Anti-aliasing

Anti-Aliasing

Let's imagine a curved line drawn on a grid:

Let's say we want to draw this line on a computer screen. Each little square in the above figure represents one pixel of the screen. A pixel is the smallest area we can draw, so where the line passes through a square, that square should be filled in if we want to draw a continuous line. There can't be a square that is only partly filled. Each square must be either filled in or not.

But when we do this, the line becomes jagged instead of smooth:

That's aliasing. That's what happens when you try to portray a curved line on a digital screen that can only deal with discrete elements of a fixed size (pixels).

Anti-aliasing

Anti-aliasing attempts to fill in some of the pixels adjacent to the jagged line with colors that are in-between the two adjoining colors. For instance, a medium gray is a color between the black and the white, so some gray squares placed in the grid might help the eye round out the line:

Well, you can't see too much difference here, but "in real life" this looks much smoother. For example, here' s a word written in Paintshop Pro with the anti-aliasing option turned off:

Here's the same word written with the anti-aliasing option on:

The first is jagged, the second smooth. On the other hand, the outline is a little blurred or fuzzy. In most cases this doesn't matter much, but it can be a problem with text, which has to be read. If the text is very small, and is anti-aliased, it can be hard to read.

Remember that an image (including the text) is usually anti-aliased when ever it is resized, and that this blurs it slightly. It's therefore best to get your image to its final size (which you decide as you make it!) and only then add text.