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 thresholding.

OPTIONS

       -c     Specify the compression to use for data written to the output  file:  none  for  no
              compression,  packbits  for  PackBits  compression,  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  output  image  to undergo horizontal
              differencing before it is encoded; a value of 1 forces each scanline to be  encoded
              without   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 threshold 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(3TIFF)

       Libtiff library home page: http://www.remotesensing.org/libtiff/