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The abbreviation HCI is used for high contrast imaging generally meaning imaging of an object that is very near a bright object, such as imaging an extra-solar planet despite the much-brighter light from its host star. A number of specific techniques are used to accomplish this. Generally, a coronagraph is incorporated into the instrument or observation.
High contrast spectroscopy (or high contrast spectrography, or sometimes HCS) is spectrography of such targets. Post-processing is used to isolate the planet's spectrum through knowledge of the star's spectrum, which inevitably is not entirely suppressed, despite the coronagraph. A spectrograph with a high spectral resolution (HDS for high velocity dispersion spectrograph or HRS for high resolution spectrograph) assists in this improvement of the signal-to-noise ratio. The term HCI+HDS has been used for this combination of techniques.