graphics - technical definition

(1) May refer to the computer's display system. For example, "what kind of graphics does this PC have?" means what speed and quality is the graphics rendering on screen. See display adapter and graphics pipeline.

(2) The creation and manipulation of picture images in the computer. In such cases, the subject is typically called "computer graphics," but it is defined here as "graphics" in order to group similar terms together.

A fast desktop computer is required for graphics work, and although a mouse can be used for drawing, graphics tablets are also widely used for CAD (computer-aided design) applications.

Vector Graphics and Bitmapped Graphics

Vector graphics and bitmapped graphics are the two major categories of graphics structures in a computer. In order to learn about computer graphics, understanding these two formats and how they are created and intertwine is essential.

Vector Graphics for CAD and Drawing

Vector graphics images 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 entire image is commonly stored in the computer as a list of vectors.

Vector Graphics Are Easily Scaled
A vector graphics image is a collection of graphic elements, such as lines, squares, rectangles and circles. Although grouped together, each element maintains its own identity and can be selected and manipulated independently of the others. Most importantly, any element can be scaled (resized) smaller or larger in an instant.

From Vectors to Bitmaps
Although there are x-y plotters that "draw" images directly from a list of vectors, most printers today are inkjet and require bitmapped images as input. Likewise, all monitors today display bitmaps. Thus, the vectors 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 Graphics

3D images use 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.

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 acquired from paper documents by scanners, from the real world by digital cameras and from a running software application by screen capture programs.

Many Formats, All Digital
Unlike TV, which uses one standard (NTSC) for the country, there are dozens of bitmapped graphics standards (JPEG, GIF, BMP, TIFF, etc.). Also, unlike TV, which records and displays the dots as infinitely variable shades and colors (analog), computer graphics have a finite number of shades and colors (digital).

Bits Per Pixel
When you scan an image or paint an object into the computer, the bitmap is created in a reserved area of memory 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" to the screen's resolution or size of the printed page.