This task applies a gamma filter to a raster, to reduce speckle while preserving edges in radar images. Filtered pixels are replaced with values calculated from local statistics.

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

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('GammaAdaptiveFilter')
 
; Define an input raster
Task.INPUT_RASTER = Raster
 
; Define task inputs
Task.LOOKS = 1
 
; 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('GammaAdaptiveFilter')

Input parameters (Set, Get): INPUT_RASTER, LOOKS, 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


INPUT_RASTER (required)

Specify a raster on which to perform gamma adaptive filtering.

LOOKS (optional)

Specify the effective number of looks. The default value is 1. This parameter is used to calculate the noise variance by 1/(number of looks).

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.

WINDOW_SIZE (optional)

Specify a square filtering window size. The default value is 3.

Output Parameters


OUTPUT_RASTER

This is a reference to the output raster of filetype ENVI.

Methods


Execute

Parameter

ParameterNames

Properties


DESCRIPTION

DISPLAY_NAME

NAME

REVISION

TAGS

Version History


ENVI 5.3

Introduced

See Also


ENVITask, AdditiveLeeAdaptiveFilter Task, AdditiveMultiplicativeLeeAdaptiveFilter Task, EnhancedFrostAdaptiveFilter Task, EnhancedLeeAdaptiveFilter Task, FrostAdaptiveFilter Task, BitErrorAdaptiveFilter Task, KuanAdaptiveFilter Task, LocalSigmaAdaptiveFilter Task, MultiplicativeLeeAdaptiveFilter Task, Masking Support in ENVITasks