Still image display of a recent video image of tissue as a reference still image prior to a switch in the mode of illumination of the tissue. The still image is displayed concurrently with live video of the tissue under a different mode of illumination, to facilitate discrimination between healthy and diseased tissue, and further facilitate therapeutic intervention. The reference still image may be displayed either as an insert (picture-in-picture), side-by-side, or the like concurrently with the live video image. In some embodiments, when a practitioner switches a light source from “excitation-light” to “white light”, the “excitation-light” video may be frozen/captured and displayed as a reference still image as a PIP, and the “white-light” live video is displayed concurrently. When the source is switched again, the “white-light” video may be frozen/captured and displayed as a reference still image, and the “excitation-light” live video is displayed concurrently.
