bwfilter — apply a 3x3 filter to a black and white bw file
bwfilter
[-f type
] [-v ] [-d div
] [-O offset
] [-s squaresize
] [-w width
] [-n height
] [-o out_file
] [file.bw
] > newfile.bw
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:
low pass, the default.
high pass
vertical gradient
horizontal gradient
laplacian
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.