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Saturday, March 1, 2008
What is vector?
Vector graphics (also called geometric modeling or object-oriented graphics) is the use of geometrical primitives such as points, lines, curves, and polygons, which are all based upon mathematical equations to represent images in computer graphics.
Vector graphics is an alternative to raster graphics, which is the representation of images as a collection of pixels, as is typically used for the representation of photographic images.[1]
Overview
Most computer displays translate vector representations of an image to a raster format. The drawing software is used for creating and editing vector graphics. The image can be changed by editing these objects. They can be stretched, twisted, coloured, and so on with a series of tools. The raster image containing a value for every pixel on the screen is stored in memory. Starting in the earliest days of computing in the 1950s and into the 1980s, a different type of display, the vector graphics system, was used. In these "calligraphic" systems the electron beam of the CRT display monitor was steered directly to trace out the shapes required, line segment by line segment, with the rest of the screen remaining black. This process was practiced many times a second ("stroke refresh") to achieve a flicker-free or near flicker-free picture. These systems allowed very high-resolution line art and moving images to be displayed without the (for that time) unthinkably huge amounts of memory that an equivalent-resolution raster system would have needed, and allowed entire subpictures to be moved, rotated, blinked, etc. by modifying only a few words of the graphic data "display file." These vector-based monitors were also known as X-Y displays.
A special type of vector display is known as the storage tube, which has a video tube that operates very similar to an Etch A Sketch. As the electron beam moves across the screen, an array of small low-power electron flood guns keep the path of the beam continuously illuminated. This allows the video display itself to act as a memory storage for the computer. The detail and resolution of the image can be very high, and the vector computer could slowly paint out paragraphs of text and complex images over a period of a few minutes, while the storage display kept the previously written parts continuously visible. The image retention of a storage display can last for many hours with the vector storage display powered, but the screen can clear instantly with the push of a button or a signal from the driving vector computer.
One of the first uses of vector graphic displays was the US SAGE air defense system. Vector graphics systems were only retired from U.S. en route air traffic control in 1999, and are likely still in use in military and specialised systems. Vector graphics were also used on the TX-2 at the MIT Lincoln Laboratory by computer graphics pioneer Ivan Sutherland to run his program Sketchpad in 1963.
Subsequent vector graphics systems include Digital's GT40 [1]. There was a home gaming system that used vector graphics called Vectrex as well as various arcade games like Asteroids and Space Wars. Storage scope displays, such as the Tektronix 4014, could also create dynamic vector images by driving the display at a lower intensity.
Modern vector graphics displays can sometimes be found at laser light shows, using two fast-moving X-Y mirrors to rapidly draw shapes and text on a large screen.
The term vector graphics is mainly used today in the context of two-dimensional computer graphics. It is one of several modes an artist can use to create an image on a raster display. Other modes include text, multimedia and 3D rendering. Virtually all modern 3D rendering is done using extensions of 2D vector graphics techniques. Plotters used in technical drawing still draw vectors directly to paper.
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