Adobe Illustrator is a vector graphics application, with most of its tools and operations designed for creating and modifying vector-based graphics. Adobe's companion product, Photoshop, is meant for working with raster-based graphics, also referred to as images. Illustrator does provide the ability to add an image to a document and perform operations like resize and crop. Another useful image operation in Illustrator will cut out a shape from an image, allowing you to create a variety of interesting effects.
Using Illustrator to Remove an Object from Image
The concept of a clipping mask is used by Illustrator to let you create a shape that's used on an image or other graphic object to cut away the area inside or outside the shape. It's a bit like making cookies, with the image being the rolled out dough and the cookie-cutter acting as a clipping mask. In Illustrator a clipping mask is created as a vector shape, but it can be used to cut away a portion of any type of graphic object, including a raster image.
Start by creating an object to use as a clipping mask. It can be a circle, rectangle or any shape that can be created with vectors. Place the clipping mask into a layer or group with the image you want to mask, with the image under the clipping mask. You can confirm the order in the Layers panel. After selecting the name of the group or layer in the panel, select the Make/Release Clipping Masks button. You can also use the Make Clipping Mask command, found on the Layers panel menu, to activate the clipping mask.
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Cutting with Illustrator Knife and Scissors Tools
You can use the Knife and Scissors tools in Illustrator to cut out a shape from a photo or other image, although this method may be cumbersome if you want to cut out a complex shape. Both tools can be picked by pressing and holding on the Eraser tool in the main tools panel, then selecting the Knife or Scissors from the dropdown menu. The Knife tool lets you drag a path for cutting along an image. The image will separate at the cut line, giving you two image fragments that you can edit or delete as needed.
The Scissors tool is very similar to the Knife, but it's designed to provide a more precise cutting option. Instead of dragging to specify a cutting line, you use anchor points to split an image. Like the Knife, the Scissors tool may require repeated cuts if you want to remove a complicated shape from an image.
Using Eraser Tool with Images
The Eraser is a powerful tool for removing sections of a project, allowing you to specify the shape and diameter of the eraser path. It's available by pressing Shift+E or picking the Eraser tool on the main tools panel. Photoshop allows you to use an Eraser on an image and it will either make pixels transparent or change the, to the background color. Unfortunately, the Illustrator eraser tool won't erase on raster images. It also doesn't work on text, symbol or graph objects.
As a workaround, you can mimic the effect of erasing on an image in Illustrator. Use the Brush tool to draw over an area on the image and then create a clipping mask from the brush shape. Even with this workaround, many Photoshop users are disappointed when they can't erase parts of an image in Illustrator. If you have access to both products, it may make more sense to first modify your image in Photoshop using whatever tools you want and then copy and paste the edited image into Illustrator.