Creating Selections

Lasso Tool

Freehand marquees are created with the Lasso Tool. With the Lasso Tool selected, just click on the image, hold the mouse button down and draw. Once you release the mouse button the marquee is closed automatically (which can be a mixed blessing).

The Polygonal Lasso Tool just draws straight lines. Click at each point where you want the lines to begin and end. You can close the selection by either double clicking where you are or by joining the end line with the start line and clicking once (a small circle appears at the cursor when you are close enough to join the beginning and ending segments).

You can access the Polygonal Lasso Tool from the Lasso Tool by pressing the option key and clicking start and end points for the straight lines. Just make sure that you have the mouse button held down before you let go of the option key, otherwise you selection is inconveniently closed from that point.

Magnetic Lasso Tool

The Magnetic Lasso Tool is quite handy for selecting items along a high contrast border. The tool works by clicking where you want the selection to start (you don't need to hold down the mouse button as you draw) and then dragging along the high contrast line. The computer (more or less) automatically calculates where the line should be drawn. As you draw, anchor points are placed down at certain intervals to keep the line in place.

If the line begins to deviate, you can force and anchor point by clicking at the place where you want the line to go. If an anchor point goes down in the wrong place you can remove it by pressing the Delete key.

In the toolbar, you can set parameters for how the Magnetic Lasso Tool works. Width specifies how wide of an area to detect for edges. Contrast sets how strong an edge must be to be the one where the line gets laid down, 1% means barely any contrast and 100% means an ultimately strong contrasting edge. Frequency is how often an anchor point gets laid down. The only parameter I usually change from the defaults is the pixel width, I'll decrease the width if it is a real "edgy" image and the line is deviating all over the place, increase it if I am working on a high resolution image.