Holography and photography

When an object is illuminated, we can see it because the light waves scattered by the object enter our eyes. The light wave of an object can be characterized by two parameters: amplitude corresponding to brightness or intensity and phase corresponding to the shape of the object. Amplitude and phase are usually described by complex amplitude. Complex amplitude contains all the complete information of an object. When object light irradiates recording media, such as photographic film or CCD camera, because these recording media are only sensitive to light intensity, only the change of light intensity is recorded on the plane of the recording media. The recorded light intensity change is a photo. Therefore, in photography, because of this intensity recording method, the phase information of light waves emitted by the original three-dimensional scene is completely lost. The loss of the phase information of the light field essentially destroys the three-dimensional characteristics of the scene, that is, when looking at the photo from different perspectives, we can't observe the changing perspective (parallax), so we can't perceive the depth of the original three-dimensional object. In essence, a photograph is a two-dimensional record of a three-dimensional scene.

Holography is a method invented by Gabor in 1948. This method not only records the amplitude information of the light field, but also records its phase information. In the process of holographic recording, the recording medium records complex amplitude, that is, the amplitude and phase information of the original light wave are recorded at the same time. The intensity changes recorded in this way are called holograms. After that, when the hologram is properly illuminated, our eyes will observe the same intensity produced by the complex light field. Once the accurate complex light field is restored, the human eye can observe the original complex light field. The recovered complex light field gives all the parallax and depth information of the original complex light field. Through the translation (synthesis) of our brains, it is like seeing the same original three-dimensional object.