EnhancedFrostAdaptiveFilter Task

This task applies an enhanced Frost filter to a raster, to reduce speckling in radar imagery while simultaneously preserving texture information.

The Enhanced Frost filter is an adaptation of the Frost filter and similarly uses local statistics (coefficient of variation) within individual filter windows. Each pixel is put into one of three classes, which are treated as follows:

Homogeneous: The pixel value is replaced by the average of the filter window.
Heterogeneous: An impulse response is used as a convolution kernel to determine the pixel value.
Point target: The pixel value is not changed.

Reference: Lopes, A., R. Touzi, and E. Nezry. "Adaptive Speckle Filters and Scene Heterogeneity", IEEE Transactions on Geoscience and Remote Sensing 28, No. 6 (1990): 992-1000.

Example

; Start the application

e = ENVI()

; Open an input file

File = Filepath('elev_t.jpg', Subdir=['examples','data'])

Raster = e.OpenRaster(File)

; Get the task from the catalog of ENVITasks

Task = ENVITask('EnhancedFrostAdaptiveFilter')

; Define the task's input raster

Task.INPUT_RASTER = Raster

; Define the homogeneous cutoff value

Task.HOMOGENEOUS_CUTOFF = 0.6

; Define the heterogeneous cutoff value

Task.HOMOGENEOUS_CUTOFF = 1.8

; Define the damping factor value

Task.DAMPING_FACTOR = 1.25

; 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('EnhancedFrostAdaptiveFilter')

Input parameters (Set, Get): DAMPING_FACTOR, HETEROGENEOUS_CUTOFF, HOMOGENEOUS_CUTOFF, 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 inversely defines the extent of the exponential damping in the weighted average for the heterogeneous class. A larger damping factor produces less averaging.

HETEROGENEOUS_CUTOFF (optional)

Specify a floating-point value that represents the coefficient of variation cutoff for heterogeneous areas. The default value is 1.732.

HOMOGENEOUS_CUTOFF (optional)

Specify a floating-point value that represents the coefficient of variation cutoff for homogeneous areas. The default value is 0.523.

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.