Isis 3 Application Documentation
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Blends a list of images together along the overlapping areas.
| Overview | Parameters | Example 1 |
DescriptionThis application is a translation of the Davinci script "blend" into Isis 3. 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, but sacrifices the scientific value of the pixel values in the process. Only the pixel values of the overlapping area will be changed, however. Consequently, this application is best suited to blend images that have relatively low contrast between them. As part of the THEMIS mosaicking pipeline, it is customary to use the Isis 3 application "sigmastretch" (itself a translation of another Davinci script, "sstretch") to reduce contrast. Each output pixel value is simply 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 over the other, the more heavily its value will be weighted in favor of that image. The "closeness" of a pixel from one image versus another is determined by the aforementioned ramp. The ramp is 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]
Here, "overlap" could refer to the overlapping area in either image, as
both will be adjusted by the same calculation. The "ramp" is the 0.0 to
1.0 map, "image_1" is the first image, "image_2" is the second image, and
"i" is the unique index of the current pixel being adjusted.
The output of this application is a list of images, setup nicely to move on to mosaicking (see "automos" and "mapmos") as a logical next step. All the overlaps between these images will share the same pixel values. This program is conceptually very similar to "noseam", in that it takes a list of images and attempts to smooth out the boundaries between them. Unlike that program, however, "blend" does not perform the mosaicking as part of the blending routine. CategoriesRelated Objects and DocumentsApplicationsHistory
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Parameter GroupsFiles
Options
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Files: FROMLIST
Description
A list of map projected cubes to blend. The Mapping groups must match in order to do the blending.
Note that the order of the images in this list can have a significant impact on the output results. The order of blending will proceed in the order of the list, regardless of the actual spatial ordering (in planetary coordinates) of the images.
Each time an image is processed (from the top of the list to the bottom), it is blended with every image that cam prior in the list, ensuring that every image gets blended once and only once with every other image. Since every blend of one image to another is a separate operation, pixels that overlap with more than two images can change depending on the order of the individual image blends.
| Type | filename |
|---|---|
| File Mode | input |
Files: TOLIST
Description
This list of output files must contain a file name to correspond to each input file in the FROMLIST. Input files will be associated with output files by index, so that the blended product of the first file in the FROMLIST will be written to the name and location of the first file in the TOLIST, and so on. Each output file will be written to the exact location with the exact name specified, unless the location and name happen to be identical to those of its corresponding input file, in which case an error will be thrown.
If this list is not specified, the output files will be placed in the directories of their input files, and named the same with the exception of an added ".blend" extension (e.g. "foobar.cub" becomes "foobar.blend.cub").
| Type | filename |
|---|---|
| File Mode | input |
| Internal Default | Automatic |
Options: STOP
Description
Defines how far from image boundaries the "blend ramp" will be calculated between two images. After moving "stop" steps from the image border, all remaining values in the ramp will be considered the same distance from the edge. By choosing a lower value, the algorithm will work much faster, but the ramp will also be much sharper and shorter.
The default value is an excessively large number to indicate that the ramp-creation process should calculate distance values for the entire overlapping area. A typical value for this parameter would be 100 for most THEMIS images. This will typically result in a smooth ramp indistinguishable from letting the distance calculation run to completion.
| Type | integer |
|---|---|
| Default | 100000 |
Example 1Two Images, Side-By-Side Description
This example shows the most typical use of the blend application. The
input is simply two images laid side by side in map-projected space.
The stop value is set to a typical value, 200, so that the ramp will
only be calculated out to 200 pixels from the image boundary.
Command Line
blend
fromlist=fromlist.lis stop=200
Specify a list of images to blend along with a stop value, specifying
how many "distance steps" to calculate from the image border before
stopping. After "stop" number of steps, all remaining values in the
ramp will be filled in with the stop value.
GUI Screenshot
Input Image
Data FileLinks open in a new window.
Output Image
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