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**NAME**

pgmkernel - generate a convolution kernel

**SYNOPSIS**

pgmkernel[-weightw]width[height]

**DESCRIPTION**

Generates a portable graymap array of sizewidthxheight(orwidthxwidthifheightis not specified) to be used as a convolution file bypnmconvol. The data in the convolution array K are computed according to the formula: K(i,j) = 1 / ( 1 + w * sqrt((i-width/2)^2 + (j-height/2)^2)) wherewis a coefficient specified via the-weightflag, andwidthandheightare the X and Y filter sizes. The output PGM file is always written out in ASCII format.

**OPTIONS**

The optional-weightflag should be a real number greater than -1. The default value is 6.0.

**BUGS**

The computation time is proportional towidth*height. This increases rapidly with the increase of the kernel size. A better approach could be using a FFT in these cases.

**SEE** **ALSO**

pnmconvol(1), pnmsmooth(1)

**AUTHOR**

Alberto Accomazzi (alberto@cfa.harvard.edu). 10 December 1992 pgmkernel(1)