There are two types of hologram, an amplitude modulation and a phase modulation ones. Recently, not only amplitude modulation ones but also phase modulation ones have been used in liquid crystal displays. We constructed an electro-holography system with a phase modulation type liquid crystal display and compared it to a system using current amplitude electro-holography. In the amplitude hologram, the reconstructed image darkens because the contrast of the hologram is low when the gray level is increased. It lightens most when binary. However, the phase hologram with high diffraction efficiency has produced an excellent result. The reconstructed image is bright even if the gray level is increased, and all the information of the liquid crystal display can be used at 256 gray levels.
