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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 threholding.
- -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.
The dither
algorithm is taken from the tiffmedian(1)
program (written by Paul Heckbert).
pal2rgb(1)
, fax2tiff(1)
, tiffinfo(1)
, tiffcp(1)
, tiff2bw(1)
, libtiff(3)
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