This document provides instructions on running the JWST Science Calibration Pipeline (referred to as “the pipeline”) and individual pipeline steps.

The pipeline currently consists of ramps-to-slopes processing for all observing modes, Level-2b processing for all imaging modes, Level-2b processing for most spectroscopic modes (everything but Wide-Field Slitless Spectroscopy), and Level-3 processing for imaging.

The ramps-to-slopes (Level-2a) processing consists of detector-level corrections that are necessary to perform on a group-by-group basis before ramp fitting is applied. The output of Level-2a processing is a countrate image per exposure or per integration for some models. Details of this pipeline can be found at Level-2a Pipeline Step Flow (calwebb_sloper).

Level-2b processing consists of additional corrections and calibrations to produce a fully calibrated exposure. The details differ for imaging and spectroscopic exposures, and there are some corrections that are unique to certain instruments or modes. Details are at Level-2b Imaging Pipeline Step Flow (calwebb_image2) and Level-2b Spectroscopic Pipeline Step Flow (calwebb_spec2).

Level-3 processing consists of routines that combine the data from multiple exposures, for all observing modes. Level-3 processing is only available at this time for imaging observations. Details are at Level-3 Imaging Pipeline Step Flow (calwebb_image3).

This document discusses pipeline configuration files and examples of running pipelines either as a whole or in individual steps.

CRDS Reference Files

CRDS reference file mappings are usually set by default to always give access to the most recent reference file deliveries and selection rules. On occasion it might be necessary or desirable to use one of the non-default mappings in order to, for example, run different versions of the pipeline software or use older versions of the reference files. This can be accomplished by setting the environment variable CRDS_CONTEXT to the desired project mapping version, e.g.

$ export CRDS_CONTEXT='jwst_0234.pmap'

The current storage location for all JWST CRDS reference files is:


Each pipeline step records the reference file that it used in the value of a header keyword in the output data file. The keyword names use the syntax “R_<ref>”, where <ref> corresponds to the first 6 characters of the reference file type, such as R_DARK, R_LINEAR, and R_PHOTOM.

Running From the Command Line

Individual steps and pipelines (consisting of a series of steps) can be run from the command line using the strun command:

$ strun <class_name or cfg_file> <input_file>

The first argument to strun must be either the python class name of the step or pipeline to be run, or the name of a configuration (.cfg) file for the desired step or pipeline (see Configuration Files below for more details). The second argument to strun is the name of the input data file to be processed.

For example, running the full ramps-to-slopes pipeline or an individual step by referencing their class names is done as follows:

$ strun jwst.pipeline.SloperPipeline jw00017001001_01101_00001_nrca1_uncal.fits
$ strun jwst.dq_init.DQInitStep jw00017001001_01101_00001_nrca1_uncal.fits

When a pipeline or step is executed in this manner (i.e. by referencing the class name), it will be run using all default parameter values. The same thing can be accomplished by using the default configuration file corresponding to each:

$ strun calwebb_sloper.cfg jw00017001001_01101_00001_nrca1_uncal.fits
$ strun dq_init.cfg jw00017001001_01101_00001_nrca1_uncal.fits

If you want to use non-default parameter values, you can specify them as keyword arguments on the command line or set them in the appropriate cfg file. To specify parameter values for an individual step when running a pipeline use the syntax --steps.<step_name>.<parameter>=value. For example, to override the default selection of a dark current reference file from CRDS when running a pipeline:

$ strun jwst.pipeline.SloperPipeline jw00017001001_01101_00001_nrca1_uncal.fits
$ strun calwebb_sloper.cfg jw00017001001_01101_00001_nrca1_uncal.fits

You can get a list of all the available arguments for a given pipeline or step by using the ‘-h’ (help) argument to strun:

