tiffdither
==========

.. program:: tiffdither

Synopsis
--------

**tiffdither** [ *options* ] *input.tif* *output.tif*

Description
-----------

:program:`tiffdither` converts a single channel 8-bit greyscale image to a bilevel image
using Floyd-Steinberg error propagation with thresholding.

Options
-------

.. option:: -c compress

  Specify the compression to use for data written to the output file:

  ===========  ===================================
  Compression  Description
  ===========  ===================================
  none         no compression
  packbits     PackBits compression
  lzw          Lempel-Ziv & Welch compression
  zip          Deflate compression
  g3           CCITT Group 3 (T.4) compression
  g4           for CCITT Group 4 (T.6) compression
  ===========  ===================================

  By default :program:`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.

.. option:: -f

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

.. option:: -r

  Make each strip have no more than the given number of rows.

.. option:: -t

  Set the threshold value for dithering.
  By default the threshold value is 128.

Notes
-----

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

See also
--------

:doc:`pal2rgb` (1),
:doc:`fax2tiff` (1),
:doc:`tiffinfo` (1),
:doc:`tiffcp` (1),
:doc:`tiff2bw` (3tiff)