Pstopnm User Manual(1) General Commands Manual Pstopnm User Manual(1)
NAME
pstopnm - convert a PostScript file to a PNM image
SYNOPSIS
pstopnm
[-stdout]
[-forceplain]
[-help]
[-dpi=dpi]
[-xsize=pixels] [-ysize=pixels]
[-xborder=frac] [-yborder=frac] [-landscape]
[-portrait]
[-nocrop]
[-pbm
|-pgm
|-ppm]
[-llx=s] [-lly=s] [-urx=s] [-ury=s]
[-verbose]
[-xmax=pixels] [-ymax=pixels]
[-textalphabits={1,2,4}]
psfile[.ps]
OPTION USAGE
Minimum unique abbreviation of option is acceptable. You may use double
hyphens instead of single hyphen to denote options. You may use white
space in place of the equals sign to separate an option name from its
value.
DESCRIPTION
This program is part of Netpbm(1).
pstopnm reads a PostScript or PDF file as input and produces PBM, PGM,
or PPM images as output. This program simply uses GhostScript to render
a PostScript file with its PNM device drivers. If you don't have Ghost-
Script installed or the version you have installed was not built with
the relevant PNM device drivers, pstopnm will fail. You can see if you
have the proper environment by issuing the command gs --help . If it
responds and lists under "Available Devices" pbm, pbmraw, pgm, pgmraw,
pnm, pnmraw, ppm, or ppmraw, you're in business.
It's important to understand that pstopnm is a Netpbm image file format
converter only in the broadest sense of the word, because Postscript is
far from an image file format. What pstopnm really is is a Postscript
renderer - an image generator. One place you'll notice the difference
is where you expect pstopnm | pnmtops to be idempotent (which is not the
case). There are details on this kind of conversion below.
pstopnm uses the value of the GHOSTSCRIPT environment variable as the
file name for the Ghostscript program. If GHOSTSCRIPT is not set,
pstopnm searches your PATH for a regular file named gs. If it doesn't
find one, it assumes Ghostscript is in the file /usr/bin/gs.
pstopnm does not use the Netpbm libraries to generate the output files,
so may not be entirely consistent with most Netpbm programs.
psfile[.ps] is the name of the input file. pstopnm will add the ps to
the end of the name you specify if no file exists by the exact name you
specify, but one with .psadded does. For Standard Input, use - or just
don't give any argument.
If you use the -stdout option or your input is from Standard Input,
pstopnm outputs images of all the pages as a multi-image file to Stan-
dard Output. Otherwise, pstopnm creates one file for each page in the
Postscript input. The files are named as follows: If the input file is
named psfile.ps, the name of the files will be psfile001.ppm, ps-
file002.ppm, etc. The filetype suffix is .ppm, .pgm, or .pbm, depending
on which kind of output you choose with your invocation options. If the
input file name does not end in .ps, the whole file name is used in the
output file name. For example, if the input file is named psfile.old,
the output file name is psfile.old001.ppm, etc.
Note that the output file selection is inconsistent with most Netpbm
programs, because it does not default to Standard Output. This is for
historical reasons, based on the fact that the Netpbm formats did not
always provide for a sequence of images in a single file.
When your input is from Standard Input, you may feed multiple Encapsu-
lated Postscript documents, one after another, and pstopnm converts
every document and places it in the Standard Output stream as an image.
But if your input is from a named file, pstopnm expects the file to be
an Encapsulated Postscript file, which means it contains only one Enap-
sulated Postscript document. If the file contains multiple concatenated
documents, pstopnm ignores every document but the first. This distinc-
tion does not exist for non-EPSF Postscript input - pstopnm generates an
output image for each page of the input regardless of whether the input
is from Standard Input or from a named file.
Note that you can generate both kinds of files - concatenated EPSF and
multi-page non-EPSF - with pnmtops, selecting with the -setpage option.
Each output image contains a rectangular area of the page to which it
pertains. See ]8;;#dimensions\the Dimensions section]8;;\ for details on what part of the
input image goes into the output image and how big it is in the output
and what borders and margins are in the output image.
It has been reported that on some Postscript Version 1 input, Ghost-
script, and therefore pstopnm, produces no output. To solve this prob-
lem, you can convert the file to Postscript Version 3 with the program
ps2ps. It is reported that the program pstops does not work.
Dimensions
This section describes what part of the input image gets used in the
output and the dimensions of the output, including borders and back-
ground.
Note that an output image is associated with a single input page.
pstopnm starts by taking a rectangular area from the input page. That
is called the subject image.
pstopnm may add borders to the subject image to form what is called the
bordered subject image.
pstopnm places the bordered subject image in the center of the output
image and clips the edges as necessary to fit the computed output image
size.
The location of the subject image in the Postscript input page is de-
fined by four numbers, the lower left corner and the upper right corner
x and y coordinates. These coordinates are usually specified by the
BoundingBox DSC statement (a Postscript comment) in the PostScript file,
but they can be overridden by the user by specifying one or more of the
following options: -llx, -lly, -urx, and -ury.
