Man1 - tiffdither.1

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

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.

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

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

while -f msb2lsb will force data to be written with the FillOrder tag set to

-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).

*pal2rgb*(1), *fax2tiff*(1), *tiffinfo*(1), *tiffcp*(1), *tiff2bw*(1), *libtiff*(3TIFF)

Libtiff library home page: http://www.simplesystems.org/libtiff/