Preface Understanding an astronomical CCD image Counts, photons and electrons Burp Not all counts are light Your detector is not ideal Construction of an artificial (but realistic) image Calibration overview Image combination Calibration choices you need to make Handling overscan, trimming, and bias subtraction Inspect your images and make a choice about next steps Subtract overscan, if desired Trim, if needed Combine bias images to make master Dark current and hot pixels The ideal case: your dark frames measure dark current, which scales linearly with time Reality: most of your dark frame is noise and not all of the time dependent artifacts are dark current Identifying hot pixels Make a choice about next steps for darks Subtract bias, if necessary Interlude: Image masking Identifying bad pixels Creating a mask incorporating the mask in reduction Flat corrections There are no perfect flats Make a choice about next steps for flats Calibrating the flats Subtract overscan and trim, if necessary Subtract bias, if necessary Subtract dark current, scaling if necessary (scale down when possible) Combining flats Reducing science images Initial reduction Subtract overscan and trim, if necessary Subtract bias, if necessary Subtract dark current, scaling if necessary (scale down when possible) Flat correct Cosmic ray removal Combining images Combine without aligning to create a sky flat Combination with alignment via WCS Combination with alignment based on star positions in the image