DecorrelateALKernelMapper

class lsst.ip.diffim.DecorrelateALKernelMapper(*args, **kwargs)

Bases: lsst.ip.diffim.DecorrelateALKernelTask, lsst.ip.diffim.ImageMapper

Task to be used as an ImageMapper for performing A&L decorrelation on subimages on a grid across a A&L difference image.

This task subclasses DecorrelateALKernelTask in order to implement all of that task’s configuration parameters, as well as its run method.

Methods Summary

calculateVariancePlane(vplane1, vplane2, …) Full propagation of the variance planes of the original exposures.
computeCommonShape(*shapes) Calculate the common shape for FFT operations.
computeCorrectedDiffimPsf(corrft, psfOld) Compute the (decorrelated) difference image’s new PSF.
computeCorrectedImage(corrft, imgOld) Compute the decorrelated difference image.
computeDiffimCorrection(kappa, svar, tvar) Compute the Lupton decorrelation post-convolution kernel for decorrelating an image difference, based on the PSF-matching kernel.
computeScoreCorrection(kappa, svar, tvar, …) Compute the correction kernel for a score image.
computeVarianceMean(exposure)
emptyMetadata() Empty (clear) the metadata for this Task and all sub-Tasks.
estimateVariancePlane(vplane1, vplane2, …) Estimate the variance planes.
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.
padCenterOriginArray(A, newShape[, useInverse]) Zero pad an image where the origin is at the center and replace the origin to the corner as required by the periodic input of FFT.
run(subExposure, expandedSubExposure, …[, …]) Perform decorrelation operation on subExposure, using expandedSubExposure to allow for invalid edge pixels arising from convolutions.
timer(name, logLevel) Context manager to log performance data for an arbitrary block of code.

Methods Documentation

calculateVariancePlane(vplane1, vplane2, varMean1, varMean2, c1ft, c2ft)

Full propagation of the variance planes of the original exposures.

The original variance planes of independent pixels are convolved with the image space square of the overall kernels.

Parameters:
vplane1, vplane2 : numpy.ndarray of float

Variance planes of the original (before pre-convolution or matching) exposures.

varMean1, varMean2 : float

Replacement average values for non-finite vplane1 and vplane2 values respectively.

c1ft, c2ft : numpy.ndarray of complex

The overall convolution that includes the matching and the afterburner in frequency space. The result of either computeScoreCorrection or computeDiffimCorrection.

Returns:
vplaneD : numpy.ndarray of float

The variance plane of the difference/score images.

Notes

See DMTN-179 Section 5 about the variance plane calculations.

Infs and NaNs are allowed and kept in the returned array.

computeCommonShape(*shapes)

Calculate the common shape for FFT operations. Set self.freqSpaceShape internally.

Parameters:
shapes : one or more tuple of int

Shapes of the arrays. All must have the same dimensionality. At least one shape must be provided.

Returns:
None.

Notes

For each dimension, gets the smallest even number greater than or equal to N1+N2-1 where N1 and N2 are the two largest values. In case of only one shape given, rounds up to even each dimension value.

computeCorrectedDiffimPsf(corrft, psfOld)

Compute the (decorrelated) difference image’s new PSF.

Parameters:
corrft : numpy.ndarray

The frequency space representation of the correction calculated by computeCorrection. Shape must be self.freqSpaceShape.

psfOld : numpy.ndarray

The psf of the difference image to be corrected.

Returns:
correctedPsf : lsst.meas.algorithms.KernelPsf

The corrected psf, same shape as psfOld, sum normed to 1.

Notes

There is no algorithmic guarantee that the corrected psf can meaningfully fit to the same size as the original one.

computeCorrectedImage(corrft, imgOld)

Compute the decorrelated difference image.

Parameters:
corrft : numpy.ndarray

The frequency space representation of the correction calculated by computeCorrection. Shape must be self.freqSpaceShape.

imgOld : numpy.ndarray

The difference image to be corrected.

Returns:
imgNew : numpy.ndarray

The corrected image, same size as the input.

computeDiffimCorrection(kappa, svar, tvar)

Compute the Lupton decorrelation post-convolution kernel for decorrelating an image difference, based on the PSF-matching kernel.

Parameters:
kappa : numpy.ndarray of float

A matching kernel 2-d numpy.array derived from Alard & Lupton PSF matching.

svar : float > 0.

Average variance of science image used for PSF matching.

tvar : float > 0.

Average variance of the template (matched) image used for PSF matching.

Returns:
corrft : numpy.ndarray of float

The frequency space representation of the correction. The array is real (dtype float). Shape is self.freqSpaceShape.

cnft, crft : numpy.ndarray of complex

The overall convolution (pre-conv, PSF matching, noise correction) kernel for the science and template images, respectively for the variance plane calculations. These are intermediate results in frequency space.

