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Plan 9 - man page for floyd (plan9 section 9)

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FLOYD(9.1)									       FLOYD(9.1)

       floyd, halftone, hysteresis - create 1-bit images by dithering

       fb/floyd [ input ]

       fb/halftone screen [ input ]

       fb/hysteresis low high [ input ]

       Floyd  reads  a	grey-scale input file (default standard input), and reduces it to one bit
       per pixel using Floyd-Steinberg error-diffusion dither,	as  improved  by  Ulichney.   The
       resulting TYPE=bitmap picture file is written to standard output.

       Ulichney's algorithm involves randomly varying the Floyd-Steinberg diffusion coefficients.
       As the random number generator is seeded from the clock, floyd may produce different  out-
       put if rerun on the same input.

       Halftone  reduces grey-scale images to one bit per pixel using ordered dither.  The screen
       argument is the name of a file containing a dither matrix.  Halftone searches for  screens
       in /lib/fb/screens.

       Hysteresis creates one-bit-per-pixel images by thresholding with hysteresis.  Any value in
       the input image less than low is mapped to zero.  Any input value less than high is mapped
       to  zero  if any of its eight neighbors is less than low.  If low and high are equal, this
       is just an ordinary thresholding operation.

       Hysteresis makes a useful edge-detection operator if used on a high-pass filtered image.




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