Help Content > Basic Module > Intensity Processing > Filtering

Purpose

This tool allows reducing noise in an image by applying a not-SAR-specific filter. It emphasizes edge and lines, or other significative details, and remove non-significative parts of the image leading to a noiseless interpretation of the image.

Technical Note

This tool implements the Anisotropic Diffusion filtering approach proposed by Perona-Malik (1990) "Scale-Space and Edge Detection Using Anisotropic Diffusion" in http://image.diku.dk/imagecanon/material/PeronaMalik1990.pdf.

The anisotropic diffusion is defined as:

where ∆ is the Lapalcian operator, ∇ is the gradient, c(x, y, t) is the flux function which controls the rate of diffusion at any point in the image.

A choice of c such that it follows the gradient magnitude at the point enables to restrain the diffusion process as the region boundaries are approached. Perona & Malik suggest the following flux function in order to offer a trade-off between edge-preservation and blurring (smoothing) homogeneous regions:

The function above is governed by the free parameter K which determines the edge-strength to consider as a valid region boundary. A large value of K leads into an isotropic-like solution.

A discrete numerical solution of the diffusion equation can be derived for the anisotropic case using the FTCS (Forward-Time Central-Space) method as follows:

where {N,S,W,E} correspond to the pixel above, below, left and right of the pixel under consideration (i,j). λ plays the role of a contrast parameter separating forward (low contrast) from backward (high contrast) diffusion areas. t is the time of evolution and it's λ-incremented at each filtering iteration.

Input Files

Input file list

Input file names (e.g. _pwr, _rsp, _geo). This file(s) is mandatory.

Parameters - Principal Parameters

In order to optimally exploit the potential of the Anisotropic Non-Linear Diffusion filter, the eight parameters listed here below shall be set/tuned depending on the input data. For instance different setting has to be considered when different data types (e.g. SAR amplitude, SAR Interferometric coherence, Optical images, etc.) or data with different spatial resolution are used as input.

Gaussian Blur By setting this flag to True a preliminary Gaussian Blur filtering with fixed window size of 3x3 is applied.

Maximum time

This parameter can be used to tune the filtering iterations number. The higher, the greater the number of filtering iterations.

Lambda

This parameter is a positive float value that can be used to reshape the gradient sensitivity function of the diffusion.

K factor

This value controls the sensitivity to edges and it usually chosen experimentally. Low values of this parameters produce smooth curves (isotropic diffusion decreases slowly around edges) whereas high values lead to sharper curves (isotropic diffusion decreases quickly around edges).

Parameters - Global

It brings to the general section of the Preferences parameters. Any modified value will be used and stored for further processing sessions.

Parameters - Other Parameters

It brings to the general section of the Preferences parameters. Any modified value will be used and stored for further processing sessions.

Output Files

Output file list

Output file names. This file(s) is mandatory.

_fil

Filtered Intensity image and associated header files (.sml, .hdr).

Details specific to the Units of Measure and Nomenclature of the output products can be found in the Data Format section.

General Functions

Exec

The processing step is executed.

Store Batch

The processing step is stored in the batch list. The Batch Browser button allows to load the batch processing list.

The window will be closed.

Help

Specific help document section.

Specific Function(s)

None.

Basic Module - Intensity Processing - Filtering - Single image ANLD filtering

Basic Module - Intensity Processing - Filtering - Single image ANLD filtering