Binary correlation video tracker

• US 4,364,089 A
• Filed: 10/31/1979
• Issued: 12/14/1982
• Est. Priority Date: 10/31/1979
• Status: Expired due to Term

• Current Assignee: Northrop Grumman Corporation
• Original Assignee: Westinghouse Electric Company LLC (Brookfield Asset Management Incorporated)
• Inventors: Woolfson, Martin G.
• Primary Examiner(s): Blum, Theodore M.
• Application Number:
  US06/089,688
• Time in Patent Office: 1,140 Days
• Field of Search: 358/125, 358/126, 250/203 R, 250/203 CT
• US Class Current: 348/169
• CPC Class Codes: G01S 3/7865 using correlation of the live video image with a stored image

Abstract

A binary correlation video tracker and a video preprocessor included therein, which function cooperatively to form binary patterns of values for the picture elements (pixels) in a predetermined pixel array of each of a plurality of frames of video gray level information generated by an electro-optical sensor, is disclosed. Histograms are formed for selected pixel arrays in the predetermined array of a video frame in accordance with a set of predetermined gray level values. The formed histograms are combined in accordance with a discriminant function to form a composite histogram from which at least one gray level value of the set is selected. Those pixels of the predetermined array which have gray level values corresponding to the selected at least one gray level value are assigned one of two predetermined values, the other pixels being assigned the other of the two predetermined values, whereby a binary pattern of values for the predetermined pixel array is formed. Accordingly, the video tracker selects a reference binary pattern of pixels from the formed binary pattern of the predetermined pixel array of one video frame. The selected reference binary pattern is used for performing auto and cross-correlation operations in the video tracker in accordance with a binary correlation coefficient function. In the cross-correlations, another reference binary pattern of pixels and position thereof in the predetermined array is derived for each of the video frames generated subsequent the one video frame, the results being used in the computation of tracking errors in the video tracker. In the auto correlations, a maximum autocorrelation value is derived for use in determining when the reference binary pattern may be updated with the another reference binary pattern for further binary correlation processing.

Claims

1. A video preprocessor for forming a binary pattern of gray level values for the picture elements (pixels) in a predetermined array of a frame of video gray level information generated from an electrical sensor, said preprocessor comprising:

means for distributing the pixels of one selected pixel array within said predetermined pixel array of said video frame into a first gray level histogram based on a predetermined set of gray level values;

means for distributing the pixels of at least one other selected pixel array within said predetermined pixel array of said video frame into a second gray level histogram based on said predetermined set of gray level values;

means for selecting at least one gray level value of said predetermined set based on a discriminant function of said first and second gray level histogram distributions; and

means for assigning one of two predetermined values to those pixels in said predetermined pixel array of said video frame which have a selected gray level value and for assigning the other of said two predetermined values to those pixels in said predetermined pixel array of said video frame which have an unselected gray level value, whereby a binary pattern of gray level values are formed for the pixels in the predetermined pixel array of said video frame.

2. The video preprocessor in accordance with claim 1 wherein the one and at least one other selected pixel arrays within the predetermined pixel array are disjoint, one being an inner pixel array and the at least one other being the annulus pixel array of said inner pixel array within the predetermined pixel array.

3. The video preprocessor in accordance with claim 2 wherein the means for selecting the at least one gray level value includes:

means for subtracting the pixel distributions of corresponding gray level values of the histograms of the selected inner and annulus pixel arrays to form a composite histogram of gray level values;

means for identifying groups of consecutive gray level values of said formed composite histogram which have pixel difference values of one polarity;

means for selecting at least one identified group of consecutive gray level values which has a maximum pixel difference value with respect to the pixel difference values of said other identified groups; and

means for governing the assigning means based on said selected at least one identified group of consecutive gray level values.

4. The video preprocessor in accordance with claim 3 including means for extending the consecutive gray level values of the selected at least one identified group of consecutive gray level values by including all of the consecutively increasing and decreasing gray level values on either side of the selected at least one identified group which have a pixel difference value in the composite histogram of substantially zero.

