ISIS Application Documentation

median

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Set pixels to median of surrounding pixel values

Overview

Parameters

Example 1

Example 2

Description

This program accepts a user-defined boxcar and loops through the input image. It finds the median pixel value in the boxcar, and sets the output center pixel to that median value. This will acheive a "blurring" effect, similar to the lowpass filter.

History

Brendan George	2005-11-04	Original version
Brendan George	2006-06-05	Added Minopt parameter, modified user interface
Brendan George	2006-06-19	Modified user interface

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File Modified: 02/21/2025 19:28:12

Parameter Groups

Files

Name	Description
FROM	Input Cube
TO	Output Cube

Boxcar Size

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

Boxcar settings

Name	Description
LOW	The minimum value of a valid pixel
HIGH	The maximum value of a valid pixel
MINOPT	Sets minimum to be either a count or a percentage
MINIMUM	Minimum boxcar pixels required for filter
REPLACEMENT	Replacement value if minimum number of pixels does not exist

Non-Special Pixel Filtering

Name	Description
FILTER	The style of filtration

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

This is the cube from which we will gather our data.

Type	cube
File Mode	input
Filter	*.cub

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Files: TO

Description

This is the cube to which we will write the modified data.

Type	cube
File Mode	output
Filter	*.cub

Close Window

Boxcar Size: SAMPLES

Description

This will determine how many samples the boxcar will have. This value must be odd and cannot exceed twice the number of samples in the cube. Note that the larger the boxcar size, the slower the program will run. The size of the boxcar will also have an impact on the blurring effect. The larger the boxcar, the greater the blurring.

Type	integer
Minimum	1 (inclusive)
Odd	This value must be an odd number

Close Window

Boxcar Size: LINES

Description

This will determine how many lines the boxcar will have. This value must be odd and cannot exceed twice the number of lines in the cube. Note that the larger the boxcar size, the slower the program will run. The size of the boxcar will also have an impact on the blurring effect. The larger the boxcar, the greater the blurring.

Type	integer
Minimum	1 (inclusive)
Odd	This value must be an odd number

Close Window

Boxcar settings: LOW

Description

This value indicates the minimum value of a valid pixel. If a pixel holds a value below the minimum value, it will either be filtered or skipped over, depending on user input in the "Filter Style" area.

Type	double
Internal Default	Use all
Less Than	HIGH

Close Window

Boxcar settings: HIGH

Description

This value indicates the maximum value of a valid pixel. If a pixel holds a value over the maximum value, it will either be excluded or included, depending on user input in the "Filter Style" area.

Type	double
Internal Default	Use all
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 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, if there are not enough valid pixels in the boxcar to meet the minimum requirement. The default is to replace it with the current value, and the other option will 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 the input value if there are not enough valid pixels to meet the minimum requirement.
NULL	Pixel value NULL	This sets the center pixel of the boxcar to the special pixel value of NULL, if there are not enough valid pixels to meet minimum requirement.

Close Window

Non-Special Pixel Filtering: FILTER

Description

These options determine which pixels are to be included in the filtering process. ALL filters all pixels, regardless of value, VALID only filters those pixels with values between LOW and HIGH, and INVALID only filters those pixels with values outside LOW and HIGH. Note that these only determine which Non-Special pixels to filter. Also, the median will only be calculated from pixel values between LOW and HIGH.

Type

string

Default

ALL

Option List:

Option	Brief	Description
ALL	Filter All	This option filters all Non-Special pixels, regardless of value. It only filters Special Pixels indicated by the user, and the median will only be calculated from pixel values between LOW and HIGH.
INSIDE	Filter Piexls Between Low and High	This option filters only those pixels with values between LOW and HIGH, as well as any Special Pixels indicated by the user, and the median will only be calculated from pixel values between LOW and HIGH.
OUTSIDE	Filter Pixels Outside Low and High	This option filters only those pixels with values outside LOW and HIGH, as well as any Special Pixels indicated by the user, and the median will only be calculated from pixel values between LOW and HIGH.

Close Window

Special Pixel Filtering: NULL

Description

This determines whether NULL pixels are considered valid for the purposes of filtering. This, along with the user input in the "Filter Style" section, will determine whether NULL pixels are included in the filter.

Type	boolean
Default	TRUE

Close Window

Special Pixel Filtering: HRS

Description

This determines whether HRS pixels are considered valid for the purposes of filtering. This, along with the user input in the "Filter Style" section, will determine whether HRS pixels are included in the filter.

Type	boolean
Default	TRUE

Close Window

Special Pixel Filtering: HIS

Description

This determines whether HIS pixels are considered valid for the purposes of filtering. This, along with the user input in the "Filter Style" section, will determine whether HIS pixels are included in the filter.

Type	boolean
Default	TRUE

Close Window

Special Pixel Filtering: LRS

Description

This determines whether LRS pixels are considered valid for the purposes of filtering. This, along with the user input in the "Filter Style" section, will determine whether LRS pixels are included in the filter.

Type	boolean
Default	TRUE

Close Window

Special Pixel Filtering: LIS

Description

This determines whether LIS pixels are considered valid for the purposes of filtering. This, along with the user input in the "Filter Style" section, will determine whether LIS pixels are included in the filter.

Type	boolean
Default	TRUE

Close Window

Example 1

Running median with a 3x3 boxcar

Description

This demonstrates running the median program on a sample cube using a 3x3 boxcar.

Command Line

median from= peaks.cub to=3x3median.cub samples=3 lines=3

This demonstrates the commands necessary to run median on a file named "peaks.cub" with a 3x3 boxcar. The small size of the boxcar will only produce a slight blur.

GUI Screenshot

median gui

Example GUI

Screenshot of the GUI set to filter all pixels for the image using a 3x3 boxcar.

Input Image

input cube

Input image before medain filter

Parameter Name: FROM

This is the original cube. The areas of greatest interest are those with a great deal of contrast such as edges.

Output Image

median output

Output of 3x3 boxcar median filter

Parameter Name: TO

This is the image after the filter. You may notice that the whole image is slightly softer, particularly around areas of sharp contrast. Due to the small size of the boxcar, the effect is subtle and difficult to notice.

Example 2

Running median with a 15x15 boxcar

Description

This demonstrates running the median program on a sample cube using a 15x15 boxcar.

Command Line

median from= peaks.cub to=15x15median.cub samples=15 lines=15

This demonstrates the commands necessary to run median on a file named "peaks.cub" with a 15x15 boxcar. The large size of the boxcar produces a marked blurring effect.

GUI Screenshot

median gui

Example GUI

Screenshot of the GUI set to filter all pixels for the image using a 15x15 boxcar.

Input Image

input cube

Input image before medain filter

Parameter Name: FROM

This is the original cube. The areas of greatest interest are those with a great deal of contrast such as edges.

Output Image

median output

Output of 3x3 boxcar median filter

Parameter Name: TO

This is the output image for a 15x15 boxcar. You will notice the entire image is noticeably blurrier. It is now virtually impossible to make out any but the largest of features.

Quick Links

Documentation Versions

median

Description

Categories

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