There are three lasso selection tools. The first of these tools is the standard Lasso Tool. This tool allows you to draw your selection area freehanded. For more control select the Polygonal or Magnetic Lasso Tools. The Polygonal Lasso allows you to draw straight lines to create a selection area in any shape. Hold the Shift key down to draw 45 degree angles and the Alt Key to draw freehanded. The Magnetic Lasso Tool is one of my favorites. It works best if you are trying to select an object that contrasts well with its background. Click on the edge of the object and move your curser around the outside of it. The magnetic lasso will automatically create anchor points around the outside of the object. You can manually add anchor points where necessary by clicking on a specific spot. If your lasso takes the wrong path simply press delete to erase the previous anchor points, then redraw the lasso or manually add anchor points where you want them.
Here is a flower cut out with the Lasso Tool.
Here is a flower cut out with the Polygonal Lasso Tool.
Here is a flower cut out with the Magnetic Lasso Tool.
The Lasso Tool and Polygonal Lasso Tool have the same options available to them in their menu bars. There are four selection options. They are New Selection, Add to Selection, Subtract from Selection, and Intersect with Selection.
The default option is New Selection. This means that if you draw with the lasso tool on your image, it will draw a new selection area. If you need to deselect a portion of the selected area, choose Subtract from Selection and draw around the area you want deselected. Likewise, Add to Selection increases the selected area. You can also add to your selection by pressing shift while selecting regardless of which option you have active. Intersect with Selection allows you to draw two areas and the overlapping portion will be the selection area. You can continue to draw as many overlapping shapes as you would like until you have the correct area selected.
The next option on the menu bar is the Feather option. Feathering the selection allows you to create faded edges around the selected area. Say you decide that you would like to feather the selection by 20px and then draw a lasso on the area you want selected. You will not see any changes to the image you selected. You will not see the difference feathering makes until you do something with your selection. If you move your selection or copy and paste your selection you will see the difference feathering makes. Anti-alias smoothes the edges of the selection.
This flower was selected with a 20px feather.
The Refine Edge button allows you to refine your selection and view your selection against a neutral background so you can more clearly see how your selection will look. Select a portion of your image, and then click on this button. By default when you choose this, everything outside of your selection will appear white so you can more clearly see what you have selected. You can then use the sliders to adjust the selection area. Make sure Preview is checked so you can see the results of your changes.
Radius controls the size of the area inside the selection boundary where the edge refinement occurs. The higher the number the more contracted from the original selection area. Contrast sharpens the edges of the selection. The higher the Contrast number the more defined the edges will be. Smooth controls irregularities in the selection boundary. The higher the number, the more smoothed out the selection boundary will be. Feathering the selection will create a faded transition from the selected area to the area outside the selection. The higher the number, the larger the feathered area will be up to 250 pixels. Contract/Expand enlarges or minimizes the selection boundary. Positive numbers expand and negative numbers contract. This tool in conjunction with others can help fix problems in your selection boundary. For example, if some of the background is still visible around the edge of your selection, contract the boundary. Below the sliders are five options that allow you to adjust how your selection is previewed with descriptions below that describe each option.
The Magnetic Lasso Tool has the same options as the other two lasso tools along with some additions. The first extra option is Width. This option adjusts the amount of pixels the Magnetic Lasso tool considers for finding contrast. In other words, the Magnetic Lasso will only detect edges within a certain distance of the curser. It is best to use a large number for areas that contrast greatly, and a low value for tight areas without as much contrast. If you need to change the width while making a selection press the right bracket (]) to increase the width and the left bracket ([) to decrease it by 1 pixel.
The contrast value is a percentage between 1 and 100. This determines the lasso’s sensitivity to the edges. A higher value only detects edges that contrast greatly from the rest of the image. A lower value detects edges that do not contrast as much.
The frequency value is a number between 1 and 100 that determines how often points are placed as you move the cursor around the object. A higher number anchors the selection border more quickly.
The pen icon is for Stylus Pressure. You only need to worry about this option if you are using a Stylus Tablet.