If the keyword PREFTIME is > 0, the Preflash Image Reference file is scaled and subtracted from the input science image. The Preflash image is multiplied by the preflash lamp exposure time (obtained from the keyword PREFTIME in the input science image header and expressed in seconds) and then subtracted from the input science image. If the keyword PREFTIME = 0, the CTE fixup is applied. The names of the Preflash or CTE image and its DQF must be provided in the keywords PREFFILE and PREFDFIL.
