pnmtotiffcmyk(1) - phpMan

pnmtotiffcmyk(1) General Commands Manual 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. Option-
ally 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 algo-
rithms 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 (appar-
ently) some readers cannot read this, so you may want to select a different algo-
rithm (-none,-packbits). For LZW compression, a -predictor value of 2 forces hori-
zontal differencing of scanlines before encoding; a value of 1 forces no differenc-
ing.

-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 de-
fault 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 cal-
culations (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 con-
version 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 explana-
tion clearer.

-theta deg
The basic conversion from RGB to CMY uses C = 1-R, M = 1-G, Y = 1-B. -theta pro-
vides 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 ro-
tates 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 im-
ages 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 (nor-
malised 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 ar-
eas contain all four inks, which can make high contrast areas, like lettering, ap-
pear 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 fuzzi-
ness 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:

Author: Patrick J. Naughton naughton AT wind.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 copy-
right notice appear in all copies and that both that copyright notice and this per-
mission 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 dam-
ages.

9 December 1999 pnmtotiffcmyk(1)

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