How do I compute coordinate of an image in Matlab?

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Alexander Killam
Alexander Killam on 10 Feb 2014
Edited: Thomas on 10 Feb 2014
I have an image. Lets say I call it bug...(It is an image of a small red bug with a white background). I want to be able to find the coordinates of where that bug is on matlab. I would like to be able to do this so that if I had another image in a different location I could track where the bug is in the new image. I am trying to learn matlab on my own so any in depth explanation would be greatly appreciated. Thank you very much!

Accepted Answer

Thomas
Thomas on 10 Feb 2014
Edited: Thomas on 10 Feb 2014
It really depends upon what you want. If you only want to track a single point, or a few points within your image series this can be done very easily with the image processing toolbox function impixel:
The following script will let you open up a series of JPEG files, and allow you to interactively identify single or multiple points of interest in each image. The image coordinates are output to a cell matching the order of the input images, coords.
% Open all images using dialogue box
[FileName,PathName] = uigetfile('.JPG', 'select image files','multiselect', 'on');
images = transpose(FileName);
% open each image and interactively define the point of interest using impixel
% store output in a cell (coords)
coords = cell(size(images,1),1);
for i = 1:size(images)
im = imread(strcat(PathName, images{i}));
[xi,yi,P] = impixel(im);
coords{i} = horzcat(xi,yi); % store xy coordinates from each point of interest
end
You may need to be more specific if you want something more sophisticated (i.e. to track all non white pixels.
Thomas
  3 Comments
Thomas
Thomas on 10 Feb 2014
Another route might be compute the barycentre of the non white pixels (i.e. identify each pixel where
im(:,:,1) < 255 || im(:,:,2) < 255 || im(:,:,3) < 255;
or set some other threshold and find their centre of mass). You would be including some of that fuzz around the bug into the calculation though.

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