Anti-aliasing and ‘Halo’ formation

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You’ll remember from the article on Transparent Gifs that “halos” are form around objects once the background color is made transparent in a gif image. Actually, these ‘halos’ appear ONLY when the object is anti-aliased. Anti-aliasing causes pixels at the edges to have varying hues of a color – Refer Anti-Aliasing.

The ‘halos’ consist of such pixels. When you make the background color transparent, the pixels that carry other hues remain in the image, leading to the ‘halo’ effect.

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Preventing ‘Halo’ formation

‘Halos’ appear when a transparent image, made originally for a particular background color, is displayed on a contrasting background color. The ‘halos’ would not be discernible to the human eye if the two colors, the original color in the image which is made transparent and the color of the web page that shows in places of the original color are quite close (such as white and pale-yellow)… though the “halos” would be very much there.

There are several methods with which you can suppress halos or stop their appearance altogether.

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