ProcessCcdTask

ProcessCcdTask provides a preliminary astrometric and photometric calibration for a single frame (a raw dataset), yielding a calexp dataset. ProcessCcdTask is available as a command-line task, processCcd.py.

Processing summary

ProcessCcdTask runs this sequence of operations:

  1. Removes instrumental signature from the raw dataset by calling the isr subtask (default: IsrTask).

    This is the ISR step. In the LSST Science Pipelines, individual cameras tune the configurations for the isr subtask. By running this task, you automatically leverage expertise from the camera’s builders and community.

  2. Characterizes the post-ISR exposure by calling the charImage subtask (default: CharacterizeImageTask):

    • Models the background.
    • Models the PSF.
    • Repairs cosmic ray hits.
    • Detects and measures bright sources.
    • Measures an aperture correction.

  3. Calibrates the post-characterization exposure by calling the calibrate subtask (default: CalibrateTask):

    • Detects sources more completely (using PSF and aperture corrections from the previous step).
    • Fits an improved WCS.
    • Fits a photometric zeropoint.

    Note: you can disable the calibration step with the doCalibrate configuration field.

processCcd.py command-line interface

processCcd.py REPOPATH [@file [@file2 ...]] [--output OUTPUTREPO | --rerun RERUN] [--id] [other named arguments]

Key arguments:

REPOPATH

The input Butler repository’s URI or file path.

Key options:

--id

The data IDs to process.

See also

See Command-line task argument reference for details and additional options.

Python API summary

from lsst.pipe.tasks.processCcd import ProcessCcdTask
classProcessCcdTask(butler=None, psfRefObjLoader=None, astromRefObjLoader=None, photoRefObjLoader=None, **kwargs)

! Assemble raw data, fit the PSF, detect and measure, and fit WCS and zero-point...

attributeconfig

Access configuration fields and retargetable subtasks.

methodrunDataRef(sensorRef)

Process one CCD...

See also

See the ProcessCcdTask API reference for complete details.

Butler datasets

When run as the processCcd.py command-line task, or directly through the runDataRef method, ProcessCcdTask obtains datasets from the input Butler data repository and persists outputs to the output Butler data repository. Note that configurations for ProcessCcdTask and its subtasks affect what datasets are persisted, and what their content is.

Input datasets

raw
Raw dataset from a camera, as ingested into the input Butler data repository. Unpersisted by the isr subtask.

Output datasets

calexp

The calibrated exposure. Persisted by the calibrate subtask.

The default subtask (CalibrateTask) adds the following metadata:

MAGZERO_RMS
The RMS (standard deviation) of MAGZERO, measured by the photoCal subtask.
MAGZERO_NOBJ: Number of stars used to estimate ``MAGZERO.
This is ngood reported by the photoCal subtask.
COLORTERM1
Always 0.0.
COLORTERM2
Always 0.0.
COLORTERM3
Always 0.0.
calexpBackground
Background model for the calexp calibrated exposure. Persisted by the calibrate subtask.
icExp
The characterized exposure. Persisted by the charImage subtask.
icExpBackground
Background model of the icExp exposure.
icSrc
The source catalog of the characterized exposure, icExp. Persisted by the charImage subtask.
postISRCCD
Post-ISR exposure. Persisted by the charImage subtask.
src
Table of sources measured in the calibrated exposure. Persisted by the calibrate subtask.
srcMatch
Table of matches between the sources and reference objects, created by the astrometry solver. Persisted by the calibrate subtask.
srcMatchFull
Denormalized version of srcMatch. Persisted by the calibrate subtask.

Retargetable subtasks

calibrate

Default
lsst.pipe.tasks.calibrate.CalibrateTask
Field type
ConfigurableField
Task to perform astrometric and photometric calibration:
  • refine the WCS in the exposure
  • refine the PhotoCalib object in the exposure
  • detect sources, usually at low S/N

charImage

Default
lsst.pipe.tasks.characterizeImage.CharacterizeImageTask
Field type
ConfigurableField
Task to characterize a science exposure:
  • detect sources, usually at high S/N
  • estimate the background, which is subtracted from the image and returned as field “background”
  • estimate a PSF model, which is added to the exposure
  • interpolate over defects and cosmic rays, updating the image, variance and mask planes

isr

Default
lsst.ip.isr.isrTask.IsrTask
Field type
ConfigurableField
Task to perform instrumental signature removal or load a post-ISR image; ISR consists of:
  • assemble raw amplifier images into an exposure with image, variance and mask planes
  • perform bias subtraction, flat fielding, etc.
  • mask known bad pixels
  • provide a preliminary WCS

Configuration fields

doCalibrate

Default
True
Field type
bool Field
Perform calibration?

Examples

Simple command-line usage

ProcessCcdTask is used as a command-line task that processes raw datasets into a Butler repository.

As an example, you can use raw datasets in the obs_test package. First, set up the relevant packages on the command line:

setup lsst_distrib
setup -k obs_test

Then run the processCcd.py task:

processCcd.py $OBS_TEST_DIR/data/input --output processCcdOut --id

Using the --id option without any data ID keys finds all available raw data in the Butler dataset for processing. The output calexp and src datasets are written to the processCcdOut directory.

Important

If processCcdOut already exists, you’ll need to either delete the existing directory or give the --output option a different directory name.

Debugging

ProcessCcdTask does not have debug output, though its subtasks may.