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1 .\"
2 .\" Copyright (c) 1990-1997 Sam Leffler
3 .\" Copyright (c) 1991-1997 Silicon Graphics, Inc.
4 .\"
5 .\" Permission to use, copy, modify, distribute, and sell this software and
6 .\" its documentation for any purpose is hereby granted without fee, provided
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24 .if n .po 0
25 .TH TIFFDITHER 1 "September 20, 2005" "libtiff"
26 .SH NAME
27 tiffdither \- convert a greyscale image to bilevel using dithering
28 .SH SYNOPSIS
29 .B tiffdither
30 [
31 .I options
32 ]
33 .I input.tif
34 .I output.tif
35 .SH DESCRIPTION
36 .I tiffdither
37 converts a single channel 8-bit greyscale image to a bilevel image
38 using Floyd-Steinberg error propagation with thresholding.
39 .SH OPTIONS
40 .TP
41 .B \-c
42 Specify the compression to use for data written to the output file:
43 .B none
44 for no compression,
45 .B packbits
46 for PackBits compression,
47 .B lzw
48 for Lempel-Ziv & Welch compression,
49 .B zip
50 for Deflate compression,
51 .B g3
52 for CCITT Group 3 (T.4) compression,
53 and
54 .B g4
55 for CCITT Group 4 (T.6) compression.
56 By default
57 .I tiffdither
58 will compress data according to the value of the
59 .I Compression
60 tag found in the source file.
61 .IP
62 The
63 .SM CCITT
64 Group 3 and Group 4 compression algorithms can only
65 be used with bilevel data.
66 .IP
67 Group 3 compression can be specified together with several
68 T.4-specific options:
69 .B 1d
70 for 1-dimensional encoding,
71 .B 2d
72 for 2-dimensional encoding,
73 and
74 .B fill
75 to force each encoded scanline to be zero-filled so that the
76 terminating EOL code lies on a byte boundary.
77 Group 3-specific options are specified by appending a ``:''-separated
78 list to the ``g3'' option; e.g.
79 .B "\-c g3:2d:fill"
80 to get 2D-encoded data with byte-aligned EOL codes.
81 .IP
82 .SM LZW
83 compression can be specified together with a
84 .I predictor
85 value.
86 A predictor value of 2 causes
87 each scanline of the output image to undergo horizontal
88 differencing before it is encoded; a value
89 of 1 forces each scanline to be encoded without differencing.
90 LZW-specific options are specified by appending a ``:''-separated
91 list to the ``lzw'' option; e.g.
92 .B "\-c lzw:2"
93 for
94 .SM LZW
95 compression with horizontal differencing.
96 .TP
97 .B \-f
98 Specify the bit fill order to use in writing output data.
99 By default,
100 .I tiffdither
101 will create a new file with the same fill order as the original.
102 Specifying
103 .B "\-f lsb2msb"
104 will force data to be written with the
105 .I Fill\%Order
106 tag set to
107 .SM LSB2MSB ,
108 while
109 .B "\-f msb2lsb"
110 will force data to be written with the
111 .I Fill\%Order
112 tag set to
113 .SM MSB2LSB .
114 .TP
115 .B \-t
116 Set the threshold value for dithering.
117 By default the threshold value is 128.
118 .SH NOTES
119 The dither algorithm is taken from the
120 .BR tiffmedian (1)
121 program (written by Paul Heckbert).
122 .SH "SEE ALSO"
123 .BR pal2rgb (1),
124 .BR fax2tiff (1),
125 .BR tiffinfo (1),
126 .BR tiffcp (1),
127 .BR tiff2bw (1),
128 .BR libtiff (3TIFF)
129 .PP
130 Libtiff library home page:
131 .BR http://www.remotesensing.org/libtiff/