1. Technical Field
The present invention relates to camouflage. More particularly, the present invention relates to reactive camouflage. Still more particularly the present invention relates to a method and system for disguising an object using reactive camouflage.
2. Description of Related Art
During World War II, allied torpedo bomber aircraft were assigned the task of hunting and sinking German submarines on the surface of the open ocean. The bombers were largely unsuccessful because submarine lookouts could see the bombers from a distance, silhouetted against a bright sky, allowing the submarines ample time to dive to safety. An allied invention using one element contained in the present invention was used to greatly increase the number of German submarines that were sunk by torpedo bombers. A row of simple incandescent lights was placed on the leading edge of the wing of the torpedo bombers to fill in the forward-facing silhouette of the torpedo bomber with light. After this invention was implemented, German submarine captains reported that they could hear the engines of the torpedo bomber before they could see it.
In order to camouflage an object to blend with its background when viewed by the human eye, it is generally accepted that the contrast between the object and its background must be reduced. In order to reduce the contrast, the color and intensity of the light coming from the object toward the viewer""s eye must simulate the color and intensity of the light coming toward the viewer""s eye from the background immediately behind the object. Most methods of camouflage vary the shape, texture and surface color of an object in order to make it reflect light in such a manner that the viewer sees a color and intensity of reflected light (also known as diffuse reflection and/or specular reflection) similar to the object""s background. Traditional camouflaging techniques provide passive color shading and, therefore, cannot react to changing backgrounds which silhouette a moving object. Furthermore, passive camouflage cannot fill in light, which has been blocked by the object, or increase lighting levels when the object is less radiant than its background.
Another, potentially serious problem with current camouflage techniques is that a camouflaged object has approximately the same color shading from any angle. This is a critical flaw for a moving object that gives observers different views of the object against different backgrounds. While an object may be obscured from one observer by its camouflage pattern, a second observer from a second vantage point might distinguish the object against a different background with different lighting conditions, even though the two observers are roughly equal distances from the object.
It is important to understand that, in many regional conflicts, the weaponry utilized by the adversaries is less technologically advanced. Most regional armies rely upon weapons that require visual acquisition of a target. These weapons are generally less effective at longer ranges, so the longer it takes for an advisory to detect an object and identify the object as a threat, the less chance that the advisory can bring weapons to bear on the object before it moves out of range.
It would be advantageous to provide an object with a camouflage that matches the lighting intensity of the object""s background by actively generating such intensity of light as may be appropriate to the object""s background. It would also be advantageous to provide an object with a camouflage, which varies in color and intensity with the viewpoint from which an observer views the object, providing simultaneously differing images in differing directions. It would also be advantageous to provide an object with a camouflage which utilizes its capability of projecting simultaneously differing images in differing directions to vary in color and intensity with varying background changes as the object moves from one position to another with respect to the observer. It would be further advantageous to utilize such advanced projection techniques to create an image that is intentionally visible, but which creates an illusion to mimic some other object.
In accordance with an illustrative embodiment of the present invention, a camouflage system comprises variable light transmitters covering the surface of an object, which are used to blend the object with its background, making it difficult to visually distinguish from its background. Variable light transmitters covering an object are each individually controlled by a controller, which varies the light color and intensity coming from the light transmitters. In order to blend the object with its background, light sensors are placed on the opposite sides of the object, and paired through a controller or controllers to individual light transmitters. Each light sensor senses the color and intensity of light coming from one side of an object, and a controller uses this information to vary the color and intensity of light transmitted from a paired light transmitter on the opposite side of the object, exactly matching the color and intensity of background light. For example, if a viewer sees the object against a bright blue sky, the light transmitters covering the object which are facing the viewer would be transmitting bright blue light to match the background light as sensed by paired sensors on the opposite side.
Note that xe2x80x9ccolor and intensityxe2x80x9d of light in the description of the present invention means the specular power distribution, luminance, and other specular characteristics of light. Note also that the matching of colors in the present invention is metameric color matching, meaning that the simulated colors need not have specular characteristics identical in every way to the original color, but need only appear to the human eye to be a perfect match because of the limited range of color sensitivity in the human eye and other psychophysical and psychological factors.
In some applications a viewer may view the object from an oblique angle, seeing the object against different background light than would be seen if viewed from a xe2x80x9cstraight onxe2x80x9d view at a right angle to the surface of the object. In order to allow for camouflage from oblique views, light sensors and transmitters are designed to be directional and are designed to receive or transmit light at varying angles. Each light transmitter transmits light rays outward essentially parallel to a single axis. Transmission of light outward from light transmitters that do not create diffuse light, but transmit light in a narrow dispersion of nearly parallel light rays, can be accomplished with a variety of existing technologies. For example, light sources can be equipped with lenses or view limiting devices so that only nearly parallel light rays are emitted from individual light transmitters, and light can only be viewed by viewers directly in line with a light transmitter""s aiming path. Light sensors are similarly fitted with lenses or view limiting devices so that light is only sensed from sources directly in line with the aiming path of each sensor. A light transmitter with an aiming path that is at a right angle to the surface of the camouflaged object is varied by a controller to match light measured by sensors on the same aiming axis as the transmitter but with an aiming path pointed in the exact opposite direction on the opposite side of the object. Light transmitters with an aiming path that is at an oblique angle to the object would be varied by a controller to match light measured by sensors on the same axis as the transmitter, but with an aiming path pointed in exactly the opposite direction. Light transmitters with aiming paths at a variety of angles are interspersed in close proximity to each other on the surface of the object so that transmitted light originating from all parts of the surface of the object would be visible to a viewer from any perpendicular or oblique viewing angle, without any xe2x80x9cblankxe2x80x9d spots visible on the object from any angle.
As an alternative to individual placement, directional transmitters may be grouped in tightly integrated clusters, with each cluster containing enough light transmitters aimed outward at varying angles to transmit light in a near-180 degree semispherical pattern. xe2x80x9cBlankxe2x80x9d spots would be avoided by covering the entire surface of the object with tightly integrated clusters. In addition, to avoid xe2x80x9cblankxe2x80x9d spots when viewing the object from various oblique angles, individual transmitters must not transmit light in perfectly parallel light rays, but must allow a small aspect angle light dispersion. The size of the aspect angle dispersion would correspond to the angular displacement between light transmitters occupying a single cluster on the surface of the object. Each cluster may also contain directional light sensors paired to transmitters on the various other sides of the object. Each cluster could be thought of as a xe2x80x9cpixelxe2x80x9d similar to the concept of a pixel on a video monitor, except that each cluster would contain multi-directional light transmission capability. Each such modular cluster will be termed a xe2x80x9cdirectional pixelxe2x80x9d in connection with the present invention. Any application of a xe2x80x9cdirectional pixelxe2x80x9d in the present invention may also be accomplished using a non-integrated grouping of directional light transmitters and receivers arranged in a variety of aiming paths such that the same coverage is achieved as with integrated directional pixels.
In applications where the entire surface of the object is covered by both sensors and light transmitters, the transmission of light may reflect off of moisture, dust, smoke or other objects and interfere with the light sensors mounted on the same side of the object. As an alternative, in order to avoid light reflection back toward sensors in certain applications, the light transmitters do not transmit light continuously. Instead, the transmitters transmit light in a very rapid succession of light bursts (such as strobes flashing in excess of 30 times per second) that appears as continuous light or nearly continuous light to the human eye, yet allows a very short interval in between light bursts for the light sensors to obtain readings that are not influenced by outwardly-transmitted light. Alternating the light sensing cycle with the light transmission cycle also allows use of the same light transmission channel, such as an optical fiber, for both reception of light to be sensed at a central location, and transmission of light outward from a central location.
It should be noted that the type of light transmitters used by the system may be virtually any type of light source that could be made available in the application, such as the light transmission technologies currently utilized by a wide variety of audio-visual equipment, which produces light over all or most of the range of the visible light spectrum (or is capable of being filtered or modified in such a way that it produces light over most or all of the range of the visible light spectrum). The choice of light source depends on the complexity of the camouflage system that has been implemented, the level of resolution that is needed, and the frequency of camouflage update that is needed.
For example, light transmitters for a stationary system with slow update and low resolution may be simple incandescent bulbs, with light output varied by color filters and with apertures or electrical power regulators which are controlled with manual inputs after a human controller takes manual readings from light sensors pointed in the opposite direction. In such an example, the xe2x80x9clight controllerxe2x80x9d would be direct human input. As another example, light transmitters for a moving system with rapid update and resolution requirements may be supplied with light by a centrally mounted strobe light or series of strobe lights with light channeled to directional transmitters on the surface of the object by means of optical fibers, with color and intensity varied by means of liquid quartz display technology or any other light filtering technology with rapid update capability. Similarly, light could be generated at a central location in such a manner that it is directional (essentially parallel light rays) and reflected outward in selected directions by computer controlled movable mirrors utilizing systems currently in use in a variety of audio-visual or electronic cinematographic applications.
