Lasso Tool

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PSDTUTS Photoshop Wiki / Photoshop Tools / Lasso Tool

Using the marquee tools, your selections are limited by the constraints of shape. Sometimes you need to select a certain part of your image, and the marquee shapes won’t do the trick. This is where the lasso comes in – freehand selection.

The keyboard shortcut for the lasso is L. You can deselect a lasso selection using the menu option Select > Deselect.

The lasso tool can be tricky, so go slow, concentrate, and if possible zoom in on the area you want to select so you can get a more accurate selection. The lasso options bar provides you with New Selection, Add to Selection, Subtract from Selection and Intersect with Selection options as well as the feather and anti-aliasing features. All of these are present in the marquee tool and you can find a description of them here.

There are three lasso tools: lasso, polygonal lasso, and magnetic lasso. You can alternate between them using the Shift+L keyboard shortcut.

[edit] Polygonal Lasso

The polygonal lasso allows you to draw custom shaped selections. Instead of dragging the mouse to draw a shape, you simply click on the different points of your polygon and then double click on the final point to form the selection.

If you make a mistake when selecting your points, hit the Delete key to go back to the point before it.

[edit] Magnetic Lasso

The magnetic lasso is often considered the most useful of the three lasso tools, since the first two don’t provide as much precision. The magnetic lasso detects changes in contrast and attempts to lock on to the shape of the area you’re selecting.

Obviously, when there’s little contrast between objects, or between the foreground and background, this tool is not as effective. Like the polygonal lasso, you can create points by clicking and thus guide the formation of the selection. You can also use the Delete key to remove an accidental point.

The magnetic lasso has some new options bar settings:

• Width determines how many pixels to read in its measurements of contrast. The general rule is to use more pixels when there’s high contrast in the image, or less when the image has very little contrast.
• Edge Contrast determines what percentage of contrast between pixels there needs to be in order to find the boundaries. If the tool is having a hard time finding the edges even with adjustments to the width setting, adjust the edge contrast.
• Frequency is a setting between 1 and 100 that determines how often points are placed as you move the mouse around. You want to find the optimal number for your image that creates accurate enough constraints while still having few enough to delete and manipulate.

If you need to use the freehand lasso in the middle of a magnetic lasso selection, hold down the Alt or Option key. Release the key when you wish to return to magnetic mode. Double-click to automatically complete the shape selection based on your beginning and ending points.

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