lowpass
Apply lowpass or blurring filter to a cube
This program applies a lowpass or blurring filter to a cube. An NxM boxcar is
moved through the cube and average of the boxcar at each position is computed.
This average, which effectively blurs the data, is written to the
output cube. The user has the ability to choose which input pixels are filtered
including 1) all pixels, 2) pixels within a user specified range, 3) pixels
outside a user specified range, and 4) special pixels. In general, the larger
the boxcar the more the output cube is blurred. For example, a 101x101 boxcar
will cause more blurring than a 3x3 boxcar.
Categories
Related Applications to Previous Versions of ISIS
This program replaces the following application existing in previous versions of ISIS:- boxfilter
Related Objects and Documents
Applications
History
| Eric Eliason | 1988-05-20 | Original version |
| Jeff Anderson | 2002-07-10 | Ported to Isis 3.0 |
| 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 | 2005-08-17 | Added examples |
| Brendan George | 2005-11-21 | Modified user interface |
| Elizabeth Miller | 2005-11-22 | Fixed appTest parameters and documentation |
| Brendan George | 2006-05-31 | Added Minopt parameter, modified user interface |
| Brendan George | 2006-06-19 | Reorganized user interface |
Parameters
Files
Input cube to filter
| Type | cube |
|---|---|
| File Mode | input |
| Filter | *.cub |
The resultant filtered cube
| Type | cube |
|---|---|
| File Mode | output |
Boxcar Size
This is the total number of samples in the boxcar. It must be odd and
can not exceed twice the number of samples in the cube. In general, the
size of the boxcar does not cause the program to operate significantly
slower.
| Type | integer |
|---|---|
| Minimum | 1 (inclusive) |
| Odd | This value must be an odd number |
This is the total number of lines in the boxcar. It must be odd and
can not exceed twice the number of lines in the cube. In general, the
size of the boxcar does not cause the program to operate significantly
slower.
| Type | integer |
|---|---|
| Minimum | 1 (inclusive) |
| Odd | This value must be an odd number |
Boxcar Settings
Valid minimum pixel value that will be used in boxcar computation. If
a pixel value is less than LOW then it will not be used when computing
the average.
| Type | double |
|---|---|
| Internal Default | Use all pixels |
| Less Than | HIGH |
Valid maximum pixel value that will be used in boxcar computation. If
a pixel value is greater than HIGH then it will not be used when
computing the average.
| Type | double |
|---|---|
| Internal Default | Use all pixels |
| Greater Than | LOW |
This parameter determines whether the minimum
parameter is to be interpreted as a count of pixels, or a
percentage of all pixels in the boxcar.
| Type | string | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Default | COUNT | |||||||||
| Option List: |
|
This option is the minimum number of valid pixels
required in a boxcar for filtering to begin.
| Type | double |
|---|---|
| Default | 1 |
This determines what to put in the center pixel,
in the event that there aren't enough valid, non-special
pixels in the boxcar to meet the minimum. The
default is to replace it with the current value,
and the other option is to replace it with NULL.
| Type | string | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Default | CENTER | |||||||||
| Option List: |
|
Non-Special Pixel Filtering
These options choose which pixels to filter. The options are ALL,
VALID and INVALID. If the first is chosen, the filter will be run on
all pixels inside the LOW-HIGH range, and all Specials declared valid.
If the second option is chosen, the filter is only run when the center
pixel is valid, and the third option only runs the filter when the
center is invalid. Regardless of which option is chosen, the average is only
calculated from values between LOW and HIGH.
| Type | string | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Default | ALL | ||||||||||||
| Option List: |
|
Special Pixel Filtering
If the center pixel of a boxcar is NULL, and this box is checked,
the pixel will be overwritten with the average value of the boxcar
as a whole. If this box is not checked, the pixel will be left alone.
| Type | boolean |
|---|---|
| Default | TRUE |
If the center pixel of a boxcar is HRS, and this box is checked,
the pixel will be overwritten with the average value of the boxcar
as a whole. If this box is not checked, the pixel will be treated according
to the REPLACEMENT parameter.
| Type | boolean |
|---|---|
| Default | TRUE |
If the center pixel of a boxcar is HIS, and this box is checked,
the pixel will be overwritten with the average value of the boxcar
as a whole. If this box is not checked, the pixel will be treated according
to the REPLACEMENT parameter.
| Type | boolean |
|---|---|
| Default | TRUE |
If the center pixel of a boxcar is LRS, and this box is checked,
the pixel will be overwritten with the average value of the boxcar
as a whole. If this box is not checked, the pixel will be treated according
to the REPLACEMENT parameter.
| Type | boolean |
|---|---|
| Default | TRUE |
If the center pixel of a boxcar is LIS, and this box is checked,
the pixel will be overwritten with the average value of the boxcar
as a whole. If this box is not checked, the pixel will treated according
to the REPLACEMENT parameter.
| Type | boolean |
|---|---|
| Default | TRUE |
Example 1
Running a 3x3 boxcar on all pixels
The lowpass filter
Command Line
This configuration creates a relatively small filter, resulting in a
slight amount of blurring.
lowpass
from= peaks.cub
to=3x3lowpass.cub
samples=3
lines=3
GUI Screenshot
Example GUI
lowpass guiScreenshot of the GUI set to filter all pixels for the image using a three by three boxcar. Note that as many of the default parameters as are allowed are being used.
Input Image
Input image before the lowpass filter.
The image before the filter
Parameter Name:
FROM
Here we see the original cube. The areas of greatest interest are those with a great deal of contrast such as edges.
Output Image
Output image after lowpass
The image after the filter
Parameter Name:
TO
After the filter, the entire image is somewhat softer. The difference may be hard to detect on uniform areas, but the sections of the image that previously were sharply contrasted are now blurred. As this particular configuration has been set for a small filter, the results are obtained quickly and are more subtle than a large filter.
Example 2
Running a 21x21 boxcar on all pixels
The lowpass filter is used again here, but at a much more intense level
Command Line
This configuration creates a relatively large filter, resulting in a
great amount of blurring.
lowpass
from= peaks.cub
to=bigLowpass.cub
samples=21
lines=21
GUI Screenshot
Example GUI
lowpass guiScreenshot of the GUI set to filter all pixels for the image using a 21 by 21 boxcar. This configuration will be slightly slower than in the previous example, due to the increased boxcar size.
Input Image
Input image before the lowpass filter.
The image before the filter
Parameter Name:
FROM
Here we see the original cube. The areas of greatest interest are those with a great deal of contrast such as edges.
Output Image
Output image after lowpass
The image after the filter
Parameter Name:
TO
As seen here, the 21 by 21 boxcar blurs the image to a great extent. In fact, there seems to be little purpose for ever using a square boxcar this large, except for the purpose of illustrating the effect of the lowpass.