Reference Files

The Jump step uses two reference files: GAIN and READNOISE. The gain values are used to temporarily convert the pixel values from units of DN to electrons. The read noise values are used as part of the noise estimate for each pixel. Both are necessary for proper computation of noise estimates.

CRDS Selection Criteria

The readnoise reference file is selected by instrument, detector, readpatt and, where necessary, subarray.

The gain reference file is selected based on instrument, detector and, where necessary, subarray.

Gain Reference File Format

The gain reference file is a FITS file with a single IMAGE extension, with EXTNAME=SCI, which contains a 2-D floating-point array of gain values (in e/DN) per pixel. The REFTYPE value is GAIN.

Read Noise Reference File Format

The read noise reference file is a FITS file with a single IMAGE extension, with EXTNAME=SCI, which contains a 2-D floating-point array of read noise values per pixel. The units of the read noise should be DN and should be the CDS (Correlated Double Sampling) read noise, i.e. the effective noise between any pair of non-destructive detector reads. The REFTYPE value is READNOISE.