The relationship between holographic projection and shadow

The relationship between holographic projection and shadow is linear propagation. Holographic projection can be simply regarded as a three-dimensional projection, but it is very complicated. It records the intensity and phase information of reflected light through the interference of light. The process is shown in the figure. A beam of light is divided into two parts by the beam splitter before it is irradiated on the object. One part of the light propagates along the original route, and after it is irradiated on the object, it will produce scattered light on the holographic negative. At the same time, another part of the light is also reflected by the mirror and directly shines on the negative (we call this light reference light). At this time, two rays will interfere, resulting in a seemingly random interference pattern. In fact, the phase and changing density of light have been recorded in the negative. What can I say? Because according to the diffraction theory, if every point on the object is regarded as a point light source, the scattered light generated by all point light sources will interfere with the reference light, so the interference pattern we see is the superposition of the interference patterns of all point light sources and reference light, which is the biggest difference from general photography. General photography records images, but holographic photography records light information instead of images.