+static PyObject* py_combine(PyObject* self, PyObject* args)
+{
+ const unsigned char *im_bg;
+ const unsigned char *im_fg;
+ int size;
+
+ int i;
+ long int sum;
+ int area;
+
+ if (!PyArg_ParseTuple(args, "s#s#", &im_bg, &size, &im_fg, &size)) return NULL;
+
+ sum = 0;
+ area = 0;
+ for (i=0; i < size; i++) {
+ if (im_fg[i]){
+ sum += im_bg[i];
+ area++;
+ }
+ }
+
+ return Py_BuildValue("d", ((double) sum) / area);
+}
+