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Averaged Bias Frame

An average bias frame of a set of bias frames.


munipack bias [.. parameters ..] file(s)


A bias frame is a zero-time exposure with no light. The exposure with the shortest possible exposure time provided by a device. One maps a pre-amplifier bias (offset) of readout electronics. This routine creates an average bias frame, sometimes named as a masterbias.

Because bias exposure times are really short (1/100s or less), it is recommended to acquire and average a lot of exposures (>10).

An output bias Bij is computed as the average of every pixel of input images (Ik)ij:

Bij = 〈 Ikij,

where i,j is an index of a pixel and k is an index of an image.

Two methods of averaging are implemented. An arithmetical mean is fast and memory conserving while a robust mean is significantly slower and requires much more memory. Use of the robust mean is preferred because random defects (cosmics, interferences) are greatly suppressed.

Both chip temperatures or exposure times are checked to be nearly the same during processing when FITS_KEY_TEMPERATURE and FITS_KEY_EXPTIME environment variables are set to values of corresponding quantities.

Input And Output

On input, list of frames representing the bias is expected.

On output, the only one file as mean bias frame is created.


use arithmetical mean instead of default robust mean
--tol-temp temp
limit for nearby temperatures (default = 1K)
--tol-exp exptime
limit for nearby exposure times (default = 1 μsec)
-B bitpix
set numerical type of output images, see Common options (default -32)
-o filename
save to the output file, see Common options

Also see Common options


$ munipack bias -o bias.fits bias_*.fits
Arithmetical mean (duration 0.2 sec)
Robust mean (duration 3.5 sec)

See Also

Light Curve Tutorial, Photometric corrections tutorial, Averaged dark frame.