2-D and 3-D Graphics

Computerworld - Between a 2-D image and its 3-D counterpart stand hundreds of thousands of calculations and a world of space and time.

Computer artists create a 2-D image on a plane, just as they would on paper. They can add textures and lighting effects, create reflections and blur backgrounds to simulate the mist of a distant horizon.

But should they want to change a noonday sun to a setting sun, they must also alter the drawing's colors, textures, shadows and highlights to reflect that change in lighting position.

What if the artist created that image with a 3-D program? Because calculations describing each object are an intrinsic part of 3-D images, the application could automatically make the changes.

2-D Basics

The differences begin with 2-D applications, which produce images that are either bit-mapped (raster) or vector.

A line drawn in a bit-mapped application is described in bits/pixel. At its simplest, 1 pixel is 1 bit, black or white. Higher definitions yield more colors - 8-bit definition yields 256 colors; 24-bit allows for 16 million.

A common 2-D bit-map application such as San Jose-based Adobe Systems Inc.'s Photoshop costs about $600 and is a basic tool for computer graphic artists.

A line drawn in a vector graphics program is described mathematically, not visually, and looks the same whether it's displayed at 100% or 5,000%.

To change a bit-mapped line, the artist must redraw it. To change a vector line, one need only change the equation that describes the line.

A vector application, such as Adobe's Illustrator, interprets each line drawn on an x-y matrix as two points connected by a line, or a vector. A circle or other shape is composed of many tiny vectors.

Whereas data on every pixel - even those in a blank background - must be stored in a bit-map image, only data on the drawing itself is stored for vector images. Thus, vector files are usually smaller than bit-map files.

The Third Dimension

3-D images are vector format drawings defined on an x-y-z matrix - that is, height, width and depth. To describe complex shapes and surfaces, a 3-D application views objects as composed of triangles - fewer triangles for broad, smooth planes, but more for uneven surfaces.

An important use of 3-D graphics is in computer-aided design (CAD) applications, such as San Rafael, Calif.-based Autodesk Inc.'s AutoCAD, which has been the industry standard.

Increasingly, CAD packages have 3-D capabilities that can convert 2-D drawings of a building into a 3-D representation through which viewers can do a virtual walk-through.