Reference Files¶
The IPC deconvolution step uses an IPC reference file.
IPC Reference File¶
- REFTYPE
IPC
- Data model
The IPC reference file contains a deconvolution kernel.
Reference Selection Keywords for IPC¶
CRDS selects appropriate IPC references based on the following keywords. IPC is not applicable for instruments not in the table. All keywords used for file selection are required.
Instrument |
Keywords |
|---|---|
FGS |
INSTRUME, DETECTOR, DATE-OBS, TIME-OBS |
MIRI |
INSTRUME, DETECTOR, DATE-OBS, TIME-OBS |
NIRCam |
INSTRUME, DETECTOR, DATE-OBS, TIME-OBS |
NIRISS |
INSTRUME, DETECTOR, DATE-OBS, TIME-OBS |
NIRSpec |
INSTRUME, DETECTOR, 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 IPC¶
In addition to the standard reference file keywords listed above, the following keywords are required in IPC reference files, because they are used as CRDS selectors (see Reference Selection Keywords for IPC):
Keyword |
Data Model Name |
|---|---|
DETECTOR |
model.meta.instrument.detector |
Reference File Format¶
IPC reference files are FITS format, with 1 IMAGE extension. The FITS primary HDU does not contain a data array. The format and content of the file can be one of two forms, as described below:
EXTNAME |
XTENSION |
NAXIS |
Dimensions |
Data type |
|---|---|---|---|---|
SCI |
IMAGE |
2 |
nkern x nkern |
float |
or |
||||
SCI |
IMAGE |
4 |
ncols x nrows x nkern x nkern |
float |
Two formats are currently supported for the IPC kernel: a small 2-D array or a 4-D array. If the kernel is 2-D, its dimensions should be odd, for example 3 x 3 or 5 x 5 pixels. The value at the center pixel will be larger than 1 (e.g. 1.02533) and the sum of all pixel values will be equal to 1.
A 4-D kernel may be used to allow the IPC correction to vary from pixel to pixel across the image. In this case, the axes that are most rapidly varying (the last two in Python notation; the first two in IRAF/FITS notation) have dimensions equal to those of a full-frame image. At each point in that image, there will be a small, 2-D kernel as described in the previous paragraph.