$ strun dq_init.cfg -h
$ strun jwst.pipeline.SloperPipeline -h

If you want to consistently override the default values of certain arguments and don’t want to have to specify them on the command line every time you execute strun, you can specify them in the configuration (.cfg) file for either the pipeline or the individual step. For example, to always run SloperPipeline using the override in the previous example, you could edit your calwebb_sloper.cfg file to contain the following:

name = "SloperPipeline"
class = "jwst.pipeline.SloperPipeline"

       override_dark = 'my_dark.fits'

Note that simply removing the entry for a step from a pipeline cfg file will NOT cause that step to be skipped when you run the pipeline (it will simply run the step with all default parameters). In order to skip a step you must use the skip = True argument for that step (see Skip below).

Alternatively, you can specify arguments for individual steps within the step’s configuration file and then reference those step cfg files in the pipeline cfg file, such as:

name = "SloperPipeline"
class = "jwst.pipeline.SloperPipeline"

       config_file = my_dark_current.cfg

where my_dark_current.cfg contains:

name = "dark_current"
class = "jwst.dark_current.DarkCurrentStep"
override_dark = 'my_dark.fits'

Running From Within Python

You can execute a pipeline or a step from within python by using the call method of the class:

from jwst.pipeline import SloperPipeline
result ='jw00017001001_01101_00001_nrca1_uncal.fits')

from jwst.linearity import LinearityStep
result ='jw00001001001_01101_00001_mirimage_uncal.fits')

The easiest way to use optional arguments when calling a pipeline from within python is to set those parameters in the pipeline cfg file and then supply the cfg file as a keyword argument:'jw00017001001_01101_00001_nrca1_uncal.fits', config_file='calwebb_sloper.cfg')

Universal Parameters

Output File

When running a pipeline, the stpipe infrastructure automatically passes the output data model from one step to the input of the next step, without saving any intermediate results to disk. If you want to save the results from individual steps, you have two options:

  • Specify save_results

    This option will save the results of the step, using a filename created by the step.

  • Specify a file name using output_file

    This option will save the step results using the name specified.

For example, to save the result from the dark current step of calwebb_sloper in a file named dark_sub.fits, use

$ strun calwebb_sloper.cfg jw00017001001_01101_00001_nrca1_uncal.fits

You can also specify a particular file name for saving the end result of the entire pipeline using the --output_file argument also

$ strun calwebb_sloper.cfg jw00017001001_01101_00001_nrca1_uncal.fits

Output File and Associations

The Level 2 pipelines can take both individual file or an association as input. When given an association, output_file is ignored, in favor of using the product names defined in the associations. Level 3 pipelines always require an association, hence output_file is never used for them.

Output Directory

By default, all pipeline and step outputs will drop into the current working directory, i.e., the directory in which the process is running. To change this, use the output_dir argument. For example, to have all output from calwebb_sloper, including any saved intermediate steps, appear in the sub-directory calibrated, use

$ strun calwebb_sloper.cfg jw00017001001_01101_00001_nrca1_uncal.fits

output_dir can be specified at the step level, overriding what was specified for the pipeline. From the example above, to change the name and location of the dark_current step, use the following

$ strun calwebb_sloper.cfg jw00017001001_01101_00001_nrca1_uncal.fits

Override Reference File

For any step that uses a calibration reference file you always have the option to override the automatic selection of a reference file from CRDS and specify your own file to use. Arguments for this are of the form --override_<ref_type>, where ref_type is the name of the reference file type, such as mask, dark, gain, or linearity. When in doubt as to the correct name, just use the -h argument to strun to show you the list of available override arguments.

To override the use of the default linearity file selection, for example, we would use:

$ strun calwebb_sloper.cfg jw00017001001_01101_00001_nrca1_uncal.fits

Logging Configuration

If there’s no stpipe-log.cfg file in the working directory, which specifies how to handle process log information, the default is to display log messages to stdout. If you want log information saved to a file, you can specify the name of a logging configuration file either on the command line or in the pipeline cfg file.

