Method and system for determining motion based on difference image correlation
View Patent ↗An imager captures successive images of an object. One image is then subtracted from another image to generate difference images. Each difference image is then correlated with itself or with one of the images used to generate the difference image to determine the relative motion between the imager an the object.
1. A method for determining a navigation vector for a device, comprising:
capturing a first image of an object;
capturing a second image of the object;
subtracting the first image from the second image to generate a difference image;
performing a correlation using the difference image, wherein the difference image is correlated with one of the first image or the second image; and
determining the navigation vector from a result of the correlation, wherein the navigation vector represents relative motion between the device and the object.
2. The method of claim 1 , wherein generating the difference image comprises subtracting grayscale values in the first image from grayscale values in the second image to generate the difference image.
3. The method of claim 1 , further comprising prior to determining the navigation vector, performing a thresholding operation on a result of the correlation.
4. The method of claim 1 , further comprising repeatedly:
capturing a subsequent image;
subtracting a preceding image from a subsequent image to generate a difference image;
correlating the difference image with one of the images used to generate the difference image; and
determining the navigation vector based on a result of the correlation.
5. The method of claim 1 , further comprising storing the first image in memory.
6. A system for determining the relative motion of a device, comprising:
an imager configured to capture a plurality of images;
a difference image generator electrically coupled to the imager and configured to generate difference images using pairs of captured images; and
a correlator electrically coupled to the difference image generator and configured to receive each difference image and one of the captured images used to create each difference image and correlate the received captured image with its respective difference image.
7. The system of claim 6 , wherein the difference image generator subtracts grayscale values in a first image from grayscale values in a second image for each pair of images to generate the difference images.
8. The system of claim 6 , further comprising a processing circuit electrically coupled to an output of the correlator and configured to determine the relative motion of the device based on each result of the correlation.
9. The system of claim 6 , further comprising a processing circuit electrically coupled to an output of the correlator and configured to perform a thresholding operation on each result of the correlation.
10. The system of claim 6 , further comprising memory electrically coupled to the imager and the difference image generator.
11. The system of claim 6 , further comprising a clock electrically coupled to the imager.