Section: User Commands (1)
Updated: April 2007
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potrace - transform bitmaps into vector graphics.
potrace [options] [filename...]
potrace is a utility for tracing a bitmap, which means,
transforming a bitmap into a smooth, scalable image. The input is a
bitmap, which means, a pixel-based image composed of the two colors
black and white only. The default output is an encapsulated PostScript
file (EPS). A typical use is to create EPS files from scanned data,
such as company or university logos, handwritten notes, etc. The
resulting image is not "jaggy" like a bitmap, but smooth. It can then
be rendered at any resolution.
potrace can read bitmaps in the following formats: PBM, PGM, PPM
(collectively known as PNM, see pnm(5)), as well as BMP (Windows and
OS/2 bitmap formats). The input image should only use the two colors
black and white. If other pixel values appear in the input, they will
be converted to black and white using a simple threshold method.
potrace can currently produce the following output formats: EPS,
PostScript, PDF, SVG, PGM, and XFIG. An experimental gimppath backend
is also available. Additional backends might be added in the future.
The following options are supported. Dimensions (arguments of type
dim) can have optional units, e.g. 6.5in, 15cm, 100pt.
The default unit is inches (or centimeters, if this was configured at
compile time, see COMPILE TIME CONFIGURATION below). For pixel-based
output formats such as PGM and gimppath, the default unit is pixels.
- -h, --help
print help message and exit.
- -v, --version
print version info and exit.
- -l, --license
print license info and exit.
- -V, --show-defaults
print the defaults which were compiled into this version of potrace,
display a progress bar for each bitmap that is processed. This is
useful for interactive use, and requires a terminal. The default
behavior is not to show any progress information.
If filename arguments are given, then potrace will by default
create one output file for each input filename given. The name of the
output file is obtained from the input filename by changing its suffix
according to the chosen backend. If changing the suffix is impossible
because the names of the input and output files would be identical,
then the output filename is created by adding the "-out" suffix to the
name of the input file. If no filename arguments are given, then
potrace acts as a filter, reading from standard input and
writing to standard output. A filename of "-" may be given to specify
reading from standard input.
- -o filename, --output filename
write output to this file. All output is directed to the specified
file. If this option is used, then multiple input filenames are
allowed only for those backends which can handle multiple bitmaps;
these are currently the PostScript and PGM backends. In this case,
each input file may contain one or more bitmaps, and all the bitmaps from
all the input files are processed and the output concatenated into a
single file. A filename of "-" may be given to specify writing to
- -b name, --backend name
Select backend by name, where name is one of eps, postscript,
ps, pdf, svg, pgm, gimppath, xfig. Backend names can be abbreviated by
an unambiguous prefix.
- -e, --eps
Encapsulated PostScript backend (default). The input is a single
bitmap; the output is a stand-alone, encapsulated PostScript file
which can be included in other documents.
- -p, --postscript
PostScript backend. For this backend, the input may consist of
multiple concatenated bitmaps, which will be turned into a multi-page
- -b pdf, --backend pdf
PDF backend. For this backend, the input may consist of multiple
concatenated bitmaps, which will be turned into a multi-page PDF
- -s, --svg
SVG backend. This backend produces a scalable vector graphics (SVG)
file. This backend can process one bitmap per output file.
- -g, --pgm
PGM backend. This backend produces a portable greymap (PGM) file. It
is a convenient backend for antialiasing a bitmap image. The input may
consist of multiple concatenated bitmaps, in which case multiple greymaps
will be written to the output.
- -b gimppath, --backend gimppath
Experimental gimppath backend. This backend produces a path which can
be imported by the GNU Image Manipulation Program (Gimp) (in the
Layers, Channels & Paths dialog, select Paths, then right-click and
select Import Path). Note that Gimp's paths have some peculiar
features: they have no bounding box, they cannot be scaled, and all
control points are forced to be integers. For these reasons, it is
difficult to produce good Gimp paths at low resolutions. The gimppath
backend ignores almost all scaling and placement options; instead, the
--unit option must be used to set the desired magnification. The
--rotate option is also recognized. Note that the imported path
can lie outside the bounds of the current image in Gimp; in this case,
one needs to move the path (alt-click) or work with a larger image.
