CalibrateImageTask¶

CalibrateImageTask performs “single frame processing” on one (single visit) or two (two snap visit) post- Instrument Signature Removal single detector exposure (postISRCCD). This involves merging two snaps (if provided) into one visit exposure, repairing cosmic rays and defects, detecting and measuring sources on the exposure to make an initial estimation of the point spread function (PSF), re-doing detection and measurement with that fitted PSF to compute the astrometric and photometric calibrations, and computing summary statistics of the exposure and measured catalog. Its primary outputs are a calibrated exposure (initial_pvi, pixel values in nanojansky) and catalog (initial_stars_detector) of bright (S/N >= 10) isolated point-like sources that were used as inputs to calibration and that are suitable for downstream use (for example as kernel candidates in difference imaging). This task replaces the two older tasks CharacterizeImageTask (roughly repair/estimate PSF/aperture correct) and CalibrateTask (roughly detect/measure/astrometry/photometry).

Processing summary¶

CalibrateImageTask runs this sequence of operations:

If two snap exposures are input, combine them into one visit exposure.
Find stars to estimate the PSF, via two passes of repair/detect/measure/estimate PSF:
1. Install a simple Gaussian PSF in the exposure and subtract an initial estimate of the image background.
2. Perform cosmic ray repair, source detection to \(S/N >= 50\), and a minimal list of measurement plugins to compute a first estimate of the PSF.
3. Install an updated Gaussian PSF representation of that first PSF estimate (to reduce noise and help with convergence) and re-run repair/detect/measure/estimate PSF as above.
4. Use that final fitted PSF to redo repair and measurement (hopefully with all cosmic rays now removed), resulting in the optional initial_psf_stars_detector and initial_psf_stars_footprints_detector output catalogs. Note that these catalogs do not have sky coordinates or calibrated fluxes.
Compute an aperture correction for the exposure using the final catalog measured after the PSF fit.
Find stars to use as potential calibration sources:
1. Detect sources with a peak \(S/N >= 10\).
2. For the detected sources, deblend, measure, aperture correct, and set flags based on blendedness, footprint size, and other properties.
3. Select non-“bad” flagged, unresolved, \(S/N >= 10\), isolated sources to pass to the subsequent calibration steps and to be saved as the initial_stars_detector and initial_stars_footprints_detector output catalogs. Note that these catalogs do not have sky coordinates or calibrated fluxes: those are computed at a later step.
Match the list of stars from the two steps above, to propagate flags (e.g. calib_psf_candidate, calib_psf_used) from the psf stars catalog into the second, primary output catalog.
The steps above perform several rounds of background fitting, which together are saved as the initial_pvi_background output.
Fit the astrometry to a reference catalog using an affine WCS fitter that requires a reasonable model of the camera geometry, to produce a SkyWcs for the exposure and compute on-sky coordinates for the catalog of stars. The star/refcat matches used in the astrometric fit is saved as the optional initial_astrometry_match_detector catalog.
Fit the photometry to a reference catalog, to produce a PhotoCalib for the exposure and calibrate both the image and catalog of stars to have pixels and fluxes respectively in nanojansky. Note that this results in the output exposure having a PhotoCalib identically 1; the applied PhotoCalib is saved as the initial_photoCalib_detector output. The star/refcat matches used in the photometric fit is saved as the optional initial_photometry_match_detector catalog.
Finally, the measurements and fits performed above are combined into a variety of summary statistics which are attached to the exposure, which is saved as the initial_pvi output.

Python API summary¶

from lsst.pipe.tasks.calibrateImage import CalibrateImageTask

classCalibrateImageTask(initial_stars_schema=None, **kwargs): Compute the PSF, aperture corrections, astrometric and photometric calibrations, and summary statistics for a single science exposure, and produce a catalog of brighter stars that were used to calibrate it...

attributeconfig: Access configuration fields and retargetable subtasks.

methodrun(*, exposures, id_generator=None, result=None): Find stars and perform psf measurement, then do a deeper detection and measurement and calibrate astrometry and photometry from that...

