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ISIS Application Documentation


spechighpass

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Apply a spectral high pass filter to a cube

Overview Parameters Example 1 Example 2

Description

This program applies a spectral high pass filter to a cube. The spectral component means that this will be a high pass amongst the bands of an image as opposed to averaging the lines and samples on the spacial plane with high pass. A highpass filter involves subtracting a lowpass, the average, from the original value.

Categories


Related Applications to Previous Versions of ISIS

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

Related Objects and Documents

Applications


History

Stacy Alley2008-09-02 Original version
Mackenzie Boyd2009-06-04 Added examples, modified documentation about boxcar size, added exception handling for too many bands

Parameter Groups

Files

Name Description
FROM Input file
TO Output spechighpass cube

Boxcar Size

Name Description
BANDS Number of bands in boxcar

Boxcar Settings

Name Description
LOW Minimum valid DN
HIGH Maximum valid DN
X

Files: FROM


Description

Input cube to filter

Type cube
File Mode input
Filter *.cub
Close Window
X

Files: TO


Description

The resultant filtered cube

Type cube
File Mode output
Pixel Type real
Filter *.cub
Close Window
X

Boxcar Size: BANDS


Description

This is the total number of bands in the boxcar. It must be odd and can not exceed twice the number of bands 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
X

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
X

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

Example 1

Example of usage of the spectral highpass filter.

Description

This example shows a spectral highpass filter being applied to the image with a 15 depth boxcar. This cube has 256 bands so 15 is relatively small. Although no averaging is done within a single band, the averaging of the pixels of many bands will cause some averaging and smoothing of the image if there is much difference between bands. Here is an image which highlights which pixels a single pass would average. The image shows a 9x9 dot instead of a single pixel highlighted to make it more visible. In this picture the boxcar would be seven or more bands, with the output pixel being one of the visible pixels. Depending on how large the boxcar was many of the values taken in could not be original, at a minimum, one value will be mirrored since there are only six available bands.
              
        

Command Line

spechighpass from=/work1/salley/CM_1514302573_1.cub to=/work1/mboyd/postSHP.cub bands=15
This example will filter the image using 15 bands and no limits on high or low.

GUI Screenshot

spechighpass gui

Example GUI

Screenshot of the GUI with parameters set to perform the spechighpass filter with a 15 band boxcar on the image CM_1514302573_1.ir.cub.

Input Image

The image graph before the filter

Input image spectral graph before spechighpass filter

Parameter Name: FROM

This is the spectral plot of the center point of the image, (32, 32), and shows all bands, 1- 256. No averaging has been applied, this is clear partialy because of th extreme peaks visible in the first half. The peaks are related to values which differ significantly from the bands around them.

Output Image

The image graph after the filter

Output image spectral graph after being filtered

Parameter Name: TO

This is the image after the filter. Although there are still sharp peaks, everything has been brought closer to zero. In the before image nearly all values are above zero, now the values are on either side of zero and are smaller.


Example 2

Example of usage of the spectral highpass filter.

Description

In this example the spechighpass filter is used to filter an image using a boxcar of size 63 and a high tolerance of .075 on a photo with 256 bands.

Command Line

spechighpass from=/work1/salley/CM_1514302573_1.ir.cub to=/work1/mboyd/post63.cub bands=63 high=.075
This example will filter the image using 63 bands and a high limit of 0.075.

GUI Screenshot

spechighpass gui

Example GUI

Screenshot of the GUI with parameters set to perform the spechighpass filter with a 63 band boxcar on the image CM_1516302573_1.ir.cub.

Input Image

The image graph before the filter

Input image spectral graph before spechighpass filter

Parameter Name: FROM

This is the spectral graph of the input image at location (32, 32), notice the sharp peaks and all values greater than zero.

Output Image

The image graph after the filter

Output image after being filtered

Parameter Name: TO

In this image the differences is that everything has been lowered except for the values already at zero. Some values which were positive are now negative as well.