FocalPlaneBackground

class lsst.pipe.tasks.background.FocalPlaneBackground(config, dims, transform, values=None, numbers=None)

Bases: object

Background model for a focal plane camera

We model the background empirically with the “superpixel” method: we measure the background in each superpixel and interpolate between superpixels to yield the model.

The principal difference between this and lsst.afw.math.BackgroundMI is that here the superpixels are defined in the frame of the focal plane of the camera which removes discontinuities across detectors.

The constructor you probably want to use is the fromCamera classmethod.

There are two use patterns for building a background model:

• Serial: create a FocalPlaneBackground, then addCcd for each of the CCDs in an exposure.
• Parallel: create a FocalPlaneBackground, then clone it for each of the CCDs in an exposure and use those to addCcd their respective CCD image. Finally, merge all the clones into the original.

Once you’ve built the background model, you can apply it to individual CCDs with the toCcdBackground method.

Methods Summary

addCcd(exposure)	Add CCD to model
clone()
fromCamera(config, camera)	Construct from a camera object
fromSimilar(other)	Construct from an object that has the same interface.
getStatsImage()	Return the background model data
merge(other)	Merge with another FocalPlaneBackground
toCcdBackground(detector, bbox)	Produce a background model for a CCD

Methods Documentation

addCcd(exposure)

Add CCD to model

We measure the background on the CCD (clipped mean), and record the results in the model. For simplicity, measurements are made in a box on the CCD corresponding to the warped coordinates of the superpixel rather than accounting for little rotations, etc. We also record the number of pixels used in the measurement so we can have a measure of confidence in each bin’s value.

Parameters:

exposure : lsst.afw.image.Exposure

CCD exposure to measure

clone()

classmethod fromCamera(config, camera)

Construct from a camera object

Parameters:

config : FocalPlaneBackgroundConfig

Configuration for measuring backgrounds.

camera : lsst.afw.cameraGeom.Camera

Camera for which to measure backgrounds.

classmethod fromSimilar(other)

Construct from an object that has the same interface.

Parameters:

other : FocalPlaneBackground-like

An object that matches the interface of FocalPlaneBackground but which may be different.

Returns:

background : FocalPlaneBackground

Something guaranteed to be a FocalPlaneBackground.

getStatsImage()

Return the background model data

This is the measurement of the background for each of the superpixels.

merge(other)

Merge with another FocalPlaneBackground

This allows multiple background models to be constructed from different CCDs, and then merged to form a single consistent background model for the entire focal plane.

Parameters:

other : FocalPlaneBackground

Another background model to merge.

Returns:

self : FocalPlaneBackground

The merged background model.

toCcdBackground(detector, bbox)

Produce a background model for a CCD

The superpixel background model is warped back to the CCD frame, for application to the individual CCD.

Parameters:

detector : lsst.afw.cameraGeom.Detector

CCD for which to produce background model.

bbox : lsst.geom.Box2I

Bounding box of CCD exposure.

Returns:

bg : lsst.afw.math.BackgroundList

Background model for CCD.