**NAME**

pgmkernel - generate a convolution kernel

**SYNOPSIS**

**pgmkernel** [**-weight** *w*] *width* [*height* ]

**DESCRIPTION**

This program is part of **Netpbm**.

**pgmkernel** generates a convolution kernel that you can use with **pnmcon-**

**vol**. The kernel is one where the weight of each location is inversely

proportional to its distance from the center of the kernel.

**pgmkernel** generates a PGM image of size *width* by *height* (or *width* by

*width* if you don't specify *height*.

**pgmkernel** computes the convolution function K as follows.

K(i,j) = 1 / ( 1 + w * sqrt(i^2 + j^2))

where *w* is a coefficient specified via the **-weight** option. *i* and *j*

are measured in pixels. K is zero everywhere beyond the specified

kernel width and height.

**pgmkernel** generates the output PGM file in the Plain (text) variation

of PGM.

**OPTIONS**

The optional **-weight** value should be a real number greater than -1.

The default value is 6.0.

**LIMITATIONS**

The computation time is proportional to *width***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**, **pnmsmooth** **pamgauss** **pgm**

**AUTHOR**

Alberto Accomazzi (*alberto@cfa.harvard.edu*).

netpbm documentation 10 December 1992 Pgmkernel User Manual(0)