# Reference Files¶

The dq_init step uses a MASK reference file.

REFTYPE

Data model

MaskModel

The MASK reference file contains pixel-by-pixel DQ flag values that indicate problem conditions.

### Reference Selection Keywords for MASK¶

CRDS selects appropriate MASK references based on the following keywords. MASK is not applicable for instruments not in the table.

Instrument

Keywords

FGS

INSTRUME, DETECTOR, SUBARRAY, EXP_TYPE, DATE-OBS, TIME-OBS

MIRI

INSTRUME, DETECTOR, SUBARRAY, DATE-OBS, TIME-OBS

NIRCam

INSTRUME, DETECTOR, SUBARRAY, DATE-OBS, TIME-OBS

NIRISS

INSTRUME, DETECTOR, SUBARRAY, DATE-OBS, TIME-OBS

NIRSpec

INSTRUME, DETECTOR, SUBARRAY, READPATT, DATE-OBS, TIME-OBS

### Standard Keywords¶

The following table lists the keywords that are required to be present in all reference files. The first column gives the FITS keyword names. The second column gives the jwst data model name for each keyword, which is useful when using data models in creating and populating a new reference file. The third column gives the equivalent meta tag in ASDF reference file headers, which is the same as the name within the data model meta tree (second column).

FITS Keyword

Data Model Name

ASDF meta tag

AUTHOR

model.meta.author

author

DATAMODL

model.meta.model_type

model_type

DATE

model.meta.date

date

DESCRIP

model.meta.description

description

FILENAME

model.meta.filename

N/A

INSTRUME

model.meta.instrument.name

instrument: {name}

PEDIGREE

model.meta.pedigree

pedigree

REFTYPE

model.meta.reftype

reftype

TELESCOP

model.meta.telescope

telescope

USEAFTER

model.meta.useafter

useafter

NOTE: More information on standard required keywords can be found here: Standard Required Keywords

### Type Specific Keywords for MASK¶

In addition to the standard reference file keywords listed above, the following keywords are required in MASK reference files, because they are used as CRDS selectors (see Reference Selection Keywords for MASK):

Keyword

Data Model Name

Instruments

DETECTOR

model.meta.instrument.detector

All

SUBARRAY

model.meta.subarray.name

All

EXP_TYPE

model.meta.exposure.type

FGS only

NIRSpec only

### Reference File Format¶

MASK reference files are FITS format, with one IMAGE extension and 1 BINTABLE extension. The FITS primary HDU does not contain a data array. The format and content of the file is as follows:

EXTNAME

XTENSION

NAXIS

Dimensions

Data type

DQ

IMAGE

2

ncols x nrows

integer

DQ_DEF

BINTABLE

2

TFIELDS = 4

N/A

The values in the DQ array give the per-pixel flag conditions that are to be propagated into the science exposure’s PIXELDQ array. The dimensions of the DQ array should be equal to the number of columns and rows in a full-frame readout of a given detector, including reference pixels. Note that this does not include the reference output for MIRI detectors.

The DQ_DEF extension contains the bit assignments used in the DQ array. It contains the following 4 columns:

TTYPE

TFORM

Description

BIT

integer

The bit number, starting at zero

VALUE

integer

The equivalent base-10 value of BIT

NAME

string

The mnemonic name of the data quality condition

DESCRIPTION

string

A description of the data quality condition

NOTE: For more information on standard bit definitions see: Data Quality Flags.