Video correlation tracker

• US 4,133,004 A
• Filed: 11/02/1977
• Issued: 01/02/1979
• Est. Priority Date: 11/02/1977
• Status: Expired due to Term

• Current Assignee: Hughes Aircraft Company (Rtx Corporation)
• Original Assignee: Hughes Aircraft Company (Rtx Corporation)
• Inventors: Fitts, John M.
• Primary Examiner(s): Richardson, Robert L.
• Assistant Examiner(s): Coles, Edward L.
• Application Number:
  US05/847,866
• Time in Patent Office: 426 Days
• Field of Search: 358/125, 358/126, 244/3.16, 244/3.15, 250/203 R, 250/203 CT
• US Class Current: 348/169
• CPC Class Codes: G01S 3/043 Receivers
• CPC Class Codes: G01S 3/7865 using correlation of the live video image with a stored image

Abstract

A correlation tracker for generating correlation error tracking signals over an entire video frame. Video information from a scanning receiver is inputted into the correlation tracker in serial form. The correlation tracker first incorporates apparatus to generate a reference map in pixel format. Reference map pixel information for one video frame plus one video line is stored in a memory to allow the calculation of azimuth and elevation optimal weighting values for each pixel in the field of view. Each video pixel of data being received during the current frame is then summed with the corresponding reference map pixel from the prior frame and the result multiplied by the appropriate weighting function. Each resultant product is then combined in an accumulator to form azimuth and elevation correlation error signals which are composite indications of the frame-to-frame correlation over the entire field of view. The weighting factors for each pixel are also combined and accumulatively added over the entire image plane to form three adaptive scale factors at the end of each frame which are combined with the azimuth and elevation correlation error signals to eliminate cross-coupling and generate cross-coupling-free correlation error signals. Drift compensation may also be provided by combining the adaptive scale factors and several predetermined constants to recursively calculate a drift correction which when combined with the cross-coupling-free correlation error signals generates drift-free correlation error signals.

Claims

1. A correlation tracker for generating correlation tracking error signals said tracker having a receiver for receiving electromagnetic information from a scene to form an input signal having a plurality of sets of pixel values each set representing pixel data for one video frame, said correlation tracker comprising:

(a) a reference map generator for receiving said pixel values and generating a reference map having a plurality of reference map values corresponding to said pixel values;

(b) a weighting function generator coupled to said map generator for generating at least one weighting value for each pixel value;

(c) a scale factor generator coupled to said weighting function generator for combining the weighting values to form at least one pixel correlation scale factor and accumulating said pixel correlation scale factors to form at least one correlation scale factor for each video frame; and

(d) a correlation error signal generator coupled to said weighting function generator, to said scale factor generator, and to said map generator for generating at least one correlation error value from said reference map pixel values, said input signal pixel values, and said weighting function for each pixel and accumulating a plurality of said correlation error values which is scaled by one of said scale factors to form at least one correlation error signal for each video frame.

2. The correlation tracker of claim 1 further comprising a normalized error signal generator coupled to said scale factor generator and said correlation error signal generator whereby the value of said correlation error signal generated each video frame is multiplied by a function of said correlation scale factors to form at least one normalized correlation tracking error signal for each video frame.

3. The correlation tracker of claim 2 further comprising a drift compensator coupled to said normalized error signal generator and oriented to correct said normalized video error signals for one video frame as a function of the normalized video error signals from at least one prior video frame to generate at least one drift-free correlation tracker error signal for each video frame.

4. A correlation tracker for generating correlation tracking error signals said tracker having a receiver for receiving electromagnetic energy from an observed scene and generating therefrom a video signal V_ij (k) useful in sequentially energizing a plurality of pixels P_ij (k) on a display to sequentially form a plurality of frames of the observed scene thereon, said correlation tracker comprising:

6. The correlation tracker of claim 4 wherein said scale factor generator further comprises means for generating a cross-coupling scale factor Ced(k) where said cross-coupling scale factor is a measure of the negative of the cross-partial second derivative of the cross-correlation function between the reference map and the observation scene.

8. The correlation tracker of claim 4 wherein said weighting functions are generated according to the relationship ##EQU12## where Δ

e and Δ

d are the respective dimensions of the pixels of said display along said first and second directions.

