pnmtotiffcmyk(1) - phpMan

Pnmtotiffcmyk User Manual(0) Pnmtotiffcmyk User Manual(0)

NAME
pnmtotiffcmyk - convert a Netpbm image into a CMYK encoded TIFF file

DESCRIPTION
This program is part of Netpbm(1).

pnmtotiffcmykreads a PNM image as input and produces a CMYK encoded TIFF file as output.
It optionally modifies the color balance and black level, and modifies removal of CMY from
under K.

Output is to Standard Output, but unlike with most Netpbm programs, Standard Output must
be a seekable file. An ordinary file is fine, but you cannot pipe the output to another
program. Furthermore, the program replaces any content currently in the file even if it
was opened for appending.

pamtotiff generates many other kinds of TIFF files.

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 you don't
select an algorithm, pnmtotiffcmyk assumes -default and the appropriate options
(-theta,-gamma,-gammap) can appear anywhere.

-none,-packbits,-lzw,-predictor
Tiff files can be compressed. By default, pnmtotiffcmyk uses LZW decompression, but
(apparently) 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 horizontal
differencing of scanlines before encoding; a value of 1 forces no differencing.

-msb2lsb,-lsb2msb
These options 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.

-knormal,-kremove,-konly
These options control the calculation of the CMYK ink levels. They are useful only for
testing and debugging the code.

-kremove sets the black (K) levels to zero while leaving the other ink levels as they
would be if the black level were normal.

-konly sets all inks to the normal black value.

-default,-negative
These options control what ink levels pnmtotiffcmyk uses to represent each input color.

-negative selects a simple algorithm that generates a color negative. None of the follow-
ing options apply to this algorithm. The algorithm is included as an example in the
source code to help implementors of other conversions.

-default is not necessary, unless you have to countermand a -negative on the same command
line.

The default conversion from RGB to CMYK is as follows: The basic values of the 3 pigments
are C = 1-R, M = 1-G, Y = 1-B. From this, pnmtotiffcmyk chooses a black (K) level which
is the minimum of those three. It then replaces that much of the 3 pigments with the
black. I.e. it subtracts K from each of the basic C, M, and Y values.

The options below modify this conversion.

-theta deg
-theta provides a simple correction for any color bias that may occur in the printed image
because, in practice, inks do not exactly complement the primary colors. It rotates the
colors (before black replacement) by deg degrees in the color wheel. Unless you are try-
ing to produce unusual effects you will need to use small values. Try generating three
images at -10, 0 (the default) and 10 degrees and see which has the best color balance.

-gamma n
-gamma applies a gamma correction to the black (K) value described above. Specifically,
instead of calculating the K value as min(C,M,Y), pnmtotiffcmyk raises that value (nor-
malised to the range 0 to 1) 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 black replacement.

If you specify -gammap, pnmtotiffcmyk uses the specified gamma value in computing how much
ink to remove from the 3 pigments, but still uses the regular gamma value (-gamma option)
to generate the actual amount of black ink with which to replace it.

Values of n from 0.01 to 10 are valid.

For example, it may be best to only subtract black from the colored inks in the very dark-
est regions. In that case, n should be a large value, such as 5.

As a special case, if n is -1, pnmtotiffcmyk does not remove any pigment (but still adds
the black ink). This means dark areas are even darker. Furthermore, when printed, dark
areas contain a lot of ink which can make high contrast areas, like lettering, appear
fuzzy. It's hard to see what the utility of this is.

SEE ALSO
pamtotiff(1), tifftopnm(1), pnm(1)

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 uses ideas from other Netpbm 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.

DOCUMENT SOURCE
This manual page was generated by the Netpbm tool 'makeman' from HTML source. The master
documentation is at

http://netpbm.sourceforge.net/doc/pnmtotiffcmyk.html

netpbm documentation 21 March 2017 Pnmtotiffcmyk User Manual(0)

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