From d86b0642b2a87ec210e071d1e29371099d582ae7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Stefan=20Fr=C3=B6se?= <stefan.froese@udo.edu>
Date: Fri, 27 Oct 2023 14:38:38 +0200
Subject: [PATCH] flatfielding factor instead of absolute & relative

---
 ctapipe/calib/camera/calibrator.py            |  2 +-
 ctapipe/calib/camera/tests/test_calibrator.py |  6 ++++--
 ctapipe/containers.py                         | 13 ++++---------
 docs/changes/2433.bugfix.rst                  |  3 +++
 4 files changed, 12 insertions(+), 12 deletions(-)
 create mode 100644 docs/changes/2433.bugfix.rst

diff --git a/ctapipe/calib/camera/calibrator.py b/ctapipe/calib/camera/calibrator.py
index 0e29f7f228c..061558ba478 100644
--- a/ctapipe/calib/camera/calibrator.py
+++ b/ctapipe/calib/camera/calibrator.py
@@ -271,7 +271,7 @@ def _calibrate_dl1(self, event, tel_id):
                 dl1.peak_time -= remaining_shift
 
         # Calibrate extracted charge
-        dl1.image *= dl1_calib.relative_factor / dl1_calib.absolute_factor
+        dl1.image *= dl1_calib.flatfielding_factor
 
         # handle invalid pixels
         if self.invalid_pixel_handler is not None:
diff --git a/ctapipe/calib/camera/tests/test_calibrator.py b/ctapipe/calib/camera/tests/test_calibrator.py
index b70c6a4aee1..889bbf4ec97 100644
--- a/ctapipe/calib/camera/tests/test_calibrator.py
+++ b/ctapipe/calib/camera/tests/test_calibrator.py
@@ -173,6 +173,9 @@ def test_dl1_charge_calib(example_subarray):
     relative = random.normal(1, 0.01, n_pixels)
     y /= relative[:, np.newaxis]
 
+    # Define flatfielding coefficients
+    flatfielding = relative / absolute
+
     # Define pedestal
     pedestal = random.uniform(-4, 4, n_pixels)
     y += pedestal[:, np.newaxis]
@@ -191,8 +194,7 @@ def test_dl1_charge_calib(example_subarray):
     np.testing.assert_allclose(event.dl1.tel[tel_id].image, y.sum(1), rtol=1e-4)
 
     event.calibration.tel[tel_id].dl1.pedestal_offset = pedestal
-    event.calibration.tel[tel_id].dl1.absolute_factor = absolute
-    event.calibration.tel[tel_id].dl1.relative_factor = relative
+    event.calibration.tel[tel_id].dl1.flatfielding_factor = flatfielding
 
     # Test without timing corrections
     calibrator(event)
diff --git a/ctapipe/containers.py b/ctapipe/containers.py
index 3fbb88a762c..5008d90aced 100644
--- a/ctapipe/containers.py
+++ b/ctapipe/containers.py
@@ -523,16 +523,11 @@ class DL1CameraCalibrationContainer(Container):
         " This value is subtracted from the waveforms of each pixel before"
         " the pulse extraction.",
     )
-    absolute_factor = Field(
+    flatfielding_factor = Field(
         1,
-        "Multiplicative coefficients for the absolute calibration of extracted charge into "
-        "physical units (e.g. photoelectrons or photons) for each pixel",
-    )
-    relative_factor = Field(
-        1,
-        "Multiplicative Coefficients for the relative correction between pixels to achieve a "
-        "uniform charge response (post absolute calibration) from a "
-        "uniform illumination.",
+        "Multiplicative coefficients for the relative correction between "
+        "pixels to achieve a uniform charge response "
+        "(post absolute calibration) from a uniform illumination.",
     )
     time_shift = Field(
         None,
diff --git a/docs/changes/2433.bugfix.rst b/docs/changes/2433.bugfix.rst
new file mode 100644
index 00000000000..c4af68daaa7
--- /dev/null
+++ b/docs/changes/2433.bugfix.rst
@@ -0,0 +1,3 @@
+Change DL1 charge calibration in event to be a single, relative coefficient
+per channel / pixel instead of having an absolute factor for conversion to
+p.e. and a relative factor for achieving a uniform charge distrubtion.