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ISIS Documentation

stretch

Remaps pixel values in a cube

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.

Categories

Related Objects and Documents

Applications

History

Jim Torson1990-11-17 Original version
Jeff Anderson2002-09-17 Ported to Isis 3.0
K Teal Thompson2002-12-03 Add examples
K Teal Thompson2003-04-04 Make images smaller. Adjust binary stretch example.
Kim Sides2003-05-13 Added application test
Stuart Sides2003-05-16 Modified schema location from astogeology... to isis.astrogeology..."
Stuart Sides2003-05-30 Made changes to application test truth files to reflect -O1 optimization
Stuart Sides2003-07-29 Modified filename parameters to be cube parameters where necessary
Brendan George2006-06-30 Fixed application test
Jeannie Walldren2008-01-09 Modified stretch parameters (except PAIRS) to accept string instead of double so that special pixels may be set to other special pixel values.
Eric Hyer2009-04-30 Users can pass a file containing stretch pairs as well as inputing them manually as before. Also, the input side of stretch pairs can optionally be percentages instead of dn values.
Eric Hyer2010-04-23 Added support for stretch files not ending in a newline. Also did some code refactoring to eliminate duplicate code.

Parameters

Files

Input cube to stretch
Type cube
File Mode input
Filter *.cub

The resultant stretched cube
Type cube
File Mode output
Pixel Type real

Stretch Parameters

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

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

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

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

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

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

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

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

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

Example 1

run stretch

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

Command Line

stretch a Terra image. Use 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.\"

GUI Screenshot

stretch Gui

Example Gui

stretch Gui

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

Input Images

Input image

Input image for stretch

Input image

Parameter Name: FROM

This is the input image for the stretch examples.

graph demonstration

Explanation image for stretch

graph demonstration

This is a graph demonstrating the binary stretch.

Output Image

Output image showing results of the stretch application.

Output image for stretch

Output image showing results of the stretch application.

Parameter Name: TO

This is the output image that results from a binary type of stretch

Example 2

run stretch

This example shows the result of stretching dark data.

Command Line

stretch the dark data in a Terra image.
stretch f=../IN/peaks.cub:4 t=OUT/stretchDark p=\"0.:0 50.:255 255.:255.\"

GUI Screenshot

stretch Gui

Example Gui

stretch Gui

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

Input Images

Input image

Input image for stretch

Input image

Parameter Name: FROM

This is the input image for the stretch examples.

graph demonstration

Explanation image for stretch

graph demonstration

This is a graph demonstrating dark data enhancement.

Output Image

Output image showing results of the stretch application.

Output image for stretch

Output image showing results of the stretch application.

Parameter Name: TO

This is the output image that results from a dark data enhancement

Example 3

run stretch

This example shows the result of stretching light data.

Command Line

stretch the light data in a Terra image.
stretch f=../IN/peaks.cub:4 t=OUT/stretchLight p=\"0.:0 84.:0 255.:255.\"

GUI Screenshot

stretch Gui

Example Gui

stretch Gui

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

Input Images

Input image

Input image for stretch

Input image

Parameter Name: FROM

This is the input image for the stretch examples.

graph demonstration

Explanation image for stretch

graph demonstration

This is a graph demonstrating light data enhancement.

Output Image

Output image showing results of the stretch application.

Output image for stretch

Output image showing results of the stretch application.

Parameter Name: TO

This is the output image that results from a light data enhancement

Example 4

run stretch

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

Command Line

stretch a Terra image. Use inverse type of stretch.
stretch f=../IN/peaks.cub:4 t=OUT/stretchInv p=\"0.:255 255.:0.\"

GUI Screenshot

stretch Gui

Example Gui

stretch Gui

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

Input Images

Input image

Input image for stretch

Input image

Parameter Name: FROM

This is the input image for the stretch examples.

graph demonstration

Explanation image for stretch

graph demonstration

This is a graph demonstrating the inverse stretch.

Output Image

Output image showing results of the stretch application.

Output image for stretch

Output image showing results of the stretch application.

Parameter Name: TO

This is the output image that results from an inverse type of stretch

Example 5

run stretch

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

Command Line

stretch a Terra image. Input non-double parameters.
stretch f=peaks.cub:4 t=stretch NULL=lis Lis=LR Lr=hi his=Hr Hr=n

GUI Screenshot

stretch Gui

Example Gui

stretch Gui

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

Input Image

Input image

Input image for stretch

Input image

Parameter Name: FROM

This is the input image for the stretch examples.

Output Image

Output image showing results of the stretch application.

Output image for stretch

Output image showing results of the stretch application.

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.