tiffdither

TIFFDITHER(1)							TIFFDITHER(1)



NAME
       tiffdither - convert a greyscale image to bilevel using dithering

SYNOPSIS
       tiffdither [ options ] input.tif output.tif

DESCRIPTION
       tiffdither  converts  a	single	channel	 8-bit	greyscale  image to a
       bilevel image using Floyd-Steinberg error propagation  with  threhold-
       ing.

OPTIONS
       -c     Specify  the  compression to use for data written to the output
	      file: none for no compression, packbits for  PackBits  compres-
	      sion,  lzw  for Lempel-Ziv & Welch compression, zip for Deflate
	      compression, g3 for CCITT Group 3 (T.4) compression, and g4 for
	      CCITT  Group  4  (T.6) compression.  By default tiffdither will
	      compress data according to the value  of	the  Compression  tag
	      found in the source file.

	      The  CCITT  Group 3 and Group 4 compression algorithms can only
	      be used with bilevel data.

	      Group 3 compression can  be  specified  together	with  several
	      T.4-specific  options:  1d  for  1-dimensional encoding, 2d for
	      2-dimensional encoding, and fill to force each encoded scanline
	      to  be  zero-filled  so that the terminating EOL code lies on a
	      byte boundary.   Group  3-specific  options  are	specified  by
	      appending a ‘‘:’’-separated list to the ‘‘g3’’ option; e.g.  -c
	      g3:2d:fill to get 2D-encoded data with byte-aligned EOL  codes.

	      LZW  compression	can  be	 specified  together with a predictor
	      value.  A predictor value of 2 causes each scanline of the out-
	      put  image  to  undergo  horizontal  differencing	 before it is
	      encoded; a value of 1 forces each scanline to be encoded	with-
	      out   differencing.   LZW-specific  options  are	specified  by
	      appending a ‘‘:’’-separated list to the  ‘‘lzw’’	option;	 e.g.
	      -c lzw:2 for LZW compression with horizontal differencing.

       -f     Specify  the  bit fill order to use in writing output data.  By
	      default, tiffdither will create a new file with the  same	 fill
	      order  as	 the original.	Specifying -f lsb2msb will force data
	      to be written with the FillOrder tag set to LSB2MSB , while  -f
	      msb2lsb  will  force  data to be written with the FillOrder tag
	      set to MSB2LSB .

       -t     Set the threshold value for dithering.  By default the  thresh-
	      old value is 128.

NOTES
       The  dither algorithm is taken from the tiffmedian(1) program (written
       by Paul Heckbert).

SEE ALSO
       pal2rgb(1),   fax2tiff(1),   tiffinfo(1),    tiffcp(1),	  tiff2bw(1),
       libtiff(3)



			       October 15, 1995			TIFFDITHER(1)