JWST Imaging Pipeline Caveats

JWST Science Calibration Pipeline features and potential caveats specific to various kinds of JWST imaging data are described in this article. 

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See also: Getting Started with JWST Datafile header contents

Several instruments on JWST provide imaging data of various kinds. For an overview of imaging, refer to the materials and video excerpts from JWebbinar 13 (open the "Materials and Videos" tab, and scroll down to JWebbinar 13, "CEERS NIRCam and MIRI Imaging." Or go directly to the CEERS Overview video on the JWST Observer YouTube channel).

JWST imaging data are processed by the JWST Science Calibration Pipeline. As with other instrument modes, the pipeline is run with various default parameters that are generally appropriate and produce science quality products, but may or may not be optimal for a particular science case. Additionally, imaging modes are often used to produce mosaics of areas larger than a single field of view of the instrument in question, which produces additional complexity for aligning and calibrating the data.

Data products

Software documentation outside JDox: Science Products 

The current defaults for rejection of outliers/bad pixels and cosmic rays are based on what has been learned from the detector performance to date, and are aimed at providing satisfactory rejection for most datasets. However, users may want to try non-default parameters to fine-tune this step for specific types of data.

The current defaults for image alignment/tweakreg and catalog creation are aimed at providing satisfactory results for most datasets, but they could be fine-tuned for specific types of data and run offline.


Image mosaics in different filters are not necessarily aligned on the same x,y pixel grid, but the RA, Dec astrometry is expected be consistent for the same source in different filters.

Also, mosaics are created with a pixel scale equal to the detector pixel size, so observations that take advantage of sub-pixel dithering might benefit from being processed offline with a finer pixel scale.

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Originally published