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.\" $Header: /d1/sam/tiff/man/RCS/tiffdither.1,v 1.17 1997/08/29 21:48:03 sam Exp $
.\"
.\" Copyright (c) 1990-1997 Sam Leffler
.\" Copyright (c) 1991-1997 Silicon Graphics, Inc.
.\"
.\" Permission to use, copy, modify, distribute, and sell this software and
.\" its documentation for any purpose is hereby granted without fee, provided
.\" that (i) the above copyright notices and this permission notice appear in
.\" all copies of the software and related documentation, and (ii) the names of
.\" Sam Leffler and Silicon Graphics may not be used in any advertising or
.\" publicity relating to the software without the specific, prior written
.\" permission of Sam Leffler and Silicon Graphics.
.\"
.\" THE SOFTWARE IS PROVIDED "AS-IS" AND WITHOUT WARRANTY OF ANY KIND,
.\" EXPRESS, IMPLIED OR OTHERWISE, INCLUDING WITHOUT LIMITATION, ANY
.\" WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
.\"
.\" IN NO EVENT SHALL SAM LEFFLER OR SILICON GRAPHICS BE LIABLE FOR
.\" ANY SPECIAL, INCIDENTAL, INDIRECT OR CONSEQUENTIAL DAMAGES OF ANY KIND,
.\" OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
.\" WHETHER OR NOT ADVISED OF THE POSSIBILITY OF DAMAGE, AND ON ANY THEORY OF
.\" LIABILITY, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
.\" OF THIS SOFTWARE.
.\"
.if n .po 0
.TH TIFFDITHER 1 "October 15, 1995"
.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 threholding.
.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 FillOrder tag set to
.SM LSB2MSB ,
while
.B "\-f msb2lsb"
will force data to be written with the FillOrder 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
.IR tiffmedian (1)
program (written by Paul Heckbert).
.SH "SEE ALSO"
.IR pal2rgb (1),
.IR fax2tiff (1),
.IR tiffinfo (1),
.IR tiffcp (1),
.IR tiff2bw (1),
.IR libtiff (3)
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