It’s possible a transform isn’t being cleaned up. How bad is the leak?

Using psutil I see that the heap usage in this particular example stays stable at 145 MB with linear scale, but it eats up 2 GB in less than 20 seconds for the log scale.

Our application, with less frequent updates, takes a few minutes to claim all the memory.

Agreed, this leaks on my machine using master.

Memory leak is real, is there any resolution for this issue or any temporary solution to bypass before new release?

...\site-packages\matplotlib\image.py:431: size=141 MiB, count=79, average=1833 KiB
...\site-packages\matplotlib\image.py:466: size=141 MiB, count=52, average=2785 KiB

I guess a work around is to animate by saving pngs and then calling ffmpegs or other writers.

We talked about this on the call and we suspect that the memory leak is in the c++ based resampling code for AxesImage.

Upon inspection it looks like the issue may be(?) in _image_wrapper.cpp::image_resample, specifically at

    output_array = (PyArrayObject *)PyArray_FromAny(
        py_output_array, NULL, 2, 3, NPY_ARRAY_C_CONTIGUOUS, NULL);
    if (output_array == NULL) {

where the problem is that we already allocated an array in python code and allocate another PyObject here(?); however the obvious

diff --git i/src/_image_wrapper.cpp w/src/_image_wrapper.cpp
index de65e90c8..cb9a91ce0 100644
--- i/src/_image_wrapper.cpp
+++ w/src/_image_wrapper.cpp
@@ -146,9 +146,13 @@ image_resample(PyObject *self, PyObject* args, PyObject *kwargs)
         goto error;
     }
 
-    output_array = (PyArrayObject *)PyArray_FromAny(
-        py_output_array, NULL, 2, 3, NPY_ARRAY_C_CONTIGUOUS, NULL);
-    if (output_array == NULL) {
+    if (!PyArray_Check(py_output_array)) {
+        PyErr_SetString(PyExc_ValueError, "output array must be a numpy array");
+        goto error;
+    }
+    output_array = (PyArrayObject *)py_output_array;
+    if (!PyArray_IS_C_CONTIGUOUS(output_array)) {
+        PyErr_SetString(PyExc_ValueError, "output array must be a C-contiguous");
         goto error;
     }
 
@@ -330,11 +334,10 @@ image_resample(PyObject *self, PyObject* args, PyObject *kwargs)
 
     Py_DECREF(input_array);
     Py_XDECREF(transform_mesh_array);
-    return (PyObject *)output_array;
+    Py_RETURN_NONE;
 
  error:
     Py_XDECREF(input_array);
-    Py_XDECREF(output_array);
     Py_XDECREF(transform_mesh_array);
     return NULL;
 }

(just getting the array from outside and making sure it has the right size and not messing with its refcounts at all) does not seem to fix the issue.

It was right to look at the C++ code, but it wasn't output array that leaking. I included that change as part of general cleanup, but the real leak was the input mesh.

Thanks for reporting this @ibancg !

Great, thanks for the fix!.