vector vs raster/pixel images

While there are numerous file formats and extensions, each designated by the program that saved the file, computer art falls into two basic categories- raster, or pixel based images, and vector, or line based images.

raster circle

Raster images are displayed in a rectangular grid, as horizontal lines of squares. In a 72 dpi image, each square is 1/72 of an inch; in a 300dpi image, each square is 1/300 of an inch. The greater the dpi, the smaller the square, or pixel. (Higher res images can be displayed at larger sizes without loss of quality, whereas lower res images will lose quality, or ‘pixelate’ when enlarged.) Raster files sizes are larger than vector files because the display instructions read like “make the first pixel in the line red, the second orange, the third yellow…” so the file must include instruction for every pixel in the image. 

There are different formats for different types of images, each based on the best way of displaying the image. A high resolution color photo will have many more pixels and a corresponding larger file size than an image consisting only of, say, black and white (horizontal) stripes. Further, an image of horizontal stripes will have a smaller file size than that of vertical stripes because it is more efficient to have the instruction “display 100 black pixels in a row, then display 100 white pixels in a row” than it is to “display one black pixel, then display 1 white pixel, then display one black pixel, then display 1 white pixel…” etc.

vector circle with bezier curves

For further clarification, see: http://en.wikipedia.org/wiki/Raster_graphics

Vector files, on the other hand, contain mathematical instructions for their display, such as “at the point x=10 and y=30, draw a circle that is 2 inches by three inches and fill it with this color…” which the display then interprets to display the highest quality image. They are created by placing points, then connecting those points with lines and (bezier) curves. Because they are formulas rather than pixel-based, they can be reduced or enlarged without degrading the image. Vector files are best for type and graphics.

For further clarification, see: http://en.wikipedia.org/wiki/Vector_graphics

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