Motion detection using normal optical flow

A method of detecting motion comprising:

• obtaining a plurality of at least three images of an object using a camera, the plurality of images being obtained over a predetermined period of time;
• generating a motion region image of the object from the plurality of images by isolating the object in the plurality of images from a background to generate a plurality of corresponding silhouettes, generating a difference image using the plurality of images,
• wherein the difference image isolates a portion of the object which has changed location during the plurality of images, and setting pixels of the difference image to an equal value;
• calculating normal gradients over time of the motion region image, the normal gradients having an orientation substantially perpendicular to motion of edges of the silhouettes and having a magnitude proportional to changing velocity of motion between edges of sequential silhouettes;
• removing erroneous normal gradients to provide a normal flow image;
• and
• identifying movement based on the normal flow image.

A computer readable medium comprising instructions stored thereon that when executed by a processor result in:

• generating a plurality of silhouettes from a corresponding plurality of images taken of an object over a predetermined period of time, the plurality of image including at least three images and having time-difference information associated with sequential images of the plurality,
• generating a motion region image of the object from the plurality of silhouettes;
• calculating normal gradients for edges within the motion region image, the normal gradients hang an orientation substantially perpendicular to motion of the edges of the silhouettes and having a magnitude proportional to changing velocity of motion between edges of sequential silhouettes;
• removing erroneous normal gradients to provide a normal flow image comprised of at least some of the normal gradients;
• and
• identifying a type of movement of the object based on the normal flow image.

A system comprising:

• a camera to obtain a plurality of at least three images of the object taken over a predetermined period of time, the images having time-difference information associated therewith to indicate change in velocity of movement of portions of the object;
• and
• a processor coupled to the camera, to generate a plurality of silhouettes corresponding with the plurality of at least three images, to generate a motion region image of the object from the plurality of silhouettes, to calculate normal gradients for edges of the motion region image,
• to remove erroneous normal gradients to provide a normal flow image, and to identify movement based on the normal flow image using a processor,
• wherein the normal gradients calculated by the processor have an orientation substantially perpendicular to motion of the edges of the silhouettes.