ISIS Application Documentation
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Apply Sobel or Roberts gradient to a cube
Description
Categories
Groups
Examples
History
Description
Categories
Parameter Groups
Files
| Name | Description |
|---|---|
| FROM | Input cube |
| TO | Output cube |
Gradient Settings
| Name | Description |
|---|---|
| GRADTYPE | Type of gradient (Sobel, Roberts) |
| METHOD | Method for calculating the gradient (Approximate, Exact) |
Files: FROM
Description
Use this parameter to select the filename. All bands within the file will have the gradient applied.
| Type | cube |
|---|---|
| File Mode | input |
| Filter | *.cub |
Files: TO
Description
This file will contain the estimated or exact absolute magnitude of the gradient.
| Type | cube |
|---|---|
| File Mode | output |
| Pixel Type | real |
Gradient Settings: GRADTYPE
Description
This chooses the gradient type. The possibilities are Sobel, which uses a 3 x 3 boxcar to calculate the gradient magnitude, or Roberts, which uses a 2 x 2 boxcar to calculate the gradient magnitudes.
| Type | string | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Default | SOBEL | |||||||||
| Option List: |
|
Gradient Settings: METHOD
Description
This specifies how the gradient magnitudes are calculated. The possibilities are exact, which uses the square root of the sum of squares, or approximate, which uses the sum of absolutes.
| Type | string | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Default | APPROXIMATE | |||||||||
| Option List: |
|
Examples
Example 1
Applying a sobel filter
Description
Command Line
GUI Screenshot
gradient gui
|
Example GUI Screenshot of the GUI with parameters set to filter using a sobel configuration |
Input Image
The image before the filter
|
Input image before the filter.
Parameter Name:
FROM This is the image as it was taken originally. |
Output Image
The image after the filter
|
Output image after the gradient was applied
Parameter Name:
TO As you can see, sharp edges on the image have been emphasized, while areas of more constant DNs have been de-emphasized. |
Example 2
Applying a roberts filter
Description
Command Line
GUI Screenshot
gradient gui
|
Example GUI Screenshot of the GUI with parameters set to filter using a roberts gradient |
Input Image
|
The image before the filter
|
Input image before the filter.
Parameter Name:
FROM This is the image as it was taken originally. |
Output Image
The image after the filter
|
Output image after the roberts gradient
Parameter Name:
TO The use of the Roberts gradient here creates an output image which helps to highlight the edges. Since the Roberts filter uses a smaller boxcar, less of the image is taken into consideration at each processing step and thus the image can be created faster. The tradeoff is that images that have had the Roberts gradient applied tend be effected more by noise in the image. |
History
| Tracie Sucharski | 2002-12-18 | Original version |
| Kim Sides | 2003-05-13 | Added application test |
| Stuart Sides | 2003-05-16 | Modified schema location from astogeology... to isis.astrogeology..." |
| Stuart Sides | 2003-07-29 | Modified filename parameters to be cube parameters where necessary |
| Drew Davidson | 2005-08-16 | Added examples |
| Brendan George | 2005-11-07 | Modified to handle Special Pixels |
| Ian Humphrey | 2015-05-18 | Added METHOD parameter to allow for either exact or approximate calculation of the gradient magnitude. Updated and added tests. Updated documentation. Fixes #1741. |