.\" $Id: tiffdither.1,v 1.4 2006/04/20 12:17:19 dron Exp $

.\"

.\" Copyright (c) 1990-1997 Sam Leffler

.\" Copyright (c) 1991-1997 Silicon Graphics, Inc.

.\"

.\" Permission to use, copy, modify, distribute, and sell this software and 

.\" its documentation for any purpose is hereby granted without fee, provided

.\" that (i) the above copyright notices and this permission notice appear in

.\" all copies of the software and related documentation, and (ii) the names of

.\" Sam Leffler and Silicon Graphics may not be used in any advertising or

.\" publicity relating to the software without the specific, prior written

.\" permission of Sam Leffler and Silicon Graphics.

.\" 

.\" THE SOFTWARE IS PROVIDED "AS-IS" AND WITHOUT WARRANTY OF ANY KIND, 

.\" EXPRESS, IMPLIED OR OTHERWISE, INCLUDING WITHOUT LIMITATION, ANY 

.\" WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.  

.\" 

.\" IN NO EVENT SHALL SAM LEFFLER OR SILICON GRAPHICS BE LIABLE FOR

.\" ANY SPECIAL, INCIDENTAL, INDIRECT OR CONSEQUENTIAL DAMAGES OF ANY KIND,

.\" OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,

.\" WHETHER OR NOT ADVISED OF THE POSSIBILITY OF DAMAGE, AND ON ANY THEORY OF 

.\" LIABILITY, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE 

.\" OF THIS SOFTWARE.

.\"

.if n .po 0

.TH TIFFDITHER 1 "September 20, 2005" "libtiff"

.SH NAME

tiffdither \- convert a greyscale image to bilevel using dithering

.SH SYNOPSIS

.B tiffdither

[

.I options

]

.I input.tif

.I output.tif

.SH DESCRIPTION

.I tiffdither

converts a single channel 8-bit greyscale image to a bilevel image

using Floyd-Steinberg error propagation with thresholding.

.SH OPTIONS

.TP

.B \-c

Specify the compression to use for data written to the output file:

.B none 

for no compression,

.B packbits

for PackBits compression,

.B lzw

for Lempel-Ziv & Welch compression,

.B zip

for Deflate compression,

.B g3

for CCITT Group 3 (T.4) compression,

and

.B g4

for CCITT Group 4 (T.6) compression.

By default

.I tiffdither

will compress data according to the value of the

.I Compression

tag found in the source file.

.IP

The

.SM CCITT

Group 3 and Group 4 compression algorithms can only

be used with bilevel data.

.IP

Group 3 compression can be specified together with several

T.4-specific options:

.B 1d

for 1-dimensional encoding,

.B 2d

for 2-dimensional encoding,

and

.B 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.

.B "\-c g3:2d:fill"

to get 2D-encoded data with byte-aligned EOL codes.

.IP

.SM LZW

compression can be specified together with a 

.I 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.

.B "\-c lzw:2"

for

.SM LZW

compression with horizontal differencing.

.TP

.B \-f

Specify the bit fill order to use in writing output data.

By default,

.I tiffdither

will create a new file with the same fill order as the original.

Specifying

.B "\-f lsb2msb"

will force data to be written with the

.I Fill\%Order

tag set to

.SM LSB2MSB ,

while

.B "\-f msb2lsb"

will force data to be written with the

.I Fill\%Order

tag set to

.SM MSB2LSB .

.TP

.B \-t

Set the threshold value for dithering.

By default the threshold value is 128.

.SH NOTES

The dither algorithm is taken from the

.BR tiffmedian (1)

program (written by Paul Heckbert).

.SH "SEE ALSO"

.BR pal2rgb (1),

.BR fax2tiff (1),

.BR tiffinfo (1),

.BR tiffcp (1),

.BR tiff2bw (1),

.BR libtiff (3TIFF)

.PP

Libtiff library home page:

.BR http://www.remotesensing.org/libtiff/