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 threholding.

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  algo-
              rithms 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 bound-
              ary.  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 hori-
              zontal 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 Fil-
              lOrder 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)  pro-
       gram (written by Paul Heckbert).

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

                         October 15, 1995                       1