How can I separate objects with one pixel connected after bwlabel

Hi,

I am using bwlabel to label the objects with defined connectivity after edge detection algorithm. But sometimes I encountered the objects are connected with only one pixel. How could I efficiently separate them?

Below is one example of a binary image I want to detect objects. I chose connectivity 4 to detect the objects when using bwlabel

obj_label = bwlabel(BW, 4);

Actually these two are seperate objects that I want, but the one pixel between make them difficult to label when using bwlabel.

Appriciate a lot if any suggestions are provided.

Answer 1

[DGM]

Depending on what the rest of the blobs look like, this may be one way.

% fix the image and return it to what I assume the original size was
[A,map,~] = imread('https://www.mathworks.com/matlabcentral/answers/uploaded_files/974265/image.png');
A = rgb2gray(ind2rgb(A,map))>0.5;
A = imresize(A,[30 30],'nearest');
imshow(A)

% remove foreground pixels which have at least two 
% unconnected BG pixels in their 8-neighborhood
B = ~bwmorph(~A,'bridge');
imshow(B)

[Zuhui Wang]

Thank you DGM, that's a very nice solution for this problem. Good to learn how to use bwmorph :D

Answer 2

[Matt J]

load BW

L=watershed(-bwdist(~BW));

BW=BW&L~=0;

imshow(BW)

[Zuhui Wang]

Thanks Matt, watershed is also working well in this situation.

Answer 3

[Image Analyst]

You could try imopen() or watershed().

For a thorough discussion, see Steve's blog:

Watershed transform question from tech support » Watershed transform question from tech support

Marker-Controlled Watershed Segmentation - MATLAB & Simulink Example

[Zuhui Wang]

Thanks! Will check them out.

[Matt J]

Seems hard to find a strel that will make imopen work well here.