Drawing and Erasing with Ease
The brush types we've discussed to this point—Calligraphic, Art, Scatter, Bristle, and Pattern—all work in the same way, in that they are applied as appearances along a path. You can apply these brushes directly with the Paintbrush tool and can even apply them to existing paths. If you make an adjustment to an underlying path, the appearance of the brush updates accordingly. Although this "live" behavior has many benefits, you don't have access to the actual art that these brushes create until you expand them.
For certain types of illustration, the ability to fine-tune and edit brush strokes is very important. In fact, many illustrators in the past have used a variety of Calligraphic and Art brushes to create their art, only to expand the brushes and combine them with Pathfinder commands so that they could edit the art more effectively. It's easy to see how tedious this process can be. But more importantly, it breaks the flow of creativity from the designer.
The Blob Brush tool—added in Illustrator CS4—gives designers the freedom to express their creativity without getting lost in the technical details. At a basic level, the Blob Brush tool draws art that appears no different from that drawn with the Calligraphic brush. However, behind the scenes, the Blob Brush tool automatically expands the brush strokes as you draw them (Figure 4.43 on the following page). At the same time, the Blob Brush tool intelligently combines your brush strokes with underlying objects into single, easy-to-edit shapes—shapes that can easily be adjusted or modified with the Eraser tool (Figure 4.44 on the following page).
Figure 4.43 This figure illustrates how the Blob Brush tool can be used to create these strands of hair. As each brush stroke is added (left to right), the artwork is shown in Preview mode (top) and the resulting path geometry (bottom).
Figure 4.44 As a closed and filled path, the shape is easily modified with the Eraser tool.
Using the Blob Brush Tool
Drawing with the Blob Brush tool is easy and fun. Start by selecting the Blob Brush tool (Shift-B) from the Tools panel (Figure 4.45), and then specify a stroke color (the Blob Brush tool paints using the stroke, not the fill, as you might think). Then, click and drag on the artboard. By default, as you overlap brush strokes, they automatically combine to create a single, unified shape. To better qualify that statement, brush strokes are automatically combined only if their attributes are alike. For example, if you're painting with a specific shade of brown, only underlying objects that are also filled with that same color will be merged. Objects filled with other colors, however, are left untouched (Figure 4.46). This makes it easy to modify shapes with the Blob Brush tool, because you can draw over existing objects that have the same color attributes. Most important, this makes it possible for artists to make quick edits and adjustments without having to constantly lock and unlock complex overlapping objects.
Figure 4.45 The Blob Brush tool may have a funny name, but it's a serious drawing tool.
Figure 4.46 As you draw with the Blob Brush tool, your stroke color determines which objects your brush strokes merge with, enabling you to perform edits on one shade of color without affecting other objects with different colors.
You can easily adjust the size of the Blob Brush tool by pressing the open and closed bracket keys, just as you might adjust a brush size in Photoshop. While the Blob Brush tool is selected, you can also press the Option (Alt) key to activate the Smooth tool, which you can use to smooth out the edges of selected shapes as you draw them. Using the Smooth tool to fine-tune paths drawn with the Blob Brush tool is important because the expanding and merging that happens behind the scenes as you draw with the Blob Brush can result in paths with many anchor points. Remember that you can quickly select an object by pressing the Command (Ctrl) key to temporarily activate the last-used Selection tool.
To control the behavior of the Blob Brush tool, double-click the tool in the Tools panel to open the Blob Brush Tool Options dialog box (Figure 4.47). The bottom half of the dialog box looks exactly like the Calligraphic Brush Options dialog box—which is not a coincidence. In fact, as mentioned earlier, the Blob Brush tool is based on the functionality of the Calligraphic brush (you can even select a saved Calligraphic brush in the Brushes panel and use it to paint with the Blob Brush tool).
Figure 4.47 The Blob Brush Tool Options dialog box gives you complete control over the behavior of the Blob Brush tool.
The top of the dialog box offers the following settings:
- Keep Selected. With this option deselected (the default setting), paths that you draw with the Blob brush tool will become deselected after you've released the mouse button or input pen. By selecting this option, the object will remain selected after you've drawn it, which would make it easier to immediately adjust the shape with the Smooth tool. In addition, the Keep Selected option could be useful when used in tandem with the Merge Only with Selection setting.
