in this context means that the light device Lm 1 is arranged at the upper intersection point between the y-axis and the circular line, and its light device axis Lma m1 at this point points in the direction of the y-axis. Starting from the “12 o'clock position” of the first light device Lm 1 , the other light device axes Lma 2, . . . ,7 of light devices Lm 2, . . . ,7 form an angle θ 1, . . . ,7 of 90°±10°, 230°±10°, 255°±10°, 270°±10°, 270°±10°, 285°±10°, 320°±10° with the x-axis in the clockwise direction.

FIG. 2 depicts the illumination device 1 of the invention in a side view. The optical axis O is perpendicular to the x-axis. In the depiction, in the interest of better graphic representation, five light devices Lm 5,6,7,n,1 are shown as examples. The light device axes Lma 5,6,7,n,1 of these light devices Lm 5,6,7,n,1 each form an angle φ 5,6,7,n,1 of about 45° with the optical axis O. In experiments, values between 30° and 60° have proven to be suitable for the angle φ 1, . . . , n . The value φ 1, . . . , n of about 45° has proven to be particularly advantageous. Values for the angle φ 1, . . . , n lie outside of the range from 30° to 60°, lead to a significant deterioration in the imaging results or image obtained with the monitoring camera 2 .

FIG. 3 shows a normalized depiction of illumination intensities achieved with the illumination device 1 of the invention in the monitoring region or monitoring space in front of the illumination device 1 along the optical axis O and the x-and y-axis. The angle numbers on the semicircle correspond to the corresponding spatial direction. A solid intensity curve 7 reflects the intensity distribution of the radiation, which is ordinarily achieved with known illumination devices, wherein the light device axes are aligned parallel to optical axis O of the camera. The spatial intensity distribution of radiation in space is obtained by rotation of the intensity curve 7 around the optical axis O, so that overall a “lobe-shaped” spatial intensity distribution is obtained. The height extent of curve 7 in the direction of optical axis O is a gauge of the intensity of radiation in this range. At angle number 0°, intensity curve 7 intersects optical axis O. At this point, the radiation intensity reaches a maximum. For comparison with intensity curve 7 , an intensity curve 8 , obtained using the illumination device 1 of the invention, is shown with a dotted line.

It is apparent in the schematic depiction of FIG. 3 that the intensity of the radiation in the immediate vicinity of optical axis O in the case of intensity curve 7 is distinctly higher than in intensity curve 8 . The intensity curve 7 is also higher and narrower, whereas the intensity curve 8 is lower and wider. This means in the result, that with the illumination device 1 of the invention, better and mostly more uniform illumination of the monitoring area or monitoring space situated in front of the camera is obtained. More uniform contrast distribution of the image produced with monitoring camera 2 and the illumination device 1 follows on this account. The image can be better processed and evaluated by means of automated image processing algorithms. The illumination device avoids only point-like illumination of a surveyed object situated in the region of optical axis O within the monitoring region or monitoring space, which, in the known variants of illumination devices, leads to locally undesired high contrast differences of the produced image. Overexposure of a face of a person situated, for example, at limited distance in front of the monitoring camera does not occur.

Overall, the monitoring region or monitoring space is illuminated more uniformly by means of the illumination device 1 of the invention. The monitoring camera 2 therefore produces a monitoring image with good contrast over the entire image surface. In particular, objects and details that are situated outside of the image center or are far from the optical axis O of the monitoring camera 2 are imaged much better. The images so obtained can be evaluated and processed more easily manually or with appropriate image processing algorithms—for example, for automatic image recognition, for automated access control or the like.

Because of this, a significant increase in security of monitoring of hazardous regions is obtained, for example, in civil aircraft, since details, for example, weapons or other hazardous objects that a person is carrying near the body or in the hand, can also be recognized more easily in the edge region of the monitoring images. The illumination device 1 must naturally be adapted to the geometry and condition of the space or area being monitored. Adaptation occurs as previously described in the individual case by appropriate choice of the number and type of light devices, their radiation intensity, their emission characteristics and their alignment in the space, with reference to optical axis O (angle φ, θ) of the monitoring camera 2 .

FIG. 4 shows a test image, made with a known illumination device, with an infrared monitoring camera. A test image is shown in FIG. 5 that was produced using the illumination device 1 of the invention and an infrared monitoring camera.

It is apparent that the contrast of the test image in FIG. 4 in the boundary region between the face surface of the imaged person and the background does come out somewhat higher than the contrast of the image of FIG. 5 as a whole. However, objects and details that are situated outside of the image center of the test image in FIG. 4 can only be recognized poorly, because the contrast relative to the image edge rapidly diminishes as a result of point-like overexposure of the monitoring region or monitoring space along the optical axis O of monitoring camera 2 (cf. FIG. 4 ). On the other hand, the more uniform contrast distribution over the entire surface of the test image of FIG. 5 is adopted for better evaluation of the image contents over the entire surface of the image. Overexposure of the image center is avoided by the illumination device 2 of the invention. Objects and details that are situated outside of the image center of the test image of FIG. 5 are rich in contrast and, as a result, rich in detail and easily evaluable.

Images obtained with the illumination device of the invention can consequently be better evaluated manually or by automated image processing algorithms, for example, for image recognition or for checking access authorizations. In particular, security-relevant, hazardous objects and details outside of the image center are depicted readily recognizable and imaged.

Application areas for the illumination device of the invention include aircraft cabins, luggage and product areas in aircraft, passenger doors in aircraft, as well as cockpit doors in aircraft. The illumination device of the invention, however, is not restricted to use in the field of civil and military aviation. For example, in other security-relevant areas, like room monitoring and buildings, monitoring of outside surfaces of buildings or the like, as well as monitoring of passenger stops in public local and long-distance mass transit, may be monitored better using the illumination device.

The light devices Lm 1, . . . , n of the illumination device 1 of the invention, in the case of the use of an infrared monitoring camera that is sensitive mostly to radiation in the near-infrared range of the electromagnetic spectrum, have infrared-emitting diodes (IRED). For another variant of the invention, wherein the monitoring camera 2 is sensitive essentially only to visible light, the light devices preferably have white light-emitting diodes (LED) that preferably emit light in the region of the electromagnetic spectrum visible to the human eye.

By means of the illumination device 1 of the invention for a monitoring camera 2 , uniform illumination of a monitoring region or monitoring space situated in front of monitoring camera 2 in the direction of optical axis O may be possible. Overexposure of a surveyed object situated in the region of optical axis O may be avoided, so that a more uniform contrast of an image obtained by means of the monitoring camera 2 with the aid of the illumination device 1 is produced. Off-center objects and details in the edge region of an image can be more easily recognized and evaluated. Because of this, a significant gain in security may be obtained relative to monitoring cameras that are provided with known illumination devices. Manual evaluation of the image content may be facilitated. Automatic image recognition algorithms for image recognition or for automated access control may be used more effectively.

It should be noted that the term “comprising” does not exclude other elements or steps and the “a” or “an” does not exclude a plurality. Also elements described in association with different embodiments may be combined.

It should also be noted that reference signs in the claims shall not be construed as limiting the scope of the claims.