The NIRSpec MSA imprint subtraction step removes patterns created in NIRSpec MOS and IFU exposures by the MSA structure. This is accomplished by subtracting a dedicated exposure taken with all MSA shutters closed and the IFU entrance aperture blocked.

The step has two input parameters: the target exposure and a list of one or more imprint exposures. These arguments can be provided as either file names or JWST data models.

In the event that multiple imprint images are provided, the step uses the meta data of the target and imprint exposures to find the imprint exposure that matches the observation number (keyword “OBSERVTN”) and dither pattern position number (keyword “PATT_NUM”) of the target exposure. The matching imprint image is then subtracted from the target image. If no matching imprint image is found, the step will be skipped, returning the input target image unaltered.

When subtracting the imprint data model from the target data model, the SCI data array of the imprint exposure is subtracted from the SCI array of the target exposure, and the DQ arrays of the two exposures are combined using a bitwise logical OR operation. The ERR and variance arrays are not currently used or modified.

Step Arguments

The imprint subtraction step has no step-specific arguments.

Reference File

The imprint subtraction step does not use any reference files.