Written By Steve Patterson

If someone told you there's a selection tool in Photoshop that can select an object in a photo with 100% accuracy and all you have to do is drag a loose, lazy outline around the object with your mouse, would you believe them? No? Good for you. That person is just messin' with your head.

But what if someone told you there's a selection tool that can select an object with, say, 80-90% accuracy and all you have to do is drag that same lazy outline around it? Would you believe them now? Still no? Well, that's too bad, because there really is a selection tool like that. It's called the Magnetic Lasso Tool, and with a little practice and a basic understanding of how it works, not only will you be a believer, but you just may find yourself hopelessly attracted to it.

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The Magnetic Lasso Tool is one of three lasso tools in Photoshop. We've already looked at the first two - the standard Lasso Tool and the Polygonal Lasso Tool - in previous tutorials. Like the Polygonal Lasso Tool, the Magnetic Lasso Tool can be found nested behind the standard Lasso Tool in the Tools panel. To access it, click and hold your mouse button down on the Lasso Tool until a fly-out menu appears, then select the Magnetic Lasso Tool from the list:

Once you've selected the Magnetic Lasso Tool, it will appear in place of the standard Lasso Tool in the Tools panel. To switch back to the Lasso Tool later, or to select the Polygonal Lasso Tool, click and hold on the Magnetic Lasso Tool until the fly-out menu reappears, then select either of the other two lasso tools from the list:

You can cycle through the three lasso tools from your keyboard. Just hold down your Shift key and press the letter L repeatedly to switch between them (note that you may not need to include the Shift key depending on how you have things set up in Photoshop's Preferences).

Why is it called the Magnetic Lasso Tool? Well, unlike the standard Lasso Tool which gives you no help at all and relies entirely on your own ability to manually trace around the object, usually with less than stellar results, the Magnetic Lasso Tool is an edge detection tool, meaning that it actively searches for the edge of the object as you're moving around it, then snaps the selection outline to the edge and clings to it like a magnet!

Does this mean that Photoshop actually recognizes the object in the photo that you're trying to select? It can certainly appear that way, but no. As we learned when we looked at why we need to make selections in Photoshop, all Photoshop ever sees is pixels of different color and brightness levels, so the Magnetic Lasso Tool tries to figure out where the edges of an object are by looking for differences in color and brightness values between the object you're trying to select and its background.

A Better Icon For Better Selections

Of course, if the Magnetic Lasso Tool was forced to always look at the entire image as it tried to find the edges of your object, chances are it wouldn't do a very good job, so to keep things simple, Photoshop limits the area where the tool looks for edges. The problem is that by default, we have no way of seeing how wide this area is, and that's because the mouse cursor for the Magnetic Lasso Tool doesn't really tell us anything. The little magnet lets us know that we have the Magnetic Lasso Tool selected, of course, but that's about it:

For a much more useful icon, press the Caps Lock key on your keyboard. This switches the icon to a circle with a small crosshair in the center. The circle represents the width of the area that Photoshop looks for edges. Only the area inside the circle is looked at. Everything outside of it is ignored. The closer a potential edge is to the crosshair in the center of the circle, the more importance Photoshop gives it when trying to determine where the edges of your object are:

Using The Magnetic Lasso Tool

Here's a photo I have open in Photoshop of a Chinese sculpture. The edges of the sculpture are well defined, so I could try to select it by tracing around it with the standard Lasso Tool. At least, I could do that if I was looking for an excuse to pull my hair out in frustration. A much better choice here would be the Magnetic Lasso Tool since it will end up doing most of the work for me:

To begin a selection with the Magnetic Lasso Tool, simply move the crosshair in the center of the circle directly over an edge of the object and click once, then release your mouse button. This sets a starting point for the selection. Once you have your starting point, move the Magnetic Lasso Tool around the object, always keeping the edge within the boundaries of the circle. You'll see a thin line extending out from the cursor as you drag, and Photoshop will automatically snap the line to the edge of the object, adding anchor points as it goes along to keep the line fastened in place. Unlike the standard Lasso Tool, there's no need to keep your mouse button held down as you drag around the object:

To zoom in on the image as you're dragging around the edges, press Ctrl++ (Win) / Command++ (Mac). Press Ctrl+- (Win) / Command+- (Mac) later to zoom out. To scroll the image around inside the document window when you're zoomed in, hold down your spacebar, which temporarily switches you to the Hand Tool, then click and drag the image around as needed. Release the spacebar when you're done.

Changing The Width Of The Circle

You can adjust the width of the circle, which changes the size of the area that Photoshop looks at for edges, using the Width option in the Options Bar. If the object you're selecting has a well-defined edge, you can use a larger width setting, which will also allow you to move faster and more freely around the object. Use a lower width setting and move more slowly around objects where the edge is not so well defined.

The only problem with the Width option in the Options Bar is that you have to set it before you click to begin your selection, and there's no way to change it once you've started dragging around the object. A more convenient way to adjust the width of the circle is by using the left and right bracket keys on your keyboard. This gives you the ability to adjust the size of the circle on the fly as you're working, which is great since you'll often need to adjust its size as you pass over different parts of the image. Press the left bracket key ( [ ) to make the circle smaller, or the right bracket key ( ] ) to make it larger. You'll see the value for the Width option changing in the Options Bar as you press the keys, and you'll see the circle itself changing size in the document window:

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