vircam_dark_combine
[Recipes]

Name:

vircam_dark_combine

Purpose:

Combine a list of darks to form a mean dark frame.

Description:

A list of darks with the same exposure parameters is combined with rejection to form a mean dark. If a master dark is supplied, then a difference image is formed between it and the combined result from the current frame list. This difference image can be useful for looking at the evolution of the structure of the dark current and the reset anomaly with time. If a channel table is given, then the difference image is broken into lots of little cells. The median value of the difference image as well as the RMS in each cell is written to a difference image statistics table.

Language:

C

Parameters:

• comb (int): Determines the type of combination that is done to form the output map. Can take the following values:
  • (1): The output pixels are medians of the input pixels
  • (2): The output pixels are means of the input pixels
• scale (int): Determines how the input data are scaled or offset before they are combined. Can take the following values:
  • (0): No scaling of offsetting
  • (1): All input frames are biassed additively to bring their backgrounds to a common mean.
  • (2): All input frames are scaled multiplicatively to bring their backgrounds to a common mean.
  • (3): All input frames are scaled to a uniform exposure time and then additively corrected to bring their backgrounds to a common mean.
• xrej (int): If set, then an extra rejection cycle will be run.
• thresh (float): The rejection threshold in numbers of sigmas.
• ncells (int): If a difference image statistics table is being done, then this is the number of cells in which to divide each readout channel. The value should be a power of 2, up to 64.
• ext (int): The image extension of the input files to be done on this run. If all of the extensions are to be processed, then this should be set to zero.

Input File Types:

The following list gives the file types that can appear in the SOF file. The word in bold is the DO CATG value.

• DARK (required): A list of raw dark images for combining
• REFERENCE_DARK (optional): A library reference dark frame. If this is given, then a difference image will be formed and some basic statistics run on it.
• MASTER_BPM or MASTER_CONF (optional): If either is given, then it will be used to mask out bad pixels during and statistical analysis that is done.
• MASTER_CHANNEL_TABLE or CHANNEL_TABLE_INIT (optional): If this is given then the channels in difference image will be broken up into a number of cells. Basic statistics will be done on the cells and written to the difference image statistics table. No linearity information is used, hence either type of channel table is acceptable.

Output Products:

The following list gives the output data products that are generated by this recipe. The word in bold gives the PRO CATG keyword value for each product:

• The output mean/median dark frame, formed by either a mean or median combination of the input raw frames with rejection (MASTER_DARK).
• The output difference image, formed by subtracting the input master dark frame from the current mean/median dark frame. This is only done if a master dark frame is specified from the outset (DIFFIMG_DARK).
• The output difference image statistics table. The exact columns contained in this file are described at length in section 5.7 in the VIRCAM Data Reduction Library Design document (DIFFIMG_STATS_DARK).

Output QC Parameters:

• DARKMED The median value of the combined dark frame.
• DARKRMS The RMS value of the mean dark frame.
• DARKDIFF_MED The median of the dark difference image
• DARKDIFF_RMS The RMS of the dark difference image
• PARTICLE_RATE The average number of cosmic ray hits per pixel per second per frame.
• STRIPERMS The RMS of the stripe pattern on the output mean dark frame
• NHOTPIX The number of hot pixels on the mean frame
• HOTFRAC The fraction of pixels on the mean frame that are hot

Notes

None.

Fatal Error Conditions:

• NULL input frameset
• Input frameset headers incorrect meaning that RAW and CALIB frame can't be distinguished
• No dark frames in the input frameset
• Unable to save data products

Non-Fatal Error Conditions:

• Exposure time missing from header. Assumed to be 1 second.
• No master dark. No difference image formed.
• No master bad pixel or confidence map. All pixels considered to be good.
• No channel table. No difference image stats table created.

Conditions Leading To Dummy Products:

• Dark frame image extensions wouldn't load.
• The detector for the current image extension is flagged dead
• Combination routine failed
• Master dark frame image extension won't load or is flagged as a dummy
• Channel table fits extension won't load, won't verify or is flagged as a dummy.

Author:

Jim Lewis, CASU

Code Reference:

vircam_dark_combine.c

---