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Pstopnm User Manual(0) Pstopnm User Manual(0)
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 added 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,
psfile002.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 concate-
nated documents, pstopnm ignores every document but the first. This
distinction 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 generated 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
defined by four numbers, the lower left corner and the upper right cor-
ner 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
Input, pstopnm does not use the BoundingBox values (due to the techni-
cal 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 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
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
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
device resolution to use, using the -dpi option. If you say for exam-
ple -dpi=300 and the bordered subject image is 2 inches by 2 inches,
the PNM output will be 600 pixels by 600 pixels.
Or you can set the output image dimensions with -xsize and -ysize. For
example, if you say -xsize=1000 -ysize=1000 and the bordered subject
image is 2 inches by 2 inches, the output image is 1000 by 1000 pixels,
with each pixel representing 1/500 inch of input image.
If you specify one of -xsize and -ysize and not the other, pstopnm
defaults the other such that the output image has the same aspect ratio
as the bordered subject 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,
respectively.
The final case, the default, is where you don't specify any size or
resolution options of -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.
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 pstopnm | pnmtops,
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 \
-stdout -quiet testimg.ps
XSIZE and YSIZE above are the image dimensions, which you can get from
.ps file can awk or sed:
$ 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)
$ pstopnm -xborder=0 -yborder=0 $xysize ... testimg.ps
OPTIONS
-forceplain
forces the output file to be in plain (text) format. Other-
wise, it is in raw (binary) format. See pbm(5) , etc.
-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.
-portrait
renders the image in portrait orientation.
-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
default 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) , pnm-
split(1) , pstofits
COPYRIGHT
Copyright (c) 1992 Smithsonian Astrophysical Observatory
PostScript is a Trademark of Adobe Systems Incorporated.
AUTHOR
Alberto Accomazzi, WIPL, Center for Astrophysics.
netpbm documentation 04 July 2011 Pstopnm User Manual(0)
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