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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/