Enforce gain usage in CTI construction and application.

python/lsst/ip/isr/deferredCharge.py

@@ -232,13 +232,17 @@ class DeferredChargeCalib(IsrCalib):
     _SCHEMA = 'Deferred Charge'
     _VERSION = 1.0
 
-    def __init__(self, **kwargs):
+    def __init__(self, useGains=True, **kwargs):
         self.driftScale = {}
         self.decayTime = {}
         self.globalCti = {}
         self.serialTraps = {}
 
         super().__init__(**kwargs)
+
+        units = 'electrons' if useGains else 'ADU'
+        self.updateMetadata(USEGAINS=useGains, UNITS=units)
+
         self.requiredAttributes.update(['driftScale', 'decayTime', 'globalCti', 'serialTraps'])
 
     def fromDetector(self, detector):
@@ -560,11 +564,19 @@ def run(self, exposure, ctiCalib, gains=None):
         # true, but no external gains were supplied, use the nominal
         # gains listed in the detector.  Finally, if useGains is
         # false, fake a dictionary of unit gains for ``gainContext``.
-        if self.config.useGains:
+        useGains = True
+        if "USEGAINS" in ctiCalib.getMetadata().keys():
+            useGains = ctiCalib.getMetadata()["USEGAINS"]
+            self.log.info(f"useGains = {useGains} due to calibration")
+        else:
+            useGains = self.config.useGains
+            self.log.info(f"useGains = {useGains} due to config")
+
+        if useGains:
             if gains is None:
                 gains = {amp.getName(): amp.getGain() for amp in detector.getAmplifiers()}
 
-        with gainContext(exposure, image, self.config.useGains, gains):
+        with gainContext(exposure, image, useGains, gains):
             for amp in detector.getAmplifiers():
                 ampName = amp.getName()
 

python/lsst/ip/isr/isrStatistics.py

@@ -41,6 +41,11 @@ class IsrStatisticsTaskConfig(pexConfig.Config):
         doc="Measure CTI statistics from image and overscans?",
         default=False,
     )
+    doApplyGainsForCtiStatistics = pexConfig.Field(
+        dtype=bool,
+        doc="Apply gain to the overscan region when measuring CTI statistics?",
+        default=True,
+    )
 
     doBandingStatistics = pexConfig.Field(
         dtype=bool,
@@ -283,7 +288,10 @@ def measureCti(self, inputExp, overscans, gains):
                     osMean = afwMath.makeStatistics(overscanImage.image.array[:, column],
                                                     self.statType, self.statControl).getValue()
                     columns.append(column)
-                    values.append(gain * osMean)
+                    if self.config.doApplyGainsForCtiStatistics:
+                        values.append(gain * osMean)
+                    else:
+                        values.append(osMean)
 
                 # We want these relative to the readout corner.  If that's
                 # on the right side, we need to swap them.

python/lsst/ip/isr/isrTask.py

@@ -975,6 +975,9 @@ def validate(self):
             self.maskListToInterpolate.remove(self.saturatedMaskName)
         if self.doNanInterpolation and "UNMASKEDNAN" not in self.maskListToInterpolate:
             self.maskListToInterpolate.append("UNMASKEDNAN")
+        if self.doCalculateStatistics and self.isrStats.doCtiStatistics:
+            if self.doApplyGains != self.isrStats.doApplyGainsForCtiStatistics:
+                raise ValueError("doApplyGains must match isrStats.applyGainForCtiStatistics.")
 
 
 class IsrTask(pipeBase.PipelineTask):

tests/test_deferredCharge.py

@@ -23,7 +23,8 @@
 import tempfile
 import lsst.utils.tests
 
-from lsst.ip.isr import DeferredChargeCalib, DeferredChargeTask, SerialTrap
+from lsst.ip.isr import (DeferredChargeCalib, DeferredChargeTask, SerialTrap,
+                         IsrTaskConfig)
 
 
 class SerialTrapTestCase(lsst.utils.tests.TestCase):
@@ -135,6 +136,32 @@ def testTaskMethods(self):
         # As above + ~320 deposited in prescan
         self.assertAlmostEqual(np.sum(corrected), 821733.2317048, 5)
 
+    def testConfigLogic(self):
+        config = IsrTaskConfig()
+        config.doFlat = False
+        config.doCalculateStatistics = True
+        config.isrStats.doCtiStatistics = True
+
+        # Confirm that image and overscan are treated the same.
+        config.doApplyGains = True
+        config.isrStats.doApplyGainsForCtiStatistics = False
+        with self.assertRaises(ValueError):
+            config.validate()
+
+        config.doApplyGains = False
+        config.isrStats.doApplyGainsForCtiStatistics = True
+        with self.assertRaises(ValueError):
+            config.validate()
+
+        # these should not raise
+        config.doApplyGains = True
+        config.isrStats.doApplyGainsForCtiStatistics = True
+        config.validate()
+
+        config.doApplyGains = False
+        config.isrStats.doApplyGainsForCtiStatistics = False
+        config.validate()
+
 
 class MemoryTester(lsst.utils.tests.MemoryTestCase):
     pass