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lpsmooth(1)            DragonFly General Commands Manual           lpsmooth(1)


NAME

       lpsmooth - smooth an image preserving thin lines (v1.2)


SYNOPSIS

       lpsmooth [-options] in_file | - out_file | -


DESCRIPTION

       lpsmooth reads a portable graymap(5) or a portable pixmap(5) as input,
       smooth the image slightly preserving thin lines, and produces a
       portable 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
       pixels 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 ALSO

       pgm(5), ppm(5)


REFERENCES

       L.S. Davis and A. Rosenfeld, "Noise Cleaning by Iterated Local
       Averaging," 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)

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