``Sigma'' - sigma filter

VFX name:

iSigma

IMPROMPTU Equivalent:

Sigma

purpose:

Run the sigma filter on an input volume [17]. The filter smooths noise, preserves edges, and can leave thin lines untouched.

For each voxel in the input volume, the filter calculates the mean value of a set of voxels within 2$\times sigma$ graylevel values of the voxel of interest. Only voxels within a prespecified local neighborhood are considered in this calculation. If too few points within the local neighborhood lie within the 2$\times sigma$ range, then the voxel of interest is left unchanged; otherwise, the calculated mean value is assigned to the voxel.

input:

An 8-bit volume.

output:

An 8-bit volume.

parameters:

Default parameters menu is

x_filter_dimension = 3
y_filter_dimension = 3
z_filter_dimension = 3
standard_deviation = 20
iterations = 1

The parameter ``standard_deviation'' is the parameter sigma (in graylevels) mentioned above.

comments:

1.

This filter is good at saving thin lines.

2.

The SNN or maximum-homogeneity filters may reduce noise better.

3.

Iterating the filter can improves results.

4.

The algorithm takes moderate computation.