reference star differential imaging

Reference star differential imaging (RDI) is a speckle-suppression technique for high contrast imaging used with coronagraphy, e.g., for attempting direct imaging of extra-solar planets. It consists of also imaging a similar star (i.e., the reference star) to capture the noise pattern created by the telescope, then subtracting that pattern from the image of the source you are trying to image. My impression is that RDI is generally used for direct imaging and often not mentioned or merely indirectly mentioned, such as mention of the reference star or of differential imaging.

Images have been captured using combined RDI and angular differential imaging (ADI), i.e., ADI+RDI.