- -b xfig, --backend xfig
XFig backend. Note that XFig uses X-splines instead of
Bezier curves, thus it is not possible to translate the output of
potrace into the XFig format with absolute accuracy. This backend
does a reasonable approximation using two control points for each Bezier
curve segment. Note that the -u option has no effect for this
backend, as control points are always rounded to the nearest 1/1200 of
an inch in XFig. Rotation and color are implemented. Curve
optimization is disabled.
For more detailed information on these options, see TECHNICAL
- -z policy, --turnpolicy policy
specify how to resolve ambiguities in path decomposition. Must be one of
black, white, right, left, minority, majority, or random. Default is
minority. Turn policies can be abbreviated by an unambigous prefix,
e.g., one can specify min instead of minority.
- -t n, --turdsize n
suppress speckles of up to this many pixels.
- -a n, --alphamax n
set the corner threshold parameter. The default value is 1. The
smaller this value, the more sharp corners will be produced. If this
parameter is negative, then no smoothing will be performed and the
output is a polygon. The largest useful value is 4/3 or 1.334, which
suppresses all corners and leads to completely smooth output.
- -n, --longcurve
turn off curve optimization. Normally potrace tries to join
adjacent Bezier curve segments when this is possible. This option
disables this behavior, resulting in a larger file size.
- -O n, --opttolerance n
set the curve optimization tolerance. The default value is
0.2. Larger values allow more consecutive Bezier curve segments to be
joined together in a single segment, at the expense of accuracy.
- -u n, --unit n
set output quantization. Coordinates in the output are rounded to
1/unit pixels. The default of 10 usually gives good results. For some
of the debug modes, a value of 100 gives more accurate output. In the
case of the gimppath backend, the -u option is used to set
the desired magnification. This option has no effect for the XFig
backend, which always rasterizes to 1/1200 inch.
- -d n, --debug n
produce debugging output of type n. This has different effects for
different backends. For the PostScript/EPS backends, the values
n=1,2,3 illustrate the intermediate stages of the potrace
Scaling and placement options:
- -W dim, --width dim
set the width of output image. If only one of width and height is specified,
the other is adjusted accordingly so that the aspect ratio is
- -H dim, --height dim
set the height of output image. See -W for details.
- -r n[xn], --resolution n[xn]
set the resolution (in dpi). One inch in the output image corresponds
to this many pixels in the input. Note that it follows that a larger
value results in a smaller output image. It is possible to specify
different resolutions in the x and y directions by giving an argument
of the form nxn. This option has no effect for the PGM
- -x n[xn], --scale n[xn]
set the scaling factor (PGM backend only). A value greater than 1
enlarges the output, a value between 0 and 1 makes the output
smaller. It is possible to specify different scaling factors in the x
and y directions by giving an argument of the form nxn.
- -S n, --stretch n
set the aspect ratio. A value greater than 1 means the image will be
stretched in the y direction. A value between 0 and 1 means the image
will be stretched in the x direction.
- -A angle, --rotate angle
set the rotation angle (in degrees). The output will be rotated
counterclockwise by this angle. This is useful for compensating for
images that were scanned not quite upright.
- -M dim, --margin dim
set all four margins. The effect of this depends on the backend. For
variable-sized backends (EPS, PGM, SVG), the margins will simply
be added around the output image (or subtracted, in case of negative
margins). For fixed-size backends (PostScript, XFig), the margins
settings can be used to control the placement of the image on the
page. If only one of the left and right margin is given, the image
will be placed this distance from the respective edge of the page, and
similarly for top and bottom. If margins are given on opposite sides,
the image is scaled to fit between these margins, but not if the
scaling is already determined explicitly by one or more of the
-W, -H, -r, or -x options.
- -L dim, --leftmargin dim
set the left margin. See -M for details.
- -R dim, --rightmargin dim
set the right margin. See -M for details.
- -T dim, --topmargin dim
set the top margin. See -M for details.
- -B dim, --bottommargin dim
set the bottom margin. See -M for details.
These options are only supported by certain backends.
- -C #rrggbb, --color #rrggbb
set the foreground color of the output image. The default is
black. This option works for the PS/EPS, SVG, and XFig backends.
