Reconnaissance/Surveillance System Utilizing Color Signature of Target

(a) Field of the Invention

Broadly speaking, this invention relates to photo-reconnaissance and surveillance. More particularly, in a preferred embodiment, this invention relates to a photo-reconnaissance and surveillance system which utilizes color signature information to identify specified targets.

(B) Discussion of the Prior Art

One of the disadvantages to the use of photography in intelligence work is the slowness of the information gathering process. For example, in a typical photo-reconnaissance mission the flight is made; the aircraft returns to its base; the film is processed, then scanned by an interpreter who determines if any potential targets are present; the targets, if found, are geographically located, then the information relayed to the Field Commander for action. By the time that this process is completed the theatre of operation may have moved to an entirely different area and the intelligence, thus, becomes useless. Radar, infra-red, and laser sensors have all been proposed as substitutes for photography because these sensors have the ability to provide real-time access to intelligence information. None of these sensors, however, can really compete with photography which is an instant storage medium capable of providing intelligence with extremely fine resolution.

As a solution to this and other problems, the instant invention discloses methods and apparatus for utilizing photographic information as a target-detecting device in such a manner that the information can be relayed to the Field Commander in near-real time.

More specifically, the invention disclosed and claimed herein analyzes potential targets in terms of their color signature. As is well known, much work has been done in the past to correlate potential targets on a monochrome photographic surveillance film in terms of the size and shape of the target, but it soon becomes evident to even the uninitiated that the scale, angle of view, size and resolution of the target images all interfere with such an analysis.

As an example, let us assume that we have photographed red, blue and green compact station wagons and a military jeep on monochrome film. If, as will generally be the case, the details on the vehicles are not visible, it is more than likely that all four vehicles will be photographed as grey rectangles of similar size and shape with the only distinguishing factor being a slight variation in the tone of grey. However, if the vehicles were photographed with color film, either reversal or negative, one could immediately discern the differences between the cars because each target would have a unique color signature. This signature can be distinguished by the human eye (assuming the observer is not color blind) but it may also readily be distinguished by the use of a photo-receptor (e.g. a photocell or phototransistor) that can measure the absorption of the exposed film to red, blue or green light.

If then, the target images on the film are scanned with a red, green or blue light source which is smaller than the smallest target image on the film, a change in the response of the photoreceptor will be immediately detected and this change can be related to a particular color. If, for example, we are only interested in detecting the jeep as a target, we can adjust the electronic detector to respond only when the receptor has sensed the color signature of the jeep.

In a preferred embodiment, the invention comprises apparatus for detecting a target of known color signature. The apparatus comprises color sensitive means for viewing a scene suspected of containing said target and for producing an electrical output signal representative thereof and means responsive to the output signal for examining successive regions of the scene to determine the ratio between at least two specified color components thereof, thereby to ascertain the presence of said target.

The invention and its mode of operation will be more fully understood from the following detailed description, when taken with the appended drawings in which:

FIG. 1 is a partially schematic, partially diagrammatic drawing of a first illustrative embodiment of the invention;

FIG. 2 is an isometric, partially schematic view, of a portion of the apparatus shown in FIG. 1.

In the process to be described below, color negative film is used in-flight to photograph an area of interest. The film is then processed using any of several known rapid color processing techniques. When the film exits from the last stage of the processor, it is passed between a bank of light sources and a corresponding bank of photoreceptors. A two-color filter moves rapidly in the path of light beams emitted from the light sources so that the photoreceptors can measure the light transmitted by the film for each filter. The signature of the targets of interest can then be related to the response of the photocell to two of the primary colors, e.g., red and blue, or red and green, or blue and green, et cetera. More specifically, as shown in FIG. 1, color sensitive film 10 is fed from supply reel 11 through a pair of idler rollers 12--12 into a photo-reconnaissance camera 13. Thence, the film passes into a rapid processor 16 for development. The developed and dried film then passes through a second pair of idler rollers 14--14 into a scanner 17. As shown in greater detail in FIG. 2, scanner 17 comprises a rotating color wheel 21 driven by a motor 22. An illuminating source 23 which comprises a plurality of discrete light sources 24 illuminates film 10 through rotating filter 21. An analyzer 26, which comprises a plurality of discrete photocells or phototransistor 27, receives the light from illuminating source 23. The outputs from photocells 27 are connected to a logic circuit 28 for analysis.

To avoid clutter, FIG. 2 only shows three light sources 24 and three photocells 27. Obviously, a practical device would have many more such elements typically arranged in an n.sub.x m matrix. As shown, rotating filter 21 comprises two green filter segments 33 and two red filter segments 32. Again, a practical device might have more or less filter segments than those shown in FIG. 2 and other color combinations are also contemplated. The outputs of the photocells 27 are shown connected to logic circuit 28 via an electronic switch 31 which, thus, scans across the array.

Although not shown in the drawing, it is obviously necessary to synchronize this scanning with the rotation of filter wheel 21. This is diagrammatically shown by the line 34 which connects electronic switch 31 and the motor 22 for filter wheel 21. After the film leaves the scanner 17 it passes over a third set of idler rollers 41--41 thence to take-up spool 42.

It is self-evident from the above that by the appropriate choice of color filters, analyzer 26 can be programmed to respond to only certain colors. Thus, if the color signature of the target to be identified is known a priori, logic circuit 28 will only indicate that target and reject all others. Logic circuit 28 can also successfully detect a green target that is camouflaged with green foliage, for example. The reason for this is that the green foliage will have a slightly different color signature than the painted object. Further, striking color contrasts can be achieved by using infra-red sensitive, camouflage detection film rather than ordinary color film. As is well known, when this special film is used, natural deciduous foliage will photograph as red and painted objects will photograph blue.

The specific location of a target can easily be found from code information recorded on the frame by the use of fiducial marks, and/or by the location in the matrix of the photocell that gave the color signature response. A second station can then be provided that transmits a detailed photograph of the actual target that was pin-pointed by the detector to the ground location. For example, the photographic image can be scanned and transmitted to ground using facsimile or slow scan TV techniques.

It should be understood that the instant invention is not limited to in-flight systems as it also has application in photo-interpretation ground stations where it can be used to rapidly scan surveillance or reconnaissance film which were priorly recorded. Yet another application of the invention is the use of the color signature of a target to identify a friend or foe in a battlefield situation. Friendly forces would arrange to utilize a specific color coding for their equipment, tarpaulins, et cetera that could be photographed with either conventional film or a photographic emulsion that has a spectral response especially designed to match the output of the color code.

Initial tests which were performed to prove the feasibility of the concept of photographic color signature were made by photographing a scene containing two military vehicles standing on a grass-covered area. One vehicle was painted dark green and the other olive drab. The density of the area of interest to red, green and blue light was read on a color densitometer and green-to-blue ratios determined. The color densities were as follows:

From the above, it will be seen that the green colors can be easily separated.

The above example presents the most difficult detection problem, i.e., the problem of distinguishing between several green objects. Any other color would immediately stand out in contrast.

One skilled in the art may make various changes and substitutions to the arrangement of parts shown without departing from the spirit and scope of the invention.