GraphicsMagick

Octave will use GraphicsMagick for reading and writing your images (not for plots, only used for image processing). This means that the GraphicsMagick configuration you have on you system will determine what your Octave installation can do. Most systems will have it on their own repositories. Unfortunately, their configuration is not always the best for image analysis as it can limit the bit depth when reading and writing of images.

To solve the problem, GraphicsMagick needs to be rebuilt with the appropriate settings. See below for tracking dependencies and the reasoning behind each flag. Once done, the following commands should work to build GraphicsMagick.

./configure --with-quantum-depth=16 --enable-shared --disable-static --with-magick-plus-plus=yes
make
make check
sudo make install

if after the build, you get "error while loading shared libraries: libGraphicsMagick.so.3: cannot open shared object file: No such file or directory" you need to run ldconfig. For security and performance reasons, Linux maintains a cache of the shared libraries installed in "approved" locations and this command will update it.

Quantum depth

The most common problem is the following warning when using imread() or imwrite():

warning: your version of GraphicsMagick limits images to <N> bits per pixel

...where N can be 8, 16 or 32. For instance:

warning: your version of GraphicsMagick limits images to 8 bits per pixel

This warning means that GraphicsMagick was compiled with --with-quantum-depth <N>, which implements that limitation. The INSTALL-unix page of GraphicsMagick documentation explains the rationale of this option.

There are several bug reports requesting package maintainers to compile GraphicsMagick with higher values. You should not create a new bug; instead look for open bugs for your system, and leave a comment there. For convenience, here are the links for the bugs reported against Debian, Ubuntu, and Fedora.

As versions with higher values are not available on the repositories, there are two ways to address this. The easiest is to suppress the warning, as suggested in the relevant bug report, if you know it won't affect your code. To do this, add the following command to your script:

warning('off', 'Octave:GraphicsMagic-Quantum-Depth');

The proper solution is to compile GraphicsMagick yourself, to pass the desired value to --with-quantum-depth. You will also need to recompile Octave to use the freshly compiled Magick++ library.

Increasing quantum depth may have a dramatic increase in memory usage. If you use QuantumDepth 32, all images will be read with that precision, even if they were saved with 8bit. This means that a 100MB 8bit image will temporarily take 400MB memory, or more if the image was compressed (and they usually are), before Octave resizes it back down to 100MB. Because of this, because images using 32 bit integers are rare, and because GraphicsMagick does not handle floating point, it's recommended to use QuantumDepth of 16.

Magick++

Magick++ is the C++ application programming interface to GraphicsMagick. This is what Octave uses so you will need this when compiling GraphicsMagick. This will be enabled by default but if you don't have a C++ compiler installed (such as g++) GraphicsMagick will build just fine without a warning, just a small note during the run of configure.

Shared libraries

The default is to disable shared libraries but that won't work with Octave. You will need to pass the --enable-shared option. If you do not, Octave will give the following warning when running configure:

GraphicsMagick++ library fails tests.  The imread function for reading image files will not be fully functional.

Dependencies

Compiling from source means tracking the dependencies yourself which may be a kind of painful. There's no wiki for GraphicsMagick so the following table hopes to makes things easier. Note however that this is the list of all dependencies and suggestions. For Octave purposes only, you definetely will not need all of these.

To start with you will obviously need the following

• a C compiler such as gcc
• a C++ compiler such as g++
• make

Main dependencies

These are the ones which support being enabled or disabled via the configure script options and are shown in the summary status at the end of the configure script run. You will need them at compile time.

Dependency	Debian Wheezy	Ubuntu Precise	OpenSUSE 13.2
BZLIB	libbz2-dev	libbz2-dev	libbz2-devel
FlashPIX
FreeType 2.0	libfreetype6-dev	libfreetype6-dev	freetype2-devel
Ghostscript	ghostscript	ghostscript
Ghostscript-fonts	gsfonts	gsfonts
JBIG	libjbig-dev		libjbig-devel
JPEG v1	libjpeg8-dev	libjpeg-dev	libjpeg62-devel
JPEG-2000	libjasper-dev	libjasper-dev	libjasper-devel
LCMS v2	liblcms2-dev	liblcms2-dev	liblcms2-devel
ltdl	libltdl-dev	libltdl-dev	libtool
LZMA	liblzma-dev	liblzma-dev	xz-devel
PNG	libpng12-dev	libpng12-dev	libpng12-devel
TIFF	libtiff5-dev	libtiff5-dev	libtiff-devel
WEBPD	libwebp-dev		libwebp-devel
WMF	libwmf-dev	libwmf-dev	libwmf-devel
X11	libx11-dev libxext-dev libsm-dev
XML	libxml2-dev	libxml2-dev	libxml2-devel
ZLIB	zlib1g-dev	zlib1g-dev	zlib-devel

the following libraries are not listed because:

• Trio is only needed/useful on certain archaic systems which lack secure vsnprintf variants.
• DPS has been deprecated and should not be used.
• Ghostscript library support is not recommended by GraphicsMagick on Unix type systems. Read their README.txt file.
• there are both v1 and v2 LCMSlibraries but GraphicsMagick only needs one of them.

Other dependencies

These other dependendies are easily added via a user-editable text file after building and installation. They are much more specific and most users will have no need for them.

Dependency	Debian Wheezy	Ubuntu Precise
dcraw	dcraw	dcraw
dvips	texlive-base	texlive-base
dot	graphviz	graphviz
fig2dev	transfig	transfig
gnuplot	gnuplot	gnuplot
hp2xx	hp2xx	hp2xx
html2ps	html2ps	html2ps
lp	cups-client	cups-client
lpr	cups-bsd	cups-bsd
mpeg2decode
mpeg2encode
pgpv	pgpgpg	pgpgpg
povray
ra_ppm	radiance	radiance
rawtorle
scanimage	sane-utils	sane-utils