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<title>TIFFDITHER</title>
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<h1 align=center>TIFFDITHER</h1>
<a href="#NAME">NAME</a><br>
<a href="#SYNOPSIS">SYNOPSIS</a><br>
<a href="#DESCRIPTION">DESCRIPTION</a><br>
<a href="#OPTIONS">OPTIONS</a><br>
<a href="#NOTES">NOTES</a><br>
<a href="#SEE ALSO">SEE ALSO</a><br>
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<a name="NAME"></a>
<h2>NAME</h2>
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<p>tiffdither − convert a greyscale image to bilevel
using dithering</p>
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<a name="SYNOPSIS"></a>
<h2>SYNOPSIS</h2>
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<p><b>tiffdither</b> [ <i>options</i> ] <i>input.tif
output.tif</i></p>
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<h2>DESCRIPTION</h2>
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<p><i>tiffdither</i> converts a single channel 8-bit
greyscale image to a bilevel image using Floyd-Steinberg
error propagation with thresholding.</p>
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<a name="OPTIONS"></a>
<h2>OPTIONS</h2>
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<p><b>−c</b></p>
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<p>Specify the compression to use for data written to the
output file: <b>none</b> for no compression, <b>packbits</b>
for PackBits compression, <b>lzw</b> for Lempel-Ziv &
Welch compression, <b>zip</b> for Deflate compression,
<b>g3</b> for CCITT Group 3 (T.4) compression, and <b>g4</b>
for CCITT Group 4 (T.6) compression. By default
<i>tiffdither</i> will compress data according to the value
of the <i>Compression</i> tag found in the source file.</p>
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<p>The <small>CCITT</small> Group 3 and Group 4 compression
algorithms can only be used with bilevel data.</p>
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<p>Group 3 compression can be specified together with
several T.4-specific options: <b>1d</b> for 1-dimensional
encoding, <b>2d</b> for 2-dimensional encoding, and
<b>fill</b> 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</b> to get 2D-encoded data with byte-aligned EOL
codes.</p>
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<p><small>LZW</small> compression can be specified together
with a <i>predictor</i> 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</b> for <small>LZW</small> compression with horizontal
differencing.</p>
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<p><b>−f</b></p>
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<p>Specify the bit fill order to use in writing output
data. By default, <i>tiffdither</i> will create a new file
with the same fill order as the original. Specifying
<b>−f lsb2msb</b> will force data to be written with
the <i>FillOrder</i> tag set to <small>LSB2MSB ,</small>
while <b>−f msb2lsb</b> will force data to be written
with the <i>Fill- Order</i> tag set to <small>MSB2LSB
.</small></p>
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<p><b>−t</b></p>
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<p>Set the threshold value for dithering. By default the
threshold value is 128.</p>
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<a name="NOTES"></a>
<h2>NOTES</h2>
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<p>The dither algorithm is taken from the
<b>tiffmedian</b>(1) program (written by Paul Heckbert).</p>
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<a name="SEE ALSO"></a>
<h2>SEE ALSO</h2>
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<p><b>pal2rgb</b>(1), <b>fax2tiff</b>(1),
<b>tiffinfo</b>(1), <b>tiffcp</b>(1), <b>tiff2bw</b>(1),
<b>libtiff</b>(3TIFF)</p>
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<p>Libtiff library home page:
<b>http://www.remotesensing.org/libtiff/</b></p>
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