This is the command pnmtotiffcmyk that can be run in the OnWorks free hosting provider using one of our multiple free online workstations such as Ubuntu Online, Fedora Online, Windows online emulator or MAC OS online emulator
PROGRAM:
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.
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