pnmtotiffcmyk



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




NAME

       pnmtotiffcmyk - convert a Netpbm image 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

       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.



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 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 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 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  com-
       pressed  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 following 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,  pnmto-
       tiffcmyk 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
       substracts 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  comple-
       ment  the primary colors.  It rotates the colors (before black replace-
       ment) by deg degrees in the color wheel.  Unless you are trying to pro-
       duce 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 (normalised 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 darkest 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 pig-
       ment (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

       pnmtotiff(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:

       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.




netpbm documentation           07 February 2004   Pnmtotiffcmyk User Manual(0)

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