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. When a practitioner switches a light source from a “first light” to a “second light”, the second light video may be frozen/captured and displayed as a reference still image as a PIP, and the second light live video is displayed concurrently. The second light can be infrared and/or near infrared light. The second light can include structured light to project a structured light pattern to facilitate structure measurements. The second light source is configured with a numerical aperture greater than the first light source.