The presence and thickness of a border to be added to the subject image
to form the bordered subject image is controlled by the options -xborder
and -yborder. If pstopnm does not find a BoundingBox statement in the
input, and you don't specify image area coordinates on the command line,
pstopnm uses default values. If your input is from Standard Input,
pstopnm does not use the BoundingBox values (because of the technical
difficulty of extracting that information and still feeding the file to
Ghostscript), so you either have to specify the image area coordinates
or take the default.
The output image size is a confusing thing. In a Postscript file,
things have spatial dimensions. For example, a particular line may be 3
centimeters long. A Postscript printer is supposed to print the line 3
centimeters long, using however many pixels that takes, without regard
to how big the sheet of paper on which it is printing is. In a PNM im-
age, by contrast, there is no spatial dimension; there are only pixels.
You might have a line that is 100 pixels long, but the PNM image says
nothing about how long that line should be on a printed page.
pstopnm fills the role of a Postscript printer. The PNM image is a vir-
tual printed page. pstopnm must determine how many pixels it will use
in the output image to represent an inch of input image, which is the
"output device resolution." Think of it as the number of dots per inch
the virtual printer prints on the virtual page.
The simplest thing is for you to tell pstopnm exactly what output device
resolution to use, using the -dpi option. If you say for example
-dpi=300 and the bordered subject image is 2 inches by 3 inches, the PNM
output will be 600 pixels by 900 pixels. Using this method, the output
device resolution has to be the same in both directions.
Or you can set the output image dimensions with -xsize and -ysize. For
example, if you say -xsize=1200 -ysize=1800 and the bordered subject im-
age is 2 inches wide by 3 inches high, the output image is 1200 by 1800
pixels, with each pixel representing 1/600 inch of input image.
In the unlikely event that you want different output device resolutions
in the two directions, you could use -xsize and -ysize to do that. In
the above example, if you change -ysize to 900, a pixel still represents
1/600 inch horizontally, but 1/300 inch vertically.
If you specify one of -xsize and -ysize and not the other, pstopnm de-
faults the other such that the output device resolution is the same in
both directions.
The "x" and "y" of -xsize and -ysize refer to the image being printed on
the page, not the page. So if pstopnm prints it in landscape orienta-
tion, "x" would pertain to the vertical direction on the page, i.e. the
vertical direction in the output PNM image.
If you specify neither the output size nor the output device resolution,
pstopnm does some weird computation which exists mainly for historical
reasons:
If you specify -nocrop, pstopnm uses the values of -xmax and -ymax for
the output image dimensions. These default to 612 and 792 pixels, re-
spectively.
The final case, the default, is where you don't specify any size or res-
olution options or -nocrop. This is the most complicated case. In this
case, pstopnm first chooses an output device resolution that would gen-
erate the number of pixels indicated by -xmax and -ymax from the bor-
dered subject image. Then, based on that resolution, it chooses an out-
put image size that is just large enough to accommodate the subject im-
age (no borders). Remember (above) that pstopnm trims the edges of the
bordered subject image to fit the computed output size.
Ghostscript Limitations
Tests done in 2013 with Ghostscript 8.71 indicate that Ghostscript's
pgmraw output driver has some kind of rounding error that causes the
pixel values to change slightly, and that means pstopnm generates incor-
rect output when you have monochrome Postscript input. But with color
Postscript input, pstopnm uses Ghostscript's ppmraw output driver and
generates correct PPM output.
Usage Notes
There is some good advice on converting to and from Postscript, in the
document Postcript File Conversions" (1) by Andrew T. Young.
Reversible Conversion
If you're trying to do the equivalent of the naive pnmtops | pstopnm,
the following steps will do it.
$ pnmtops -nocenter -equalpixels -dpi 72 -noturn testimg.ppm > testimg.ps
$ pstopnm -xborder=0 -yborder=0 -xsize=XSIZE -ysize=YSIZE \
-portrait -stdout -quiet testimg.ps >testimg2.ppm
XSIZE and YSIZE above are the image dimensions, which you can get from
testimg.ps like in the following example (the grep, awk and echo com-
mands are just to help demonstrate how the other commands work - you
wouldn't use those in a program).
$ grep "BoundingBox" testimg.ps
%%BoundingBox: 0 0 227 149
$ awk '/%%BoundingBox/ {print $4,$5}' testimg.ps
227 149
$ xysize=$(awk '/%%BoundingBox/ {print "-xsize="$4,"-ysize="$5}' testimg.ps)
$ echo $xysize
-xsize=227 -ysize=149
$ pstopnm -xborder=0 -yborder=0 $xysize -portrait ... testimg.ps
Note that Ghostscript bugs can keep this from doing a perfect reversible
conversion.
