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