Using the Lasso Tools in Photoshop
The Lasso Tools
The Lasso Tools let you draw either free-form selections with curves or straight-edged selections for irregular polygonal selection shapes. The Magnetic Lasso Tool is a really neat selection tool that allows the selection’s border to “snap” to the pixilated edges of an element of the image that you trace. This can be very useful for selecting objects with complex, irregular edges set against a high-contrast background. Because each tool behaves differently, we will have to look at how you can use each tool in the set on an individual basis. Let’s start by examining the Lasso Tool.
To use the Lasso Tool, click the “Lasso Tool” button in the Toolbox. Once again, in the Options Bar you can select the type of selection you want to make, just as you did with the Marquee Tools. To then create a selection, click and drag with the mouse to draw a freehand selection. Trace the outline of the area that you wish to select, making sure that you drag it back to the origin (starting) point. If you release the mouse before dragging it back to the starting point, Photoshop will draw a straight line from where you stopped dragging back to the origin point for you. If you wish to draw a straight line as you are drawing, you can hold down the “Alt” key on your keyboard and click from where you want the line to begin to where you want it stop to create a straight line and add a fastening point to “hold” the selection in place. This will draw straight lines between the points that you click. If you wish to delete a fastening point, you can press “Delete” on your keyboard to remove the fastening point at the last place that you clicked. When you are finished, release the “Alt” key on your keyboard to finish the selection. Note that you can mix this method with the freehand drawing as well.
To use the Polygonal Lasso Tool, click the “Polygonal Lasso Tool” button in the Toolbox. Once again, in the Options Bar you can select the type of selection you want to make, just as you did with the Marquee Tools. To use the Polygonal Lasso Tool, click from point to point where you want to draw a straight line for your selection. Once again, you want to end by clicking on the initial starting point of your selection. You will see a small circle next to the lasso tool when you are over the starting point. Click at that point to finish the selection. Also, like the Lasso Tool, if you hold down the “Alt” key on your keyboard you can draw a freehand line until you release the “Alt” key. So this is the inverse of the behavior of the Lasso Tool.
To use the Magnetic Lasso Tool, click the “Magnetic Lasso Tool” button in the Toolbox. Then look at the options that you can set in the Options Bar. The first few options are the same that you can set for any of your selection tools. However, the Magnetic Lasso Tool has a few more options after the “Anti-alias” checkbox. The first is the “Width:” text box. In this text box you can type a pixel range from the pointer within which the Magnetic Lasso Tool will look for the border of the item of which it is tracing. Next, you can set the “Edge Contrast:” as a percentage. This sets the sensitivity of the Magnetic Lasso Tool to variations in the contrast between pixels, which is how this tool finds the edges of image elements. Setting a higher percentage sets the tool to only find edges that sharply contrast with their surroundings. A lower number detects lower-contrast variations in color. The “Frequency:” text box allow you to input a number between 0 and 100. A high value increases the frequency with which the Magnetic Lasso Tool sets its fastening points for the edge of the image element as you trace its border. If using a stylus tablet, you can check or uncheck the “Pen Pressure” checkbox. If this is checked, an increase on the pen pressure causes the edge width setting to decrease.
Once you have the settings you desire set, you then click and drag the pointer of the Magnetic Lasso Tool around the border of the image element that you are trying to select. As you do this, it will add fastening point anchors where it discerns the edges of the object. If it adds a point that you would rather not have, you can press “Delete” on your keyboard to delete the fastening points that you have created as you drag. Then you can back up and re-drag the line. You can also manually click at any point as you are dragging to manually set a fastening point. You may need to do this is crevasses and corners of the image element. To finish the selection trace your way back to the starting point and place the Magnetic Lasso Tool over the origin point until you see a small circle next to the tool. Click there to close the selection. You can also close any selection you have made by double-clicking at any point along the way, which will draw a line from where you double-clicked back to the origin.