morphological opening of volumetric data.

i understand the concept of opening of 2D binary images but never used such opening on volumetric date as in the code below. please explain

nhood = ones([3 3 3]); 
bw = imopen(bw,nhood); % bw is binary volumetric MRI data (28 slices)

Answer 1

[Image Analyst]

What's your question? A morphological opening is a local min followed by a local max. If you have a question, please ask it.

[Muhammad Shoaib]

if i create a structure element of ones(3), ones([3 3]) this mean it has three row and three columns but in the code it is ones([3 3 3]) one 3 for number of rows the other for number of columns and remaining 3 is for ?

[Muhammad Shoaib]

waiting for an answer . . .

[Image Analyst]

The remaining 3 is the number of "planes" or "slices" in the third dimension. For an analogy, the first two would describe a sheet of paper 3 cm wide by 3 cm long, and the next 3 would mean that there are 3 sheets of paper stacked on top of each other in the third, or "z", direction. So essentially you're telling it to look at every one of the 27 voxels in a 3-by-3-by-3 cube. If you set any of those voxels to 0 or false, then it would tell it so skip considering that/those voxel(s) when computing the local min and local max.

Answer 2

[Thorsten]

For 3D data you need a 3D morphological structuring element, given by a 3D matrix. You create a block of ones of height, width and depth = 3 using

ones([3 3 3])