The film that records the interference fringe becomes a hologram, or called holographic photo after image development,
photographic fixing and other processing procedures; the second step is to reproduce the light wave information of the object by using the principle of diffraction, which is the imaging process: the holographic image is like a complex grating, and a diffracted light wave of a linearly recorded sinusoidal hologram generally gives two images under the coherent laser illumination, namely, the original image (also known as the initial image) and the conjugate image.