Holograms and high-quality reconstructions have been made by using a two-beam interferometric technique. The extraneous twin image and other interfering terms have been eliminated. Two types of objects have been used which are not suitable for the conventional wavefront reconstruction technique: objects which do not transmit a strong background wave (e.g., transparent lettering against a dark background) and continuous-tone objects.
EMMETT N. LEITH and JURIS UPATNIEKS, "Wavefront Reconstruction with Continuous-Tone Objects," J. Opt. Soc. Am. 53, 1377-1381 (1963)