For spectrographic images, geometric correction is done first, so it is the C0 image that is fully corrected. The C2 file is a list of the locations of reseau marks found in the raw flat field.
Positions are in photocathode coordinates.
No other processing is done on flat fields. The Standard Header Packet, Unique Data log, and Data Quality files are not used in the calibration. Values in the header specify the instrument configuration, such as the filters and the relay. The Data Quality file is an image having the same dimension and size as the Science Data file. Each pixel in the data quality file is a flag used to identify invalid data points.