bwboundaries : missing coordinates of one of the two borders of my image

HI,

I have a problem with the function bwboundaries. When I use it with a black and white image (containing 2 pores), I can extract only the coordinates of a single border (whereas I have two). The plot gives me two disctinct border.

How can I have the coordinates for both borders?

I put the short code and the picture below.

Thank you

Image = imread('GDgeoRE2.bmp');
I     = im2bw(Image);
Ifill = imfill(I,'holes');
B = bwboundaries(Ifill);
for k = 1:length(B)
    b = B{k};
    plot(b(:,1),b(:,2),'r','linewidth',2);
end

c1  = downsample(b(:,1),1);
c2  = downsample(b(:,2),1);

disp(b)
disp(c1)
disp(c2)

Answer 1

[Guillaume]

The problem has nothing to do with bwboundary. The problem is with you calling plot in a loop without hold on, so each time you call plot it erases the previous plot. Hence you're left with just the last boundary plot.

figure;
hold on;
for k = 1:length(B)
    b = B{k};
    plot(b(:,1),b(:,2),'r','linewidth',2);
end

would fix that.

[Ad Mo]

Hi Guillaume,

Thank you for your awnser.

That's true (I forgot to put it in the copied code).

My problem can be solved in the same way I think. Indeed, B{k} erases the previous coordinates.

I need to add a loop like

v=[]
for h=1:length(B)
    v=[v,B{h}]
end

[Guillaume]

I don't really understand what you are saying.

You could indeed concatenate all the boundaries into one array and plot it all at once but you'll get a line linking all the boundaries.

The concatenation can be done more efficiently without a loop:

v = [B{:}];

[Ad Mo]

Guillaume,

It works well.

Thank you very much