Mysteries of the Eraser Tool — Revealed!
Contributed by Brenda Sutherland, Illustrator Team Rowing Captain
In my last post, I talked about <a href=””>Pathfinder and how Illustrator uses the Pathfinder engine to power other great features as well. One of those features is the Eraser Tool, which erases away parts of an object as if were a vector Art Gum.
You might wonder how this could be tied to Pathfinder, and more importantly, how an understanding of its underlying technology will benefit you. Let me explain it this way; the tool can’t read your mind, although it might sometimes seem that way as it erases some objects and not others. I for one love a great mystery, but I think this tool will be even more useful to you if I demystified it by sharing how it works, what it’s limitations are, and the best ways around those limitations.
If you have used the tool, you have probably noticed that it’s very similar to a calligraphic brush. In fact, it can even be used with a pressure sensitive tablet to vary its size, angle and roundness. Double clicking on the tool opens up its Option dialog, where you can customize it’s settings.
The options dialog isn’t the only place were settings can be changed. Just like the Calligraphic Brush, the diameter can be changed by using the bracket keys, ] and [ respectively to increase and decrease the size.
If you have already made the assumption from this that the tool is in fact, creating a Calligraphic Brush stoke then you get a gold star! That’s exactly what it’s doing. The next thing it does is expand the brush stroke in the same way you would manually by choosing Object>Expand, to make it a simple or compound path, and no longer a brush stroke. Then the next step is it runs Pathfinder to cut away the Eraser Tool created object from either the current selection, or if there is no current selection, all valid objects that are touched by the eraser object. Whew, that’s a lot of steps! But the Eraser tool does all of this behind the scenes, so all you need to think about is what you want to erase.As simple as this tool is to use, the results are not always exactly what you expect. Now that you understand how it works, let me give you some tips on how to get the results you are after ALL the time:
- The Eraser tool works based on selection. When you have an object selected, it will erase only that object. When there is no object selected it will erase any valid object it comes in contact with (valid meaning an object type that is erasable). Objects can be on any layer, or in a group, but they must be unlocked.
- Objects that are not erased by the Eraser tool are: Images, Text, symbols, Graphs, and Gradient Meshes. The preview works on all objects, so it looks like these objects will erase, but on mouse up, they are not changed.
- To erase Type, you can expand or create outlines first. To erase Symbols, you can expand or break link first. To erase Graphs, you can ungroup first. In all of these cases, the objects will no longer retain their type, symbol or graph attributes.
- Some objects will erase, but their appearance changes due to rerendering of attributes applied to the object. For example when a brush stroked object is erased, it is broken into separate paths. The brush stroke is then reapplied to each path, which can drastically change its appearance. To erase a brush stroked object and not have it’s appearance change, choose Object>Expand Appearance first.
- When objects have an effect, like Roughen, applied to them, the effect will be reapplied to the new path created by erasing. This will look very different from the preview you see when you first drag the eraser over the object. In order to get the same results as the preview appearance, expand the appearance of your objects with Live Effects, like Roughen, applied.
- When objects have strokes applied to them and you do not want the stroke rendered for all edges of the new paths created by erasing, then expand the object first. If the object has multiple fills or strokes you will need to expand appearance first, then choose object>expand to expand the strokes.