lsst.cp.pipe.ptc.measurePtcGen2Task.MeasurePhotonTransferCurveTask Class Reference

Inheritance diagram for lsst.cp.pipe.ptc.measurePtcGen2Task.MeasurePhotonTransferCurveTask:

Public Member Functions
def	__init__ (self, *args, **kwargs)
def	runDataRef (self, dataRefList)

Static Public Attributes
	RunnerClass = DataRefListRunner
	ConfigClass = MeasurePhotonTransferCurveTaskConfig

Detailed Description

A class to calculate, fit, and plot a PTC from a set of flat pairs.
The Photon Transfer Curve (var(signal) vs mean(signal)) is a standard
tool used in astronomical detectors characterization (e.g., Janesick 2001,
Janesick 2007). If ptcFitType is "EXPAPPROXIMATION" or "POLYNOMIAL",
this task calculates the PTC from a series of pairs of flat-field images;
each pair taken at identical exposure times. The difference image of each
pair is formed to eliminate fixed pattern noise, and then the variance
of the difference image and the mean of the average image
are used to produce the PTC. An n-degree polynomial or the approximation
in Equation 16 of Astier+19 ("The Shape of the Photon Transfer Curve
of CCD sensors", arXiv:1905.08677) can be fitted to the PTC curve. These
models include parameters such as the gain (e/DN) and readout noise.
Linearizers to correct for signal-chain non-linearity are also calculated.
The `Linearizer` class, in general, can support per-amp linearizers, but
in this task this is not supported.
If ptcFitType is "FULLCOVARIANCE", the covariances of the difference
images are calculated via the DFT methods described in Astier+19 and the
variances for the PTC are given by the cov[0,0] elements at each signal
level. The full model in Equation 20 of Astier+19 is fit to the PTC
to get the gain and the noise.

Parameters
----------
*args: `list`
    Positional arguments passed to the Task constructor. None used at this
    time.
**kwargs: `dict`
    Keyword arguments passed on to the Task constructor. None used at this
    time.

Definition at line 64 of file measurePtcGen2Task.py.

Constructor & Destructor Documentation

__init__()

def lsst.cp.pipe.ptc.measurePtcGen2Task.MeasurePhotonTransferCurveTask.__init__	(		self,
		*	args,
		**	kwargs
	)

Definition at line 100 of file measurePtcGen2Task.py.

    def __init__(self, *args, **kwargs):
        super().__init__(**kwargs)
        self.makeSubtask("extract")
        self.makeSubtask("solve")
 

Member Function Documentation

runDataRef()

def lsst.cp.pipe.ptc.measurePtcGen2Task.MeasurePhotonTransferCurveTask.runDataRef	(		self,
			dataRefList
	)

Run the Photon Transfer Curve (PTC) measurement task.
For a dataRef (which is each detector here),
and given a list of exposure pairs (postISR) at different exposure times,
measure the PTC.

Parameters
----------
dataRefList : `list` [`lsst.daf.peristence.ButlerDataRef`]
    Data references for exposures.

Definition at line 106 of file measurePtcGen2Task.py.

    def runDataRef(self, dataRefList):
        """Run the Photon Transfer Curve (PTC) measurement task.
        For a dataRef (which is each detector here),
        and given a list of exposure pairs (postISR) at different exposure times,
        measure the PTC.
 
        Parameters
        ----------
        dataRefList : `list` [`lsst.daf.peristence.ButlerDataRef`]
            Data references for exposures.
        """
        if len(dataRefList) < 2:
            raise RuntimeError("Insufficient inputs to combine.")
 
        # setup necessary objects
        dataRef = dataRefList[0]
        camera = dataRef.get('camera')
 
        if len(set([dataRef.dataId[self.config.ccdKey] for dataRef in dataRefList])) > 1:
            raise RuntimeError("Too many detectors supplied")
        # Get exposure list.
        expList = []
        for dataRef in dataRefList:
            try:
                tempFlat = dataRef.get("postISRCCD")
            except RuntimeError:
                self.log.warn("postISR exposure could not be retrieved. Ignoring flat.")
                continue
            expList.append(tempFlat)
        expIds = [exp.getInfo().getVisitInfo().getExposureId() for exp in expList]
 
        # Create dictionary of exposures, keyed by exposure time
        expDict = arrangeFlatsByExpTime(expList)
        # Call the "extract" (measure flat covariances) and "solve" (fit covariances) subtasks
        resultsExtract = self.extract.run(inputExp=expDict, inputDims=expIds)
        resultsSolve = self.solve.run(resultsExtract.outputCovariances, camera=camera)
 
        # Fill up the photodiode data, if found, that will be used by linearity task.
        # Get expIdPairs from one of the amps
        expIdsPairsList = []
        ampNames = resultsSolve.outputPtcDataset.ampNames
        for ampName in ampNames:
            tempAmpName = ampName
            if ampName not in resultsSolve.outputPtcDataset.badAmps:
                break
        for pair in resultsSolve.outputPtcDataset.inputExpIdPairs[tempAmpName]:
            first, second = pair[0]
            expIdsPairsList.append((first, second))
 
        resultsSolve.outputPtcDataset = self._setBOTPhotocharge(dataRef, resultsSolve.outputPtcDataset,
                                                                expIdsPairsList)
        self.log.info("Writing PTC data.")
        dataRef.put(resultsSolve.outputPtcDataset, datasetType="photonTransferCurveDataset")
 
        return
 

Member Data Documentation

ConfigClass

lsst.cp.pipe.ptc.measurePtcGen2Task.MeasurePhotonTransferCurveTask.ConfigClass = MeasurePhotonTransferCurveTaskConfig

static

Definition at line 97 of file measurePtcGen2Task.py.

RunnerClass

lsst.cp.pipe.ptc.measurePtcGen2Task.MeasurePhotonTransferCurveTask.RunnerClass = DataRefListRunner

static

Definition at line 96 of file measurePtcGen2Task.py.

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The documentation for this class was generated from the following file:

• /j/snowflake/release/lsstsw/stack/lsst-scipipe-0.6.0/Linux64/cp_pipe/22.0.1-18-gb17765a+2264247a6b/python/lsst/cp/pipe/ptc/measurePtcGen2Task.py