divfilter

This program divides the pixel being processed by a low pass filter. This has the general effect of highlighting the edges of grouped contrasted DN values in the image, and therefore, feature changes will be emphasized. Predominant changes will be emphasized with larger boxcars, and smaller changes can be searched for using smaller boxcars.

This is done by convolving an NxM boxcar through the data, where N and M are odd integers. In other words, the average DN value of the boxcar is divided into its middle pixel DN value. Please refer to the following diagram:

Thus, P(output) = P(input) / lowPassFilter, or P(s,l) = P(s,l) / average(s,l,N,M) where P is the target pixel, s and l are the sample and line position in the boxcar, N and M are the size of the boxcar (in this case 3x3) and average(s,l,N,M) is the average of the NxM centered box.

For details on the box filtering see the following references:

      M. J. McDonnell, Box-Filtering Techniques, Computer Graphics
      and Image Processing, Vol. 17, 1981, pages 65-70

      E. M. Eliason and L. A. Soderblom, An Array Processing System
      for Lunar Geochemical and Geophysical Data,
      Porc. Lunar Sci. Conf. (8th) , 1977, pages 1163-1170.
    

Description

Input cube to filter

Description

The resultant filtered cube

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, due to the computational algorithm, the size of the boxcar does not cause the program to operate significantly slower. (See Eliason/Soderblom document)

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, due to the computational algorithm, the size of the boxcar does not cause the program to operate significantly slower. (See Eliason/Soderblom document)

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.

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.

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.

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.

Description

This option is used to define how special pixels are handled. If the center pixel of the boxcar(input) is a special pixel, the output pixel will contain the same special pixel, or set to NULL depending on the value of this parameter.