Munipack ‒ Averaged bias frame

# Averaged bias frame

An average bias frame of a set of bias frames.

## Synopsis

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

## Description

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 = 〈 Ik 〉ij,

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

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, a list of bias frames is expected.

On output, a single file representing of the mean bias frame is created. Masked values (if parameter `-bitmask` is presented) are set to the frame mean.

## Parameters

`-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 A temperature and exposure time parameteres are set via Environment variables.

## Examples

    $ munipack bias -o bias.fits bias_*.fits

Mean bias frame

## See also

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