3d Morphological operations (erosion, dilation)

[Anand]

Hi,

How can we perform erosion adn dilation operations in 3d in matlab?
Are there any functions in matlab to perform erosion and dilation of a
3d image? If then, what are they?

Thanks,
Anand.

[Peter Bone]

I don't think there are any functions for this but maybe you can do the morphological operation on each xy layer of the 3D matrix and then do it again on each xz layer. That may not work very well though because it would erode twice in places.

[Steve Eddins]

Almost all of the morphological functions in the Image Processing
Toolbox can work in any number of dimensions. Use imdilate and imerode.

--
Steve Eddins
http://blogs.mathworks.com/steve

[Dahai]

Beautiful. I googled and found this answer, and---It worked. ---
Very useful as I am a CT person.
Thanks.
DX

[Dahai]

Well, no quite. After a careful inspection of the resulting image, it is obvious that the dilation only worked on (x,y) slices, and did not work through z direction, even though my strel is [1 1 1;1 1 1;1 1 1], a cube. How can we deal with that?

Thanks. DX

[Matt]

"Dahai " <daha...@merck.com> wrote in message <h9e31e$e5l$1...@fred.mathworks.com>...

> Well, no quite. After a careful inspection of the resulting image, it is obvious that the dilation only worked on (x,y) slices, and did not work through z direction, even though my strel is [1 1 1;1 1 1;1 1 1], a cube. How can we deal with that?

Is it binary erosion? If so, you can get the equivalent by doing

result = convn(logical(A),[1 1 1;1 1 1;1 1 1]/9,'same')>=1

Since [1 1 1;1 1 1;1 1 1] is also separable, you can accelerate computation, possibly, by doing the convolution separably.

[Bruno Luong]

Try this:
http://www.mathworks.com/matlabcentral/fileexchange/24705

Bruno

[Steve Eddins]

[1 1 1;1 1 1;1 1 1] is a square strel, not a cube. ones(3,3,3) is a cube.

>> a = zeros(3,3,3);
>> a(2,2,2) = 1
a(:,:,1) =
0 0 0
0 0 0
0 0 0
a(:,:,2) =
0 0 0
0 1 0
0 0 0
a(:,:,3) =
0 0 0
0 0 0
0 0 0
>> imdilate(a,ones(3,3,3))
ans(:,:,1) =

1 1 1
1 1 1
1 1 1

ans(:,:,2) =

1 1 1
1 1 1
1 1 1

ans(:,:,3) =

1 1 1
1 1 1
1 1 1

---
Steve Eddins
http://blogs.mathworks.com/steve/

[Dave]

"Anand" <suresh...@gmail.com> wrote in message <1158850263.0...@m7g2000cwm.googlegroups.com>...

On top of Steve's solution, I just wanted to share a quick method for getting a BW-compatible ball element, since strel's built-in one seems to be completely incompatible with logical/BW.

[xgrid, ygrid, zgrid] = meshgrid(-radius:radius);
ball = (sqrt(xgrid.^2 + ygrid.^2 + zgrid.^2) <= radius);

This gives you a 3-d ball matrix of any size.