• Directory of Internet terms
  • Aliasing, anti-aliasing — Pictures on your computer monitor are made up of square pixels. When the edge of a solid colored object in a GIF image is a diagonal or curved line, and it is displayed against a contrasting color, the edges appear jagged, like stair steps. This jagged appearance is called aliasing. The jagged appearance can be softened by filling in adjacent pixels with intermediate colors between the object and the background. This softening of the edges is called anti-aliasing. Software like PhotoShop can apply anti-aliasing for you automatically. It is often the default setting. One problem with anti-aliasing GIF images is that it increases the number of colors used, necessarily increasing the file size. You must decide whether quick loading or smoothed edges serves your needs better. A second problem can occur when you create transparent GIFs. If the edges are anti-aliased against a different color background than the background it will be displayed against, the intermediate color pixels will be the wrong color and a halo effect occurs around the image. Make sure that when you anti-alias transparent GIFs, that you do it against the transparency or the final background color. If you are using a tiled background image where the background color changes, you must anti-aias against a transparent background. Feathering is a similar technique of putting partially transparent pixels around the edge to soften the aliasing. Aliased,magnified5 times Anti-aliased,Magnified5 times Transparentanti-aliasedagainstwrongbackground