Words in bold are GUI menus/
panels or data software packages;
bold italics are buttons in GUI
tools or package parameters.
Unless otherwise stated, the algorithms described are the baseline version.
Steps for both NIR and MIR data
Note that all steps in this module are common to both NIR and MIR data (but not all steps are applicable to all observation modes).
Software documentation outside JDox: Assign WCS
The information to transfer the pixel coordinates to astronomical coordinates (e.g., RA and Dec) is added to the data with this step. The needed information is described in the standard World Coordinate System (WCS) format—basically standard FITS WCS keywords and a distortion model. The WCS information and distortion model are provided by instrument and detector specific calibration reference files. The image data itself is not modified by this step.
Software documentation outside JDox: Background Image Subtraction
If an APT specified background target was observed, a combined background image constructed from all exposures of that target is subtracted from the science target exposure. The background observations can be specified by the user when the calibration pipeline is rerun manually.
Flat field correction
Software documentation outside JDox: Flat Field Correction
The flat field corrects for the pixel-to-pixel variations and large scale variations in the instrument+telescope responsivity. The flat field image is taken from instrument- and detector-specific calibration reference files.
Software documentation outside JDox: Photometric Calibration
The multiplicative conversion factor between counts/s and MJy/sr is applied to the data and recorded in the file header. A second conversion factor between counts/s and micro-Jy/sq arcsec is also recorded in the header, with both of these conversion factors being FITS keywords. The pixel area reference file is also attached to the data allowing conversion between surface brightness and flux density for each pixel. Details of the calculation of these calibration factors can be found in the JWST Data Absolute Flux Calibration article.
Rectified 2-D product
Software documentation outside JDox: Resampling
As a product for the Archive, rectified 2-D images are created, by removing the distortion and resampling the images onto a grid where all the pixels have the same spatial scale. This rectified 2-D product is not used in the calibration pipeline itself, it is useful for visual browsing of the data.