diff --git a/tools/python/src/image.cpp b/tools/python/src/image.cpp
index 261c3e2d0..f6d3be6c9 100644
--- a/tools/python/src/image.cpp
+++ b/tools/python/src/image.cpp
@@ -580,23 +580,23 @@ std::vector<point> py_find_peaks2 (
 // ----------------------------------------------------------------------------------------
 
 template <typename T>
-numpy_image<T> py_hysteresis_threshold (
+numpy_image<unsigned char> py_hysteresis_threshold (
     const numpy_image<T>& img,
     T lower_thresh,
     T upper_thresh
 )
 {
-    numpy_image<T> out;
+    numpy_image<unsigned char> out;
     hysteresis_threshold(img, out, lower_thresh, upper_thresh);
     return out;
 }
 
 template <typename T>
-numpy_image<T> py_hysteresis_threshold2 (
+numpy_image<unsigned char> py_hysteresis_threshold2 (
     const numpy_image<T>& img
 )
 {
-    numpy_image<T> out;
+    numpy_image<unsigned char> out;
     hysteresis_threshold(img, out);
     return out;
 }