``morpholog. gradient'' -- morphological gradient

purpose:

Calculate the morphological gradient, a measure of edge strength, for the voxels in a grayscale volume [25]. The specific operation done here is the following:

where volume is the input volume, local average refers to the (pseudo) lowpass filtering operation of local averaging, and local max/min refer to the operation of local maximum/minimum.

The ``local average'' step is optional. If left out, the morphological gradient reduces to

input:

An 8-bit grayscale volume.

output:

An 8-bit grayscale volume.

parameters:

Default parameters menu is

x filter dim = 3
y filter dim = 3
z filter dim = 3
function = unsmoothed
threshold = 0
input from vol # = 0
copy output to vol # = 0

The ``function = unsmoothed'' option does not use the local average before doing the maximum or minimum operations; the option ``function = smoothed'' does.

The parameter ``threshold = '' can be used to zero out points will small morphological gradient.

comments:

1. A moderate speed function, much faster than the Kirsch and difference-of-Gaussians operations.
2. Using the ``smoothed'' option (i.e., using the local averaging before the max or min) gives smoother results.
3. The gradient values are semi-comparable to the Kirsch operator. The Kirsch operator is more directionally focused and will give larger gradient values at edges.

Updated: Fri May 19 14:39:07 CDT