Move _apply_correction into the ImageExtractor parent class

 - _apply_correction is now a static method from ImageExtractors parent
   class
 - _calculate_correction is moved to the parent ImageExtractors class
   to avoid writing the docstrings multiple times. It needs to be
   overwritten by the child components

src/ctapipe/image/extractor.py

@@ -359,15 +359,6 @@ def integration_correction(
     return correction
 
 
-def _apply_correction(charge, correction, selected_gain_channel):
-    """
-    Helper function for applying the integration correction for certain `ImageExtractor`s.
-    """
-    if selected_gain_channel is None:
-        return (charge * correction[:, np.newaxis]).astype(charge.dtype)
-    return (charge * correction[selected_gain_channel]).astype(charge.dtype)
-
-
 class ImageExtractor(TelescopeComponent):
     def __init__(self, subarray, config=None, parent=None, **kwargs):
         """
@@ -402,6 +393,37 @@ def __init__(self, subarray, config=None, parent=None, **kwargs):
             for tel_id, telescope in subarray.tel.items()
         }
 
+    def _calculate_correction(self, tel_id):
+        """
+        Calculate the correction for the extracted charge such that the value
+        returned would equal 1 for a noise-less unit pulse. `ImageExtractor` types
+        calculating corrections need to overwrite this method.
+
+        This method should be decorated with @lru_cache to ensure it is only
+        calculated once per telescope.
+
+        Parameters
+        ----------
+        tel_id : int
+
+        Returns
+        -------
+        correction : ndarray
+        The correction to apply to an extracted charge using this ImageExtractor
+        Has size n_channels, as a different correction value might be required
+        for different gain channels.
+        """
+        pass
+
+    @staticmethod
+    def _apply_correction(charge, correction, selected_gain_channel):
+        """
+        Helper function for applying the integration correction for certain `ImageExtractor`s.
+        """
+        if selected_gain_channel is None:
+            return (charge * correction[:, np.newaxis]).astype(charge.dtype)
+        return (charge * correction[selected_gain_channel]).astype(charge.dtype)
+
     @abstractmethod
     def __call__(
         self, waveforms, tel_id, selected_gain_channel, broken_pixels
@@ -476,24 +498,6 @@ class FixedWindowSum(ImageExtractor):
 
     @lru_cache(maxsize=128)
     def _calculate_correction(self, tel_id):
-        """
-        Calculate the correction for the extracted charge such that the value
-        returned would equal 1 for a noise-less unit pulse.
-
-        This method is decorated with @lru_cache to ensure it is only
-        calculated once per telescope.
-
-        Parameters
-        ----------
-        tel_id : int
-
-        Returns
-        -------
-        correction : ndarray
-        The correction to apply to an extracted charge using this ImageExtractor
-        Has size n_channels, as a different correction value might be required
-        for different gain channels.
-        """
         readout = self.subarray.tel[tel_id].camera.readout
         return integration_correction(
             readout.reference_pulse_shape,
@@ -515,7 +519,7 @@ def __call__(
         )
         if self.apply_integration_correction.tel[tel_id]:
             correction = self._calculate_correction(tel_id=tel_id)
-            charge = _apply_correction(charge, correction, selected_gain_channel)
+            charge = self._apply_correction(charge, correction, selected_gain_channel)
 
         # reduce dimensions for gain selected data to (n_pixels, )
         if selected_gain_channel is not None:
@@ -562,24 +566,6 @@ class GlobalPeakWindowSum(ImageExtractor):
 
     @lru_cache(maxsize=128)
     def _calculate_correction(self, tel_id):
-        """
-        Calculate the correction for the extracted charge such that the value
-        returned would equal 1 for a noise-less unit pulse.
-
-        This method is decorated with @lru_cache to ensure it is only
-        calculated once per telescope.
-
-        Parameters
-        ----------
-        tel_id : int
-
-        Returns
-        -------
-        correction : ndarray
-        The correction to apply to an extracted charge using this ImageExtractor
-        Has size n_channels, as a different correction value might be required
-        for different gain channels.
-        """
         readout = self.subarray.tel[tel_id].camera.readout
         return integration_correction(
             readout.reference_pulse_shape,
@@ -619,7 +605,7 @@ def __call__(
         )
         if self.apply_integration_correction.tel[tel_id]:
             correction = self._calculate_correction(tel_id=tel_id)
-            charge = _apply_correction(charge, correction, selected_gain_channel)
+            charge = self._apply_correction(charge, correction, selected_gain_channel)
 
