tiffdither - convert a greyscale image to bilevel using
dithering
tiffdither [ options ] input.tif
output.tif
tiffdither converts a single channel 8-bit greyscale image
to a bilevel image using Floyd-Steinberg error propagation with
thresholding.
- -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 .
- -r
- Make each strip have no more than the given number of rows.
- -t
- Set the threshold value for dithering. By default the threshold value is
128.
The dither algorithm is taken from the tiffmedian(1)
program (written by Paul Heckbert).