ISIS Application Documentation

lowpass

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Apply lowpass or blurring filter to a cube

Overview

Parameters

Example 1

Example 2

Description

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.

Related Applications to Previous Versions of ISIS

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

boxfilter

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

U.S. Department of the Interior | U.S. Geological Survey
ISIS | Privacy & Disclaimers | Astrogeology Research Program
To contact us, please post comments and questions on the USGS Astrogeology Discussion Board
To report a bug, or suggest a feature go to: ISIS Github
File Modified: 02/21/2025 19:28:12

Parameter Groups

Files

Name	Description
FROM	Input file
TO	Output lowpass cube

Boxcar Size

Name	Description
SAMPLES	Number of samples in boxcar
LINES	Number of lines in boxcar

Boxcar Settings

Name	Description
LOW	Minimum valid DN
HIGH	Maximum valid DN
MINOPT	Sets minimum to be either a count or a percentage
MINIMUM	Minimum boxcar pixels required for filter
REPLACEMENT	Replacement if minimum not met

Non-Special Pixel Filtering

Name	Description
FILTER	Which pixels to filter

Special Pixel Filtering

Name	Description
NULL	Filter NULL Pixels
HRS	Filter HRS Pixels
HIS	Filter HIS Pixels
LRS	Filter LRS Pixels
LIS	Filter LIS Pixels

Files: FROM

Description

Input cube to filter

Type	cube
File Mode	input
Filter	*.cub

Close Window

Files: TO

Description

The resultant filtered cube

Type	cube
File Mode	output

Close Window

Boxcar Size: 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

Close Window

Boxcar Size: 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

Close Window

Boxcar Settings: 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 the average.

Type	double
Internal Default	Use all pixels
Less Than	HIGH

Close Window

Boxcar Settings: 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 the average.

Type	double
Internal Default	Use all pixels
Greater Than	LOW

Close Window

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.

Close Window

Boxcar Settings: MINIMUM

Description

This option is the minimum number of valid pixels required in a boxcar for filtering to begin.

Type	double
Default	1

Close Window

Boxcar Settings: REPLACEMENT

Description

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.

Close Window

Non-Special Pixel Filtering: FILTER

Description

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

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Special Pixel Filtering: NULL

Description

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

Close Window

Special Pixel Filtering: HRS

Description

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

Close Window

Special Pixel Filtering: HIS

Description

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

Close Window

Special Pixel Filtering: LRS

Description

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

Close Window

Special Pixel Filtering: LIS

Description

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

Close Window

Example 1

Running a 3x3 boxcar on all pixels

Description

The lowpass filter

Command Line

lowpass from= peaks.cub to=3x3lowpass.cub samples=3 lines=3

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

Command Line

lowpass from= peaks.cub to=bigLowpass.cub samples=21 lines=21

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.

Quick Links

Documentation Versions

lowpass

Description

Categories

Related Applications to Previous Versions of ISIS

Related Objects and Documents

Applications

History

Parameter Groups

Files

Boxcar Size

Boxcar Settings

Non-Special Pixel Filtering

Special Pixel Filtering

Files: FROM

Description

Files: TO

Description

Boxcar Size: SAMPLES

Description

Boxcar Size: LINES

Description

Boxcar Settings: LOW

Description

Boxcar Settings: HIGH

Description

Boxcar Settings: MINOPT

Description

Boxcar Settings: MINIMUM

Description

Boxcar Settings: REPLACEMENT

Description

Non-Special Pixel Filtering: FILTER

Description

Special Pixel Filtering: NULL

Description

Special Pixel Filtering: HRS

Description

Special Pixel Filtering: HIS

Description

Special Pixel Filtering: LRS

Description

Special Pixel Filtering: LIS

Description

Example 1

Description

Command Line

GUI Screenshot

Input Image

Output Image

Example 2

Description

Command Line

GUI Screenshot

Input Image

Output Image