DeferredChargeTask

class lsst.ip.isr.DeferredChargeTask(config: Optional[Config] = None, name: Optional[str] = None, parentTask: Optional[Task] = None, log: Optional[Union[logging.Logger, lsst.utils.logging.LsstLogAdapter]] = None)

Bases: lsst.pipe.base.Task

Task to correct an exposure for charge transfer inefficiency.

This uses the methods described by Snyder et al. 2021, Journal of Astronimcal Telescopes, Instruments, and Systems, 7, 048002. doi:10.1117/1.JATIS.7.4.048002 (Snyder+21).

Methods Summary

emptyMetadata()	Empty (clear) the metadata for this Task and all sub-Tasks.
flipData(ampData, amp)	Flip data array such that readout corner is at lower-left.
getFullMetadata()	Get metadata for all tasks.
getFullName()	Get the task name as a hierarchical name including parent task names.
getName()	Get the name of the task.
getTaskDict()	Get a dictionary of all tasks as a shallow copy.
local_offset_inverse(inputArr, drift_scale, …)	Remove CTI effects from local offsets.
local_trap_inverse(inputArr, trap[, …])	Apply localized trapping inverse operator to pixel signals.
makeField(doc)	Make a lsst.pex.config.ConfigurableField for this task.
makeSubtask(name, **keyArgs)	Create a subtask as a new instance as the name attribute of this task.
run(exposure, ctiCalib[, gains])	Correct deferred charge/CTI issues.
timer(name, logLevel)	Context manager to log performance data for an arbitrary block of code.

Methods Documentation

emptyMetadata() → None

Empty (clear) the metadata for this Task and all sub-Tasks.

static flipData(ampData, amp)

Flip data array such that readout corner is at lower-left.

Parameters:

ampData : numpy.ndarray, (nx, ny)

Image data to flip.

amp : lsst.afw.cameraGeom.Amplifier

Amplifier to get readout corner information.

Returns:

ampData : numpy.ndarray, (nx, ny)

Flipped image data.

getFullMetadata() → lsst.pipe.base._task_metadata.TaskMetadata

Get metadata for all tasks.

Returns:

metadata : TaskMetadata

The keys are the full task name. Values are metadata for the top-level task and all subtasks, sub-subtasks, etc.

Notes

The returned metadata includes timing information (if @timer.timeMethod is used) and any metadata set by the task. The name of each item consists of the full task name with . replaced by :, followed by . and the name of the item, e.g.:

topLevelTaskName:subtaskName:subsubtaskName.itemName

using : in the full task name disambiguates the rare situation that a task has a subtask and a metadata item with the same name.

getFullName() → str

Get the task name as a hierarchical name including parent task names.

Returns:

fullName : str

The full name consists of the name of the parent task and each subtask separated by periods. For example:

• The full name of top-level task “top” is simply “top”.
• The full name of subtask “sub” of top-level task “top” is “top.sub”.
• The full name of subtask “sub2” of subtask “sub” of top-level task “top” is “top.sub.sub2”.

getName() → str

Get the name of the task.

Returns:

taskName : str

Name of the task.

See also

getFullName

getTaskDict() → Dict[str, weakref.ReferenceType[lsst.pipe.base.task.Task]]

Get a dictionary of all tasks as a shallow copy.

Returns:

taskDict : dict

Dictionary containing full task name: task object for the top-level task and all subtasks, sub-subtasks, etc.

static local_offset_inverse(inputArr, drift_scale, decay_time, num_previous_pixels=15)

Remove CTI effects from local offsets.

This implements equation 10 of Snyder+21. For an image with CTI, s’(m, n), the correction factor is equal to the maximum value of the set of:

Parameters:

inputArr : numpy.ndarray, (nx, ny)

Input image data to correct.

drift_scale : float

Drift scale (Snyder+21 A_L value) to use in correction.

decay_time : float

Decay time (Snyder+21 tau_L) of the correction.

num_previous_pixels : int, optional

Number of previous pixels to use for correction. As the CTI has an exponential decay, this essentially truncates the correction where that decay scales the input charge to near zero.

Returns:

outputArr : numpy.ndarray, (nx, ny)

Corrected image data.

static local_trap_inverse(inputArr, trap, global_cti=0.0, num_previous_pixels=6)

Apply localized trapping inverse operator to pixel signals.

This implements equation 13 of Snyder+21. For an image with CTI, s’(m, n), the correction factor is equal to the maximum value of the set of:

Parameters:

inputArr : numpy.ndarray, (nx, ny)

Input image data to correct.

trap : lsst.ip.isr.SerialTrap

Serial trap describing the capture and release of charge.

global_cti: `float`

Mean charge transfer inefficiency, b from Snyder+21.

num_previous_pixels : int, optional

Number of previous pixels to use for correction.

Returns:

outputArr : numpy.ndarray, (nx, ny)

Corrected image data.

classmethod makeField(doc: str) → lsst.pex.config.configurableField.ConfigurableField

Make a lsst.pex.config.ConfigurableField for this task.

Parameters:

doc : str

Help text for the field.

Returns:

configurableField : lsst.pex.config.ConfigurableField

A ConfigurableField for this task.

Examples

Provides a convenient way to specify this task is a subtask of another task.

Here is an example of use:

class OtherTaskConfig(lsst.pex.config.Config):
    aSubtask = ATaskClass.makeField("brief description of task")

makeSubtask(name: str, **keyArgs) → None

Create a subtask as a new instance as the name attribute of this task.

Parameters:

name : str

Brief name of the subtask.

keyArgs

Extra keyword arguments used to construct the task. The following arguments are automatically provided and cannot be overridden:

• “config”.
• “parentTask”.

Notes

The subtask must be defined by Task.config.name, an instance of ConfigurableField or RegistryField.

run(exposure, ctiCalib, gains=None)

Correct deferred charge/CTI issues.

Parameters:

exposure : lsst.afw.image.Exposure

Exposure to correct the deferred charge on.

ctiCalib : lsst.ip.isr.DeferredChargeCalib

Calibration object containing the charge transfer inefficiency model.

gains : dict [str, float]

A dictionary, keyed by amplifier name, of the gains to use. If gains is None, the nominal gains in the amplifier object are used.

Returns:

exposure : lsst.afw.image.Exposure

The corrected exposure.

timer(name: str, logLevel: int = 10) → Iterator[None]

Context manager to log performance data for an arbitrary block of code.

Parameters:

name : str

Name of code being timed; data will be logged using item name: Start and End.

logLevel

A logging level constant.

See also

timer.logInfo

Examples

Creating a timer context:

with self.timer("someCodeToTime"):
    pass  # code to time