FrostAdaptiveFilter Task

This task applies a Frost filter to a raster, to reduce speckling while preserving edges.

The Frost filter is an exponentially damped circularly symmetric filter that uses local statistics. The pixel being filtered is replaced with a value calculated based on the distance from the filter center, the damping factor, and the local variance.

Reference: Zhenghao Shi and Ko B. Fung, “A Comparison of Digital Speckle Filters,” Proceedings of IGARSS 94, August 8-12, 1994, pp. 2129-2133.

Example

; Start the application

e = ENVI()

; Open an input file

File = Filepath('qb_boulder_msi', Subdir=['data'], $

  Root_Dir=e.Root_Dir)

Raster = e.OpenRaster(File)

; Get the task from the catalog of ENVITasks

Task = ENVITask('FrostAdaptiveFilter')

; Define the input raster

Task.INPUT_RASTER = Raster

; Define the damping factor

Task.DAMPING_FACTOR = 1.0

; Run the task

Task.Execute

; Get the collection of data objects currently available in the Data Manager

DataColl = e.Data

; Add the output to the Data Manager

DataColl.Add, Task.OUTPUT_RASTER

; Display the result

View = e.GetView()

Layer = View.CreateLayer(Task.OUTPUT_RASTER)

Syntax

Result = ENVITask('FrostAdaptiveFilter')

Input parameters (Set, Get): DAMPING_FACTOR, INPUT_RASTER, OUTPUT_RASTER_URI, WINDOW_SIZE

Output parameters (Get only): OUTPUT_RASTER

Parameters marked as "Set" are those that you can set to specific values. You can also retrieve their current values any time. Parameters marked as "Get" are those whose values you can retrieve but not set.

Input Parameters

DAMPING_FACTOR (optional)

Specify a floating-point damping factor that determines the amount of exponential damping. A value of 1.0 (the default) is sufficient for most radar images. Larger damping values preserve edges better but smooth less. A damping value of 0 results in the same output as a low pass filter.

INPUT_RASTER (required)

Specify a raster on which to perform Frost adaptive filtering.

OUTPUT_RASTER_URI (optional)

Specify a string with the fully qualified filename and path of the associated OUTPUT_RASTER.

If you do not specify this parameter, or set it to an exclamation symbol (!), ENVI creates a temporary file.
If you set it to the hash symbol (#), ENVI creates a file in the temporary directory, but this file will not be deleted when ENVI closes.