- --fillcolor #rrggbb
set the fill color of the output image, i.e., the color of the "white"
parts. The default is to leave these parts transparent. This option
works for the PS/EPS, SVG, and XFig backends. Implies --opaque.
fill in the white parts of the image opaquely, instead of leaving
them transparent. This only applies to interior white parts, i.e.,
those which are enclosed inside a black outline. This option
works for the PS/EPS and SVG backends. Opaqueness is always in effect
for the XFig backend.
try to group related paths together in the SVG output. Each path is
grouped together with all paths that are contained inside it, so that
they can be moved around as a unit with an SVG editor. This makes
coloring individual components slightly more cumbersome, and thus it
is not the default.
- -P format, --pagesize format
set page size. This is primarily used for the PostScript backend. In
case of the EPS backend, it may influence the default image size. The
following formats can be specified: a4, a3, a5, b5, letter, legal,
tabloid, statement, executive, folio, quarto, 10x14. Also, an argument
of the form dimxdim is accepted to specify arbitrary
dimensions. The default page size is letter (or a4, if this was
configured at compile time, see COMPILE TIME CONFIGURATION below).
Page format names can be abbreviated by an unambigous prefix.
- -c, --cleartext
do not compress the output. This option disables the use of
compression filters in the PostScript output. If the -q option
is also used, the resulting output can be easily read by other
programs or even by humans.
- -2, --level2
use PostScript level 2 compression (default). The resulting file size
is ca. 40% smaller than if the -c option is used.
- -3, --level3
use PostScript level 3 compression, if available. This gives slightly
smaller files than using -2, but the resulting files may not
print on older PostScript level 2 printers. If support for PostScript
level 3 compression has been disabled at compile time, a warning
message is printed and level 2 compression is used instead.
- -q, --longcoding
turn off optimized numerical coding. Normally, potrace uses a
very compact numerical format to represent Bezier curves in
PostScript, taking advantage of some redundancy in the curve
parameters. This option disables this behavior, resulting in longer,
but more readable output (particularly if the -c option is also
- -G n, --gamma n
set the gamma value for anti-aliasing (default is 2.2). Most computer
displays do not render shades of grey linearly, i.e., a grey value of
0.5 is not displayed as being exactly half-way between black and
white. The gamma parameter corrects for this, and therefore leads to
nicer looking output. The default value of 2.2 is appropriate for most
normal CRT displays.
- -k n, --blacklevel n
set the threshold level for converting input images to bitmaps. The
potrace algorithm expects a bitmap, thus all pixels of the input
images are converted to black or white before processing begins.
Pixels whose brightness is less than n are converted to black,
all other pixels to white. Here n is a number between 0 and
1. One case is treated specially: if the input is in an indexed color
format with exactly 2 colors, then the blacklevel is ignored and the
darker of the two colors is mapped to black.
Note: the method used by potrace for converting greymaps to
bitmaps is very crude; much better results can be obtained if a
separate program, such as mkbitmap(1), is used for this
purpose. In particular, mkbitmap(1), which is distributed with
potrace, has the ability to scale and interpolate the image
before thresholding, which results in much better preservation of
- -i, --invert
invert the input bitmap before processing.
COMPILE TIME CONFIGURATION
Certain aspects of the behavior of potrace can be configured at
compile time by passing the following options to the ./configure
compile potrace without the zlib compression library. This means
PostScript level 3 compression will not be available.
compile potrace with centimeters as the default unit instead of
compile potrace with A4 as the default page size.
The exit status is 0 on successful completion, 1 if the command line
was invalid, and 2 on any other error.
Peter Selinger <selinger at users.sourceforge.net>
For a detailed technical description of the potrace algorithm,
see the file potrace.pdf, which is available from the potrace
web site. For information on the Potrace library API, see potracelib.pdf.
WEB SITE AND SUPPORT
The latest version of potrace is available from
http://potrace.sourceforge.net/. This site also contains a list of
frequently asked questions, as well as information on how to obtain
Copyright (C) 2001-2007 Peter Selinger
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307,
USA. See also http://www.gnu.org/.
- General options:
- Input/output options:
- Backend selection:
- Algorithm options:
- Scaling and placement options:
- Output options:
- PostScript/EPS options:
- PGM options:
- Frontend options:
- COMPILE TIME CONFIGURATION
- EXIT STATUS
- TECHNICAL DOCUMENTATION
- WEB SITE AND SUPPORT
- SEE ALSO
linux.jgfs.net manual pages