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Raster Graphics vs Vector Graphics

Ted Stahl, 2002

Most monitors (i.e., televisions and picture tube-based devices) "rasterize" images to the screen. These are called rastor display devices. This requires an electron beam generated at the back of the cathode ray tube (CRT) to bombard the inner surface at the front of the CRT thus illuminating the phosphor that coats the inside of the glass. This is accomplished through a repeated pattern of horizontally drawing one line after another from top to bottom and repeating.

Vector graphic monitors control the electron beam differently. The beam is directed to draw only the outline of the graphics on the screen. The beam does not touch the areas of the screen where nothing is to exist at that time. Essentially the beam is directed to connect the dots for all of the visual elements within the game. In the case of Asteroids, the electron beam draws the outline of all of the asteroids and the ships as well as the weapon fire.

Each approach has its own advantage. Raster monitors can create more colorful images and, depending on the resolution, can approach photographic realism. However, the more accurate the images they display, the more powerful the processor must be to refresh such an image. Conversely, vector monitors can create razor sharp images with little processing power. Unfortunately, they do not offer much in the way of color and, by their nature, are not very realistic.

Perhaps the greatest downfall of vector graphic monitors is their failure rate. Since a standard raster picture tube requires its electron beam to fire a simple and predictable linear pattern repeatedly, they tend to last for years. In contrast, the vector monitors force the electron gun to draw irregular shapes constantly to the surface of the CRT in order to display images. This puts much more wear and tear on the mechanism that controls the electron beam and tends to wear it out much more easily. Though this technology was improved over the years, this was the typical reason associated with the malfunctions of the original Cinematronics Space Wars displays.

 

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