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ENVILogStretchRaster

ENVILogStretchRaster

This function constructs an ENVIRaster from a source raster that has a logarithmic stretch applied. This is a non-linear stretch where the low-range brightness is enhanced. The logarithmic stretch is useful for enhancing features lying in the darker parts of the original image.

The result is a virtual raster, which has some additional considerations with regard to methods and properties. See Virtual Rasters for more information.

Example


; Start the application
e = ENVI()
 
; Open a file
filename  = FILEPATH('qb_boulder_msi', $
  ROOT_DIR=e.ROOT_DIR, SUBDIRECTORY = ['data'])
raster = e.openraster(filename)
 
; Create the stretch raster
stretchRaster =  ENVILogStretchRaster(raster, $
  MIN=[138,154,92,52], MAX=[1492,2047,1785,1807])
 
; Display the results
view = e.GetView()
layer = view.CreateLayer(stretchRaster)

Syntax


Result = ENVILogStretchRaster(Input_Raster [, Keywords=value])

Return Value


This routine returns an ENVIRaster that has had a Log stretch applied.

Arguments


Input_Raster

Specify the input ENVIRaster.

Methods


This virtual raster inherits methods and properties from ENVIRaster; however the following methods will override the ENVIRaster methods:

Dehydrate

Hydrate

Keywords


BRIGHTNESS (optional)

Set this keyword to an integer value from 0 to 100, indicating the brightness level to display. The default value is 50 if no brightness is specified. You can also set this value to a scalar or an array with the same number of elements as the raster has bands.

ERROR (optional)

Set this keyword to a named variable that will contain any error message issued during execution of this routine. If no error occurs, the ERROR variable will be set to a null string (''). If an error occurs and the routine is a function, then the function result will be undefined.

When this keyword is not set and an error occurs, ENVI returns to the caller and execution halts. In this case, the error message is contained within !ERROR_STATE and can be caught using IDL's CATCH routine. See IDL Help for more information on !ERROR_STATE and CATCH.

See Manage Errors for more information on error handling in ENVI programming.

MIN (required)

Set this keyword to the minimum value to be considered, also known as the "black point." If this value is a scalar, it applies to all bands. If it is an array, it must have the same number of elements as the input raster has bands.

MAX (required)

Set this keyword to the maximum value to be considered, also known as the "white point." If the value is a scalar, it applies to all bands. If it is an array, it must have the same number of elements as the input raster has bands.

NAME

Specify a string that identifies the raster.

Version History


ENVI 5.2

Introduced

ENVI 5.3, Service Pack 1

Documented the dehydrated form of this virtual raster

ENVI 5.4

Added Dehydrate and Hydrate methods; added NAME keyword

API Version


3.2

See Also


ENVIEqualizationStretchRaster, ENVIGaussianStretchRaster, ENVILinearPercentStretchRaster, ENVILinearRangeStretchRaster, ENVIOptimizedLinearStretchRaster, ENVIRaster, ENVIRootStretchRaster



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