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.\" $Id: tiffdither.1,v 1.4 2006-04-20 12:17:19 dron Exp $
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.\" Copyright (c) 1990-1997 Sam Leffler
.\" Copyright (c) 1991-1997 Silicon Graphics, Inc.
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.if n .po 0
.TH TIFFDITHER 1 "September 20, 2005" "libtiff"
.SH NAME
tiffdither \- convert a greyscale image to bilevel using dithering
.SH SYNOPSIS
.B tiffdither
[
.I options
]
.I input.tif
.I output.tif
.SH DESCRIPTION
.I tiffdither
converts a single channel 8-bit greyscale image to a bilevel image
using Floyd-Steinberg error propagation with thresholding.
.SH OPTIONS
.TP
.B \-c
Specify the compression to use for data written to the output file:
.B none 
for no compression,
.B packbits
for PackBits compression,
.B lzw
for Lempel-Ziv & Welch compression,
.B zip
for Deflate compression,
.B g3
for CCITT Group 3 (T.4) compression,
and
.B g4
for CCITT Group 4 (T.6) compression.
By default
.I tiffdither
will compress data according to the value of the
.I Compression
tag found in the source file.
.IP
The
.SM CCITT
Group 3 and Group 4 compression algorithms can only
be used with bilevel data.
.IP
Group 3 compression can be specified together with several
T.4-specific options:
.B 1d
for 1-dimensional encoding,
.B 2d
for 2-dimensional encoding,
and
.B 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.
.B "\-c g3:2d:fill"
to get 2D-encoded data with byte-aligned EOL codes.
.IP
.SM LZW
compression can be specified together with a 
.I 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.
.B "\-c lzw:2"
for
.SM LZW
compression with horizontal differencing.
.TP
.B \-f
Specify the bit fill order to use in writing output data.
By default,
.I tiffdither
will create a new file with the same fill order as the original.
Specifying
.B "\-f lsb2msb"
will force data to be written with the
.I Fill\%Order
tag set to
.SM LSB2MSB ,
while
.B "\-f msb2lsb"
will force data to be written with the
.I Fill\%Order
tag set to
.SM MSB2LSB .
.TP
.B \-t
Set the threshold value for dithering.
By default the threshold value is 128.
.SH NOTES
The dither algorithm is taken from the
.BR tiffmedian (1)
program (written by Paul Heckbert).
.SH "SEE ALSO"
.BR pal2rgb (1),
.BR fax2tiff (1),
.BR tiffinfo (1),
.BR tiffcp (1),
.BR tiff2bw (1),
.BR libtiff (3TIFF)
.PP
Libtiff library home page:
.BR http://www.remotesensing.org/libtiff/