pnmtotiffcmyk(1)
NAME
pnmtotiffcmyk - convert a portable anymap into a CMYK encoded TIFF file
SYNOPSIS
pnmtotiffcmyk [Compargs][Tiffargs][Convargs][ pnmfile ]
Compargs:
[-none|-packbits|-lzw [-predictor n]]
Tiffargs:
[-msb2lsb|-lsb2msb] [-rowsperstrip n]
[-lowdotrange n] [-highdotrange n]
[-knormal|-konly|-kremove]
Convargs:
[[-default][Defargs]|-negative]
Defargs:
[-theta deg] [-gamma n] [-gammap -1|-gammap n]
DESCRIPTION
Reads a portable anymap as input. Produces a CMYK encoded TIFF file as output. Optionally modifies the colour balance and black level, and removes CMY from under K.
OPTIONS
The order of most options is not important, but options for particular
conversion algorithms must appear after the algorithm is selected
(-default,-negative). If no algorithm is selected then -default is
assumed and the appropriate options (-theta,-gamma,-gammap) can appear
anywhere.
-none,-packbits,-lzw,-predictor
Tiff files can be compressed. By default LZW decompression is
used, but (apparently) some readers cannot read this, so you may
want to select a different algorithm (-none,-packbits). For LZW
compression, a -predictor value of 2 forces horizontal
differencing of scanlines before encoding; a value of 1 forces
no differencing.
-msb2lsb,-lsb2msb
These flags control fill order (default is -msb2lsb).
-rowsperstrip
This sets the number of rows in an image strip (data in the Tiff
files generated by this program is stored in strips - each strip
is compressed individually). The default gives a strip size of
no more than 8 kb.
-lowdotrange,-highdotrange
These options set tag values that may be useful for printers.
They have not been tested.
-knormal,-kremove,-konly
These options modify the values written to the Tiff file after
the conversion calculations (described below) are completed.
They are useful only for testing and debugging the code.
-kremove sets the black (K) layer to zero while -konly sets all
inks to the black value.
-default,-negative
-negative selects a simple algorithm that generates a colour
negative. None of the following options apply to this
algorithm, which is included as an example in the source to help
implementors of other conversions. -default is not needed,
unless it is used to countermand a -negative on the same command
line. The default conversion from RGB to CMYK can be modified
by altering the options listed below.
The CMYKTiff web site includes tests on the conversion
parameters. The test images illustrate the command line options
in practice and may make the following explanation clearer.
-theta deg
The basic conversion from RGB to CMY uses C = 1-R, M = 1-G, Y =
1-B. -theta provides a simple correction for any colour bias
that may occur in the printed image because, in practice, inks
do not exactly complement the primary colours. It rotates the
colours by the amount given (deg) in degrees. Unless you are
trying to produce unusual effects you will need to use small
values (try generating three images at -10, 0 (the default) and
10 degrees and seeing which has the best colour balance.
-gamma n
The black (K) component of the image is calculated as
min(C,Y,M). -gamma applies a gamma correction to this level.
In other words, the final black level is K (normalised to the
range 0 to 1) raised to the nth power. In practice this means
that a value greater than 1 makes the image lighter and a value
less than 1 makes the image darker. The range of allowed values
is 0.1 to 10.
-gammap n
This option controls the removal of CMY under K. If n is -1
then no removal occurs and C, M, Y and K are calculated as
above. This means that, when printed, dark areas contain all
four inks, which can make high contrast areas, like lettering,
appear fuzzy.
By default, when -gammap is not given on the command line, the
colours are reduced in dark areas by subtracting the black
level. The value subtracted is calculated with the same gamma
correction given by -gamma. Hopefully this will reduce
fuzziness without changing the appearance of the image
significantly.
If -gammap n is given, with n between 0.01 and 10, then black is
still subtracted, but the subtracted value is calculated using n
rather than any value supplied with -gamma. For example, it may
be best to only subtract black from the coloured inks in the
very darkest regions. In that case, n should be a large value,
such as 5.
BUGS
This program is not self-contained. It must be used with NetPbm and libtiff must be available (libtiff is included in the 1mar94 release of NetPbm).
SEE ALSO
pnmtotiff(1), tifftopnm(1), pnm(5)
AUTHOR
Copyright (c) 1999 Andrew Cooke (Jara Software). Released under the
GPL with no warranty. See source or COPYRIGHT and LICENCE files in
distribution for full details.
Much of the code (and man page!) uses ideas from other pnm programs,
written by Jef Poskanzer (thanks go to him and libtiff maintainer Sam
Leffler). A small section of the code - some of the tiff tag settings
- is derived directly from pnmtotiff, by Jef Poskanzer, which, in turn,
acknowledges Patrick Naughton with the following text:
Derived by Jef Poskanzer from ras2tif.c, which is:
Copyright (c) 1990 by Sun Microsystems, Inc.
Author: Patrick J. Naughton naughton@wind.sun.com
Permission to use, copy, modify, and distribute this software
and its documentation for any purpose and without fee is hereby
granted, provided that the above copyright notice appear in all
copies and that both that copyright notice and this permission
notice appear in supporting documentation.
This file is provided AS IS with no warranties of any kind. The
author shall have no liability with respect to the infringement
of copyrights, trade secrets or any patents by this file or any
part thereof. In no event will the author be liable for any
lost revenue or profits or other special, indirect and
consequential damages.
9 December 1999 pnmtotiffcmyk(1)
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