Variance calibration

docs/changes/2636.features.rst

@@ -0,0 +1 @@
+Makes changes to the CameraCalibrator in ctapipe.calib.camera.calibrator that allows it to correctly variance images generated with the VarianceExtractor

src/ctapipe/calib/camera/calibrator.py

@@ -218,7 +218,7 @@
             calibration_monitoring_id=r1.calibration_monitoring_id,
         )
 
     def _calibrate_dl1(self, event, tel_id):
         waveforms = event.dl0.tel[tel_id].waveform
         if self._check_dl0_empty(waveforms):
             return
@@ -283,7 +283,11 @@
             )
 
             # correct non-integer remainder of the shift if given
-            if self.apply_peak_time_shift.tel[tel_id] and remaining_shift is not None:
+            if (
+                self.apply_peak_time_shift.tel[tel_id]
+                and remaining_shift is not None
+                and dl1.peak_time is not None
+            ):
                 dl1.peak_time -= remaining_shift
 
         # Calibrate extracted charge
@@ -292,13 +296,21 @@
             and dl1_calib.absolute_factor is not None
         ):
             if selected_gain_channel is None:
-                dl1.image *= dl1_calib.relative_factor / dl1_calib.absolute_factor
+                if extractor.__class__.__name__ == "VarianceExtractor":
+                    dl1.image *= np.sqrt(
+                        dl1_calib.relative_factor / dl1_calib.absolute_factor
+                    )
+                else:
+                    dl1.image *= dl1_calib.relative_factor / dl1_calib.absolute_factor
             else:
                 corr = (
                     dl1_calib.relative_factor[selected_gain_channel, pixel_index]
                     / dl1_calib.absolute_factor[selected_gain_channel, pixel_index]
                 )
-                dl1.image *= corr
+                if extractor.__class__.__name__ == "VarianceExtractor":
+                    dl1.image *= np.sqrt(corr)
+                else:
+                    dl1.image *= corr
 
         # handle invalid pixels
         if self.invalid_pixel_handler is not None:

src/ctapipe/calib/camera/tests/test_calibrator.py

@@ -16,6 +16,7 @@
     GlobalPeakWindowSum,
     LocalPeakWindowSum,
     NeighborPeakWindowSum,
+    VarianceExtractor,
 )
 from ctapipe.image.reducer import NullDataVolumeReducer, TailCutsDataVolumeReducer
 
@@ -130,6 +131,23 @@ def test_check_dl0_empty(example_event, example_subarray):
     assert (event.dl1.tel[tel_id].image == 2).all()
 
 
+def test_dl1_variance_calib(example_event, example_subarray):
+    # test the calibration of variance images
+    tel_id = list(example_event.r0.tel)[0]
+    calibrator = CameraCalibrator(
+        subarray=example_subarray,
+        image_extractor=VarianceExtractor(subarray=example_subarray),
+        apply_waveform_time_shift=False,
+    )
+    calibrator(example_event)
+    image = example_event.dl1.tel[tel_id].image
+    assert image is not None
+    assert image.shape == (
+        1,
+        1764,
+    )
+
+
 def test_dl1_charge_calib(example_subarray):
     # copy because we mutate the camera, should not affect other tests
     subarray = deepcopy(example_subarray)

src/ctapipe/image/extractor.py

@@ -1308,7 +1308,7 @@ def __call__(
         self, waveforms, tel_id, selected_gain_channel, broken_pixels
     ) -> DL1CameraContainer:
         container = DL1CameraContainer(
-            image=np.nanvar(waveforms, dtype="float32", axis=2),
+            image=np.nanvar(waveforms, dtype="float32", keepdims=False, axis=2),
         )
         container.meta["ExtractionMethod"] = str(VarianceType.WAVEFORM)
         return container