Reference File

The linearity correction step uses a LINEARITY reference file.

CRDS Selection Criteria

Linearity reference files are selected by INSTRUME and DETECTOR.

Reference File Format

Linearity reference files are FITS format with 2 IMAGE extensions and 1 BINTABLE extension. The primary data array is assumed to be empty. The 2 IMAGE extensions have the following characteristics:

EXTNAME NAXIS Dimensions Data type
COEFFS 3 ncols x nrows x ncoeffs float
DQ 2 ncols x nrows integer

Each plane of the COEFFS data cube contains the pixel-by-pixel coefficients for the associated order of the polynomial. There can be any number of planes to accomodate a polynomial of any order.

The BINTABLE extension uses EXTNAME=DQ_DEF and contains the bit assignments of the conditions flagged in the DQ array.