For example:

$ strun calwebb_sloper.cfg jw00017001001_01101_00001_nrca1_uncal.fits

and the file pipeline-log.cfg contains:

handler = file:pipeline.log
level = INFO

In this example log information is written to a file called pipeline.log. The level argument in the log cfg file can be set to one of the standard logging level designations of DEBUG, INFO, WARNING, ERROR, and CRITICAL. Only messages at or above the specified level will be displayed.

Output File Names

Pipelines and steps will use default output file names or names provided by the user via the output_file argument. In the absence of a user-specified output file name, pipelines and steps use different schemes for setting a default output name, which are explained below.

Pipeline Outputs

In the absence of a user-specified output file name, the various level-2a, 2b, and 3 pipeline modules will use the input root file name along with a set of predetermined suffixes to compose output file names. The output file name suffix will always replace the suffix of the input file name. Each pipeline module uses the appropriate suffix for the product(s) it is creating. The list of suffixes is shown in the following table.

Product Suffix
Uncalibrated Level-1b input uncal
Corrected Level-2a ramp data ramp
Corrected Level-2a countrate image rate
Level-2a countrate per integration rateints
Optional fitting results from ramp_fit step fitopt
Level-2b background-subtracted image bsub
Per integration background-subtracted image bsubints
Calibrated Level-2b image cal
Calibrated per integration images calints
1D extracted spectrum x1d
1D extracted spectra per integration x1dints
Resampled image i2d
Resampled spectrum s2d
Resampled 3D IFU cube s3d

Individual Step Outputs

If individual steps are executed without an output file name specified via the output_file argument, the stpipe infrastructure automatically uses the input file name as the root of the output file name and appends the name of the step as an additional suffix to the input file name. For example:

$ strun dq_init.cfg jw00017001001_01101_00001_nrca1_uncal.fits

produces an output file named “jw00017001001_01101_00001_nrca1_uncal_dq_init.fits.”

Configuration Files

Configuration (.cfg) files can be used to specify parameter values when running a pipeline or individual steps, as well as for specifying logging options.

You can use the collect_pipeline_cfgs task to get copies of all the cfg files currently in use by the jwst pipeline software. The task takes a single argument, which is the name of the directory to which you want the cfg files copied. Use ‘.’ to specify the current working directory, e.g.

$ collect_pipeline_cfgs .

Each step and pipeline has their own cfg file, which are used to specify relevant parameter values. For each step in a pipeline, the pipeline cfg file specifies either the step’s arguments or the cfg file containing the step’s arguments.

The name of a file in which to save log information, as well as the desired level of logging messages, can be specified in an optional configuration file “stpipe-log.cfg”. This file must be in the same directory in which you run the pipeline in order for it to be used. If this file does not exist, the default logging mechanism is STDOUT, with a level of INFO. An example of the contents of the stpipe-log.cfg file is:

handler = file:pipeline.log
level = INFO

which specifies that all log messages will be directed to a file called “pipeline.log” and messages at a severity level of INFO and above will be recorded.

For a given step, the step’s cfg file specifies parameters and their default values; it includes parameters that are typically not changed between runs. Parameters that are usually reset for each run are not included in the cfg file, but instead specified on the command line. An example of a cfg file for the jump detection step is:

name = "jump"
class = "jwst.jump.JumpStep"
rejection_threshold = 4.0
do_yintercept = False
yint_threshold = 1.0

You can list all of the parameters for this step using:

$ strun jump.cfg -h

which gives the usage, the positional arguments, and the optional arguments. More information on configuration files can be found in the stpipe User’s Guide at For Users.

Available Pipelines

There are currently several pre-defined pipelines available for processing the data from different instrument observing modes. For all of the details see Pipeline Modules.

For More Information

More information on logging and running pipelines can be found in the stpipe User’s Guide at For Users.

More detailed information on writing pipelines can be found in the stpipe Developer’s Guide at For Developers.