Apply a Davinci "Sigma Stretch" (sstretch) to a cube.
Overview
Parameters
Example 1
Description
Stretch a cube according to the following formula for each pixel in the
image:
new_dn = (old_dn - avg) * (variance / stddev)
Here, avg and stddev stand for the statistical average and
standard deviation of all valid pixels in the current pixel's band,
respectively. The variance mentioned is not actually the statistical
variance of the band, but a user-specified parameter, VARIANCE, that affects
how much the histogram of the image is widened.
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.
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.
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.
GUI Screenshot
The first sigmastretch GUI
Example GUI for I01086005.cub
Screenshot of the GUI with parameters set to stretch the first
image.
The second sigmastretch GUI
Example GUI for I23851018.cub
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
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
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.
