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FLAMES-UVES Data Reduction Users’ Manual
VLT-MAN-ESO-19500-3016
6.4.1 PREPPA/FLAMES
Command Syntax: PREPPA/FLAMES frame_cat [bad_pix_mask] [filter_switch]
[x_width,y_width] [n_iterations] [kappa_sigma_thres]
[apply_cuts_switch] [low_cut,high_cut]
Input:
• frame_cat: Either a single frame or a catalog of frames (in all cases after SPLIT/UVES).
• bad_pix_mask: Optional initial bad-pixel mask, relative to the input frames. Set it to ‘+’ to disable
it. Default is +.
• filter_switch: ‘MEDIAN’ or ‘NONE’, toggles use of a median filter to derive a bad-pixel mask
(the default is set by MIDAS keyword DRS_FILT_MASK to ‘NONE’). Optional.
• x_width,y_width: If filter_switch was set to ‘MEDIAN’, width in x and y of the median
window to be used (the default is set by MIDAS keyword DRS_FILT_HW_XY to : 2,1).
• n_iterations: Maximum number of median filtering iterations (the default is set by MIDAS keyword DRS_FILT_IMAX to 300).
• kappa_sigma_thres: Difference (sigmas) between the input frame and its median filtered frame
above which a pixel is marked as bad in the mask (the default is set by MIDAS keyword DRS_FILT_KS
to 10).
• apply_cuts_switch: Should use cuts to mark saturated and cold pixels as bad in the mask (YES/NO).
The default is set by MIDAS keyword DRS_FILT_SAT_SW to YES.
• low_cut,high_cut: Cuts to be used in the cuts filter
(default is set by keywords DRS_PTHRE_MIN,DRS_PTHRE_MAX: -20,55000).
Output:
• for each frame in frame_cat: Two more frames: an error frame (*_sigma.bdf), and a bad-pixel frame
(*_mask.bdf).
Command description:
This command prepares frames read from disk for usage by the DRS commands. Its input may be a single
frame or a catalog of frames. For each indicated frame, two new frames are created, a variance frame and a
bad-pixel mask frame, with suffixes _sigma.bdf and _mask.bdf. Their names are written into the descriptors
SIGMAFRAME and BADPXFRAME of the input frame. It must be used before any other command that uses
raw (or calibration database) frames, except for the format-check frame, the wavelength calibration frame and
the order-definition frame (unless this last is used altogether with the odd and even fibre flat fields as input of
PREPFIBRE/FLAMES).
If the BADPXFRAME keyword is defined, it is assumed to contain the name of a generic bad-pixel frame
to be used as a first guess (i. e. known detector blemishes). If an input frame contains a BADPXFRAME
descriptor, this is assumed to contain the name of a first guess bad-pixel frame to be used for that specific
frame. If both the MIDAS keyword BADPXFRAME and the descriptor BADPXFRAME are defined, the
corresponding bad-pixel frames are merged.
Moreover, two additional methods to detect and flag bad pixels are provided: recursive median filtering and
clipping of values out of a given validity interval.
If recursive median filtering is enabled setting the parameter filter_switch to median, for each pixel the median
of the good pixels in a neighbourhood defined by the x_width and y_width parameters is computed and if the