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.
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.
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.
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.
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.
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.
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.
The highpass box filter is selected 7 pixels wide by 7 pixels long and parameters 'low' and 'high' default to 'use all pixels'.
GUI Screenshot
highpass GUI
Example GUI
Screenshot of GUI with parameters filled in to perform the 7x7 filter - with low, high, min default - highpass operation
Input Image
Input image
Input image for highpass
Parameter Name:
FROM
This is the input image for the 7x7 example of highpass.
Output Image
Output image showing results of the highpass application with 7 by 7 pixel filter.
Output image 7x7 example of highpass
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.