NoiseReplacer

class lsst.meas.base.NoiseReplacer(config, exposure, footprints, noiseImage=None, exposureId=None, log=None)

Bases: object

Replace sources with noise during measurement.

Parameters:

config : NoiseReplacerConfig

Configuration.

exposure : lsst.afw.image.Exposure

Image in which sources will be replaced by noise. During operation, the image will be modified in-place to replace all sources. At the end of the measurment procedure, the original sources will be replaced.

footprints : dict

Mapping of id to a tuple of (parent, Footprint). When used in single-frame measurement, id is the source ID, but in forced photometry this is the reference ID (as that is used to determine deblend families).

noiseImage : lsst.afw.image.ImageF

An image used as a predictable noise replacement source. Used during testing only.

log : lsst.log.Log, optional

Logger to use for status messages; no status messages will be recorded if None.

Notes

When measuring a source (or the children associated with a parent source), this class is used to replace its neighbors with noise, using the deblender’s definition of the sources as stored in HeavyFootprints attached to the SourceRecords. The algorithm works as follows:

1. All pixels in the source Footprints are replaced with artificially generated noise (in NoiseReplacer.__init__).
2. Before each source is measured, we restore the original pixel data by inserting that source’s HeavyFootprint (from the deblender) into the image.
3. After measurement, we again replace the source pixels with (the same) artificial noise.
4. After measuring all sources, the image is returned to its original state.

This is a functional copy of the code in the older ReplaceWithNoiseTask, but with a slightly different API needed for the new measurement framework; note that it is not an Task, as the lifetime of a NoiseReplacer now corresponds to a single exposure, not an entire processing run.

When processing the footprints parameter, this routine should create HeavyFootprints for any non-Heavy Footprints, and replace them in the dictionary. It should then create a dict of HeavyFootprints containing noise, but only for parent objects, then replace all sources with noise. This should ignore any footprints that lay outside the bounding box of the exposure, and clip those that lie on the border.

As the code currently stands, the heavy footprint for a deblended object must be available from the input catalog. If it is not, it cannot be reproduced here. In that case, the topmost parent in the objects parent chain must be used. The heavy footprint for that source is created in this class from the masked image.

Attributes Summary

exposure	Image on which the NoiseReplacer is operating (lsst.afw.image.Exposure).
footprints	Mapping of id to a tuple of (parent, Footprint) (dict).
log	Logger used for status messages.

Methods Summary

end()	End the NoiseReplacer.
getNoiseGenerator(exposure, noiseImage, …)	Return a generator of artificial noise.
insertSource(id)	Insert the heavy footprint of a given source into the exposure.
removeSource(id)	Replace the heavy footprint of a given source with noise.

Attributes Documentation

exposure = None

Image on which the NoiseReplacer is operating (lsst.afw.image.Exposure).

footprints = None

Mapping of id to a tuple of (parent, Footprint) (dict).

log = None

Logger used for status messages.

Methods Documentation

end()

End the NoiseReplacer.

Restores original data to the exposure from the heavies dictionary and the mask planes to their original state.

getNoiseGenerator(exposure, noiseImage, noiseMeanVar, exposureId=None)

Return a generator of artificial noise.

Returns:

noiseGenerator : lsst.afw.image.noiseReplacer.NoiseGenerator

insertSource(id)

Insert the heavy footprint of a given source into the exposure.

Parameters:

id : int

ID of the source to insert from original dictionary of footprints.

Notes

Also adjusts the mask plane to show the source of this footprint.

removeSource(id)

Replace the heavy footprint of a given source with noise.

The same artificial noise is used as in the original replacement.

Parameters:

id : int

ID of the source to replace from original dictionary of footprints.

Notes

Also restores the mask plane.