tiffdither



TIFFDITHER(1)                                                    TIFFDITHER(1)




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 threholding.


OPTIONS

       -c     Specify the compression to use for data written  to  the  output
              file:  none  for  no compression, packbits for PackBits compres-
              sion, 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  out-
              put  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(3)



                               October 15, 1995                  TIFFDITHER(1)

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