how to implement optical flow to get center of moving object

I am working on video segmentation using optical flow technique with horn suchunk method.

i tried code available on site given below function [u, v] = HS(im1, im2, alpha, ite, uInitial, vInitial, displayFlow, displayImg) % Horn-Schunck optical flow method % Horn, B.K.P., and Schunck, B.G., Determining Optical Flow, AI(17), No. % 1-3, August 1981, pp. 185-203 http://dspace.mit.edu/handle/1721.1/6337 % % Usage: % [u, v] = HS(im1, im2, alpha, ite, uInitial, vInitial, displayFlow) % For an example, run this file from the menu Debug->Run or press (F5) % % -im1,im2 : two subsequent frames or images. % -alpha : a parameter that reflects the influence of the smoothness term. % -ite : number of iterations. % -uInitial, vInitial : initial values for the flow. If available, the % flow would converge faster and hence would need less iterations ; default is zero. % -displayFlow : 1 for display, 0 for no display ; default is 1. % -displayImg : specify the image on which the flow would appear ( use an % empty matrix "[]" for no image. ) % % Author: Mohd Kharbat at Cranfield Defence and Security % mkharbat(at)ieee(dot)org , http://mohd.kharbat.com % Published under a Creative Commons Attribution-Non-Commercial-Share Alike % 3.0 Unported Licence http://creativecommons.org/licenses/by-nc-sa/3.0/ % % October 2008 % Rev: Jan 2009

%% Default parameters if nargin<1 nargin<2 im1=imread('1.jpg'); im2=imread('52.jpg'); end if nargin<3 alpha=1; end if nargin<4 ite=100; end if nargin<5 nargin<6 uInitial = zeros(size(im1(:,:,1))); vInitial = zeros(size(im2(:,:,1))); elseif size(uInitial,1) ==0 size(vInitial,1)==0 uInitial = zeros(size(im1(:,:,1))); vInitial = zeros(size(im2(:,:,1))); end if nargin<7 displayFlow=1; end if nargin<8 displayImg=im1; end

%% Convert images to grayscale if size(size(im1),2)==3 im1=rgb2gray(im1); end if size(size(im2),2)==3 im2=rgb2gray(im2); end im1=double(im1); im2=double(im2);

im1=smoothImg(im1,1); im2=smoothImg(im2,1);

tic;

%% % Set initial value for the flow vectors u = uInitial; v = vInitial;

% Estimate spatiotemporal derivatives [fx, fy, ft] = computeDerivatives(im1, im2);

% Averaging kernel kernel_1=[1/12 1/6 1/12;1/6 0 1/6;1/12 1/6 1/12];

% Iterations for i=1:ite % Compute local averages of the flow vectors uAvg=conv2(u,kernel_1,'same'); vAvg=conv2(v,kernel_1,'same');

    % Compute flow vectors constrained by its local average and the optical flow constraints
    u= uAvg - ( fx .* ( ( fx .* uAvg ) + ( fy .* vAvg ) + ft ) ) ./ ( alpha^2 + fx.^2 + fy.^2); 
    v= vAvg - ( fy .* ( ( fx .* uAvg ) + ( fy .* vAvg ) + ft ) ) ./ ( alpha^2 + fx.^2 + fy.^2);
end

u(isnan(u))=0; v(isnan(v))=0;

%% Plotting if displayFlow==1 plotFlow(u, v, displayImg, 5, 5); end

i only get the u,v motion values, how to get center of moving object in video. pls help out. Dimple