Notes

The maximum correction factor converges to sqrt(tvar/svar) towards high frequencies. This should be a plausible value.

computeScoreCorrection(kappa, svar, tvar, preConvArr)

Compute the correction kernel for a score image.

Parameters:
kappa : numpy.ndarray

A matching kernel 2-d numpy.array derived from Alard & Lupton PSF matching.

svar : float

Average variance of science image used for PSF matching (before pre-convolution).

tvar : float

Average variance of the template (matched) image used for PSF matching.

preConvArr : numpy.ndarray

The pre-convolution kernel of the science image. It should be the PSF of the science image or an approximation of it. It must be normed to sum 1.

Returns:
corrft : numpy.ndarray of float

The frequency space representation of the correction. The array is real (dtype float). Shape is self.freqSpaceShape.

cnft, crft : numpy.ndarray of complex

The overall convolution (pre-conv, PSF matching, noise correction) kernel for the science and template images, respectively for the variance plane calculations. These are intermediate results in frequency space.

Notes

To be precise, the science image should be _correlated_ by preConvArray but this does not matter for this calculation.

cnft, crft contain the scaling factor as well.

computeVarianceMean(exposure)
emptyMetadata() → None

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

static estimateVariancePlane(vplane1, vplane2, c1ft, c2ft)

Estimate the variance planes.

The estimation assumes that around each pixel the surrounding pixels’ sigmas within the convolution kernel are the same.

Parameters:
vplane1, vplane2 : numpy.ndarray of float

Variance planes of the original (before pre-convolution or matching) exposures.

c1ft, c2ft : numpy.ndarray of complex

The overall convolution that includes the matching and the afterburner in frequency space. The result of either computeScoreCorrection or computeDiffimCorrection.

Returns:
vplaneD : numpy.ndarray of float

The estimated variance plane of the difference/score image as a weighted sum of the input variances.

Notes

See DMTN-179 Section 5 about the variance plane calculations.

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.

static padCenterOriginArray(A, newShape: tuple, useInverse=False)

Zero pad an image where the origin is at the center and replace the origin to the corner as required by the periodic input of FFT. Implement also the inverse operation, crop the padding and re-center data.

Parameters:
A : numpy.ndarray

An array to copy from.

newShape : tuple of int

The dimensions of the resulting array. For padding, the resulting array must be larger than A in each dimension. For the inverse operation this must be the original, before padding size of the array.

useInverse : bool, optional

Selector of forward, add padding, operation (False) or its inverse, crop padding, operation (True).

Returns:
R : numpy.ndarray

The padded or unpadded array with shape of newShape and the same dtype as A.

Notes

For odd dimensions, the splitting is rounded to put the center pixel into the new corner origin (0,0). This is to be consistent e.g. for a dirac delta kernel that is originally located at the center pixel.

run(subExposure, expandedSubExposure, fullBBox, template, science, alTaskResult=None, psfMatchingKernel=None, preConvKernel=None, **kwargs)

Perform decorrelation operation on subExposure, using expandedSubExposure to allow for invalid edge pixels arising from convolutions.

This method performs A&L decorrelation on subExposure using local measures for image variances and PSF. subExposure is a sub-exposure of the non-decorrelated A&L diffim. It also requires the corresponding sub-exposures of the template (template) and science (science) exposures.

Parameters:
subExposure : lsst.afw.image.Exposure

the sub-exposure of the diffim

expandedSubExposure : lsst.afw.image.Exposure

the expanded sub-exposure upon which to operate

fullBBox : lsst.geom.Box2I

the bounding box of the original exposure

template : lsst.afw.image.Exposure

the corresponding sub-exposure of the template exposure

science : lsst.afw.image.Exposure

the corresponding sub-exposure of the science exposure

alTaskResult : lsst.pipe.base.Struct

the result of A&L image differencing on science and template, importantly containing the resulting psfMatchingKernel. Can be None, only if psfMatchingKernel is not None.

psfMatchingKernel : Alternative parameter for passing the

A&L psfMatchingKernel directly.

preConvKernel : If not None, then pre-filtering was applied

to science exposure, and this is the pre-convolution kernel.

kwargs

additional keyword arguments propagated from ImageMapReduceTask.run.

Returns:
A pipeBase.Struct containing:
  • subExposure : the result of the subExposure processing.
  • decorrelationKernel : the decorrelation kernel, currently
    not used.

Notes

This run method accepts parameters identical to those of ImageMapper.run, since it is called from the ImageMapperTask. See that class for more information.

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