tiffdither(1)

TIFFDITHER(1)            USER COMMANDS              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  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  pred-
          ictor  value.  A predictor value of 2 causes each scan-
          line of the output image  to  undergo  horizontal  dif-
          ferencing  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 Fil-
          lOrder tag set to LSB2MSB , while -f msb2lsb will force
          data  to  be  written  with  the  FillOrder  tag set to
          MSB2LSB .

                  Last change: October 15, 1995                 1

TIFFDITHER(1)            USER COMMANDS              TIFFDITHER(1)

     -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)

                  Last change: October 15, 1995                 2