% @(#)skyflaccd.hlq 17.1.1.1 (ESO-IPG) 01/25/02 17:48:55 %++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ %.COPYRIGHT (c) 1993 European Southern Observatory %.IDENT skyflaccd.hlq %.AUTHOR RHW, IPG/ESO %.KEYWORDS MIDAS, ccd package, SKYFLAT/CCD %.PURPOSE On-line help file for the command: SKYFLAT/CCD %.VERSION 930827 RHW Documentation created %--------------------------------------------------------------------- \se SECTION./CCD \es\co SKYFLAT/CCD 25-Mar-1993 RHW \oc\su SKYCOR/CCD [in_spec] [out_frm] [xboxmn,xboxmx] [yboxmn,yboxmx] [clip] [lowsig,higsig] Apply sky observation to flat field to remove illumination pattern \us\pu Purpose: Apply sky observation to flat field to remove illumination pattern \up\sy Syntax: SKYFLAT/CCD [in_spec] [out_frm] [xboxmn,xboxmx] [yboxmn,yboxmx] [clip] [lowsig,higsig] \ys\pa in_spec = single sky frame or MIDAS CCD reduction table (with the extension .tbl) containing the names of the sky frame(s) in column :SKY. Default input is taken from the keyword CCD_IN. \ap\pa out_frm = name of the illumination corrected sky flat field. Default the output file the same as the input sky flat frame. Hence, by default the input sky flat frame will be OVERWRITTEN.\\ This parameter is only used is case of single frame input for the first parameter. In case the output is taken a reduction table the output frame(s) will also OVERWRITE the original flat frames. \ap\pa xboxmn,xboxmx = minimum and maximum smoothing box size along the x axes. The minimum box size is used at the edges and grows to the maximum size in the middle of the image. This allows the smoothed image to better represent gradients at the edge of the image. If a size is less then 1 it is interpreted as a fraction of the image size. If a size is greater than or equal to 1 then it is the box size in pixels. A size greater than the size of image selects a box equal to the size of the image. Default values are taken from the keyword IL_XBOX. \ap\pa yboxmn,yboxmx = see above. Default values are taken from IL_YBOX. \ap\pa clip = Clean the input frame(s) of objects? If yes then a clipping algorithm is used to detect and exclude objects from the smoothing. Default taken from IL_CLIP. \ap\pa lowsig,higgsig = sigma clipping thresholds above and below the smoothed illumination. Default values are taken from the keyword IL_SIGMA. The keyword is only read in case clip=yes. \ap\no Note: The command operates very similar to the command REDUCE/CCD, which the exception that the command not check for the exposure type of the input frame. In case the input is an association table the command will check for the existence of the flat frames in the column :SKY in the association table. Flat frames that do not exit will be created first, provided the association table contain the :SKY column. Other relevant calibration frames for processing the flat frames, will be taken from the corresponding calibration columns.\\ After the reduced sky frame is obtained, the sky illumination frame is produced by heavily smoothing the calibrated sky frames using a moving "boxcar" average. The effects of objects in the frames may be minimized by using a sigma clipping algorithm to detect and exclude the objects from the average. This illumination frame will be used to make an illumination corrected flat field (sky flat) according to the formula: \\ f_new = f_old*ill_sky/scale, where\\ f_new is the corrected flat field, f_old is the original input flat, used to reduce the blank sky frame, ill_sky is the illumination correction determined from the sky, and scale is the nomalisation factor. \\ The original flat frame is multiplied by the scaled sky illumination correction frame to produce the illumination corrected flat. The output will OVERWRITE the original (reduced) flat frames. Hence, the output sky flat will automatically be used as flat in subsequent calibration procedure(s).\\ NOTE: THE MASTER FLAT FIELDS WILL BE OVERWRITTEN BY THE CORRECTED ONES. \\ In the case of single frame input and all calibration frames input will be taken from the SC_ keywords and must exist. Also here, by default in the output illumination corrected flat will replace the input flat.\\ The IM_SEC keyword may be used to assign a region of interest for which the correction has to be done.\\ For more information see the CCD chapter in Volume B of the User's manual. \on\see See also: SET/CCD, SHOW/CCD, HELP/CCD, REDUCE/CCD, SKYCOR/CCD, \ees\exs Examples: \ex SKYFLAT/CCD redtbl.tbl Reduce all sky frames in the the ccd reduction table redtbl.tbl. All master calibration frames will be obtained from that reduction table. Do the calibration according to the keyword settings, including the flat fielding. From the calibrated sky produce the illumination frame, using the `IL_' keyword settings. Hereafter compute the output sky flat by multiplying the illumination frame with the original flat field. The output sky flats will have overwrite the original flats. \xe\ex SKYFLAT/CCD m100rraw_sk m100rraw_sf Start the ccd reduction sequence for the frame m100rraw. The output frame will be m100rraw_sf. In case only dark and flat field correction is to be applied the names of these two calibration frames will be obtained from the keyword SC_DKFRM and SC_FFFRM, respectively. \xe\sxe