(1) The computer's display system. See display adapter, discrete graphics, integrated graphics and graphics pipeline.
(2) The creation and manipulation of picture images in the computer. Primarily called "computer graphics," it is defined here as "graphics" in order to group all graphics terms together. A fast computer is required for graphics work, and although mice are widely used to create illustrations, a drawing tablet is also used for precise illustrations (see digitizer tablet and CAD).
Vector and Bitmapped Graphics
The two major categories of digital graphics structures are vector graphics and bitmapped graphics. To be knowledgeable in the field of computer graphics, understanding how these two architectures are used and intertwine is necessary.
Drawing, Scanning and Painting
When pictures are "drawn" (top), they become vector graphics. When they are photographed or scanned, they become bitmaps (a matrix of pixels). Images can also be "painted" (see paint program
Vector Vs. Bitmap
Intricate illustrations can be made with drawing (vector) programs. However, nothing can provide the realism of a photograph or scan (bottom). (Images courtesy of Adobe Systems, Inc.)
Vector Graphics for CAD and Drawing
Vector graphics are a series of points, lines, arcs and other geometric shapes. They are created in computer-aided design (CAD) and drawing programs. As you draw, each line is stored as a vector, which is two end points on an x-y matrix. For example, a square becomes four vectors, one for each side. A circle is turned into dozens or hundreds of tiny straight lines, the number of which is determined by the resolution of the drawing. The image is stored in the computer as a list of vectors.
Vector Graphics Are Easily Scaled
Each vector element maintains its own identity and can be selected and manipulated independently of the others. Any element can be independently scaled (resized) smaller or larger.
From Vectors to Bitmaps
Monitors display pixels, and printers print dots, both of which are bitmaps. Therefore, vector images must be converted into bitmaps ("rasterized") for the screen and printer. The rasterization process is performed by the operating system and printer language (see page description language
3D images are vector graphics, but 3D CAD and drawing programs are significantly different than 2D programs. Objects are created in 3D form in a 3-dimensional workspace. They can be viewed at any angle by simply rotating them, whereas in 2D programs, the object would have to be redrawn entirely. 3D programs can render the drawing with lights and shadows, and camera angles and light sources are used to depict the objects as real-world elements.
The 3D Stage
In 3D graphics, objects are created on a 3-dimensional stage where the current view is derived from the camera angle and light sources, similar to the real world. (Image courtesy of Intergraph Computer Systems.)
Bitmapped Graphics for Imaging and Painting
Bitmapped graphics, also known as "raster graphics," are made up of dots like TV images. Each image is divided into hundreds of horizontal rows, with each row containing hundreds of "pixels" (dots). Bitmapped graphics are created manually in image editor and paint programs. They can also be scanned from paper documents, photographed by digital cameras, recorded by video cameras, as well as extracted from the computer screen (see screen capture
Many Formats, All Digital
Unlike TV, which uses one family of formats for the country, there are dozens of different vector and bitmapped graphics standards. See graphics formats
Bits Per Pixel
When an image is scanned into or "painted" on a computer, the bitmap is created in a reserved area of RAM with some number of bits corresponding to each pixel. The simplest monochrome bitmap uses one bit (on/off) per pixel. Gray scale bitmaps store a number for each pixel corresponding to a shade of gray; for example, 8 bits holds 254 gray levels plus black and white.
Color bitmaps require three times as much storage in order to represent the shades of red, green and blue. Since colors are designated with numbers, changing red to green is a process of searching for the red number and replacing it with the green number. See bit depth
Although often compressed further to save space, bitmapped image files are typically larger than their vector counterpart. Storage for each pixel is required whether part of the object or the background. A small object in a vector image requires storage of only a few vectors.
From Bitmaps to Bitmaps
Although bitmapped images are already in a raster format, they typically have to be combined with other bitmaps, vector and text elements and be "rasterized" into a bitmap of the screen's resolution or the printed page.
Drawing Vs. Painting
Although more painting tools are added to drawing programs and more drawing tools are added to paint programs, their inherent structure is different. Drawing programs (vector graphics) allow for the creation of objects that can be manipulated independently. Paint programs (bitmapped graphics) provide a canvas that can be covered with electronic paint.
Canvas Specializes in Both
Deneba Software's Canvas combines extensive drawing and imaging tools in one program. The PC drawing on top is a vector graphics rendering and the "first mouse" underneath is a bitmap. The open menu shows the image editing tools.
Getting Closer All the Time
A major goal is to create virtual people who look real, and it took 19 rendering passes in 2004 to create this lovely lady. Also, this JPEG image is 1/74th the size of the original 2.3MB TIFF file. It was compressed to 32KB to save space (see JPEG
). (Image courtesy of NVIDIA Corporation.)