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ISIS Application Documentation

highpass

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Apply a spatial high pass filter to a cube

Description
Categories
Groups
Examples
History

Description

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.

Categories

Related Applications to Previous Versions of ISIS

This program replaces the following application existing in previous versions of ISIS:

Related Objects and Documents

Applications

Parameter Groups

Files

Name Description
FROM Input file
TO Output highpass cube

Boxcar Settings

Name Description
SAMPLES Number of samples in boxcar
LINES Number of lines in boxcar
MINOPT Sets minimum to be either a count or a percentage
MINIMUM Minimum boxcar pixel count

Options

Name Description
LOW Valid minimum pixel
HIGH Valid maximum pixel
PROPAGATEPropagate special pixels
ADDBACKPercentage of input pixel to add back to the filter

Files: FROM

Description

Input cube to filter

Type cube
File Mode input
Filter *.cub

Files: TO

Description

The resultant filtered cube

Type cube
File Mode output
Pixel Type real

Boxcar Settings: SAMPLES

Description

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

Boxcar Settings: LINES

Description

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: MINOPT

Description

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.

Boxcar Settings: MINIMUM

Description

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: LOW

Description

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

Options: HIGH

Description

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

Options: PROPAGATE

Description

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

Options: ADDBACK

Description

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)

Examples

Example 1

7 by 7

Description

Use a 7 by 7 pixel filter and use all pixels.

Command Line

highpass from=2400r to=2400r.hpf7x7all samp=7 line=7
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.

Example 2

21 by 21

Description

Use a 21 by 21 pixel filter and use all pixels.

Command Line

highpass from=2400r to=2400r.hpf21x21all samp=21 line=21
The boxcar filter is selected 21 pixels wide by 21 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 21x21 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 21x21 example of highpass.

Output Image

Output image showing results of the highpass applica tion with 21 by 21 pixel filter.

Output image 21x21 example of highpass

Parameter Name: TO

This is the output image for highpass. This larger filter leaves larger features visible.

History

Eric Eliason1988-05-20 Original version
Jeff Anderson2002-07-30 Ported to Isis 3.0
K Teal Thompson2002-11-19 Add examples.
K Teal Thompson2002-12-09 Make images smaller
K Teal Thompson2003-03-19 Add move images to /image and /thumb directory.
Stuart Sides2003-04-04 Fixed problem with isiscvs not checking in the thumb and image directories.
Kim Sides2003-05-13 Added application test
Stuart Sides2003-05-16 Modified schema location from astogeology... to isis.astrogeology..."
Stuart Sides2003-07-29 Modified filename parameters to be cube parameters where necessary
Stuart Sides2004-02-17 Added addback parameter