Low false alarm rate detection for a video image processing based security alarm system

A method of evaluating a scene to determine if an perceived movement within the scene is caused by an intruder into the scene comprising:

• viewing the scene and creating an image of the scene comprising a plurality of pixels arranged in an array;
• comparing the image of the scene with a reference image thereof to produce a difference image, producing said difference image including convolving the image with an antialiasing means to eliminate any aliasing effects in the difference image, outlining any segments where possible movement has occurred, determining a ratio of light intensity between each pixel in a segment with each pixel adjacent thereto, and comparing the ratio values for the pixels in a segment of one image with the ratio values for the pixels in the corresponding segment of another image to eliminate the effects of lighting changes;
• processing the difference image to identify any segments therewithin which, based upon a first predetermined set of criteria, represent spatially constrained movements of an object fixed within the scene, and further processing the difference image to identify any segments therewithin which, based upon a second predetermined set of criteria, represent artifacts not caused by the presence of an intruder within the scene, said segments meeting said first and second sets of criteria being identified as segments not requiring further processing;
• and, further processing those segments within the difference image which remain to determine if movement therewithin is caused by an intruder.