I'm curious if imread/imwrite are still works in progress in
octave-forge. I have set it up on both a linux machine and a mac.
Right now I only have access to the linux box. I can run a command like
im = imread("file.jpg")
and then display the image with imshow. But I get error messages when
I attempt to load files in other image formats (I've tried just .png
and .gif). The imread code branches in three directions based on the
image type: if reading a .jpg file it calls jpgread.oct to import the
file; if a .png file, it calls pngread.oct; if any other format, it
calls __magick_read__.oct. In fact, though I have the image package
installed, the latter two oct-files appear not to exist at all. There
is source code for both, and I can successfully run mkoctfile on
pngread.cc, but placing the resulting pngread.oct file in the same
directory as jpgread.oct does not make reading .png files possible, as
I get the result
octave: symbol lookup error:
/home/tom/octave/image-1.0.6/x86_64-pc-linux-gnu-api-v32/pngread.oct:
undefined symbol: png_check_sig
and then Octave apparently quits un-elegantly. It is the case,
however, that after putting pngread.oct in that directory, the command
which pngread
produces the output
pngread is the dynamically-linked function from the file
/home/tom/octave/image-1.0.6/x86_64-pc-linux-gnu-api-v32/pngread.oct
When I run
mkoctfile -I/usr/include/ImageMagick __magick_read__.cc
then the compilation process produces __magick_read__.oct without
error messages. However, when I place that .oct file in the same
directory as the others and type
which __magick_read__
I get
error:
/home/tom/octave/image-1.0.6/x86_64-pc-linux-gnu-api-v32/__magick_read__.oct:
undefined symbol: _ZTIN6Magick9ExceptionE
which: `__magick_read__' is undefined
which I find surprising, given that it is the same location as
jpgread.oct and pngread.oct. I left it in that directory anyway and
tried to use imread to import a .gif, but got the message
warning: isstr is obsolete and will be removed from a future version
of Octave, please use ischar instead
error:
/home/tom/octave/image-1.0.6/x86_64-pc-linux-gnu-api-v32/__magick_read__.oct:
undefined symbol: _ZTIN6Magick9ExceptionE
error: `__magick_read__' undefined near line 73 column 33
error: evaluating if command near line 72, column 5
error: called from `imread' in file `/home/tom/octave/image-1.0.6/imread.m'
error: evaluating assignment expression near line 5, column 4
which was probably fairly predictable given the above.
One more interesting thing, which may reflect only my ignorance in
programming dynamically-linked files for Octave. I ran
mkoctfile jpgread.cc
and then replaced the working copy of jpgread.oct with the result of
the compile I did. At that point I could no longer import .jpg files.
So, my question is whether there is something fairly obvious I am, in
my ignorance, doing incorrectly? Is this behavior specific to a
certain platform like Linux (as I said, I cannot test things on my Mac
right now)? Or is it quite well known among recent users that only
.jpg files can be read using imread? If the latter, has the interface
to ImageMagick ever worked? (It has been a matter of some confusion
in the octave-maintainers list as to why .jpg and .png formats were
handled separately and only other formats resulted in calls to
Magick++ library routines, but this would certainly make the reasons
for that clearer.)
Thomas Scofield
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