Segmentation method for terminal aimpoint determination on moving objects and apparatus therefor

• US 4,959,714 A
• Filed: 08/08/1988
• Issued: 09/25/1990
• Est. Priority Date: 08/08/1988
• Status: Expired due to Term

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Hughes Aircraft Company (Rtx Corporation)
• Inventors: Lo, Thomas K., Simoni, Wayne P., Sacks, Jack M.
• Primary Examiner(s): Peng, John K.
• Application Number:
  US07/229,198
• Time in Patent Office: 778 Days
• Field of Search: 358/125, 358/126, 358/105, 358/96, 382/22
• US Class Current: 348/172
• CPC Class Codes: G06T 7/254 involving subtraction of images

Abstract

A conventional tracker 14 is used to continually aim a sensor 12 at a flying object so that it is located in substantially the same spatial location in a plurality of image frames taken at different times. Thus, the object remains in about the same spatial position in each image frame while the background clutter generally changes. By processing two or more of the image frames it is possible to calculate a more precise aimpoint for the object than is generally provided by the track point.

Claims

1. A method of detecting the spatial location of a moving object, said method comprising:

generating a track point for the object as it moves;

using the track point to continually aim a sensor at the object so that it is located in substantially the same spatial location in a plurality of image frames taken at different times whereby the object remains substantially in the same spatial position in each image frame while the background generally changes;

subtracting at least two of the image frames to generate a difference image in which pixels associated with the object will have values substantially less than those associated with the background;

applying a given threshold level to the difference image to generate a binarized signal; and

using the binarized signal to calculate an aimpoint which is more closely associated with the centroid of the object than the track point.

2. The method of claim 1 wherein the track point is calculated from infrared characteristics of the object.

3. A method of determining an aimpoint to be used by a seeking device to contact a centroid of a moving object, said method comprising:

generating a track point by sensing a physical characteristic of the object;

using the track point to continually aim an image sensor at the object so that it is located at substantially the same spatial location in a plurality of image frames taken at different times whereby the object remains substantially in the same spatial location in each image frame while the background generally changes;

processing the frames of image data to generate an aimpoint which is more closely associated with the centroid of the object than the track point said processing including the step of subtracking at least two of the image frames to generate a difference image in which pixels associated with the object have values substantially less than those associated with the background;

thresholding the difference image to generate a binarized signal; and

calculating the centroid of that portion of the binarized signal associated with the object.

4. The method of claim 3, wherein the physical characteristic is infrared energy transmitted by the object.

5. In an apparatus for generating an aimpoint for a seeking device adapted to make contact with an object moving through a cluttered background, the apparatus comprising:

video input means for providing a current image frame of pixel data containing the object;

first memory means for storing maximum pixel values for each pixel position in a plurality of earlier taken image frames where the object remains substantially in changes as the object moves through space;

first comparator means coupled to the input means and the first memory means for comparing corresponding pixel values therein and updating the memory with the maximum value;

maximum register means for storing the contents of the first memory after the first comparator means has made comparison with at least three frames of image data;

second memory means for storing minimum pixel values for each pixel position in said earlier taken image frames;

second comparator means coupled to the input means and the second memory means for comparing corresponding pixel values therein and updating the second memory with the minimum value;

minimum register means for storing the contents of the second memory means after the second comparator means has made comparison with at least three frames of image data;

subtractor means for subtracting corresponding pixels in the maximum and minimum register means whereby pixels associated with the object will have relatively low values as compared with background pixels;

third comparison means for thresholding the output of the subtractor means with a value related to noise in the image frames;

means for sensing characteristics of the object, said sensing means generating tracker error signals;

computer means coupled to the output of the third comparator means for calculating selected coordinates of geometrical characteristics of the object from the thresholded image whereby the coordinates can be combined with tracker error signals for guiding the seeking device to a predetermined geometrical location on the object.

6. The apparatus of claim 5 wherein said means for sensing characteristics of the object senses infrared characteristics of the object.

7. The apparatus of claim 5 wherein said selected coordinates are related to the centroid of the object.

8. An apparatus for detecting the spatial location of a moving object, said apparatus comprising:

means for generating a track point for said object as it moves;

means for using said track point to continually aim a sensor at said object so that it is located in a plurality of image frames taken at different times such that said object remains substantially in the same spatial position in each image frame while the background generally changes;

subtracting at least two of the image frames to generate a difference image in which pixels associated with said object will have values substantially less than those associated with the background;

means for applying a given threshold level to the difference image to generate a binarized signal; and

means for using said binarized signal to calculate an aimpoint that is more closely associated with the centroid of said object than said track point.

9. An apparatus for determining an aimpoint to be used by a seeking device to contact a centroid of a moving object, said apparatus comprising:

means for generating a track point by sensing a physical characteristic of said object;

means for using said track point to continually aim an image sensor at said object so that it is located at substantially the same spatial location in a plurality of image frames taken at different times such that said object remains substantially in the same spatial location in each image frame while the background generally changes;

means for processing the frames of image data to generate an aimpoint that is more closely associated with the centroid of said object than said track point;

said processing means includes;

means for subtracting at least two of the image frames to generate a difference image in which pixels associated with the object have values substantially less than those associated with the background;

means for thresholding the difference image to generate a binarized signal; and

means for calculating the centroid of that portion of the binarized signal associated with said object.

10. A method of determining an aimpoint to be used by a seeking device to contact a centroid of a moving object, said method comprising:

generating a track point by sensing a physical characteristic of the object;

using the track point to continually aim an image sensor at the object so that it is located at substantially the same spatial location in a plurality of image frames taken at different times whereby the object remains substantially in the same spatial location in each image frame while the background generally changes;

processing the frames of image data to generate an aimpoint which is more closely associated with the centroid of the object than the track point;

comparing the values of corresponding pixels in at least three image frames and storing the maximum value in a first memory and the minimum pixel value in a second memory;

subtracting the minimum pixel values from the maximum panel values to generate a difference image in which those pixel positions associated with the object will have a difference value close to zero while pixel positions associated with background will have substantially greater values;

applying a positive threshold value to the difference image to generate a binarized signal; and

calculating the aimpoint from the centroid of portions of the binarized signal associated with the object.