What units is the number in strel('disk', 22)?

dilated = imdilate(ImagetoDilate,strel('disk', 22));

I have this line in my code to dilate the image, but I was wondering what units the 22 is? It says it is the radius but is it measured in centimeters, percentage, pixels or something else?

Answer 1

[Walter Roberson]

Pixels.

Or more correctly, memory locations, as the result is used in multiple contexts and makes no attempt to handle multiple color planes.

[Guillaume]

You can easily look at the structuring element

>> s = strel('disk', 22)
s = 
strel is a disk shaped structuring element with properties:

      Neighborhood: [43×43 logical]
    Dimensionality: 2

and you can see that the disk overlaps 43x43 pixels.

As for it being a disk:

>> imagesc(s.Neighborhood); colormap([0 0 0; 0.8 0.8 0.8]); axis('off')