pixfilter — apply a 3x3 filter to a color pix file
pixfilter [-f type] [-v ] [-d div] [-o offset] [-w width] [-n height] [-s squaresize] [file.pix] > newfile.pix
pixfilter
applies one of several 3x3 kernel filters to a color
pix(5)
format file.
It will take a file name or else read from standard input.
The input file size will be assumed to be 512 by 512 pixels
unless the
-w,
and/or
-n,
or the
-s
flags are used to tell it otherwise.
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 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 kernel values on standard error.