Image Antialiasing

Monochrome images – usually black and white ones – suffer from jagged lines, also referred to as aliasing. Antialiasing the lines (i.e. removing the jaggs) of already existing images is somewhat difficult, but in most cases the following method will do the trick. Everything you need is a professional graphics editor like GIMP or Photoshop. We will use GIMP for this tutorial.

(Please click on the thumbnails to see larger versions.)

The first image is the one we want to antialias. It is just a simple circle with a line-thickness of 10 pixels.

Let us try to use Filters → Enhance → Antialias. The resulting image (2) is not perfect. We need another method.

The first step is to apply a gaussian blur to our image. The blur radius should be a bit smaller than the line-thickness. 8px seems to be a good value. After blurring the image, we scale it up to 800% using cubic filtering. Now we use the Colors → Threshold tool with the standard range of [127,255] and the blurry look disappears. Our last step is to scale the image down to its original size (12.5%) using cubic filtering again.

The resulting image (3) with its smooth lines looks much better than the original one. The blur radius and threshold values perhaps need to be adjusted for other types of images.