Efficiently convert System.Single[,] to numpy array

Question

Using Python 3.6 and Python for dotNET/pythonnet I have manged to get hold of an image array. This is of type System.Single[,]

I\'d like to convert that to a numpy a

Answer 1

@denfromufa - that is a very useful link.

The suggestion there is to do a direct memory copy, either using Marshal.Copy or np.frombuffer. I couldn't manage to get the Marshal.Copy version working - some shenanigans are required to use a 2D array with Marshal and that changed the contents of of the array somehow - but the np.frombuffer version seems to work for me and reduced the time to complete by a factor of ~16000 for a 3296*2471 array (~25s -> ~1.50ms). This is good enough for my purposes

The method requires a couple more imports, so I've included those in the code snippet below

import ctypes
from System.Runtime.InteropServices import GCHandle, GCHandleType

def SingleToNumpyFromBuffer(TwoDArray):
    src_hndl = GCHandle.Alloc(TwoDArray, GCHandleType.Pinned)

    try:
        src_ptr = src_hndl.AddrOfPinnedObject().ToInt32()
        bufType = ctypes.c_float*len(TwoDArray)
        cbuf = bufType.from_address(src_ptr)
        resultArray = np.frombuffer(cbuf, dtype=cbuf._type_)
    finally:
        if src_hndl.IsAllocated: src_hndl.Free()
    return resultArray