CODEWITHSUNDEEP
image-processingmatlab
Iancovici
Iancovici

Reputation: 5731

How can I use bwlabel or regionprops to extract set of pixels of each label?

I'm following this tutorial

The goal is to be able to spit out either: a. the center of each labeled object b. all pixels associated with each labeled object

in a way that I have an array of either 'a.' for each object, or 'b.' for each object

enter image description here

I'm really not sure how to go about this. Are there matlabl tools to help extract these set of pixels or centers - per - label?

Update

I did manage to circle 80% of what I wanted using reigionprops, however it doesn't capture label precisely, just sets a circle around them while capturing the background as well, is that really unavoidable? I'm just not sure how to access the set of pixel per each circled item.

r=regionprops(L, 'All'); imshow(imagergb); areas={r.Area}; Bboxes={r.BoundingBox};
for k=2:numel(r)
    if areas{k}>50 && areas{k} < 1100 
        rectangle('Position',Bboxes{k}, 'LineWidth',1, 'EdgeColor','b', 'Curvature', [1 1]); 
    end
end

So what I'm trying to do is for example.
enter image description here

I thought it might just be

r = regionprops(L, 'PixelIdxList')

then 

element1 = r(1).PixelIdxList

but couldn't figure out how to get the position of each pixel

I also tried 

Z= bwlabel(L);

but imshow(Z==1) spits out all labels and imshow(Z==2) spits out background, all labels and background. couldn't test bwlabeln since I'm not exactly sure what to enter for r and c arguments.

Upvotes: 3

Views: 7837

Answers (1)

buzjwa
buzjwa

Reputation: 2652

Using regionprops(L, 'PixelIdxList') is correct. It gives you lists of pixel indices for each label. You can then convert them to [x,y] coordinates using (for the first label, for example)

[y,x] = ind2sub(size(L), r(1).PixelIdxList)

You can get label centers by using regionprops(L, 'Centroid'). This already gives you [x,y] coordinates for each label. Note that these are subpixel coordinates, so you may need to round them if you want to use them as indices.

Upvotes: 4

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