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<H1>TIFFDITHER</H1>
Section: User Commands  (1)<BR>Updated: October 15, 1995<BR><A HREF="#index">Index</A>
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<A NAME="lbAB">&nbsp;</A>
<H2>NAME</H2>

tiffdither - convert a greyscale image to bilevel using dithering
<A NAME="lbAC">&nbsp;</A>
<H2>SYNOPSIS</H2>

<B>tiffdither</B>

[
<I>options</I>

]
<I>input.tif</I>

<I>output.tif</I>

<A NAME="lbAD">&nbsp;</A>
<H2>DESCRIPTION</H2>

<I>tiffdither</I>

converts a single channel 8-bit greyscale image to a bilevel image
using Floyd-Steinberg error propagation with threholding.
<A NAME="lbAE">&nbsp;</A>
<H2>OPTIONS</H2>

<DL COMPACT>
<DT><B>-c</B>

<DD>
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 &amp; 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.
<DT><DD>
The
<FONT SIZE="-1">CCITT</FONT>
Group 3 and Group 4 compression algorithms can only
be used with bilevel data.
<DT><DD>
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.
<DT><DD>
<FONT SIZE="-1">LZW</FONT>
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
<FONT SIZE="-1">LZW</FONT>
compression with horizontal differencing.
<DT><B>-f</B>

<DD>
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 FillOrder tag set to
<FONT SIZE="-1">LSB2MSB ,</FONT>
while
<B>-f msb2lsb</B>

will force data to be written with the FillOrder tag set to
<FONT SIZE="-1">MSB2LSB .</FONT>
<DT><B>-t</B>

<DD>
Set the threshold value for dithering.
By default the threshold value is 128.
</DL>
<A NAME="lbAF">&nbsp;</A>
<H2>NOTES</H2>

The dither algorithm is taken from the
<I><A HREF="tiffmedian+1.html">tiffmedian</A></I>(1)

program (written by Paul Heckbert).
<A NAME="lbAG">&nbsp;</A>
<H2>SEE ALSO</H2>

<I><A HREF="pal2rgb+1.html">pal2rgb</A></I>(1),

<I><A HREF="fax2tiff+1.html">fax2tiff</A></I>(1),

<I><A HREF="tiffinfo+1.html">tiffinfo</A></I>(1),

<I><A HREF="tiffcp+1.html">tiffcp</A></I>(1),

<I><A HREF="tiff2bw+1.html">tiff2bw</A></I>(1),

<I><A HREF="libtiff+3">libtiff</A></I>(3)


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<A NAME="index">&nbsp;</A><H2>Index</H2>
<DL>
<DT><A HREF="#lbAB">NAME</A><DD>
<DT><A HREF="#lbAC">SYNOPSIS</A><DD>
<DT><A HREF="#lbAD">DESCRIPTION</A><DD>
<DT><A HREF="#lbAE">OPTIONS</A><DD>
<DT><A HREF="#lbAF">NOTES</A><DD>
<DT><A HREF="#lbAG">SEE ALSO</A><DD>
</DL>
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