A common use for graphics software is to add captions and other basic objects to photographs. During this process, rounded objects, text or diagonal edges can accidentally become jagged. How do you prevent these unwanted effects creeping into your images? In most cases, the solution is to use anti-aliasing.

Computer screens and printers are made up of small dots (or pixels) that are switched on or off. These are laid out in a grid that is typically square-ish. Use a magnifying glass on a CRT screen or print out, and you will find the dots are more like overlapping blobs lined up in a grid. However, when you try to draw perfectly curved or diagonal lines along this grid, they tend to look jagged or stepped (see FIGURE 1).

Anti-aliasing is a technique that intro­duces additional pixels to the edges of an object. The extra pixels blend the edge of an object with the background colour. For example, if you type blue text (with anti-aliasing) on a white background, then you will notice light blue pixels appearing at the borders between the two areas. This effect mimics the natural overlap of lines you would normally see with real objects. The end result is that edges no longer appear blocky — your brain interprets them as a continuous, but fading, tone.

The most common tools that have anti-aliasing are the Text, Shape, Line and some select tools. Don’t expect to find it in free or low-end software such as the program that ships with Windows — Microsoft Paint. You will need a program such as Paint Shop Pro, Photoshop Elements, Photoshop or Photo­Impact.

The location of the anti-alias settings is rarely obvious. This is made even more difficult to find since the tool’s options menu is only visible when that tool is selected — and as noted above, not all the tools support anti-alias. This means that it comes down to trial and error or requires you to hunt through the help files to find where the feature is hidden (and if it is available at all). For example, when using Photoshop to paste a file in EPS format, only the Paste as Pixels option will give you the choice of anti-aliasing.

The most common use for anti-alias is to smooth out text. In your graphics program, select the T (Adobe programs) or A (most non-Adobe programs) icon from the palette. In Photoshop, the toolbar at the top of the page doesn’t even have a feature labelled anti-alias (that would be too easy), but it is present. Next to the two lower-case ‘a’ icons is a drop-down menu with headings such as Sharp, Crisp, Strong and Smooth (see FIGURE 2). Use these to set the type of anti-alias styles for your text.

In other programs, such as Paint Shop Pro, select the Text tool followed by the location where you would like to place the text. In the next window, a small box marked anti-alias will be listed along the bottom. Use this checkbox to turn the feature on or off. With Line or Object tools, the anti-alias can be found in the tool’s palette window or menu.

When to avoid anti-aliasing

Most times, you will find anti-alias is the best option for adding text or other objects. However, in a few cases, it can work against you by adding superfluous artefacts to your image or blurring smaller objects. The general rule is to avoid using this option when the object is small. For example, any font size less than 8-10 point should have anti-aliasing reduced or turned off. Using anti-alias on a small font will cause the text to become fuzzy or it may create the perception that the line is riddled with gaps.

Likewise, fine straight lines that are 1 or 2 pixels thin should be drawn without anti-alias. In these cases, the extra pixels can cause unwanted thickness (you can see the difference in the blue lines in FIGURE 1).

Finally, keep an eye on your backgrounds. Most programs will blend your current object with the existing background on which you place it. If you draw an orange object on a white background and decide to move the line to a blue background, the line is likely to carry pale orange pixels around its edge.