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Add DecorrelateALKernelTask as a subtask #63

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Jun 29, 2016
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Add DecorrelateALKernelTask as a subtask #63

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23 changes: 17 additions & 6 deletions python/lsst/pipe/tasks/imageDifference.py
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Original file line number Diff line number Diff line change
Expand Up @@ -36,10 +36,9 @@
from lsst.ip.diffim import ImagePsfMatchTask, DipoleAnalysis, \
SourceFlagChecker, KernelCandidateF, cast_KernelCandidateF, makeKernelBasisList, \
KernelCandidateQa, DiaCatalogSourceSelectorTask, DiaCatalogSourceSelectorConfig, \
GetCoaddAsTemplateTask, GetCalexpAsTemplateTask, DipoleFitTask
GetCoaddAsTemplateTask, GetCalexpAsTemplateTask, DipoleFitTask, DecorrelateALKernelTask
import lsst.ip.diffim.diffimTools as diffimTools
import lsst.ip.diffim.utils as diUtils
from lsst.ip.diffim.imageDecorrelation import decorrelateExposure

FwhmPerSigma = 2 * math.sqrt(2 * math.log(2))
IqrToSigma = 0.741
Expand Down Expand Up @@ -67,7 +66,7 @@ class ImageDifferenceConfig(pexConfig.Config):
"Ignored if doPreConvolve false.")
doDetection = pexConfig.Field(dtype=bool, default=True, doc="Detect sources?")
doDecorrelation = pexConfig.Field(dtype=bool, default=False,
doc="Perform diffim decorrelation to undo pixel correlation due to convolution? "
doc="Perform diffim decorrelation to undo pixel correlation due to A&L kernel convolution? "
"If True, also update the diffim PSF.")
doMerge = pexConfig.Field(dtype=bool, default=True,
doc="Merge positive and negative diaSources with grow radius set by growFootprint")
Expand Down Expand Up @@ -108,6 +107,10 @@ class ImageDifferenceConfig(pexConfig.Config):
target=ImagePsfMatchTask,
doc="Warp and PSF match template to exposure, then subtract",
)
decorrelate = pexConfig.ConfigurableField(
target=DecorrelateALKernelTask,
doc="Decorrelate effects of A&L kernel convolution on image difference, only if doSubtract is True",
)
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Please add a comment noting that it will be ignored if doSubtract is False (other than affecting the default value of detection.thresholdValue, which I think should be fixed).

Also, a brief explanation of WHY you only decorrelate if doSubtract is true would be nice. I assume it is because there is no noise to decorrelate.

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@djreiss djreiss Jun 28, 2016 •
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Do you actually mean a comment? Or add it to the docstring? I will add a comment.

My understanding is that if doSubtract is False, then the actual image differencing is not done, and instead a saved image difference is loaded from disk. I am considering image decorrelation as being "part of" image subtraction so if no subtraction performed, then no decorrelation. This assumption may eventually need to be changed, but if so then we need to somehow store the fact that the diffim was decorrelated in its fits header. For now I think it's reasonable to assume that decorrelation will have been run prior to saving.

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I meant please add the explanation it to the doc string. In general if a config field needs explanation, that explanation should go into the doc string.

detection = pexConfig.ConfigurableField(
target=SourceDetectionTask,
doc="Low-threshold detection for final measurement",
Expand Down Expand Up @@ -167,6 +170,10 @@ def setDefaults(self):
# DiaSource Detection
self.detection.thresholdPolarity = "both"
self.detection.thresholdValue = 5.5
# If decorrelation is turned on, no need to "hack" the detection threshold to decrease the number of
# false detections, so set it back to 5.0
if self.doDecorrelation and self.doSubtract:
self.detection.thresholdValue = 5.0
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Please add a comment explaining why you change this value.

Also, since you only run decorrelation if doSubtract is True, I suggest you apply the same test here. That makes the "doCorrelate" config parameter a bit easier to explain (e.g. "ignored if doSubtract False")

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Good points. Done and done.

self.detection.reEstimateBackground = False
self.detection.thresholdType = "pixel_stdev"

Expand Down Expand Up @@ -212,6 +219,7 @@ def __init__(self, butler=None, **kwargs):
pipeBase.CmdLineTask.__init__(self, **kwargs)
self.makeSubtask("subtract")
self.makeSubtask("getTemplate")
self.makeSubtask("decorrelate")

if self.config.doUseRegister:
self.makeSubtask("register")
Expand Down Expand Up @@ -516,10 +524,13 @@ def run(self, sensorRef, templateIdList=None):
template = self.getTemplate.run(exposure, sensorRef, templateIdList=templateIdList)
subtractedExposure.setPsf(template.exposure.getPsf())

# If doSubtract is False, then subtractedExposure was fetched from disk (above), thus it may have
# already been decorrelated. Thus, we do not do decorrelation if doSubtract is False.
if self.config.doDecorrelation and self.config.doSubtract:
self.log.info("Running diffim decorrelation; updating diffim PSF.")
subtractedExposure, _ = decorrelateExposure(templateExposure, exposure, subtractedExposure,
subtractRes.psfMatchingKernel, self.log)
decorrResult = self.decorrelate.run(templateExposure, exposure,
subtractedExposure,
subtractRes.psfMatchingKernel)
subtractedExposure = decorrResult.correctedExposure

if self.config.doDetection:
self.log.info("Running diaSource detection")
Expand Down