lpsmooth(1)lpsmooth(1)NAMElpsmooth - smooth an image preserving thin lines (v1.2)
SYNOPSISlpsmooth [-options] in_file | - out_file | -
DESCRIPTIONlpsmooth reads a portable graymap(5) or a portable pixmap(5) as input,
smooth the image slightly preserving thin lines, and produces a porta‐
ble graymap/pixmap as output.
If -p 3 (default), lpsmooth smooths the image along thin lines, whose
thickness is 1 pixel, ensuring that no line is blurred in the direction
orthogonal to the line locally.
A 3x3 mask is put on every pixel in the image. lpsmooth finds the pix‐
els whose color (or graylevel) is 1st through (N-1)th similar to that
of the central pixel, where N is given by the option "-p N." The color
of the central pixel is turned into the average color of the N pixels
including the central pixel. Color difference is measured by the
Euclidean distance in the RGB color space.
If the string "-" is passed instead of in_file, lpsmooth reads the
image from standard input. If the string "-" is passed instead of
out_file, lpsmooth writes the image to standard output.
OPTIONS-n N Specifies how many times (N) the smoothing operation is applied
to the image. The default value is N=1.
-w N The weight factor for the central pixel in each 3x3 mask. The
default value is N=1.
If -p N and -w 0, the processing is identical to the k-nearest
neighbor smoothing with k=N-1. See references for the details
of the method.
-p N Specifies the number of the using pixels including the central
pixel. The default value is N=3, i.e., 2 pixels nearest in
color (graylevel) affect the new color of the central pixel.
If the input image is noisy, -p 4 or -p 5 will be helpful.
If -p 9 and -w 1, the processing is identical to calculating the
moving average with a 3x3 mask. If -p 1, lpsmooth does nothing
except consuming some memory and enormous CPU power.
-verbose
Show processing information.
NOTES
Even if -p 3, line segments may get shorter by at most 2 pixels,
because the two pixels on the edges of a line segment are blurred
slightly.
For the color image processing, the color similarity is measured by the
Euclidian distance in RGB color space.
SEE ALSOpgm(5), ppm(5)REFERENCES
L.S. Davis and A. Rosenfeld, "Noise Cleaning by Iterated Local Averag‐
ing," IEEE Trans. SMC, vol.SMC-8, No.9, pp.705-710, 1978.
AUTHOR
Copyright (C) 2000-2002 Hideaki Goto
E-Mail: hgot@rd.isc.tohoku.ac.jp, hgot@aso.ecei.tohoku.ac.jp
Feb 2002 lpsmooth(1)
