Hologram

A technician produces a hologram of a statuette at the Grepa laboratory at the University of Strasbourg.

Philippe Plailly/Science Source/Photo Researchers, Inc.

A hologram is a 3-D photographic image created using a laser (see Holography). To create a hologram, technicians split a laser beam into two components. They direct one part of the laser beam onto a photographic plate and aim the other part of the laser beam at an object. The light waves bounce off the object and onto the photographic film, where light waves from the two beams collide and interfere with each other. The hologram is a record of the way the object interfered with the laser that bounced off of it.

British physicist Dennis Gabor first described the concept of holograms in 1948, but the existing technology could not support the creation of an actual hologram. In 1963 American physicist Emmett Leith and Latvian-American engineer Juris Upatnieks used the newly developed laser to make Gabor’s vision a reality.

Holograms have many applications. They grace credit cards, magazine covers, and the jackets of music recordings. Holograms also prove useful in medical science, enabling researchers to examine a subject from all sides. Their most significant role to date lies in storage of computer data, which is recorded as bright and dark spots in holographic images. A multifaceted hologram stores many times more data than does a traditional two-dimensional data storage device, such as a magnetic tape. Each of a hologram’s many faces holds large amounts of data. By illuminating the hologram with a laser beam at different angles, the computer can access data on each face.

C

Single Image Random Dot Stereograms

Autostereogram

An autostereogram is a remarkable kind of two-dimensional image that appears three-dimensional (3-D) when viewed in the right way. To see the 3-D image, first make sure you are viewing the expanded version of this picture. Then try to focus your eyes on a point in space behind the picture, keeping your gaze steady. An image of a person playing a piano will appear.

Small Wonders

A single image random dot stereogram (SIRDS) is a computer-generated image consisting of seemingly random dots or lines, which, when viewed properly, coalesce into a previously unseen 3-D illusion. To see the hidden illusion, the viewer must relax the eyes and focus on a point in space behind the image. SIRDS work in the same way that stereoscopes, anaglyphs, and Polaroid 3-D movies do. Each eye receives a slightly different image, which the brain integrates into a single 3-D illusion. SIRDS became popular in the early 1990s with the Magic Eye series of books.

VI

COMPUTER-GENERATED 3-D MODELS

Development of a Three-Dimensional Computer Model

Computers enable the creation of graphics that are so realistic they appear to have depth, even though they are actually just two-dimensional images displayed on a flat monitor, television, or movie screen. In a process called rendering, a computer uses a complex set of mathematical calculations to derive how an object should appear to a viewer from many angles in a given set of conditions. The resulting shape, shading, and linear perspective are so accurate that they impart the illusion of a third dimension—depth—in two-dimensional graphics.

Graphic designers and scientists use computers to create 3-D computer graphics using a process called rendering. In this case, the term 3-D refers not to stereoscopic images, but to graphics rendered with highly accurate shape, shading, and perspective using mathematical calculations on a computer. The computer mathematically derives how an object should appear to a viewer from all angles in a given set of conditions.

The first step in rendering requires the user to provide the computer with a detailed description of an object. This description can be delivered to the computer in the form of photographs or video images, or it can be created from scratch by means of a software program (see Computer Animation). The computer calculates a viewer’s perspective of the object from all angles and uses this information to create a wire-frame representation, in which every surface on the object is represented by a geometric shape.

Next, the user instructs the computer to fill the surfaces of the geometric shapes with colors, textures, and patterns that give the object a more realistic quality. Finally, the user provides the computer with detailed information about the source and angle of the lighting. From this information, the computer determines the way the light would hit each surface on the wire-frame representation and adds appropriate reflections and shadows.

Toy Story (1995), created by the animation studio Pixar and produced by the Walt Disney Company, was the first feature-length motion picture made entirely with computer animation. The film, which took four years to complete, humorously portrays the rivalry between the characters Buzz Lightyear, left, and the cowboy doll Woody, right.

Hollywood filmmakers first used 3-D computer graphics in movie shorts in the 1970s but did not apply the techniques to a major feature film until 1982 in the science fiction hits Star Trek: The Wrath of Khan and Tron. Techniques for 3-D computer animation rapidly grew more sophisticated and more common. In 1995 Toy Story became the first feature film in which all of the images were created entirely with computers.

Today, 3-D computer graphics have applications in industrial design, medical research, and many other fields. In computer-aided design and manufacturing (CAD/CAM), industrial engineers use computers to build 3-D models of complicated products, such as airplanes and automobiles. Computer-generated maps show topographical features on the surface of Earth and other planets. Medical researchers study 3-D models of cells, molecules, organs, and even the entire human body. Other applications of 3-D computer models include diagnostic radiology, pharmaceutical research, and much more.

Among the fastest growing uses for 3-D computer graphics are computer games that enable players to manipulate 3-D graphics on-screen. These games incorporate highly sophisticated real-time rendering tools that process player input and update the graphics immediately. Real-time rendering tools update computer graphics 30 or more times per second, making them appear to move in the time-frame in which events would naturally happen in the real world.