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

`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.
`computeCorrection`(kappa, svar, tvar[, …])	Compute the Lupton decorrelation post-convolution kernel for decorrelating an image difference, based on the PSF-matching kernel.
`computeVarianceMean`(exposure)
`emptyMetadata`()	Empty (clear) the metadata for this Task and all sub-Tasks.
`getAllSchemaCatalogs`()	Get schema catalogs for all tasks in the hierarchy, combining the results into a single dict.
`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.
`getSchemaCatalogs`()	Get the schemas generated by this 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

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:	psfNew : `numpy.ndarray` 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.

computeCorrection(kappa, svar, tvar, preConvArr=None)¶

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

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.
tvar : float: Average variance of the template (matched) image used for PSF matching.
preConvArr : numpy.ndarray, optional: If not None, then pre-filtering was applied to science exposure, and this is the pre-convolution kernel.

Returns:

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

Notes

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

computeVarianceMean(exposure)¶

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

getAllSchemaCatalogs()¶

Get schema catalogs for all tasks in the hierarchy, combining the results into a single dict.

Returns:	schemacatalogs : `dict` Keys are butler dataset type, values are a empty catalog (an instance of the appropriate lsst.afw.table Catalog type) for all tasks in the hierarchy, from the top-level task down through all subtasks.

Notes

This method may be called on any task in the hierarchy; it will return the same answer, regardless.

The default implementation should always suffice. If your subtask uses schemas the override Task.getSchemaCatalogs, not this method.

getFullMetadata()¶

Get metadata for all tasks.

Returns:	metadata : `lsst.daf.base.PropertySet` The `PropertySet` 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()¶

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()¶

Get the name of the task.

Returns:	taskName : `str` Name of the task.

See also

Task.getAllSchemaCatalogs

Notes

Warning

Subclasses that use schemas must override this method. The default implemenation returns an empty dict.

This method may be called at any time after the Task is constructed, which means that all task schemas should be computed at construction time, not when data is actually processed. This reflects the philosophy that the schema should not depend on the data.

Returning catalogs rather than just schemas allows us to save e.g. slots for SourceCatalog as well.

getTaskDict()¶

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)¶

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("a brief description of what this task does")

makeSubtask(name, **keyArgs)¶

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 pex_config 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, logLevel=10000)¶

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 `lsst.log` level constant.

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DecorrelateALKernelMapper¶