Find the centroid of images after real time tracking.

Hello! I would like to find the centroid formed by three markers (red colored) after tracking them. I got the available code that plots the x,y co-ords of each of these markers successfully. I have added a loop to calculate the mean of these co-ordinates to find the centroid formed by these three markers. I am not able to plot it plzz help!

imaqreset

 vid = videoinput('winvideo',1,'MJPG_640x360');
 set(vid,'FramesPerTrigger',Inf);
 set(vid, 'ReturnedColorSpace','rgb');

 vid.FrameGrabInterval =5; x=0; y=0; mx=0; my = 0;

 start(vid);

   while (vid.FramesAcquired<=200)
   data = getsnapshot(vid);

diff = imsubtract(data(:,:,1),rgb2gray(data));

diff = medfilt2(diff, [3 3]);

diff = im2bw(diff, 0.18);

diff = bwareaopen(diff , 300);

bw = bwlabel(diff , 8);

stats = regionprops(bw, 'BoundingBox', 'Centroid');

imshow(data)

hold on

for object = 1:length(stats)

bb = stats(object).BoundingBox;

bc = stats(object).Centroid;

rectangle('Position',bb,'EdgeColor','r','LineWidth',2)

plot(bc(1),bc(2), '-m+')

a=text(bc(1)+15,bc(2), strcat('X: ', num2str(round(bc(1))), ' Y: ', num2str(round(bc(2)))));

set(a, 'FontName', 'Arial', 'FontWeight', 'bold', 'FontSize', 12, 'Color', 'yellow');

x = x + round(bc(1));

y = y + round(bc(2));

mx = x/3;

my = y/3;

b = text(mx , my , strcat('XC:',round(mx) , 'XY:',round(my))); set(b, 'FontName', 'Arial', 'FontWeight', 'bold', 'FontSize', 16, 'Color', 'white');

end

hold off

end

[Image Analyst]

Please read this and fix your code: http://www.mathworks.com/matlabcentral/answers/13205-tutorial-how-to-format-your-question-with-markup

Answer 1

[Image Analyst]

You don't need a loop to find the means of the blobs. You can do it this way

centroids = [stats.Centroid]; % Make into 2 D array.
xCentroids = mean(centroids(:,1)); % Get x centroid for every blob, if you need that.
yCentroids = mean(centroids(:,2)); % Get y centroid for every blob, if you need that.
% Get mean of all the blobs
meanX = mean(xCentroids);
meanY = mean(yCentroids);

Of course if you want to plot blob-specific things like the bounding box, centroid, a text label, etc., then that part needs to be in a loop. You can use xCentroids and yCentroids inside the loop (if you do the above code before the loop starts) to make it simpler.

[Emmanuel]

Thanks!!! If I want to show the centroid using text command will

b=text(xCentroids, yCentroids), strcat('X: ', num2str(round(xCentroids)),'Y: ', num2str(round(yCentroids))));

set(b, 'FontName', 'Arial', 'FontWeight', 'bold', 'FontSize', 10, 'Color', 'white'); do?

[Image Analyst]

Lekha's "Answer" moved here since it's not an answer to the original question:

And I tried this out , but its showing the same value of a x,y co-ordinate of the object and not the mean of three co-ords

[Image Analyst]

It will plot those individual coordinates unless you delete the call to plot that plots them. Did you put in a call to plot(xMean, yMean)? It won't show that unless you explicitly call plot to tell it to show the centroid.