DeferredChargeTask#

Bases: Task

Task to correct an exposure for charge transfer inefficiency.

This uses the methods described by Snyder et al. 2021, Journal of Astronimcal Telescopes, Instruments, and Systems, 7, 048002. doi:10.1117/1.JATIS.7.4.048002 (Snyder+21).

Methods Summary

`flipData`(ampData, amp)	Flip data array such that readout corner is at lower-left.
`local_offset_inverse`(inputArr, drift_scale, ...)	Remove CTI effects from local offsets.
`local_trap_inverse`(inputArr, trap[, ...])	Apply localized trapping inverse operator to pixel signals.
`run`(exposure, ctiCalib[, gains])	Correct deferred charge/CTI issues.

Methods Documentation

static flipData(ampData, amp)#

Flip data array such that readout corner is at lower-left.

Parameters#

ampDatanumpy.ndarray, (nx, ny): Image data to flip.
amplsst.afw.cameraGeom.Amplifier: Amplifier to get readout corner information.

Returns#

ampDatanumpy.ndarray, (nx, ny): Flipped image data.

static local_offset_inverse(inputArr, drift_scale, decay_time, num_previous_pixels=15)#

Remove CTI effects from local offsets.

This implements equation 10 of Snyder+21. For an image with CTI, s’(m, n), the correction factor is equal to the maximum value of the set of:

{A_L s'(m, n - j) exp(-j t / \tau_L)}_j=0^jmax

Parameters#

inputArrnumpy.ndarray, (nx, ny): Input image data to correct.
drift_scalefloat: Drift scale (Snyder+21 A_L value) to use in correction.
decay_timefloat: Decay time (Snyder+21 tau_L) of the correction.
num_previous_pixelsint, optional: Number of previous pixels to use for correction. As the CTI has an exponential decay, this essentially truncates the correction where that decay scales the input charge to near zero.

Returns#

outputArrnumpy.ndarray, (nx, ny): Corrected image data.

static local_trap_inverse(inputArr, trap, global_cti=0.0, num_previous_pixels=6)#

Apply localized trapping inverse operator to pixel signals.

This implements equation 13 of Snyder+21. For an image with CTI, s’(m, n), the correction factor is equal to the maximum value of the set of:

{A_L s'(m, n - j) exp(-j t / \tau_L)}_j=0^jmax

Parameters#

inputArrnumpy.ndarray, (nx, ny): Input image data to correct.
traplsst.ip.isr.SerialTrap: Serial trap describing the capture and release of charge.
global_cti: float: Mean charge transfer inefficiency, b from Snyder+21.
num_previous_pixelsint, optional: Number of previous pixels to use for correction.

Returns#

outputArrnumpy.ndarray, (nx, ny): Corrected image data.

run(exposure, ctiCalib, gains=None)#

Correct deferred charge/CTI issues.

Parameters#

exposurelsst.afw.image.Exposure: Exposure to correct the deferred charge on.
ctiCaliblsst.ip.isr.DeferredChargeCalib: Calibration object containing the charge transfer inefficiency model.
gainsdict [str, float]: A dictionary, keyed by amplifier name, of the gains to use. If gains is None, the nominal gains in the amplifier object are used.

Returns#

exposurelsst.afw.image.Exposure: The corrected exposure.

Notes#

This task will read the exposure metadata and determine if applying gains if necessary. The correction takes place in units of electrons. If bootstrapping, the gains used will just be 1.0. and the input/output units will stay in adu. If the input image is in adu, the output image will be in units of electrons. If the input image is in electron, the output image will be in electron.