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This program applies a high pass filter to a cube. That is, it filters
the cube data by suppressing low frequency data (e.g., albedo) and allows
high frequency data (e.g., structure) to pass through.
This is done by convolving an NxM boxcar through the data, where N and M
are odd integers. The average of the boxcar is subtracted from the
middle pixel. The result of the subtraction is the high frequency
information. Thus, output(i,j) = input(i,j) - average(i,j,N,M) where
i and j are the sample and line position in the cube, N and M are the
size of the boxcar, and average(i,j,N,M) is the average of the NxM centered
at i,j. A small boxcar (e.g, 3x3) will allow fine
details to pass thru and will significantly suppress the albedo. A large
boxcar (e.g, 101x101) will enhance larger features and allow more albedo
information to pass through. In general, features which are half the size
of the boxcar will pass through the filter.
Fixed problem with isiscvs not checking in the thumb and image directories.
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
Stuart Sides
2004-02-17
Added addback parameter
Parameters
Files
Input cube to filter
Type
cube
File Mode
input
Filter
*.cub
The resultant filtered cube
Type
cube
File Mode
output
Pixel Type
real
Boxcar Settings
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
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:
Option
Brief
Description
COUNT
Minimum valid pixel count
This option indicates that the minimum is a minimum
count of pixels required for filtering.
PERCENTAGE
Minimum valid pixel percentage
This option indicates the the minimum parameter is to be
interpreted as a percentage of the total pixels in the
boxcar.
This is the minimum number of valid pixels which must occur inside the
NxM boxcar for filtering to occur. For example, 3x5 boxcar has 15
pixels inside. If MINIMUM=10 then the filter will occur if there are
10 or greater valid pixels. A valid pixel is one that is not special
(NULL, LIS, etc) and is in the range defined by LOW to HIGH.
Type
double
Default
1
Minimum
1
(inclusive)
Options
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 boxcar statistics.
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 boxcar statistics.
Type
double
Internal Default
Use all pixels
Greater Than
LOW
This option is used to define how special pixels are handled. If the
center pixel of the boxcar is a special pixel it will be propagated
or set to NULL depending on the value of this parameter.
Type
boolean
Default
TRUE
This option is used to specify how much of the input pixel is
added to the filter result. A value of 100 implies the entire input
pixel will be added back to the filter which is equivalent to the
sharpen program. Recall that highpass filters
suppress albedo and therefore you are essentially selecting
a percentage of albedo to addback.
Type
double
Default
0.0
Minimum
0.0
(inclusive)
Maximum
100.0
(inclusive)
Example 1
7 by 7
Use a 7 by 7 pixel filter and use all pixels.
Command Line
The highpass box filter is selected 7 pixels wide by 7 pixels long and parameters 'low' and 'high' default to 'use all pixels'.
Screenshot of GUI with parameters filled in to perform the 7x7 filter - with low, high, min default - highpass operation
Input Image
Input image for highpass
Input image
Parameter Name:
FROM
This is the input image for the 7x7 example of highpass.
Output Image
Output image 7x7 example of highpass
Output image showing results of the highpass application with 7 by 7 pixel filter.
Parameter Name:
TO
This is the output image for highpass. Notice the smoothing of abedo typical of high pass filtering, which leaves terrain more visible. This smaller filter leaves smaller features visible.
Example 2
21 by 21
Use a 21 by 21 pixel filter and use all pixels.
Command Line
The boxcar filter is selected 21 pixels wide by 21 pixels long and parameters 'low' and 'high' default to 'use all pixels'.