Additional computer processing capability, memory, and programming may be added to the present invention beyond what is needed for the basic control features, such that continuous adjustments may be made to the appearance of the object to enhance the camouflage by eliminating or reducing the effects of sunlight or other light reflected from the surface of the object (specular reflection and diffuse reflection which is referred to in the terminology of video image processing as viewing flare). In addition, substantial enhancements in image processing could allow the present invention to project an image on the surface of the object to make the object clearly visible, but with an appearance that is totally different from the camouflaged object, such as projecting the image of six enemy helicopters flying in formation onto the surface of a camouflaged military air transport aircraft, providing a plausible visible cue to match its radar echo while allowing it to land and depart from an enemy airfield in daylight without detection.
In order to compensate for viewing flare (passively reflected light from the surface of the object, both specular reflection and diffuse reflection) the computer processing unit could monitor light sensor input to determine the direction of the primary light sources and calculate which directions the light is likely to be reflected from the object and detected by a viewer. Existing algorithms have been developed in computer gaming, CAD-CAM and image simulation fields, such as the Phong model or the Torrance-Sparrow model, to determine the characteristics of light reflected from an object with a defined shape and defined reflective qualities. These are often referred to as xe2x80x9cshading modelsxe2x80x9d. After utilizing existing algorithms to determine the quality and direction of reflections from the surface of the object which is to be camouflaged (these passive reflections being known in the video monitor field as xe2x80x9cviewing flarexe2x80x9d), light transmitters aimed in the same direction as the anticipated reflections could be varied in color and intensity to mitigate the unintended reflection (canceling or reducing the effects of the xe2x80x9cviewing flarexe2x80x9d). Existing algorithms are commonly available and utilized in the field of computer video image processing to adjust light transmitted from a video screen to reduce the effects of viewing flare. These algorithms are commonly used to mitigate the effect of grey-white reflections from the surface of a monitor which require adjustment of the image displayed on the monitor in order to accurately reproduce the intended spectral qualities to be viewed by the human observer. Since viewing flare is generally white light, the existing algorithms generally result in shifting the color of transmitted light away from white (toward more saturated colors). In simplified terms, the effect of the viewing flare is cumulative with the image projected from the viewing surface, so in order to compensate for the viewing flare the spectral power distribution of the viewing flare is subtracted from the spectral power distribution of the image to be projected from the viewing surface in order to determine the appropriate adjusted spectral power distribution of the image to be projected.
As an alternative method of reducing reflections, surface panels on the object could also be physically tilted or otherwise physically modified as directed by the processing unit to redirect and minimize especially noticeable specular reflection.
Intentionally visible images could also be created by the on-board processing unit. In essence, the entire surface of the object could be treated as a near-spherical video viewing monitor, covered with directional pixels which are cumulatively capable of simulating a three dimensional object. In such an application, image generation could be controlled by a series of parallel processors instead of a single image processor, because added capacity may be necessary in order to project a slightly different image in each of the directions the light transmitters are oriented, accurately reproducing essentially all views of a three dimensional object.
As an example of this type of application, part of the surface of a military helicopter may be camouflaged to match its background while the remainder of its light transmitters may project an intentionally visible image that would make the helicopter appear to an observer to have the same shape and color as an enemy aircraft (from all viewing angles). Similarly, depending on the needs of the mission, a three dimensional image could be projected on the surface of the helicopter to simulate a flock of birds, an aircraft that has been hit and is engulfed in flames or a flying billboard with pictures or text which may be animated. If a high level of resolution is implemented, for example, a mobile missile launcher may be outfitted to appear to a viewer as a line of enemy tanks.
The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:
FIGS. 1A and 1B illustrate an object covered with light transmitters and light sensors mounted only at right angles to the surface of the object;
FIG. 2 illustrates an object covered with light transmitters and light sensors mounted at various angles from the surface of the object, some at right angles to the surface of the object and others at oblique angles to the surface of the object;
FIG. 3 illustrates the placement of remote sensors, which sense the background of the object that is immediately to the side of the object rather than directly behind the object;
FIG. 4 depicts an example of one preferred embodiment of the present invention that realizes the advantages of the present invention without the use of an automated controller;
FIGS. 5A and 5B illustrate light transmitters attached to a view-limiting device and a lens, respectively, which are used to limit transmission of light to a single aiming path in a specific direction, with minimal bleed-over to other directions;
FIG. 6 depicts a combined light source in accordance with an example of one preferred embodiment of the present invention;
FIG. 7 illustrates generation of multi-directional reactive camouflage lighting from a central control and light generation location and distributed to the surface by means of optical fibers, in accordance with a preferred embodiment of the present invention; and
FIG. 8 provides an illustration of how the ability of the present invention to camouflage an object by transmission of light may also provide the necessary means to present an intentionally visible image which may confuse, deceive, frighten, inform or entertain.