Optics. Applied to the two images of one object seen in looking at a point nearer than the object, when the right image is that seen by the right…

designating the faint sensation of light resulting from intrinsic (rather than external) excitation of the retina.

Of a visual image, esp. a photograph: showing the lights and shades (and colour values) as seen in the original. Cf. negative, adj. 10.