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 dou-
ble 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 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, depend-
ing 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 ps-
file.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 ev-
ery 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 concate-
nated documents, pstopnm ignores every document but the first. This
distinction does not exist for non-EPSF Postscript input - pstopnm gen-
erates 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 the Dimensions section ⟨#dimensions⟩ 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 -xbor-
der 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 In-
put, pstopnm does not use the BoundingBox values (because of the tech-
nical difficulty of extracting that information and still feeding the
file to Ghostscript), so you either have to specify the image area co-
ordinates 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 re-
gard to how big the sheet of paper on which it is printing is. In a
PNM image, by contrast, there is no spatial dimension; there are only
pixels. You might have a line that is 100 pixels long, but the PNM im-
age 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
virtual 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 de-
vice 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
image 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 repre-
sents 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 orien-
tation, "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 resolu-
tion, pstopnm does some weird computation which exists mainly for his-
torical 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
resolution options or -nocrop. This is the most complicated case. In
this case, pstopnm first chooses an output device resolution that would
generate the number of pixels indicated by -xmax and -ymax from the
bordered subject image. Then, based on that resolution, it chooses an
output image size that is just large enough to accommodate the subject
image (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 in-
correct 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 re-
versible conversion.
OPTIONS
In addition to the options common to all programs based on libnetpbm
(most notably -quiet, see
Common Options ⟨index.html#commonoptions⟩ ), pstopnm recognizes the
following command line options:
-forceplain
forces the output file to be in plain (text) format. Other-
wise, 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 the
Dimensions section ⟨#dimensions⟩ .
-lly=by
selects by as the lower left corner y coordinate (in inches) on
the Postscript input page of the subject image. See the
Dimensions section ⟨#dimensions⟩ .
-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 the Dimensions section ⟨#dimensions⟩ .
-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 the
Dimensions section ⟨#dimensions⟩ .
-ury=ty
selects ty as the upper right corner y coordinate (in inches) on
the Postscript input page of the subject image. See the
Dimensions section ⟨#dimensions⟩ .
-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 the Dimensions section ⟨#dimensions⟩ .
-xmax=xmax
specifies that the output image is to be xmax pixels wide. The
default is 612. See the Dimensions section ⟨#dimensions⟩ .
-xsize=xsize
specifies that the output image is to be xsize pixels wide. See
the Dimensions section ⟨#dimensions⟩ .
-yborder=frac
specifies that the top and bottom borders added to the subject
image are to be frac times the subject image height. The de-
fault value is 0.1. See the Dimensions section ⟨#dimensions⟩ .
-ymax=ymax
specifies that the output image is to be ymax pixels high. The
default is 792. See the Dimensions section ⟨#dimensions⟩ .
-ysize=ysize
specifies that the output image is to be ymax pixels high. See
the Dimensions section ⟨#dimensions⟩ .
-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 the
Dimensions section ⟨#dimensions⟩ .
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 antialiasing. 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 06 December 2013 Pstopnm User Manual(1)
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