Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
1999-11-04
2001-10-16
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S221000
Reexamination Certificate
active
06303920
ABSTRACT:
The present invention relates to an apparatus and concomitant method for image processing. More particularly, this invention relates to a method and apparatus that detects salient motion, i.e., motion with a sense of direction in an image sequence.
BACKGROUND OF THE INVENTION
Motion information, e.g., salient motion detection, plays an important role in many vision based applications or systems such as surveillance and targeting systems. Salient motion is defined to be motion that tends to move in a consistent direction over time. However, in a given situation, some motion based information is relevant to the tasks at hand, while other motion based information simply provides competing detail. Namely, image motion can arise from “noninteresting” objects as well as “interesting” ones.
For example, surveillance-defined detection and tracking tasks can benefit from certain types of visual motion, while being hampered by other types of visual motion. Depending on the specific scene conditions, the difficulty of these tasks can vary widely. Some of the more challenging domains are those in which motion is being exhibited not just by the “salient” objects or objects of interest (e.g., a person or vehicle traveling with a sense of direction through a scene), but also by other “non-salient” objects (e.g., the scintillation of specularities on water, or the oscillation of vegetation in the wind). Non-salient motions of this type are a common source of false positives for most simple motion-detection schemes, which either detect areas of frame-to-frame intensity change, or areas of intensity change with respect to some reference representation. Although the reference representation can also be a learned probability distribution of intensities at each pixel, and such a system can, over time, learn not to report non-salient changes, it will still give rise to false positives for some time until the reference representation has been learned.
Therefore, a need exists in the art for a method and apparatus for detecting salient motion.
SUMMARY OF THE INVENTION
The present invention is a method and apparatus for detecting salient motion in an image sequence using optical flow. Namely, for each pixel in an image, frame-to-frame optical flow information are collected over time for computing a rough estimate of the total image distance traveled by each pixel.
More specifically, an optical flow field is generated for every two successive image frames. The optical flow field is defined as a two-dimensional (2D) vector at each pixel location. In turn, the resulting optical flow field is applied to warp one or more intermediate measure images that contain intermediate cumulative measurements, thereby aligning these measure images with the current image. Finally, the flow fields for an image sequence are used to compute a sum of frame-to-frame optical flow fields for the image sequence to yield a cumulative flow field that can be used to generate a measure of salience for each image point. The measure of salience will provide insight as to whether an image point is part of a salient object or part of a non-salient object. In other words, the resulting salience measure allows a motion detection method and apparatus to distinguish salient objects from non-salient objects. In turn, such information is very important in surveillance or targeting applications, where it is very desirable to track and monitor salient objects.
Additionally, various alternate embodiments of the present invention are also disclosed. Specifically, variations in the computation of the flow field and salience measure are provided to address different image conditions.
REFERENCES:
patent: 5627905 (1997-05-01), Sebok et al.
Burke William J.
Le Que T.
Sarnoff Corporation
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