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  Lem-
              pel-Ziv & Welch compression, zip for Deflate com-
              pression, 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 boundary.   Group  3-specific
              options  are specified by appending a ``:''-sepa-
              rated  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 hor-
              izontal  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 com-
              pression with horizontal differencing.

       -f     Specify the bit fill order to use in writing out-
              put  data.   By default, tiffdither will create a
              new file with the same fill order as  the  origi-
              nal.  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(3)



                        October 15, 1995          TIFFDITHER(1)
