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speclowpass

Apply spectral low pass filter to a cube

This program applies a spectral low pass filter to a cube. A spectral filter works between bands as opposed to a spacial operation on a single band. Lowpass filter means it will be subtracting the average from the original pixel.

Related Applications to Previous Versions of ISIS

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

boxfilter

History

Stacy Alley	2008-09-02	Original version
Mackenzie Boyd	2009-06-09	Modified documentation, added exception handling for too many bands, modified examples

Parameters

Files

Input cube to filter

Type	cube
File Mode	input
Filter	*.cub

The resultant filtered cube

Type	cube
File Mode	output
Filter	*.cub

Boxcar Size

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

Boxcar Settings

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

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

Example 1

Example of usage of the spectral lowpass filter.

This example shows a spectral lowpass filter being applied to the image with a 5 depth boxcar. This cube has 256 bands so 5 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

This example will filter the image using 5 bands and no limits on high or low.

speclowpass 
          from=/work1/mboyd/CM_1514302573_1.cub to=/work1/mboyd/postlow.cub 
          bands=5

GUI Screenshot

Example GUI

This program's GUI

Screenshot of the GUI wit h parameters set to perform the spechighpass filter with a 5 band boxcar on the image CM_1514302573_1.ir.cub.

Input Image

Input image spectral graph before speclowpass filter

The image graph before the 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

Output image spectral graph after being filtered

The image graph after the filter

Parameter Name: TO

This is the image after the filter. Although there are still peaks, everything has been smoothed. In the before image the peaks were sharp where as now they are more curved. Differences have been leveled out to some extent.

Example 2

Example of usage of the spectral lowpass filter.

This example shows a spectral lowpass filter being applied to the image with a 61 depth boxcar. This cube has 256 bands so 61 takes in over a fifth. 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. In this case a blurry image begins to show through.