Video - Boundary Tracing

The MATLAB toolbox includes two functions you can use to find the boundaries of objects in a binary image:

• bwtraceboundary
• bwboundaries

The bwtraceboundary function returns the row and column coordinates of all the pixels on the border of an object in an image. You must specify the location of a border pixel on the object as the starting point for the trace.
The bwboundaries function returns the row and column coordinates of border pixels of all the objects in an image. For both functions, the nonzero pixels in the binary image belong to an object and pixels with the value 0 (zero) constitute the background.

The code:

clear all
close all
clc;
disp('Testing Purposes Only....');
%fin = 'sampleVideo.avi';
fin = 'smallVersion2.avi';
fout = 'test2.avi';
avi = aviread(fin);


% Convert to RGB to GRAY SCALE image.
avi = aviread(fin);
pixels = double(cat(4,avi(1:2:end).cdata))/255; %get all pixels (normalize)

nFrames = size(pixels,4); %get number of frames
for f = 1:nFrames
pixel(:,:,f) = (rgb2gray(pixels(:,:,:,f))); %convert images to gray scale
end
rows=128;
cols=160;
nrames=f;
for l = 2:nrames

%edge detection
edgeD(:,:,l) = edge(pixel(:,:,l),'canny');
g(:,:,l) = double(edgeD(:,:,l));

%subtract background
d(:,:,l)=(abs(pixel(:,:,l)-pixel(:,:,l-1))); %subtract current pixel from previous

%convert to binary image
k=d(:,:,l);
bw(:,:,l) = im2bw(k, .2);
bw1=bwlabel(bw(:,:,l));

%By default, bwboundaries finds the boundaries of all objects in an image
BW_filled = imfill(bw(:,:,l),'holes');
boundaries = bwboundaries(BW_filled);

imshow(pixel(:,:,l));

hold on
for k=1:10
b = boundaries{k};
plot(b(:,2),b(:,1),'g','LineWidth',3);
end
drawnow;
hold off

end

Results: