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ISIS Documentation

sigmastretch

Apply a Sigma Stretch to a cube.

This application is a translation of the Davinci script "sstretch" (Arizona State University, http://davinci.asu.edu). This program will stretch a cube according to the following formula for each pixel in the image: 
      new_dn = (old_dn - avg) * (variance / stddev)
where avg and stddev are the statistical average and standard deviation of all valid pixels in the current band. The variance is a user-specified parameter, VARIANCE, that affects how much the histogram of the image is widened, and does not represent the statistical variance of the image.

Categories

Related Objects and Documents

Applications

History

Travis Addair2011-09-08 Original translation of Davinci's "sstretch" script into Isis 3.
Steven Lambright2012-02-24 This program now takes advantage of multiple global processing threads.

Parameters

Files

The input cube to which the sigma stretch will be applied.
Type cube
File Mode input
Filter *.cub

The resultant cube containing the image after being stretched.
Type cube
File Mode output
Pixel Type real
Filter *.cub

Parameters

The nonuniformity of the output image's histogram. For values less than 1.0, the distribution will be closer to uniform. This value must be greater than 0.0.
Type double
Default 40.0
Minimum 0.0 (exclusive)

Example 1

Two THEMIS Images

This example shows a typical usage of sigmastretch as part of THEMIS mosaic creation. As input, the two images have very high contrast, and as such, blending the overlapping area will result in an awkward transition between the image bounds. By running sigmastretch first, the resulting images have less contrast, and can be mosaicked with good results. The default value for the VARIANCE of 40.0 here is used, as is typical in THEMIS processing.

Command Line

We're running the program once for each image. Without using multiple images, it's hard to see the differences due to "qview" automatically stretching the image for viewing. When mosaicked, however, the contrast is especially noticeable.
sigmastretch from=I01086005.cub to=I01086005.fx.cub; sigmastretch from=I23851018.cub to=I23851018.fx.cub

GUI Screenshot

The first sigmastretch GUI

Example GUI for I01086005.cub

The first sigmastretch GUI

Screenshot of the GUI with parameters set to stretch the first image.

The second sigmastretch GUI

Example GUI for I23851018.cub

The second sigmastretch GUI

Screenshot of the GUI with parameters set to stretch the second image.

Input Image

Mosaic of unstretched input images

Mosaic of the input images for sigmastretch

Mosaic of unstretched input images

Parameter Name: FROM

This is a cropped subsection of the mosaic of the input images before being stretched. Note the sharp contrast between the two images when mosaicked.

Output Image

Mosaic showing results of the sigmastretch application

Mosaic of the output images for sigmastretch

Mosaic showing results of the sigmastretch application

Parameter Name: TO

This is the same subarea of a mosaic of the output images after being stretched. The contrast is now much more subtle, making the images ready to be blended together along their overlapping areas.