Understanding selection tools: Part II, the lasso

There is more to image editing than cutting out a neat circle or trimming the outside edge of a photograph. But how do you select part of an image that is not a simple geometric shape like a square or ellipse? Many people will spend years perfecting specialised techniques to answer this question. Surprisingly, many of the tools and procedures are easy to learn — with a little practice and a lot of patience. One of simplest tools to pick up is the lasso.

The lasso is a ‘freehand’ tool for selecting part of an image (some programs even call it ‘freehand selection’ instead of lasso). In other words, you use the mouse to guide the lasso cursor and the trail it marks out will determine the selected area.

Unfortunately, trying to trace out an object with a mouse is a frustrating and clumsy affair. The common computer mouse does not have a sufficiently smooth motion for this purpose and edges are frequently full of bumps and shakes. That’s why more powerful lasso options are included with many popular programs.

At this point you are probably wondering why your software doesn’t have the enhanced features. If you use programs such as Paint Shop Pro, Photoshop or Photoshop Elements, you do have a choice of three or more lasso tools — they are simply hidden in the menus. In fact, Paint Shop Pro’s new menu system buries the lasso tool so deep that it would be easy to assume it didn’t have one at all.

To access the different types of lasso in Photoshop and Photoshop Elements, click on the icon shaped like — you guessed it — a lasso. Hold down the button for a second and a small menu will appear (see FIGURE 1). Here you can choose from three options. For Paint Shop Pro 8, the icon in the tool palette changes depending on the tool that was last selected from this mini-menu (see FIGURE 2). It can display one of three icons shaped like a lasso, rectangle or magic wand. Select the lasso. Now note how the tools palette at the top has changed. Choose the Selection Type from the palette’s drop down menu to switch between the different lasso options.

Once you have chosen a lasso, you can further customise the way it works by adjusting values such as feathering, anti-alias and mode. These values will appear in the Tools Option menu either at the top of your program or in a floating menu.

The three common lasso types are freehand, polygonal (also called ‘point to point’) and magnetic (smart edge). As mentioned above, the basic freehand option simply follows the exact path of your cursor and is a little rough — not to mention frustrating. However, it can be used as a quick and dirty way to remove clutter from an image (especially before using other specialised tools such as the magic wand). A variation of this principle is the polygonal lasso. Instead of drawing a freehand line, it uses straight lines to connect points. You click a starting place and release the mouse. Now move the cursor to a new part of your image and click again (note the line trailing the cursor). The lasso will join up the dots until you double-click or press . This will select the polygon area you have traced out. Again, this is good for rough edits, but it still lacks fine control.

By far the best choice is the magnetic lasso. It helps take the guess work out of tracing edges while removing bumps and shakes from the mouse. This option looks for areas of high contrast (these typically mark an object’s boundary) in the approximate area that you have traced. Hence, the selection should automatically run along the boundary nearest the cursor.

To use the magnetic lasso, start by trimming any unnecessary detail from the image or zooming in so that the area to be outlined fills most of the screen. If you haven’t done so already, choose the magnetic lasso option. Click a starting point on a boundary of the object, release the mouse button and move your cursor along the border — it should follow the object’s edge. It’s a good idea to lock the selection by clicking with your mouse at various points during the outline. When finished, double-click or press . Your selection is now ready for copying, pasting or other types of editing.


  • Don’t forget that you can use the add, subtract and replace options to fine-tune lasso selections (see the March 2004 PC World Here's How Graphics column).
  • The lasso can be used in conjunction with other selection tools such as the marquee and magic wand.
  • Feathering can greatly help smooth jagged edges.

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Scott Mendham

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