The difference in principle between an ordinary photograph and a hologram is that each point of a photograph bears information about the intensity (and color) of a point or a small portion of the object photographed, while the holographic carries information about each object point is distributed over the entire surface of the hologram. Electromagnetic waves are faithfully recorded by the holographic media and then are being reconstructed when the holograph appears.
Thus, the hologram is a kind of window through which the eye perceives light on the same field that produced previously recorded scene. An analogy would be comparing a box filled with light, which has the ability to reproduce objects.
Holography differs from the stereoscopic photography because of the mention that the latter records the information arrived at two points in space, so doesn’t allow the change of the perspective. Instead, the hologram allows observing objects at different distances and in all directions within a solid angle required by the relative position of the object and the hologram.
The principle of digital holography consists in decomposing the laser fascicle into two: a reference one and one object and then registering their overlap. One of the most significant advantages of digital holography techniques is represented by the concept that only with a single hologram acquired on a video camera (CCD or CMOS) it can be reconstructed in the same time the amplitude and the phase of the object wave and details about it.
In classical holography this concept was working on holographic plate, to record a figure of interference between reference light and diffracted by the object. To obtain the hologram this plate was chemical developed. The virtual image of the objects was experiment to obtain complex assembly.
In digital holography the hologram is recorded by a CCD array or CMOS, processes that have the advantage of avoiding the chemical time-consuming. With this technology objects are digitally reconstructed by a propagation algorithm based on simulation, the images being available in a electronic format, allowing image comparison with the same software object in different situations.
Digital holographic microscopy aims to obtain images of microscopic objects in real coherent light, having the advantage that phase information is lost and details depth of the order of several nm are easily highlighted.
Generating computer holograms aims to obtain holograms of virtual objects using
specific algorithms and the reconstruction, which is experimental, using a modulator
space light.
The method involves many scientific and technical fields, including mechanical and optical complex experimental montages, computational complexity but also an iterative algorithms used for filtering and processing specialized software images.
The method is complex combining optics, electronics, and processing transmission of information (images, digital databases).
