ISIS Documentation

blend

Blends a list of Level2 cubes together along the overlapping areas.

This application is a translation of the Davinci script "blend" (Arizona State University, http://davinci.asu.edu) into ISIS. The blending process itself takes a list of Level2 cubes and blends them together along their overlapping areas by creating a "ramp" from one image to the other.

The ramp-creation process creates a smooth, qualitative transition from one image to the other, and thus modifies pixel values in a manner that does not preserve the scientific integrity of the data. Only the pixel values of the overlapping area are changed, however. Consequently, this application is best suited to blend images that are similar in contrast and/or brightness. As part of the THEMIS mosaicking pipeline, it is customary to use the ISIS application "sigmastretch" (itself a translation of another Davinci script, "sstretch") to reduce and contrast differences between images.

In the "blend" script, each output pixel value is a weighted average of the pixel values taken from the two input images being examined at a time. The closer a pixel is to one image border over the other, the more heavily its value will be weighted in favor of that image.

The "closeness" of a pixel to one image versus another is determined by the aforementioned ramp. The ramp is a map of the overlapping area between two images, where every pixel position in the overlap maps to a value from 0.0 to 1.0. Here, a value of 1.0 means the pixel falls entirely within the first image, and a value of 0.0 means it falls entirely within the second image. Thus, a value of 0.5 would indicate the pixel is equidistant from the borders of the two images.

Once the ramp has been generated, each pixel in the overlap is given a new value by the formula:

        overlap[i] = ramp[i] * image_1[i] + (1.0 - ramp[i]) * image_2[i]
      
where overlap refers to the overlapping area in both images, as both will be adjusted by the same calculation; ramp is the 0.0 to 1.0 map; image_1 is the first image; image_2 is the second image; i is the unique index of the current pixel being adjusted.

This program is conceptually similar to the Isis program "noseam", in that it takes a list of images and attempts to smooth out the boundaries between them. Unlike "noseam", however, "blend" does not perform the mosaicking as part of the blending routine.

The output of this application is a list of images, formatted for easy ingestion into additional Isis mosaicking tools (see "automos" and "mapmos"), where any overlaps between images will share the same pixel values.


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History

Travis Addair2011-09-08 Original translation of the Davinci "blend" script into ISIS.
Travis Addair2011-11-30 Added new queue technique to create the ramp, resulting in significant performance gains overall.