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Device for and method of detecting motion in an image
| Details |
Inventors: Pucker, II, Leonard G.; Sofge, David B.;
Assignee: The United States of America as represented by the National Security Agency (Washington, DC)
Primary Examiner: Au; Amelia M.
Assistant Examiner: Miller; Martin
Attorney, Agent or Firm: Morelli; Robert D.
A device for and method of detecting motion between a reference image and a test image by acquiring the images; aligning the images; dividing the images into blocks; masking certain blocks; differencing corresponding blocks; median filtering the differences; low-pass filtering the outputs of the median filter; generating a normalized histogram for each output of the low-pass filter; generating a model of gaussian noise; calculating the distance between the noise model and each normalized histogram; comparing each distance calculated to a user-definable threshold; and determining if motion has occurred between the images if a certain number of distance calculations are at or above the user-definable threshold. If a scene is to be continuously monitored and no motion occurred between the previous reference image and the previous test image then a new test image is acquired and compared against the previous reference image as described above. If the scene is to be continuously monitored and motion has occurred between the previous reference image and the previous test image then replace the previous reference image with the previous test image, acquire a new test image, and compare the new test image to the new reference image as described above. |
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DETAILED DESCRIPTION It is an object of the present invention to detect motion between subsequent images of a scene.
It is another object of the present invention to detect motion between subsequent images of a scene in the presence of gaussian noise that would normally occur in a sonogram or a radar image.
The present invention is a device for and a method of detecting motion in subsequent images of a scene in the presence of gaussian noise that would normally occur in a sonogram or a radar image.
A first image, or reference image, is acquired from a scene.
The reference image is comprised of pixels.
A second image, or test image, is acquired from the scene.
The test image is also comprised of pixels.
The reference image and the test image are aligned to each other in order to eliminate one source of false motion detection.
The reference image and the test image are each divided into N.
times.
M blocks.
The user may define areas of the reference image and the test image to ignore or mask.
Corresponding blocks of the reference image and the test image that are to be considered are differenced (i.
e.
, a pixel in one block is subtracted from the corresponding pixel in the corresponding block of the other image).
To eliminate shot, or spike, noise, that may cause a false detection of motion, each block of the difference between the reference image and the test image is median filtered.
To eliminate any false detection of motion that may be caused by jitter in the acquisition of the reference image or the test image, each median filtered block is low-pass filtered.
A normalized histogram is generated for each low-pass-filtered block.
A model of gaussian noise is generated.
A distance is calculated between each normalized histogram and the noise model.
Each calculated distance is compared to a user-defined threshold.
The user may define motion as having occurred if one calculated distance is at, or above, the user-definable threshold or if a user-definable number of calculated distances representing adjoining difference blocks of the reference image and the test image are at, or above, the user-definable threshold
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