pnmtotiffcmyk(1)pnmtotiffcmyk(1)NAMEpnmtotiffcmyk - convert a a portable anymap into a CMYK
encoded TIFF file
SYNOPSISpnmtotiffcmyk [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 bal
ance 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 algo
rithm is selected then -default is assumed and the appro
priate options (-theta,-gamma,-gammap) can appear any
where.
-none,-packbits,-lzw,-predictor
Tiff files can be compressed. By default LZW
decompression is used, but (apparently) some read
ers cannot read this, so you may want to select a
different algorithm (-none,-packbits). For LZW
compression, a -predictor value of 2 forces hori
zontal 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 conver
sion 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 correc
tion 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 com
mand 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 sig
nificantly.
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 ALSOpnmtotiff(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, acknowl
edges 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, indi
rect and consequential damages.
9 December 1999 pnmtotiffcmyk(1)
