## Name

bwfilter — apply a 3x3 filter to a black and white bw file

## Synopsis

`bwfilter` [-f `type`] [-v ] [-d `div`] [-o `offset`] [-s `squaresize`] [-w `width`] [-n `height`] [`file.bw`] `>` `newfile.bw`

## DESCRIPTION

Bwfilter applies one of several 3x3 kernel filters to a black and white bw(5) format file. It will take a file name or else read from standard input. The input file size will be assumed to be 512x512 pixels unless the `-s`, `-w`, or `-n` flags are used to tell it otherwise (see brlcad(1)). By default a low pass filter is used. The `-f` `type` flag can be used to specify a different type of filter.

The type choices include:

lo

  low pass, the default.

hi

  high pass

vg

  vertical gradient

hg

  horizontal gradient

la

  laplacian

b

  boxcar low pass

Most filters divide the result of the kernel multiplication by some value about in order to scale it back to a 0->255 range. For example, the boxcar divides by nine. The `-d` flag can be used to change this divisor. Some filters also add an offset to their results. The output of a laplacian for example is "centered" about zero, thus it adds 128 to the answer to yield a difference from neutral grey. The `-o` flag can bw used to change this offset.

The `-v` flag displays the kernel values on standard error.

## BUGS

This should allow any 3x3 kernel to be specified.

## SEE ALSO

brlcad(1), bwscale(1), bw(5).

## AUTHOR

BRL-CAD Team

## COPYRIGHT

This software is Copyright (c) 1989-2013 by the United States Government as represented by U.S. Army Research Laboratory.

## BUG REPORTS

Reports of bugs or problems should be submitted via electronic mail to <devs@brlcad.org>.