imread() stopped working on Octave - image

Question

I've tried googling it and it seems nobody else has had this kind of error.
I'm using Octave 3.6.1 on Ubuntu 12.04. I've been using the imread() funcion to read images for quite some time, but just yesterday it started throwing this error:
octave:5> I = imread('example.jpg');
error: imread: invalid image file: Magick++ exception: Magick: Unable to open file (tures/example.jpg) reported by coders/jpeg.c:955 (ReadJPEGImage)
error: called from:
error: /usr/share/octave/3.6.1/m/image/imread.m at line 74, column 7
If I try to read a PNG, I get a similar error:
octave:5> I = imread('example.png');
error: imread: invalid image file: Magick++ exception: Magick: Unable to open file (tures/example.png) reported by coders/png.c:2790 (ReadPNGImage)
error: called from:
error: /usr/share/octave/3.6.1/m/image/imread.m at line 74, column 7
Does anybody know what's happening? How to fix this?
Thanks a lot!

Answer 1

I had the same problem with 3.6.4 on Windows 8.1, the simple workaround for me was this:
IMAGE_PATH = ('C:\Users\...');
where the image is stored
Image = file_in_path(IMAGE_PATH, 'image.jpg');
Of course it would be better to fix the actual function, but for now it's good enough.
Hope this helps.

Answer 2

Octave uses GraphicsMagick (or ImageMagick) to handle the reading and writing of images. GraphicsMagick does not handle directly the reading and writing of images, it's a wrapper for the many format libraries under a single API.
When you build GraphicsMagick, it checks your system for available libraries and disables/activates formats as those are presents. You probably built GraphicsMagick yourself without the development libraries libpng and libjpeg. In Ubuntu, I believe those are in the packages libpng12-dev and libjpeg8-dev. Either use the GraphicsMagick libraries that come with your system or if you need to build it yourself, see the instructions in the Octave wiki.
To confirm this is indeed your problem, run gm -version and check if those formats are activated. For example, the output in my system shows:
Feature Support:
Thread Safe yes
Large Files (> 32 bit) yes
Large Memory (> 32 bit) no
BZIP yes
DPS no
FlashPix no
FreeType yes
Ghostscript (Library) no
JBIG yes
JPEG-2000 yes
JPEG yes
Little CMS yes
Loadable Modules no
OpenMP yes (201107)
PNG yes
TIFF yes
TRIO no
UMEM no
WMF yes
X11 yes
XML yes
ZLIB yes