         # reduce dimensions for gain selected data to (n_pixels, )
         if selected_gain_channel is not None:
@@ -651,24 +637,6 @@ class LocalPeakWindowSum(ImageExtractor):
 
     @lru_cache(maxsize=128)
     def _calculate_correction(self, tel_id):
-        """
-        Calculate the correction for the extracted charge such that the value
-        returned would equal 1 for a noise-less unit pulse.
-
-        This method is decorated with @lru_cache to ensure it is only
-        calculated once per telescope.
-
-        Parameters
-        ----------
-        tel_id : int
-
-        Returns
-        -------
-        correction : ndarray
-        The correction to apply to an extracted charge using this ImageExtractor
-        Has size n_channels, as a different correction value might be required
-        for different gain channels.
-        """
         readout = self.subarray.tel[tel_id].camera.readout
         return integration_correction(
             readout.reference_pulse_shape,
@@ -691,7 +659,7 @@ def __call__(
         )
         if self.apply_integration_correction.tel[tel_id]:
             correction = self._calculate_correction(tel_id=tel_id)
-            charge = _apply_correction(charge, correction, selected_gain_channel)
+            charge = self._apply_correction(charge, correction, selected_gain_channel)
 
         # reduce dimensions for gain selected data to (n_pixels, )
         if selected_gain_channel is not None:
@@ -716,28 +684,6 @@ class SlidingWindowMaxSum(ImageExtractor):
 
     @lru_cache(maxsize=128)
     def _calculate_correction(self, tel_id):
-        """
-        Calculate the correction for the extracted charge such that the value
-        returned would equal 1 for a noise-less unit pulse.
-
-        This method is decorated with @lru_cache to ensure it is only
-        calculated once per telescope.
-
-        The same procedure as for the actual SlidingWindowMaxSum extractor is used, but
-        on the reference pulse_shape (that is also more finely binned)
-
-        Parameters
-        ----------
-        tel_id : int
-
-        Returns
-        -------
-        correction : ndarray
-        The correction to apply to an extracted charge using this ImageExtractor
-        Has size n_channels, as a different correction value might be required
-        for different gain channels.
-        """
-
         readout = self.subarray.tel[tel_id].camera.readout
 
         # compute the number of slices to integrate in the pulse template
@@ -775,7 +721,7 @@ def __call__(
 
         if self.apply_integration_correction.tel[tel_id]:
             correction = self._calculate_correction(tel_id=tel_id)
-            charge = _apply_correction(charge, correction, selected_gain_channel)
+            charge = self._apply_correction(charge, correction, selected_gain_channel)
 
         # reduce dimensions for gain selected data to (n_pixels, )
         if selected_gain_channel is not None:
@@ -813,24 +759,6 @@ class NeighborPeakWindowSum(ImageExtractor):
 
     @lru_cache(maxsize=128)
     def _calculate_correction(self, tel_id):
-        """
-        Calculate the correction for the extracted charge such that the value
-        returned would equal 1 for a noise-less unit pulse.
-
-        This method is decorated with @lru_cache to ensure it is only
-        calculated once per telescope.
-
-        Parameters
-        ----------
-        tel_id : int
-
-        Returns
-        -------
-        correction : ndarray
-        The correction to apply to an extracted charge using this ImageExtractor
-        Has size n_channels, as a different correction value might be required
-        for different gain channels.
-        """
         readout = self.subarray.tel[tel_id].camera.readout
         return integration_correction(
             readout.reference_pulse_shape,
@@ -861,7 +789,7 @@ def __call__(
 
         if self.apply_integration_correction.tel[tel_id]:
             correction = self._calculate_correction(tel_id=tel_id)
-            charge = _apply_correction(charge, correction, selected_gain_channel)
+            charge = self._apply_correction(charge, correction, selected_gain_channel)
 
         # reduce dimensions for gain selected data to (n_pixels, )
         if selected_gain_channel is not None: