stretch

This program stretchs or remaps pixels values in a cube. Note that the same stretch is applied to all bands within the cube. The underlying method for remapping pixels is defined by a set of stretch pairs and is best described using an example:

      0:0
      255:1
    

A stretch pair is two numbers separated by a colon. In this case, 0:0 and 255:1 comprise two stretch pairs. A pair is used to identify the mapping of input pixels to output pixels where the colon is a delimiter (i.e., input:output). Our first pair indicates input pixel values of 0 will be mapped to an output 0, while the second pair indicates input pixel values of 255 will be mapped to 1. All inputs between 0 and 255 will be mapped linearly (e.g., 127.5 will be mapped to 0.5). Therefore, the output cube will only have pixel values between 0 and 1. Those input pixels below 0 will be mapped to LRS and above 255 to HRS. This mapping to special pixels can be overridden. Because multiple pairs are allowed, many different types of remappings can be accomplished. For example:

      Inverse Stretch
      0:255
      255:0

      Piece-wise Linear Stretch
      20:0.0
      50:0.5
      125:1.0

      Saw-tooth Stretch
      0:0.0
      50:1.0
      100:0.0
      200:1.0

      Binary stretch
      0:0.0
      49.9999:0.0
      50:1.0.0
      79.9999:1.0
      80:0.0
      255:0.0
    

If you are having difficulty visualizing these stretches simply plot the input:output pairs on graph paper and connect the dots or see some of the examples. Note that the input value of each pair is in ascending order. As a reminder, all input pixel values less than the input value for the first pair are mapped to LRS. Likewise, all pixel values greater than the input value for the last pair are mapped to HRS.

Description

Input cube to stretch

Type	cube
File Mode	input
Filter	*.cub

Description

The resultant stretched cube

Type	cube
File Mode	output
Pixel Type	real

Description

If true the input side of the pairs are interpreted as percentages. The dn value which is used is the dn value at the specified percentage of the input cube's histogram

Type	boolean
Default	False

Description

Selects the method of pair data input. If true then read pairs from a file. Otherwise read the stretch pairs from the "PAIRS" parameter

Type	boolean
Default	False
Exclusions	PAIRS
Inclusions	INPUTFILE

Description

A string must be entered in the form of Where the input values are in ascending order (increasing). There is no limit to the number of pairs although each pair must be separated by a space. The stretch that is entered will be applied to all bands in the cube. By default "No Stretch" is applied which allows users to remap only special pixels if desired.

Type	string
Internal Default	No Stretch

Description

Read pairs from this file instead of entering them manually. Commented lines are ignored and defined as beginning with a '#'. Pairs must be separated by white space which may be new lines.

            # example 1 of a file containing stretch pairs
            0:0 1:10 15:255
          

            # example 2 of a file containing stretch pairs
            0:0
            1:10
            # this is a comment inside a file containing stretch pairs
            15:255
          

Type	filename
File Mode	input

Description

Double or alternate special pixel value used to replace all NULL special pixels. For example all NULL pixels can be replaced with -100.0. By default, the NULL special pixels will be left unchanged.

Type	string
Internal Default	NULL

Description

Double or alternate special pixel value used to replace all LIS special pixels. For example all LIS pixels can be replaced with 0.0. By default, the LIS special pixels will be left unchanged.

Type	string
Internal Default	LIS

Description

Double or alternate special pixel value used to replace all LRS special pixels. For example all LRS pixels can be replaced with 0.0. By default, the LRS special pixels will be left unchanged.

Type	string
Internal Default	LRS

Description

Double or alternate special pixel value used to replace all HIS special pixels. For example all HIS pixels can be replaced with 500.0. By default, the HIS special pixels will be left unchanged.

Type	string
Internal Default	HIS

Description

Double or alternate special pixel value used to replace all HRS special pixels. For example all HRS pixels can be replaced with 500.0. By default, the HRS special pixels will be left unchanged.

Type	string
Internal Default	HRS

This example shows a stretch operation using a binary type of stretch.

stretch f=../IN/peaks.cub:4 t=OUT/stretchBin p=\"0.:0 101.9:0 102.:255 200.:255 200.1:0. 255.:0.\"

stretch Gui

Example Gui Screenshot of GUI with parameters filled in to perform a stretch operation on the input image.

Input image	Input image for stretch Parameter Name: FROM This is the input image for the stretch examples.
graph demonstration	Explanation image for stretch This is a graph demonstrating the binary stretch.

Output image showing results of the stretch application.

Output image for stretch Parameter Name: TO This is the output image that results from a binary type of stretch

This example shows the result of stretching dark data.

stretch f=../IN/peaks.cub:4 t=OUT/stretchDark p=\"0.:0 50.:255 255.:255.\"

stretch Gui

Example Gui Screenshot of GUI with parameters filled in to perform a stretch operation on the input image.

Input image	Input image for stretch Parameter Name: FROM This is the input image for the stretch examples.
graph demonstration	Explanation image for stretch This is a graph demonstrating dark data enhancement.

Output image showing results of the stretch application.

Output image for stretch Parameter Name: TO This is the output image that results from a dark data enhancement

This example shows the result of stretching light data.

stretch f=../IN/peaks.cub:4 t=OUT/stretchLight p=\"0.:0 84.:0 255.:255.\"

stretch Gui

Example Gui Screenshot of GUI with parameters filled in to perform a stretch operation on the input image.

Input image	Input image for stretch Parameter Name: FROM This is the input image for the stretch examples.
graph demonstration	Explanation image for stretch This is a graph demonstrating light data enhancement.

Output image showing results of the stretch application.

Output image for stretch Parameter Name: TO This is the output image that results from a light data enhancement

This example shows a stretch operation using a inverse type of stretch.

stretch f=../IN/peaks.cub:4 t=OUT/stretchInv p=\"0.:255 255.:0.\"

stretch Gui

Example Gui Screenshot of GUI with parameters filled in to perform an inverse stretch operation on the input image.

Input image	Input image for stretch Parameter Name: FROM This is the input image for the stretch examples.
graph demonstration	Explanation image for stretch This is a graph demonstrating the inverse stretch.

Output image showing results of the stretch application.

Output image for stretch Parameter Name: TO This is the output image that results from an inverse type of stretch

This example shows how to input non-double parameters for the special pixel values.

stretch f=peaks.cub:4 t=stretch NULL=lis Lis=LR Lr=hi his=Hr Hr=n

stretch Gui

Example Gui Screenshot of GUI with non-double values filled in to the special pixel parameters.

Input image

Input image for stretch Parameter Name: FROM This is the input image for the stretch examples.

Output image showing results of the stretch application.

Output image for stretch Parameter Name: TO This is the output image that results from swapping special pixel values. Notice that there is no visible change since all special pixel values have the same value.