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] [-o out_file] [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 be used to change this offset.
The
-v
flag displays the max and minimum values and the kernel information on standard error.
