diff --git a/include/plugins/string_io.hpp b/include/plugins/string_io.hpp
index 743dba9a..01322b81 100644
--- a/include/plugins/string_io.hpp
+++ b/include/plugins/string_io.hpp
@@ -26,52 +26,52 @@ using namespace Gamera;
 
 template<class T>
 PyObject* _to_raw_string(const T &image) {
-	typedef typename T::value_type value_type;
-	typename T::const_vec_iterator j = image.vec_begin();
-	std::stringstream stream;
-	for (; j != image.vec_end(); ++j) {
-		stream << *j;
-	}
-	std::string str = stream.str();
-	PyObject* pystring = PyBytes_FromStringAndSize(str.c_str(),
-	                              str.length());
-	
-	return pystring;
-}
+  typedef typename T::value_type value_type;
+  typename T::const_vec_iterator j = image.vec_begin();
+  size_t image_size = image.ncols() * image.nrows() * sizeof(value_type);
+  PyObject* pystring = PyBytes_FromStringAndSize((char *)nullptr,
+						  (int)image_size);
+  if (pystring == nullptr)
+    return nullptr;
+  value_type* i = (value_type*)PyBytes_AsString(pystring);
+  if(i == nullptr){
+	  return nullptr;
+  }
+  for (; j != image.vec_end(); ++i, ++j) {
+    *i = *j;
+  }
+  return pystring;
+};
 
 template <class T>
 bool fill_image_from_string(T &image, PyObject* data_string) {
-	Py_XINCREF(data_string);
-	PyObject *s = PyObject_Bytes(data_string);
-	if (s == nullptr) {
-		PyErr_SetString(PyExc_TypeError, "could not get string from id_name tuple.");
-		return -1;
-	}
-	size_t length = PyBytes_GET_SIZE(data_string);
-	//char* s = PyString_AS_STRING(data_string);
-	//size_t length = PyString_GET_SIZE(data_string);
-	typedef typename T::value_type value_type;
-	size_t image_size = image.ncols() * image.nrows() * sizeof(value_type);
-	if (length != image_size) {
-		if (length > image_size) {
-			Py_XDECREF(data_string);
-			PyErr_SetString(PyExc_ValueError,
-			                "data_string too long for image");
-		} else {
-			Py_XDECREF(data_string);
-			PyErr_SetString(PyExc_ValueError,
-			                "data_string too short for image");
-		}
-		Py_XDECREF(data_string);
-		return false;
-	}
-	typename T::vec_iterator i = image.vec_begin();
-	value_type *j = (value_type *) s;
-	for (; i != image.vec_end(); ++i, ++j) {
-		*i = *j;
-	}
-	Py_XDECREF(data_string);
-	return true;
+  Py_XINCREF(data_string);
+  if (!PyBytes_CheckExact(data_string)) {
+    PyErr_SetString(PyExc_TypeError,
+		    "data_string must be a Python string");
+    return false;
+  }
+  char* s = PyBytes_AS_STRING(data_string);
+  size_t length = PyBytes_GET_SIZE(data_string);
+  typedef typename T::value_type value_type;
+  size_t image_size = image.ncols() * image.nrows() * sizeof(value_type);
+  if (length != image_size) {
+    if (length > image_size) {
+      PyErr_SetString(PyExc_ValueError,
+		      "data_string too long for image");
+    } else {
+      PyErr_SetString(PyExc_ValueError,
+		      "data_string too short for image");
+    }
+    return false;
+  }
+  typename T::vec_iterator i = image.vec_begin();
+  value_type* j = (value_type*)s;
+  for (; i != image.vec_end(); ++i, ++j) {
+    *i = *j;
+  }
+  Py_XDECREF(data_string);
+  return true;
 }
 
 Image* _from_raw_string(Point offset, Dim size,
@@ -127,4 +127,3 @@ Image* _from_raw_string(Point offset, Dim size,
 }
 
 #endif
-