Reference File Types

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 accommodate 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.