9. The correlation tracker of claim 4 further comprising a normalized error signal generator coupled to said scale factor generator and said correlation error signal generator whereby a first normalized error signal δ

e'"'"' (k) is generated for frame k according to the relationship ##EQU13## and a second normalized error signal δ

d(k) is generated for frame k according to the relationship ##EQU14##

10. The correlation tracker of claim 4 wherein 1/w₁ is defined to be the number of frames of video input v_ij (k) which is effectively averaged in the reference map MAP_ij (k).

11. The correlation tracker of claim 4 wherein the initial reference map is MAP_ij (1/w₁) and is generated recursively according to the relation

12. The correlation tracker of claim 4 wherein the map generator memory means comprises a register means for storing the most recently generated (Ne+1) ×

Nd pixel values of the reference map MAP_ij in frames K-1 and k.

13. The correlation tracker of claim 4 wherein the map generator memory means comprises a random access memory for storing the most recently generated (Ne+1) ×

Nd pixel values of the reference map MAP_ij in frames k-1 and k.

14. The correlation tracker of claim 4 further comprising a normalized error signal generator coupled to said scale factor generator and said correlation error signal generator whereby a first normalized error signal δ

e'"'"'(k) is generated for frame k according to the relationship ##EQU15## and a second normalized error signal δ

d(k) is generated for frame k according to the relationship ##EQU16##

15. The correlation tracker of claim 13 further comprising a drift compensator coupled to said normalized error signal generator for generating a first essentially drift-free video error signal δ

e_corr (k) according to the relation

space="preserve" listing-type="equation">δ

e.sub.corr (k) = [δ

e'"'"'(k) + δ

e.sub.DR (k) ]

where δ

e_DR (k) is recursively generated according to the relation

space="preserve" listing-type="equation">δ

e.sub.DR (k) = δ

e.sub.DR (k-1) + w.sub.1 δ

e'"'"'(k-1)

and a second substantially drift-free video error signal δ

d_corr (k) according to the relation

space="preserve" listing-type="equation">δ

d.sub.corr (k) = [δ

d'"'"'(k) + δ

d.sub.DR (k)]

where δ

d_DR (k) is recursively generated according to the relation

space="preserve" listing-type="equation">δ

d.sub.DR (k) = δ

d.sub.DR (k=1) + w.sub.1 δ

d'"'"'(k-1).

16. The correlation tracker of claim 14 wherein the map generator memory means comprises a register means for storing the most recently generated (Ne+1) + Nd pixel values of the reference map MAP_ij in frames k-1 and k.

17. The correlation tracker of claim 14 wherein the map generator memory means comprises a random access memory for storing the most recently generated (Ne+1) ×

Nd pixel values of the reference map MAP_ij in frames k-1 and k.

19. The method of claim 17 comprising the further step of generating first and second normalized correlation error signals δ

e'"'"'(k) and δ

d'"'"'(k) for each image plane frame k according to the respective relationships ##EQU21##

20. The method of claim 17 wherein 1/w₁ is defined to be the number of frames over which V_ij (k) is effectively averaged to generate the reference map values MAP_ij (k).

21. The method of claim 17 wherein the initial reference map is defined to be MAP_ij (1/w₁) and is generated recursively according to the relation

22. The method of claim 17 further comprising the steps of compensating for drift in the ε

coordinate direction to generate a first drift-free correlation error signal δ

e_corr (k) according to the relation

space="preserve" listing-type="equation">δ

e.sub.corr (k) = [δ

e'"'"'(k) - δ

e.sub.DR (k)]

where δ

e_DR (k) is recursively generated according to the relation

space="preserve" listing-type="equation">δ

d.sub.DR (k) = δ

d.sub.DR (k-1) + w.sub.1 δ

d'"'"'(k-1)

and compensating for drift in the η

coordinate direction to generate a second drift-free video error signal δ

d_corr (k) according to the relation

space="preserve" listing-type="equation">δ

d.sub.corr (k) = [δ

d'"'"'(k) + δ

d.sub.DR (k)]

where δ

d_DR (k) is recursively generated according to the relation

space="preserve" listing-type="equation">δ

e.sub.DR (k) = δ

e.sub.DR (k-1) + w.sub.1 δ

e'"'"'(k-1).

23. The method of claim 21 wherein 1/w₁ is defined as the number of frames over which V_ij (k) is effectively averaged to generate the reference map values MAP_ij (k).

24. The method of claim 21 wherein the initial reference map is defined to be MAP_ij (1/w₁) and is generated recursively according to the relation

25. The method of claim 23 further comprising the step of removing drift corruption from said correlation error values to form a first and a second drift-free correlation error signal.

27. The method of claim 25 further comprising the steps of:

(a) generating an adaptive cross-coupling scale factor representative of the negative of the cross-partial second derivative in said first and second coordinate directions of the cross-correlation function between the reference map pixel values and video signal pixels summed over all pixels in said image plane; and

(b) normalizing said first and second correlation error values utilizing said first and second adaptive scale factor and said adaptive cross-coupling scale factors to eliminate cross-coupling components between said first and second correlation error values to form first and second normalized error signals.

5. (a) a map generator for receiving said video signal V_ij (k) for each pixel identified by an i location along a first direction and a j location along a second direction in each video frame k and recursively calculating a reference map MAP_ij (k) according to the relation

View Dependent Claims (7)

7. The correlation tracker of claim 5 wherein said scale factors Ce(k), Cd(k) and Ced(k) are generated according to the relation:

##EQU10## ##EQU11## where Ne is the total number of pixels to be correlated along the first direction and Nd is the total number of pixels to be correlated along the second direction.

18. The method of generating correlation tracking error signals from input electromagnetic video signals V_ij (k) utilized to form one video frame k of a two-dimensional image plane having coordinates (ε

,η

) where ε

represents the elevation and η

represents the azimuth said image plane defined by a plurality of pixels each having a discrete location (i,j) in the image plane along coordinates ε and

η

respectively, said method comprising the steps of;

(a) generating a reference map value for each pixel according to the relation

space="preserve" listing-type="equation">MAP.sub.ij (k) = (1-w.sub.1) MAP.sub.ij (k-1) + w.sub.1 V.sub.ij (k)

where w₁ is a weighting value having a value 0≦

w₁ ≦

1,

(b) storing at least one frame plus one line of reference map values MAP_ij ;

(c) generating a first optimal weighting function We_ij (k) according to the relation ##EQU17## where Δ

e is the dimension of each pixel in said image along the ε

coordinate;

(d) generating a second weighting function Wd_ij (k) according to the relation ##EQU18## where Δ

d is the dimension of each pixel in said image plane along the η

coordinate;

(e) generating first, second and third adapative scale factors for each image plane frame according to the relationships ##EQU19## where Ne is the maximum number of pixels along the ε

coordinate and Nd is the maximum number of pixels along the η

coordinate; and

(f) generating first and second correlation error signals Ee(k) and Ed(k) for each image plane frame accordingly to the respective relationships ##EQU20##

26. The method of generating correlation tracking error signals from input electromagnetic video signals V_ij (k) utilized to form one video frame k of a two-dimensional image plane having coordinates (ε

,η

) where ε

represents the elevation and η

represents the azimuth said image plane defined by a plurality of pixels each having a discrete location (i,j) in the image plane along coordinates ε and

η

respectively, said method comprising the steps of;

(a) providing a reference map value MAP_ij for each pixel representative of previous electromagnetic signals V_ij (k);

(b) storing at least one frame and one line of reference map values MAP_ij ;

(c) generating first and second weighting functions representative of the negative derivative of the reference map values in the ε and

η

coordinate directions respectively;

(d) generating first and second adaptive scale factors said adaptive scale factors being representative of the negative second derivative of the reference map in the ε and

η

coordinate directions respectively, between the reference map pixels and the video signal pixels summed over all pixels of said image plane;

(e) generating correlation error signals along said ε and

η

coordinates by generating the difference between the reference map pixel values and the video signal pixel values, multiplying that difference by the associated pixel weighting in said first coordinate direction to form a first set of error values and in said second coordinate direction to form a second set of error values, accumulating the members of said first set of error values over each video frame and dividing the result by said first adaptive scale factors to form a first correlation error value in said first coordinate direction and accumulating the members of said second set of error values over each video frame and dividing the result by said second adaptive scale factor to form a second correlation error value in said second coordinate direction.

28. The method of claim 26 further comprising the step of removing drift corruption from said normalized error signals to form a first and a second drift-free normalized error signal.