diff --git a/esbo_etc/classes/psf/IPSF.py b/esbo_etc/classes/psf/IPSF.py
index 748bfa4..f7a741c 100644
--- a/esbo_etc/classes/psf/IPSF.py
+++ b/esbo_etc/classes/psf/IPSF.py
@@ -1,7 +1,8 @@
 from abc import ABC, abstractmethod
 import astropy.units as u
-import numpy as np
+from ..sensor.PixelMask import PixelMask
 from typing import Union
+import numpy as np
 
 
 class IPSF(ABC):
@@ -46,3 +47,35 @@ class IPSF(ABC):
             The grid with the mapped values.
         """
         pass
+
+    @staticmethod
+    def rebin(arr: np.ndarray, factor: float):
+        """
+        Rebin a 2D-array by summing or repeating the elements.
+
+        Parameters
+        ----------
+        arr : ndarray
+            Input array.
+        factor : float
+            Rebinning factor
+        Returns
+        -------
+        rebinned_array : ndarray
+            If the factor is smaller than 1, the data is summed,
+            if the factor is bigger than 1, array elements are repeated
+        See Also
+        --------
+        resize : Return a new array with the specified factor.
+        """
+        m, n = arr.shape
+        m_new, n_new = int(m * factor), int(n * factor)
+        if factor < 1:
+            res = arr.reshape((m_new, int(1 / factor), n_new, int(1 / factor))).sum(3).sum(1)
+        elif factor > 1:
+            res = np.repeat(np.repeat(arr, int(factor), axis=0), int(factor), axis=1)
+        else:
+            res = arr
+        if isinstance(arr, PixelMask):
+            res.pixel_size = res.pixel_size / factor
+        return res