pnmconvol

 

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 pnmconvol(1)                                         pnmconvol(1)
 
 
 
NAME
        pnmconvol - general MxN convolution on a portable anymap
 
SYNOPSIS
        pnmconvol convolutionfile [pnmfile]
 
DESCRIPTION
        Reads two portable anymaps as input.  Convolves the second
        using the first, and writes a portable anymap as output.
 
        Convolution means replacing each  pixel  with  a  weighted
        average of the nearby pixels.  The weights and the area to
        average are determined by  the  convolution  matrix.   The
        unsigned  numbers  in  the  convolution file are offset by
        -maxval/2 to make signed numbers, and then normalized,  so
        the  actual  values in the convolution file are only rela­
        tive.
 
        Here is a sample convolution file; it does a simple  aver­
        age  of  the  nine  immediate  neighbors,  resulting  in a
        smoothed image:
            P2
            3 3
            18
            10 10 10
            10 10 10
            10 10 10
 
        To see how this works, do the above-mentioned offset: 10 -
        18/2  gives  1.  The possible range of values is from 0 to
        18, and after the offset that's -9 to 9.   The  normaliza­
        tion  step  makes  the  range  -1 to 1, and the values get
        scaled correspondingly so they become 1/9 -  exactly  what
        you  want.   The equivalent matrix for 5x5 smoothing would
        have maxval 50 and be filled with 26.
 
        The convolution file will usually be a  graymap,  so  that
        the same convolution gets applied to each color component.
        However, if you want to use a pixmap and  do  a  different
        convolution  to  different  colors,  you  can certainly do
        that.
 
SEE ALSO
        pnmsmooth(1), pnm(5)
 
AUTHORS
        Copyright (C) 1989, 1991 by Jef Poskanzer.
        Modified    26    November    1994    by    Mike    Burns,
        burns@chem.psu.edu
 
 
 
                          26 November 1994            pnmconvol(1)

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