tiffdither(1)
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).
