Though Adobe Illustrator doesn't have an airbrush tool, the program's blur filters let you apply simulated airbrush effects to lines created with the "Paintbrush" and other drawing tools. Filters are small computer programs that run within Illustrator to realistically simulate real-world imagery, including imagery depicting objects with soft or indefinite outlines. Filters increase the time needed to display Illustrator's objects. However, one advantage to the program's filters over the filters in painting programs like those in Photoshop is that you can remove filters to restore the original image.
Click the "File" menu's "New" command, and then click "OK" to accept the default parameters for a new canvas.
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Click the tool palette icon shaped like a paintbrush to run the "Paintbrush" tool, and then drag on the canvas to draw any line or shape you'd like.
Click the tool palette icon shaped like a black arrow to run the "Selection" tool, and then click the drawing you made to select it.
Click the second leftmost dropdown control above the canvas to open the gallery for the stroke color, which is the color the lines you make with "Paintbrush" take on. Click any color from the gallery. The drawing you selected will turn the color you chose.
Click the "Filter" menu, and then click the "Blur" sub-menu, which contains several commands for softening the edges of shapes you draw in Illustrator. Click the "Gaussian" command to display a dialog box for configuring the parameters of Gaussian blur.
Click the "-" button of the "Gaussian" dialog box repeatedly to zoom the preview window out. Stop clicking when you can view a portion of the drawing in the window. Click inside the preview window, and then drag to center the drawing in the window. This step enables you to clearly see the effect of changing the parameters of "Gaussian blur." Unlike Photoshop and other graphics programs, Illustrator does not display use the program's main canvas to show a preview of filters or effects you apply.
Click the arrow at the center of the "Radius" slider. Drag the slider right to increase the blur amount, if the image of your drawing in the preview window doesn't yet have the soft edges characteristic of airbrush painting. Drag the slider to the left if the preview window shows edges that are too soft.
Click "OK" to finalize the "Gaussian blur" filter and complete the airbrush simulation.