removed some static methods

mantidimaging/core/operations/flat_fielding/flat_fielding.py

@@ -47,13 +47,21 @@ def enable_correct_fields_only(selected_flat_fielding_widget, flat_before_widget
 
 class FlatFieldFilter(BaseFilter):
     """Uses the flat (open beam) and dark images to normalise a stack of images (radiograms, projections),
+
     and to correct for a beam profile, scintillator imperfections and/or  detector inhomogeneities. This
+
     operation produces images of transmission values.
+
     In practice, several open beam and dark images are averaged in the flat-fielding process.
+
     Intended to be used on: Projections
+
     When: As one of the first pre-processing steps
+
     Caution: Make sure the correct stacks are selected for flat and dark.
+
     Caution: Check that the flat and dark images don't have any very bright pixels,
+
     or this will introduce additional noise in the sample. Remove outliers before flat-fielding.
     """
     filter_name = 'Flat-fielding'
@@ -140,20 +148,6 @@ def _compute_flat_field(index: int, array: np.ndarray, params: dict):
         array[index] -= dark_avg
         array[index] /= norm_divide
 
-    @staticmethod
-    def _divide(data, norm_divide):
-        np.true_divide(data, norm_divide, out=data)
-
-    @staticmethod
-    def _subtract(data, dark=None):
-        # specify out to do in place, otherwise the data is copied
-        np.subtract(data, dark, out=data)
-
-    @staticmethod
-    def _norm_divide(flat: np.ndarray, dark: np.ndarray) -> np.ndarray:
-        # subtract dark from flat
-        return np.subtract(flat, dark)
-
     @staticmethod
     def register_gui(form, on_change, view) -> dict[str, Any]:
         from mantidimaging.gui.utility import add_property_to_form