How to track the object using centroid ?

I need to track the object in a video using centroid. By calculating the centroid of the object in different frames, I'll be able to track the object and get the count. I'm new to matlab and guide me in completeing the task

Answer 1

[Walter Roberson]

regionprops() with the Centroid option.

You may need to convert the image to grayscale or binary first.

[aarthi ramasamy]

I have already converted it to binary image but the centroid portion is alone the problem here.

    clc
clear all
n=0;
% Read movie 
SF = 1; %Starting Frame
MV = mmreader('r2.avi'); %To read Movie
EF = MV.NumberofFrames ; %Ending Frame
img = read(MV,1); %reading particular frame 
A = double(rgb2gray(img)); %motion vector works on Gray Image formate
[height width] = size(A); %Movie size?
% motion estimation 
 h1 = figure(1);
for f = SF: EF %Frame from SF To EF
    B = A; 
    img = read(MV,f);
    A = double(rgb2gray(img)); 
    %Foreground Detection
    thresh=11;
    fr_diff = abs(A-B);
    for j = 1:width
        for k = 1:height
        if (fr_diff(k,j)>thresh)
            fg(k,j) = A(k,j);
        else
                    fg(k,j) = 0;
        end
        end
    end
    subplot(2,2,1) , imagesc(img), title (['Orignal Sequence Frame#',int2str(f)]);
    subplot(2,2,2) , imshow(mat2gray(A)), title ('Previous Frame');
    subplot(2,2,3) , imshow(mat2gray(B)), title ('Next Frame');
    sd=imadjust(fg);
    level=graythresh(sd);
    m=imnoise(sd,'gaussian',0,0.025);
    k=wiener2(m,[5,5]);
    bw=im2bw(k,level);
    bw2 = bwareaopen(bw, 20, 8);
    b1= imdilate(bw2, ones(1, 1, 5));
    b2=imfill(b1,'holes');
   % [labeled,numObjects] = bwlabel(bw,4);
   % n=n+numObjects;
    subplot(2,2,4) , imagesc(b1), title (['Foreground #',n]);
    hold off;
    %pause (.1);
% saveas(h1,strcat('Result-Paris-',num2str(f)),'jpg');
end
disp(n);

The above stated is my code. I don't know how to proceed further. My objective is to track the different objects and count it. I terribly need the guidance/code.

[Walter Roberson]

At the point where you have the commented bwlabel,

[labeled, numObjects] = bwlabel(b2, 4);
blobinfo = regionprops(labeled, 'Centroid');

now blobinfo(1).Centroid is the first centroid

[Image Analyst]

% Extract all centroids for all blobs in a 1D list.
allBlobCentroids = [blobinfo.Centroid];
% From that list, extract out the x and y coordinates of the centroids.
centroidsX = allBlobCentroids(1:2:end-1);
centroidsY = allBlobCentroids(2:2:end);

[Walter Roberson]

Alternately,

allBlobCentrods = vertcat(blobinfo.Centroid);

would produce a numObjects x 2 array, first column x, second column y.

[aarthi ramasamy]

Thanks for your guidance Mr.Roberson . How to track the object using this centroid? I can clearly get the centroid of the objects in the different frames but applying this for tracking makes a problem here. What if there are two objects present in a single frame itself?

[Walter Roberson]

More than one object present in a single frame must be expected for your application.

When objects are sufficiently separated and exist separated for multiple frames, you can form a velocity estimate by associating the updated centroid positions with the nearest previous centroid position. Then when the objects come close together, instead of necessarily updating with the nearest previous centroid, you could do a position prediction based upon the velocities in order to try to figure out which of the close objects came from where.

[aarthi ramasamy]

Mr.Roberson,I can get your idea but coding seems to be difficult part here. Do you mind giving me the code? It will be of great use to us like beginners. Kindly help us

[Walter Roberson]

Yes, I do mind giving you the code, as what you are asking for is a common homework project for computer courses.

[aarthi ramasamy]

Thanks Mr. Roberson for your kind replies

[suppy]

hi sir.. i am very much new to matlab.. i need the code for moving object tracking and its velocity determination.

[Image Analyst]

suppy ask your own question and I will supply my demo program that tracks a green object in a video.

[Thomas Koelen]

Suppy posted this in 2013 Image Analyst:P

[Image Analyst]

Oh - didn't notice. For some reason this showed up on the page of 50 most current postings. Sometimes that can happen if someone (like a spammer) replied and then it got deleted - it will show up on the current list even though the posting that got it there has now been deleted.