Centroid of alot of images in a single run?

A have 100 images(frames) of an object moving in a video. I know how to find centroid of a single image. But when I try a loop to find centroid of these 100 images, it doesn't work. Help please!

[Hamza Ahmed]

I used to find centroid of a single image. My area of interest was in black color.

Code for centroid of single image:

I = imread('images\img1.jpg');

Ibw = im2bw(I2);

Ibw = imfill(Ibw,'holes');

Ilabel = bwlabel(Ibw);

stat = regionprops(~Ilabel,'centroid');

imshow(I2); hold on;

for x = 1: numel(stat)

      plot(stat(x).Centroid(1),stat(x).Centroid(2),'ro');

end

[Geoff Hayes]

Hamza - what have you tried for looping over the 100 images? When you say it doesn't work, what exactly is the problem? Please post your code and describe the errors or unexpected behaviour that you have observed.

[Hamza Ahmed]

Geoff - this is the portion of code which is giving me trouble:

 %Cropping all the pictures and saving them (again in working directory)

 for ii = 1:length(sortedImageNames)

      img = imread(fullfile(workingDir,'images',sortedImageNames{ii}));

      imgc = imcrop(img, rect);

      %Attempt to find centroid of each cropped image.

      Ibw = im2bw(imgc);

      Ibw = imfill(Ibw,'holes');

      Ilabel = bwlabel(Ibw);

      stat = regionprops(~Ilabel,'centroid');

      imshow(imgc); hold on;

      for x = 1: numel(stat)
          plot(stat(x).Centroid(1),stat(x).Centroid(2),'ro');
      end

      % Write out to a JPEG file
      imwrite(imgc,fullfile(workingDir,'images',sprintf('imgc%d.jpg',ii)));

 end

Problem: This just gives me all the cropped frames from the video in my working directory. I wanted the centroid to show on every single cropped image. Can you kindly see where i'm making the error? Thanks

Answer 1

[Image Analyst]

That won't work. You're not finding the centroid of the entire frame, but of all the various objects in the frame. I have no idea what I2 is - what is it? What I would do is

grayImage = read(videoObject, frameNumber);
[rows, columns, numberOfColorChannels] = size(grayImage);
if numberOfColorChannels > 1
  grayImage = rgb2gray(grayImage);
end
mask = true(rows, columns);
measurements = regionprops(logical(mask), grayImage, 'WeightedCentroid');

This will give you the centroid of the entire frame instead of just whatever blobs happened to get thresholded.

[Hamza Ahmed]

Dear image analyst - Sorry for the mistake. Just replace I2 with I.

Now, I don't want to find the centroid of the entire frame. The code I gave with my question works like charm to give me the centroid I require. But it only works on a single image ofcourse. I want this code to find the centroid of all the frames in the video and save the frames in a folder. I tried a looping situation:

%Cropping all the pictures and saving them (again in working directory)

for ii = 1:length(sortedImageNames)

    img = imread(fullfile(workingDir,'images',sortedImageNames{ii}));
    imgc = imcrop(img, rect);
%Attempt to find centroid of each cropped image.

Ibw = im2bw(imgc);

Ibw = imfill(Ibw,'holes');

Ilabel = bwlabel(Ibw);

stat = regionprops(~Ilabel,'centroid');

imshow(imgc); hold on;

for x = 1: numel(stat)

    plot(stat(x).Centroid(1),stat(x).Centroid(2),'ro');
end
    % Write out to a JPEG file
    imwrite(imgc,fullfile(workingDir,'images',sprintf('imgc%d.jpg',ii)));
end

 But this just gives me all the cropped frames from the video in my working directory. I wanted the centroid to show on every single cropped image aswell. Can you kindly see where i'm making the error? Thanks

[Hamza Ahmed]

And I see why you thought I wanted centroid of the entire image, it was mentioned in my question like that. I was actually thinking of the centroid of the moving object in that image, my bad.

[Image Analyst]

For a series of separate images, see the FAQ for sample code snippets: http://matlab.wikia.com/wiki/FAQ#How_can_I_process_a_sequence_of_files.3F

For a video file, see my attached demo file.