### NAME

pgmkernel - generate a convolution kernel

### SYNOPSIS

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

### DESCRIPTION

This program is part of Netpbm(1)

**pgmkernel** generates a convolution kernel that you can use
with **pnmconvol**. 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

### AUTHOR

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