fromarray Memory Leak and proposed patch (Feature #993)

Hi there OpenCv developers,

Recently, I encountered some fairly significant memory leaks associated with the 'fromarray' functionality of the Python bindings. After doing a little research it was clear that this problem had also troubled a number of other users. Attached is a python script (fromarray_bug.py) that demonstrates at least two bugs I observed with the functionality, both of which seem to leak memory until finally crashing.

During my research on the problem I had noticed that partial patches had been submitted to address similar concerns with this functionality. These patches, however, did not seem to conform to my understanding of the Python Array Interface as described in the Numpy documentation 'Guide to NumPy' (page 230). Furthermore, in developing an understanding of how the 'fromarray' functionality was intended to work I discovered that the bindings attempted to somehow monitor the foreign memory within the bindings. To me this was a seemingly questionable approach, particularly given the memory being passed into the function is 'foreign' memory and hence not OpenCv's responsibility. Therefore, I wrote my own patch which is also attached here as cv.cpp.

The defining difference about my approach and submitted patches is that I replace the calls to pythonize_foreign_CvMat and pythonize_CvMatND with the following:

m->data = o;
m->offset = 0;

with the inclusion of upping the reference count of the input array object o (I also had to add to the python clean up for the cvmatnd structure i.e. cvmatnd_dealloc).

This patch seems to address the aforementioned memory leak(s) surrounding the 'fromarray' functionality and in such a way that conforms with the Python Array Interface usage (at least as describe in the NumPy documentation).

Kind Regards,

Matthew Baker