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.
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.
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.
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.
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.
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:
Option
Brief
Description
CENTER
Center pixel value
This sets the center pixel of the boxcar
to whatever was already there, in the event
that there are not enough valid, non-Special pixels
to meet minimum requirements.
NULL
Pixel value Null
This sets the center pixel of the boxcar
to the special pixel value fo "Null", if
there are not enough valid, non-Special pixels
to meet minimum requirements.
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:
Option
Brief
Description
ALL
Filter All Pixels
This is the option if you wish to filter all pixels, regardless
of validitity. It will only filter those Special Pixels indicated
by the user to be filtered. Also, the average will only be
calculated from the pixels with values between LOW
and HIGH.
INSIDE
Filter Pixels Between Low and High
This is the option if you only wish to run the filter when the
center pixel is valid. The filter will only run if there are
enough valid pixels to meet the requirements set by LOW, HIGH,
and MINIMUM
OUTSIDE
Filter Pixels Outside Low and High
This is the option if you only wish to run the filter when the
center pixel is invalid. The filter will only run if there are
enough valid pixels to meet the requirements set by LOW, HIGH,
and MINIMUM
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.
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.
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.
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.
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.
This configuration creates a relatively small filter, resulting in a
slight amount of blurring.
GUI Screenshot
lowpass gui
Example GUI
Screenshot 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
The image before the filter
Input image before the lowpass 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
The image after the filter
Output image after lowpass
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
Description
The lowpass filter is used again here, but at a much more intense level
This configuration creates a relatively large filter, resulting in a
great amount of blurring.
GUI Screenshot
lowpass gui
Example GUI
Screenshot 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
The image before the filter
Input image before the lowpass 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
The image after the filter
Output image after lowpass
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.