5. The video preprocessor in accordace with claim 3 wherein the subtracting means subtracts the pixel distribution of the histogram formed for the selected annulus array from the pixel distribution of the histogram formed for the selected inner array in accordance with corresponding gray level values to form the composite histogram;

wherein the identifying means identifies the groups of consecutive gray levels which have positive pixel distribution difference values; and

wherein the selecting means selects the at least one identified group which has a maximum positive pixel distribution difference value.

6. The video preprocessor in accordance with claim 3 including means for testing the determined maximum pixel difference value against a predetermined threshold value;

and means, conditionally governed by the results of said testing means, to accumulate the pixels of the pixel distribution of the composite histogram starting at an initial gray level value and continuing consecutively through increasing gray level values until the accumulative number of pixels is greater than a predetermined number of pixels, the predetermined gray level value at said greater than occurrence being the selected gray level value for governing the assigning means.

7. The video preprocessor in accordance with claim 6 wherein the accumulating means accumulates pixels of the composite histogram starting at a zero predetermined gray level value and continuing consecutively through increasing predetermined gray level values until the accumulative number of pixels is greater than one-half the maximum number of pixels in the predetermined pixel array, the predetermined gray level value at said greater than occurrence being the selected gray level value for governing the assigning means.

8. A binary correlation video tracker including an electro-optical sensor for generating sequentially a plurality of frames of video gray level information of its field-of-view, an optical system operative to guide the line-of-sight of a predetermined target image to within the field-of-view of said sensor, and a tracking servo means, governed by at least one tracking error, to control the guidance of said optical system, said binary correlation video tracker further comprising:

means for forming a binary pattern of values for the picture elements (pixels) in a predetermined pixel array of each of said plurality of frames of video gray level information generated by said sensor, said forming means further including;

means for distributing the pixels of one selected pixel array within said predetermined pixel array of each of said video frames into corresponding first gray level histograms based on a predetermined set of gray level values;

means for distributing the pixels of at least one other selected pixel array within said predetermined pixel array of each of said frames into corresponding second gray level histograms based on said predetermined set of gray level values;

means for selecting at least one gray level value of said predetermined set for each frame of video gray level information based on a discriminant function of the respectively corresponding first and second gray level histogram distributions; and

means for assigning one of two predetermined values to selected pixels in said predetermined pixel array of each of said video frames said selected pixels having a selected gray level value corresponding to the video frame in which they are contained; and

for assigning the other of said two predetermined values to the unselected pixels in said predetermined pixel array of each of said video frames;

means for selecting a reference subarray binary pattern of pixels from the predetermined pixel array of one frame of video gray level information;

means for correlating the formed binary pattern of said reference subarray with the formed binary patterns of the predetermined pixel arrays of generated video frames subsequent said one frame based on a binary correlation coefficient function; and

means for generating said at least one tracking error based on the results of said binary pattern correlations of said correlating means.

9. A binary correlation video tracker in accordance with claim 8 wherein the correlating means includes means for cross-correlating the formed binary pattern of the reference subarray with formed binary patterns of other subarrays of the predetermined pixel array of another video frame, which is generated subsequent the one frame, to identify another reference subarray and position thereof in the predetermined pixel array of said another video frame, a position difference between the reference and another reference subarrays in the predetermined array being used to generate the at least one tracking error by the tracking means.

10. A binary correlation tracker in accordance with claim 9 wherein the correlating means further includes a means for autocorrelating the formed binary pattern of the reference subarray with the formed binary patterns of predetermined other subarrays in the predetermined array of the one video frame and for autocorrelating the formed binary pattern of the identified another reference subarray with the formed binary patterns of predetermined other subarrays of the predetermined pixel array of the same video frame;

and wherein for each video frame, a maximum autocorrelation value is rendered as a result of said autocorrelation.

11. A binary correlation tracker in accordance with claim 10 wherein all pixel subarrays are similar in area, the pixels being indexed commonly in each of the subarrays;

and wherein the autocorrelation and cross-correlations are performed by their respective means by comparing the binary values of respectively indexed pixels of the subarrays and accumulating dissimilarities as a measure of binary correlation.

12. A binary correlation tracker in accordance with claim 10 wherein all pixel subarrays are similar in area, the pixels being indexed commonly in each of the subarrays;

and wherein the autocorrelations and cross-correlations are performed by their respective means by comparing the binary values of respectively indexed pixels of the subarrays and accumulating similarities as a measure of binary correlation.