#! /usr/bin/env python
import numpy as np
from stdatamodels.jwst import datamodels
from jwst.background.asn_intake import asn_get_data
from jwst.background.background_sub import background_sub
from jwst.background.background_sub_soss import subtract_soss_bkg
from jwst.background.background_sub_wfss import subtract_wfss_bkg
from jwst.stpipe import Step
__all__ = ["BackgroundStep"]
[docs]
class BackgroundStep(Step):
"""Subtract background exposures from target exposures."""
class_alias = "bkg_subtract"
spec = """
bkg_list = force_list(default=None) # List of background files. Ignored for WFSS or if asn is provided
save_combined_background = boolean(default=False) # Save combined background image
sigma = float(default=3.0) # Clipping threshold
maxiters = integer(default=None) # Number of clipping iterations
soss_source_percentile = float(default=35.0) # Threshold flux percentile to mask out source pixels
soss_bkg_percentile = float_list(min=2, max=2, default=None) # Background percentiles to use; default is [25.0, 50.0]
wfss_mmag_extract = float(default=None) # WFSS minimum abmag to extract
wfss_maxiter = integer(default=5) # WFSS iterative outlier rejection max iterations
wfss_rms_stop = float(default=0) # WFSS iterative outlier rejection RMS improvement threshold (percent)
wfss_outlier_percent = float(default=1) # WFSS outlier percentile to reject per iteration
""" # noqa: E501
# These reference files are only used for WFSS/GRISM or SOSS data.
reference_file_types = ["bkg", "wavelengthrange"]
# Define a suffix for optional saved output of the combined background
bkg_suffix = "combinedbackground"
[docs]
def process(self, step_input, input_bkg_list=None):
"""
Subtract designated background images from target exposures.
Parameters
----------
step_input : str, ImageModel or IFUImageModel
Input target data model to which background subtraction is applied or asn file
input_bkg_list : list, optional
File name list of background exposures.
Returns
-------
result : ImageModel or IFUImageModel
The background-subtracted target data model
"""
asn = self.load_as_level2_asn(step_input)
input_model, members_by_type = asn_get_data(asn)
result = input_model.copy()
if result.meta.exposure.type in ["NIS_WFSS", "NRC_WFSS"]:
# Get the reference file names
bkg_name = self.get_reference_file(result, "bkg")
wlrange_name = self.get_reference_file(result, "wavelengthrange")
if bkg_name == "N/A":
self.log.warning("No BKG reference file found. Skipping background subtraction.")
result.meta.cal_step.bkg_subtract = "SKIPPED"
input_model.close()
return result
self.log.info("Using BKG reference file %s", bkg_name)
self.log.info("Using WavelengthRange reference file %s", wlrange_name)
# Do the background subtraction for WFSS/GRISM data
rescaler_kwargs = {
"p": self.wfss_outlier_percent,
"maxiter": self.wfss_maxiter,
"delta_rms_thresh": self.wfss_rms_stop / 100,
}
result = subtract_wfss_bkg(
result,
bkg_name,
wlrange_name,
self.wfss_mmag_extract,
rescaler_kwargs=rescaler_kwargs,
)
if result is None:
result = input_model.copy()
result.meta.cal_step.bkg_subtract = "SKIPPED"
else:
result.meta.cal_step.bkg_subtract = "COMPLETE"
elif input_model.meta.exposure.type == "NIS_SOSS":
# Fetch the background reference filename
bkg_name = self.get_reference_file(input_model, "bkg")
self.log.info("Using BKG reference file %s", bkg_name)
if self.soss_bkg_percentile is None:
soss_bkg_percentile = [25.0, 50.0]
else:
soss_bkg_percentile = self.soss_bkg_percentile
result = subtract_soss_bkg(
input_model, bkg_name, self.soss_source_percentile, soss_bkg_percentile
)
if result is None:
result = input_model
result.meta.cal_step.bkg_subtract = "SKIPPED"
else:
result.meta.cal_step.bkg_subtract = "COMPLETE"
else:
# Get the background files to be subtracted
if len(members_by_type["background"]) >= 1:
bkg_list = members_by_type["background"]
elif input_bkg_list is not None:
if isinstance(input_bkg_list, str):
if "," in input_bkg_list:
bkg_list = input_bkg_list.split(sep=",")
else:
bkg_list = [input_bkg_list]
else:
bkg_list = input_bkg_list
else:
bkg_list = self.bkg_list
# Make sure to catch a trailing comma and ignore it
if bkg_list is not None:
bkg_list = [bg for bg in bkg_list if bg]
# Make sure that the background list is not empty for this case,
# or report and skip the step
if bkg_list is None or len(bkg_list) == 0:
self.log.warning("* No background list provided * Skipping step.")
result.meta.cal_step.bkg_subtract = "SKIPPED"
return result
# check if input data is NRS_IFU
tolerance = 1.0e-8
do_sub = True
if result.meta.instrument.name in ["NIRSPEC"]:
# check if GWA_XTIL & GWA_YTIL values of source
# background are the same. If not skip step
input_xtilt = result.meta.instrument.gwa_xtilt
input_ytilt = result.meta.instrument.gwa_ytilt
for bkg_file in bkg_list:
with datamodels.open(bkg_file) as bkg_model:
bkg_xtilt = bkg_model.meta.instrument.gwa_xtilt
bkg_ytilt = bkg_model.meta.instrument.gwa_ytilt
if np.allclose(
(input_xtilt, input_ytilt),
(bkg_xtilt, bkg_ytilt),
atol=tolerance,
rtol=0,
):
pass
else:
do_sub = False
break
# Do the background subtraction
if do_sub:
bkg_model, result = background_sub(result, bkg_list, self.sigma, self.maxiters)
result.meta.cal_step.bkg_subtract = "COMPLETE"
if self.save_combined_background:
comb_bkg_path = self.save_model(bkg_model, suffix=self.bkg_suffix, force=True)
self.log.info(f"Combined background written to {comb_bkg_path}.")
else:
result.meta.cal_step.bkg_subtract = "SKIPPED"
self.log.warning("Skipping background subtraction")
self.log.warning(
"GWA_XTIL and GWA_YTIL source values are not the same as bkg values"
)
input_model.close()
return result