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  Method and apparatus for detecting objects using structured light patternsUSPTO Application #: 20060038114Title: Method and apparatus for detecting objects using structured light patterns Abstract: An object detection system is provided that projects one or more patterns onto a monitored area, captures one or more live images of the monitored area, and detects objects that enter the monitored area by detecting changes in the one or more patterns in the live images. Such an object detection system may be less susceptible to dynamic lighting conditions, and more sensitive to object intrusions. One illustrative example projects a pattern of dots onto an area to be monitored, and captures images corresponding to the monitored area, comparing live images to reference images to determine whether an object has intruded a defined area. The area to be monitored does not consist solely of the area captured in the images and may include a volume illuminated by the pattern as well as a volume corresponding to the captured image area. Objects not in the field of view may be detected by the disclosed systems and methods. Several illustrative analytical methods are disclosed as well. (end of abstract) Agent: Honeywell International Inc. - Morristown, NJ, US Inventors: Darren D. Cofer, Rida M. Hamza USPTO Applicaton #: 20060038114 - Class: 250221000 (USPTO) Related Patent Categories: Radiant Energy, Photocells; Circuits And Apparatus, Optical Or Pre-photocell System, Controlled By Article, Person, Or Animal The Patent Description & Claims data below is from USPTO Patent Application 20060038114. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] This application claims priority to U.S. patent application Ser. No. 10/052,953, filed Jan. 17, 2002, entitled METHOD AND APPARATUS FOR DETECTING OBJECTS, which claims priority under 35 U.S.C..sctn.119(c)(1) to U.S. Provisional Patent Application Ser. No. 60/262,925, filed Jan. 19, 2001, and entitled OBJECT DETECTION USING MOIRE INTERFERENCE, which are both incorporated by reference herein in their entirety. This application is related to U.S. patent application Ser. No. 09/716,002, filed Nov. 17, 2000, entitled OBJECT DETECTION, U.S. Provisional Application No. 60/275,879, filed Mar. 14, 2001, entitled SAFETY CAMERA, and U.S. patent application Ser. No. 09/981,928, filed Oct. 16, 2001, entitled OBJECT DETECTION, which are all incorporated by reference herein in their entirety. FIELD [0002] The present invention relates to object detection, and more specifically, to object intrusion and/or presence detection within a monitored area or region. BACKGROUND [0003] Motion detection and object detection systems are well known in the art. Frequently, such systems monitor a user-defined area to detect when an object enters or passes through a monitored area. Such systems typically include an image capture device (such as a video camera or still camera) capable of capturing an image of the monitored area and, if required, a device for digitizing the captured images. The digitized images are analyzed in an attempt to detect whether an object has entered the monitored area. There are many different known methods and algorithms for analyzing digitized images for determining when an object has entered a monitored area. One of the most common methods is generally referred to as a change detection method. [0004] Change detection is often accomplished by examining the difference between a current live image and a reference image, where the reference image contains only the static background of the monitored area. A reference image can be thought of as a representation of the monitored area as it would appear if no transitory objects were in view. Change detection algorithms often take two digitized images as input and return the locations in the field of view where differences between the images are identified. [0005] Object detection systems are commonly used in environments that have dynamic lighting conditions. For example, in industrial settings, moving shadows can be cast on a monitored area or region, which can cause significant changes in ambient lighting conditions. Many existing object detection systems, including those that use change detection algorithms to detect objects, can be challenged by such shadows and/or other dynamic lighting conditions. SUMMARY [0006] The present invention overcomes many of the disadvantages of the prior art by providing an object detection system that is less susceptible to dynamic lighting conditions, and/or more sensitive to three-dimensional object motion and/or presence. This is preferably accomplished by projecting one or more patterns onto the monitored area, capturing one or more live images of the monitored area including the one or more patterns, and detecting objects in the monitored area by detecting changes in the one or more patterns in selected captured images. [0007] In a first illustrative embodiment of the present invention, a pattern is projected onto the monitored area. One or more live images of the monitored area are then captured at selected times, and analyzed to detect changes in the projected pattern. The changes in the pattern may indicate a topographical change in the monitored area, and thus the entry or movement of an object in the monitored area. Because the pattern is projected onto the monitored area, changes in the ambient lighting conditions may have less effect on the efficacy of the object detection system. In some embodiments, the projected pattern is provided at a wavelength which will not be affected or at least substantially affected by ambient lighting. For example, a near infrared or infrared wavelength may be chosen since such wavelengths are not as strongly affected by visible light variations in the region of interest if the visible lighting in an area changes. The particular pattern may vary widely, and may be static or dynamic. Additional variations and embodiments are further explained below. [0008] In another illustrative embodiment, an object detection system includes a step of providing an unequal illumination pattern to an area to be monitored, where the unequal illumination pattern contains a predictable pattern. At the same time, an image of the area to be monitored is captured, and data analysis is performed to determine whether the captured image contains the predicted pattern. The predictable pattern may be considered to be a form of data, and the monitoring of the area comprises a determination of the extent to which the data cast in the illumination pattern is altered as measured by the capture of the image. As such, the illustrative embodiment relies not only on the area to be monitored to provide data for analysis, but also uses the illumination pattern to observe additional data. The information in the illumination pattern does not necessarily arise from activity within the field of view of the image capture apparatus, which may be, for example, a camera. Thus events outside the field of view of the image capture apparatus may be monitored by the present invention. BRIEF DESCRIPTION OF DRAWINGS [0009] FIG. 1A is a schematic diagram showing an illustrative object detection system in accordance with one embodiment of the present invention; [0010] FIG. 1B is an overhead view corresponding to an image captured by the illustrative object detection system of FIG. 1A; [0011] FIG. 2A is a schematic diagram showing an illustrative object detection system in accordance with another embodiment of the present invention; [0012] FIG. 2B is an overhead view corresponding to an image captured by the illustrative object detection system of FIG. 2A; [0013] FIG. 3A is a schematic diagram showing an illustrative object detection system in accordance with yet another embodiment of the present invention, this time illustrating an object in the field of view of an image capture apparatus; [0014] FIG. 3B is an overhead view corresponding to an image captured by the illustrative object detection system of FIG. 3A; [0015] FIGS. 4A-4C illustrate a simplified subtraction algorithm which may be used for object detection with some embodiments of the present invention; [0016] FIG. 5A is a schematic diagram showing an illustrative object detection system in accordance with yet another embodiment of the present invention, this time illustrating the detection of an object outside of the field of view of an image capture apparatus; [0017] FIG. 5B is an overhead view corresponding to an image captured by the illustrative object detection system of FIG. 5A; [0018] FIGS. 6A-6B are schematic diagrams including a number of identified lines to aid in explaining a first illustrative analysis of pixel displacement; [0019] FIGS. 7A-7D are schematic diagrams including a number of identified lines to aid in explaining a second illustrative analysis of pixel displacement; and [0020] FIG. 8 is a schematic diagram including a number of identified lines to aid in explaining a third illustrative analysis of pixel displacement. 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