- Merge Only with Selection. As you've learned, the Blob Brush tool automatically merges new brush strokes with existing overlapping objects if those objects have similar attributes. For further control, the Merge Only with Selection option will allow the Blob Brush to merge new brush strokes only if the underlying objects have similar attributes and they are selected. Objects that are not selected, even if they share the same attributes of the brush, are not merged. In this way, you have further control over which brush strokes are merged and which are not.
- Tolerances. The Fidelity setting determines how close the vector path is drawn in relation to the movement of your mouse or input pen. A lower Fidelity setting results in a path that more closely matches the exact movement of your mouse. A higher Fidelity setting results in a path that is smoother and less jittery but that may not match your stroke exactly. If you're good with handling the mouse or if you're using an input pen, you might go with a lower setting. If you have trouble controlling the mouse or pen precisely, you might benefit from a higher Fidelity setting. The Smoothness setting refers to how much smoothing Illustrator applies to paths as you draw them. The higher the Smoothness setting, the fewer anchor points you'll see on your paths. If you're looking for more fluid strokes, increasing the Smoothness setting will help.
Using the Eraser Tool
The perfect companion to the Blob Brush tool is the Eraser tool (Shift-E). In fact, you'll find the Eraser tool right next to the Blob Brush tool, grouped with the Scissors and Knife tools (Figure 4.48). To use the Eraser tool, select it, and then click and drag over any object (or objects). If nothing is selected, the Eraser tool will erase all objects across all layers in your document, with the exception of locked objects and layers, of course. For more control, you can make a selection first and then use the Eraser tool (Figure 4.49 on the following page), at which time the tool will erase only those objects that are selected (leaving all other objects intact).
Figure 4.48 The Eraser tool (not to be confused with the Path Eraser tool) is grouped with other tools that cut or sever paths.
Figure 4.49 By selecting an object, you can quickly erase parts of one path without affecting other paths. This illustration is also a great example of how you might use the Eraser tool in a creative way, by editing shapes and colored regions.
It's important to realize that although the Eraser tool makes it seem effortless to quickly remove parts of an illustration, the tool still must abide by the general rules of how vector objects are drawn. This means if you try to erase part of a single closed path, the result will be two closed paths, not open ones. It's easiest to see this when attempting to erase paths that contain strokes (Figure 4.50). In addition, although you can certainly use the Eraser tool to erase portions of a stroke, the stroke attribute for each segment of the resulting path is reapplied (Figure 4.51). In the latter case, you can get around this by first choosing the Object > Path > Outline Stroke command before using the Eraser tool. The same applies when trying to erase paths with Calligraphic, Art, Scatter, Bristle, and Pattern brushes applied. In fact, this behavior is why the Eraser tool and the Blob Brush go so well together—the Blob Brush tool creates expanded paths that can be erased easily with the Eraser tool.
Figure 4.50 Although you may initially expect the Eraser tool to simply remove an area from an object (left), the result will actually be two closed shapes (right).
Figure 4.51 If a stroke has the Round Cap option specified, the Eraser tool may appear to create a clean break while you're using it (left), but the result will be two paths, each with its own respective round cap appearance (right).
Once you get used to the behavior of the Eraser tool, it becomes a useful (and fun!) tool to use. Just as with the Blob Brush tool, you can adjust the size of the eraser by tapping the bracket keys on your keyboard. You can also double-click the Eraser tool in the Tools panel to open the Eraser Tool Options dialog box (Figure 4.52). You can manually adjust the numerical values for the angle and roundness of the Eraser tool, or you can click and drag the black dots and the arrow in the preview near the top of the dialog box to adjust those values visually. You can adjust the size of the diameter of the eraser as well.
Figure 4.52 The Eraser Tool Options dialog box offers similar controls to that found for the Blob Brush tool and the Calligraphic brush.
By default, all the values are fixed, meaning they remain consistent as you use the Eraser tool. However, you can choose to make the values random and select a variation for each setting. Even better, if you have a pressure-sensitive tablet, you can choose other variables, including Pressure. For example, setting Diameter to Pressure with a high Variation value gives you the ability to erase with more control and flexibility.