ComputeNoiseCorrelationTask

class lsst.meas.algorithms.ComputeNoiseCorrelationTask(*args, **kwargs)

Bases: lsst.pipe.base.Task

Compute the noise correlation coefficients in a MaskedImage

The variance plane in a convolved or warped image (or a coadd derived from warped images) does not accurately reflect the noise properties of the image because variance has been lost to covariance. This Task computes a matrix of correlation coefficients of a desired size. It assumes that the noise is (at least the correlation coefficients are) stationary and uses spatial averaging to compute the correlation coefficients.

Methods Summary

emptyMetadata()	Empty (clear) the metadata for this Task and all sub-Tasks.
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.
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(maskedImage, refMaskedImage, None] = None)	Compute the correlation matrix from a maskedImage.
subtractedBackground(maskedImage)	Context manager for subtracting the background
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.

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.

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(maskedImage: lsst.afw.image.maskedImage._maskedImageContinued.MaskedImage, refMaskedImage: lsst.afw.image.maskedImage._maskedImageContinued.MaskedImage | None[lsst.afw.image.maskedImage._maskedImageContinued.MaskedImage, None] = None) → lsst.meas.algorithms.noise_covariance.CorrelationMatrix

Compute the correlation matrix from a maskedImage.

Parameters:

maskedImage : MaskedImage

Image for which to determine the correlation matrix.

refMaskedImage : MaskedImage, optional

Image from which to determine which pixels to mask. If None, it defaults to maskedImage.

Returns:

corr_matrix : CorrelationMatrix

Correlation matrix of the maskedImage.

Raises:

RuntimeError

Raised if refMaskedImage is provided and does not have the same dimensions as maskedImage.

subtractedBackground(maskedImage: lsst.afw.image.maskedImage._maskedImageContinued.MaskedImage)

Context manager for subtracting the background

We need to subtract the background so that the entire image (apart from objects, which should be clipped) will have the image/sqrt(variance) distributed about zero with unit variance. This context manager subtracts the background, and ensures it is restored on exit.

Parameters:

maskedImage : lsst.afw.image.MaskedImage

Image+mask+variance to have background subtracted and restored.

Returns:

context : context manager

Context manager that ensure the background is restored.

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