Continuous-Tone Mirage Images computed from Digitised Source Photographs

Abstract

The properties of mirage images corresponding to a given atmospheric model can be graphically summarised in two distinct ways: the image space1, and the transfer characteristic2. The former shows the apparent heights of surfaces of constant elevation, and is useful for estimating images of objects that possess considerable longitudinal extent, i.e. varying distance from the observer. The transfer characteristic is more convenient for objects concentrated near a single plane at a fixed distance from the observer. Detailed image construction, however, is laborious with both representations: typically, the points on a line drawing of the object are individually mapped into new apparent positions and joined by straight lines to create a line drawing of the image3. Entry of object data is slow; either individual x,y coordinates are entered by hand, or the object can be traced on a digitising tablet. Because the computed image is still only a line drawing, it is not entirely satisfactory. Certainly it is not convincingly realistic when compared with a direct photograph of a mirage.