AUTOMATIC VIDEO CONTRAST TRACKER

• US 3,829,614 A
• Filed: 01/22/1973
• Issued: 08/13/1974
• Est. Priority Date: 02/11/1970
• Status: Expired due to Term

• Current Assignee: Sten H. Ahlbom, Sture J.H. Hansson
• Original Assignee: Sten H. Ahlbom, Sture J.H. Hansson
• Inventors: Ahlbom, Sten H., Hansson, Sture J. H.
• Primary Examiner(s): Britton, Howard W.
• Assistant Examiner(s): Masinick, Michael A.
• Application Number:
  US05/325,814
• Time in Patent Office: 568 Days
• Field of Search: 178/6.8,DIG.20,DIG.21 250/23CT
• US Class Current: 348/170
• CPC Class Codes: G01S 3/7864 T.V. type tracking systems
• CPC Class Codes: G01S 3/7865 using correlation of the live video image with a stored image

Abstract

In a video tracker, each scan line is broken into a predetermined number of uniform short segments. An electronic tracking window thus comprises a matrix of data points, each a line segment, and its edges are on coordinates defined by data points. Video signal content of each line segment in the window area is digitized by comparison to automatically adjustable reference level signals and generation of either a '"'"''"'"''"'"''"'"'one'"'"''"'"''"'"''"'"' or a '"'"''"'"''"'"''"'"'zero'"'"''"'"''"'"''"'"' bit, depending upon relationship of video signal content to reference levels. For each frame scanned, data points in the window are compored, set by set, with a bit pattern preselected for best correspondence to target configuration, comparisons being made sequentially across and down the window. A correlation number is obtained for each comparison. Location and value of the highest correlation number for each scan is stored and used for tracking.

Claims

1. Method of tracking a moving object with the use of an electro-optical sensor that makes a line-by-line and frame-byframe scan of a field of view and produces a video signal for each scanned line that has a varying magnitude along the line, and wherein such video signals are utilized to produce an output signal that corresponds to the position of an object being tracked relative to a selected point in the field of view of the sensor, which output signal can be used to maintain the axis of the sensor aligned on the object, said method being characterized by:

A. generating a timing signal which is synchronized to the beginning of each line scan and which defines a succession of time intervals of uniform duration, each substantially shorter than the time required to scan a line and thus corresponding to a segment of a scanned line;

B. by reference to the timing signal, defining a rectangular window having a height of a predetermined number of lines and a width of a predetermined number of line segments and which window is smaller than the total scanned field of view but is large enough to assure that those portions of the video signals that connote locations within the window include all information signifying the object;

C. digitizing the information in those portions of the video signals that connote locations within the window by producing, during each of said time intervals that occur during said portions of the video signals, 1. a signal information bit of one binary value when the video signal has a magnitude during the time interval that is outside a predetermined reference magnitude range, and 2. a signal information bit of the other binary value when the video signal has a magnitude during the time interval that is within said range;

D. temporarily storing the binary signal information bits produced during the scanning of a succession of lines, with the stored bits arranged in an order that is related to the location in the window that each bit connotes;

E. defining a reference pattern of binary bits that corresponds at least approximately to a digitized image of the object;

F. making a sequence of comparisons between said reference pattern and the stored signal information bits, taking the latter set by set, and for each such comparison that has meaning issuing 1. a correlation signal that signifies the ratio of agreement between the compared signal information bit set and the reference pattern, and 2. a location signal signifying the location within the window of the set being compared;

G. temporarily preserving information concerning the highest ratio correlation signal obtained for each sequence of comparisons and the location within the window connoted by the set of signal information bits for which that correlation signal was obtained; and

H. producing an output signal that corresponds to the last mentioned location.

2. filter means for producing a binary bit signal of one signification for each such segment having a signal magnitude that is within a predetermined range of magnitudes and for producing a binary bit signal of the other signification for each such segment having a signal magnitude lying outside said predetermined range of magnitudes;

C. a plurality of binary memory cells, there being at least as many such memory cells as there are binary data bits in a predetermined pattern of binary bit signals that corresponds to the image of the target object;

D. a plurality of serially connected shift register banks connected with said digitizing means to have binary bit signals fed therethrough sequentially,

3. In apparatus which produces a substantially continuous signal of varying magnitude for each line of a field of view being scanned in a line-by-line, frame-by-frame sequence, means for detecting, during each sequence, those portions of said signals which correspond to a target object within the field of view that has a predetermined pattern and for thereby determining the position of that target object relative to a selected point in the field of view, said means comprising:

A. gate means to which said signals are fed and by which only those portions of said signals are passed that correspond to a selected rectangular window area within the field of view, which area is substantially smaller than the field of view but large enough to encompass the target object;

B. means connected with said gate means for digitizing the portions of said signals that pass the gate means, comprising

4. The apparatus of claim 3, wherein said filter means comprises:

a. average formator means to which said signals are fed and which produces an output having a magnitude that substantially corresponds to the average value of said signals;

b. first adder means connected to receive as an input the output of said average formator means and which is also connected to receive as an input an incremental signal having a predetermined augmenting magnitude, to produce an output signal corresponding to an upper level of said range of magnitudes;

c. second adder means connected to receive as an input the output of said average formator means and which is also connected to receive as an input a decremental signal having a predetermined magnitude and of sign opposite to that of the output of the average formator means, To produce an output signal corresponding to a lower level of said range of magnitudes;

d. first comparator means having an input to which the output of the first adder means is fed and having another input to which at least said portions of said substantially continuous signals are fed, and the output of which is an intermittent signal of constant magnitude corresponding to those parts of said continuous signal portions that have a magnitude which is above said range of magnitudes; and

e. second comparator means having an input to which the output of the first adder means is fed and having another input to which at least said portions of said substantially continuous signals are fed, and the output of which is another intermittent signal of constant magnitude, having the same sign as the first mentioned intermittent signal, which other intermittent signal corresponds to those parts of said continuous signal portions that have a magnitude which is below said range of magnitudes.