diff --git a/mu_map/util.py b/mu_map/util.py
index a2637bed3268385e0e7dc4dc0d70223cce3e5516..259a7bbb970f2b2aa8132355f8eb367664d8adb4 100644
--- a/mu_map/util.py
+++ b/mu_map/util.py
@@ -26,3 +26,14 @@ def to_grayscale(
     _img = (img - min_val) / (max_val - min_val)
     _img = (_img * 255).astype(np.uint8)
     return _img
+
+
+def grayscale_to_rgb(img: np.ndarray):
+    """
+    Convert a grayscale image to an rgb image by repeating it three times.
+
+    :param img: the grayscale image to be converted to rgb
+    :return: the image in rgb
+    """
+    assert img.ndim == 2, f"grascale image has more than 2 dimensions {img.shape}"
+    return img.repeat(3).reshape((3, *img.shape))