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biasflat

biasflat makes bias and flat-field corrections to all CCD frames of an image set. Depending on input, biasflat does one of several things:

• subtract bias level using column and row overscan regions
• subtract bias level using overscan regions and a bias image.
• subtract bias and divide by a flat-field image.

• input bias and/or flatfield frame names and the name of frames to process on the command line.
• input bias and/or flatfield frame names on the command line. biasflat will prompt for frames to be processed.
• input only frames to process on command lines; biasflat will use bias and flatfield frames listed in the parameter file.
• input nothing on command line. biasflat will prompt for all input.

biasflat returns a new set of image files framename_b_cn.fits, for bias corrected frames, and framename_f_cn.fits for bias and flat corrected frames. biasflat may be used for either direct of spectroscopic frames; if spectroscopic, the flat field frame should have been prepared with Sflats.

Details:

At a minimum, biasflat used the overscan regions to do bias corrections., and corrects, for IMACS, for the relative gains of the 8 chips. If a bias file is specified, either on the command line or in the parameter file, that image is first subtracted from the data frames, before a final overscan correction is made. If a flat field frame is specified, either on the command line or in the parameter file, the bias-corrected frame is divided by the flat field frame. The flat field frame must either (1) have already been bias-corrected, or (2) have the same bias levels and overscan regions as the other frames.

In the case of spectroscopic data, the flat field frame should have been prepared with Sflats, which properly normalizes each flat field spectrum.

As of COSMOS 2.19, the user can no longer edit the gain values in the parameter file.

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