Bias
Overview
This file describes the data model for the Bias
image.
This is written to disk as a multi-extension FITS file prefixed by
Bias
in the Calibrations/
folder.
This is generally a simple combination of all input bias frames.
Inspecting
The first extension is the stacked image. You can view it with any standard image viewer, e.g.:
ginga Calibrations/Bias_A_1_01.fits
It should resemble any one of your input bias frames aside from:
Having been overscan subtracted
Being only a trimmed portion of the image
Re-oriented so that vertical is the spectral dimension with blue at the bottom
Here is an example for the keck_lris_red spectrograph.
Pretty boring, as expected. Note that this is only 1 of the 2 detectors for this spectrograph.
Trouble Shooting
If your image appears to be in err, here are the things to consider:
Is one or more of your input bias frames junk?
Is one or more of your input bias frames mis-labeled?
Current BiasImage Data Model
Internally, the image is held in
BiasImage
,
which subclasses from PypeItImage
and
DataContainer
.
The datamodel written to disk is:
Version 1.3.0
HDU Name |
HDU Type |
Data Type |
Description |
---|---|---|---|
|
… |
Empty data HDU. Contains basic header information. |
|
|
floating |
Primary image data |
|
|
floating |
Inverse variance image |
|
|
The detector (see |