Retargetable subtasks¶

astrometry¶

Default: lsst.meas.astrom.astrometry.AstrometryTask
Field type: ConfigurableField

Task to perform astrometric calibration to fit a WCS.

compute_summary_stats¶

Default: lsst.pipe.tasks.computeExposureSummaryStats.ComputeExposureSummaryStatsTask
Field type: ConfigurableField

Task to to compute summary statistics on the calibrated exposure.

install_simple_psf¶

Default: lsst.meas.algorithms.installGaussianPsf.InstallGaussianPsfTask
Field type: ConfigurableField

Task to install a simple PSF model into the input exposure to use when detecting bright sources for PSF estimation.

measure_aperture_correction¶

Default: lsst.meas.algorithms.measureApCorr.MeasureApCorrTask
Field type: ConfigurableField

Task to compute the aperture correction from the bright stars.

photometry¶

Default: lsst.pipe.tasks.photoCal.PhotoCalTask
Field type: ConfigurableField

Task to perform photometric calibration to fit a PhotoCalib.

psf_detection¶

Default: lsst.meas.algorithms.detection.SourceDetectionTask
Field type: ConfigurableField

Task to detect sources for PSF determination.

psf_measure_psf¶

Default: lsst.pipe.tasks.measurePsf.MeasurePsfTask
Field type: ConfigurableField

Task to measure the psf on bright sources.

psf_repair¶

Default: lsst.pipe.tasks.repair.RepairTask
Field type: ConfigurableField

Task to repair cosmic rays on the exposure before PSF determination.

psf_source_measurement¶

Default: lsst.meas.base.sfm.SingleFrameMeasurementTask
Field type: ConfigurableField

Task to measure sources to be used for psf estimation.

psf_subtract_background¶

Default: lsst.meas.algorithms.subtractBackground.SubtractBackgroundTask
Field type: ConfigurableField

Task to perform intial background subtraction, before first detection pass.

snap_combine¶

Default: lsst.pipe.tasks.snapCombine.SnapCombineTask
Field type: ConfigurableField

Task to combine two snaps to make one exposure.

star_apply_aperture_correction¶

Default: lsst.meas.base.applyApCorr.ApplyApCorrTask
Field type: ConfigurableField

Task to apply aperture corrections to the selected stars.

star_catalog_calculation¶

Default: lsst.meas.base.catalogCalculation.CatalogCalculationTask
Field type: ConfigurableField

Task to compute extendedness values on the star catalog, for the star selector to remove extended sources.

star_deblend¶

Default: lsst.meas.deblender.sourceDeblendTask.SourceDeblendTask
Field type: ConfigurableField

Split blended sources into their components.

star_detection¶

Default: lsst.meas.algorithms.detection.SourceDetectionTask
Field type: ConfigurableField

Task to detect stars to return in the output catalog.

star_measurement¶

Default: lsst.meas.base.sfm.SingleFrameMeasurementTask
Field type: ConfigurableField

Task to measure stars to return in the output catalog.

star_selector¶

Default

'science'

Field type

Single-selection RegistryField

Choices

'science': lsst.meas.algorithms.sourceSelector.ScienceSourceSelectorTask
'references': lsst.meas.algorithms.sourceSelector.ReferenceSourceSelectorTask
'null': lsst.meas.algorithms.sourceSelector.NullSourceSelectorTask
'objectSize': lsst.meas.algorithms.objectSizeStarSelector.ObjectSizeStarSelectorTask
'flagged': lsst.meas.algorithms.flaggedSourceSelector.FlaggedSourceSelectorTask
'astrometry': lsst.meas.algorithms.astrometrySourceSelector.AstrometrySourceSelectorTask
'matcher': lsst.meas.algorithms.matcherSourceSelector.MatcherSourceSelectorTask

Task to select isolated stars to use for calibration.

star_set_primary_flags¶

Default: lsst.meas.algorithms.setPrimaryFlags.SetPrimaryFlagsTask
Field type: ConfigurableField

Task to add isPrimary to the catalog.

star_sky_sources¶

Default: lsst.meas.algorithms.skyObjects.SkyObjectsTask
Field type: ConfigurableField

Task to generate sky sources (‘empty’ regions where there are no detections).

Configuration fields¶

astrometry_ref_loader¶

Data type: lsst.meas.algorithms.loadReferenceObjects.LoadReferenceObjectsConfig
Field type: ConfigField

Configuration of reference object loader for astrometric fit.

connections¶

Data type: lsst.pipe.base.config.CalibrateImageConfigConnections
Field type: ConfigField

Configurations describing the connections of the PipelineTask to datatypes

id_generator¶

Data type: lsst.meas.base._id_generator.DetectorVisitIdGeneratorConfig
Field type: ConfigField

Configuration for how to generate catalog IDs from data IDs.

optional_outputs¶

Default: ['psf_stars', 'psf_stars_footprints', 'astrometry_matches', 'photometry_matches']
Field type: str ListField (optional)

Which optional outputs to save (as their connection name)? If None, do not output any of these datasets.

photometry_ref_loader¶

Data type: lsst.meas.algorithms.loadReferenceObjects.LoadReferenceObjectsConfig
Field type: ConfigField

Configuration of reference object loader for photometric fit.

saveLogOutput¶

Default: True
Field type: bool Field

Flag to enable/disable saving of log output for a task, enabled by default.

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