PDF is a subset of Postscript, so pstopnm can convert from PDF to Netpbm
format, but often produces the wrong size image because of pstopnm's re-
liance on a BoundingBox DSC statement, which PDF does not have. With
pure text PDFs, it works fine. In other cases, you can get better re-
sults by converting to general Postscript with the pdf2ps program that
comes with Ghostscript. For more information about converting to and
from PDF, see ]8;;index.html#document\Document/Graphics Software]8;;\ .
OPTIONS
In addition to the options common to all programs based on libnetpbm
(most notably -quiet, see ]8;;index.html#commonoptions\ Common Options]8;;\ ), pstopnm recognizes the fol-
lowing command line options:
-forceplain
forces the output file to be in plain (text) format. Otherwise,
it is in raw (binary) format. See pbm(1), etc. Use this instead
of the -plain common option if you need plain format output.
-llx=bx
selects bx as the lower left corner x coordinate (in inches) on
the Postscript input page of the subject image. See ]8;;#dimensions\the Dimen-
sions section]8;;\ .
-lly=by
selects by as the lower left corner y coordinate (in inches) on
the Postscript input page of the subject image. See ]8;;#dimensions\the Dimen-
sions section]8;;\ .
-landscape
renders the image in landscape orientation.
If you specify neither -portrait nor -landscape, pstopnm chooses
the orientation that best fits the image on the output page.
Landscape means printed sideways on the page, not printed the
long way. Those are different things if the long edge of the
page is the top one.
-portrait
renders the image in portrait orientation.
See -landscape.
-nocrop
This option causes pstopnm to make the output image exactly the
dimensions of the bordered subject image. By default, pstopnm
makes the output image the dimensions specified by -xmax and
-ymax. See ]8;;#dimensions\the Dimensions section]8;;\ .
-pbm
-pgm
-ppm selects the format of the output file. By default, all files are
rendered as PPM.
-stdout
causes output to go to Standard Output instead of to regular
files, one per page (see description of output files above). Use
pnmsplit to extract individual pages from Standard Output.
-urx=tx
selects tx as the upper right corner x coordinate (in inches) on
the Postscript input page of the subject image. See ]8;;#dimensions\the Dimen-
sions section]8;;\ .
-ury=ty
selects ty as the upper right corner y coordinate (in inches) on
the Postscript input page of the subject image. See ]8;;#dimensions\the Dimen-
sions section]8;;\ .
-verbose
prints processing information to stdout.
-xborder=frac
specifies that the left and right borders added to the subject
image are to be frac times the subject image width. The default
value is 0.1. See ]8;;#dimensions\the Dimensions section]8;;\ .
-xmax=xmax
specifies that the output image is to be xmax pixels wide. The
default is 612. See ]8;;#dimensions\the Dimensions section]8;;\ .
-xsize=xsize
specifies that the output image is to be xsize pixels wide. See
]8;;#dimensions\the Dimensions section]8;;\ .
-yborder=frac
specifies that the top and bottom borders added to the subject
image are to be frac times the subject image height. The default
value is 0.1. See ]8;;#dimensions\the Dimensions section]8;;\ .
-ymax=ymax
specifies that the output image is to be ymax pixels high. The
default is 792. See ]8;;#dimensions\the Dimensions section]8;;\ .
-ysize=ysize
specifies that the output image is to be ymax pixels high. See
]8;;#dimensions\the Dimensions section]8;;\ .
-dpi=dpi
specifies the output device resolution, in dots per inch, of the
Postscript printer that pstopnm simulates. This is the number of
PNM pixels pstopnm generates for each inch of image. See ]8;;#dimensions\the Di-
mensions section]8;;\ .
This option was new in Netpbm 10.21 (March 2004).
-textalphabits={1,2,4}
This controls subsample antialiasing of text. Antialiasing is a
form of smoothing that eliminates jagged edges on characters.
Subsample antialiasing is a kind of antialiasing that uses sub-
pixels in a box, and the value of this option is the size of that
box. 4 gives you the best looking output, while 1 causes no an-
tialiasing. Smaller numbers make pnmtops use less CPU time.
Pstopnm uses Ghostscript's TextAlphaBits parameter for this.
The default is 4.
This option was new in Netpbm 10.53 (December 2010). Older ver-
sions of pstopnm do no antialiasing.
LIMITATIONS
The program will produce incorrect results with PostScript files that
initialize the current transformation matrix. In these cases, page
translation and rotation will not have any effect. To render these
files, probably the best bet is to use the following options:
pstopnm -xborder 0 -yborder 0 -portrait -nocrop file.ps
Additional options may be needed if the document is supposed to be ren-
dered on a medium different from letter-size paper.
SEE ALSO
gs, pnmtops(1), psidtopgm(1), pbmtolps(1), pbmtoepsi(1), pnmsplit(1),
pstofits
COPYRIGHT
Copyright (c) 1992 Smithsonian Astrophysical Observatory
PostScript is a Trademark of Adobe Systems Incorporated.
AUTHOR
Alberto Accomazzi, WIPL, Center for Astrophysics.
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/pstopnm.html
netpbm documentation 21 February 2024 Pstopnm User Manual(1)
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