Changing a Selection’s Edge

Another way to modify selections is to alter the edge of the selection path. Photoshop contains several menu commands as well as a new Refine Edge feature that allow you to make edge adjustments. The command options include a Border command for converting a selection path to a soft, border-only selection; a Smooth command for simplifying detailed selections and rounding sharp corners; a Feather command for softening edges; and an Invert command for reversing the selection area. The new Refine Edge  command allows you to apply both a soft and smooth edge to a selection all at once.

Refine Edge
The new Refine Edge dialog box is excellent for cleaning up a selection of an object that you’d like to remove from its background. You can adjust a selection path by using the Refine Edge dialog box. Click the Refine Edge button in the Options palette to access the dialog, or choose Select --> Modify --> Refine Edge.

The Refine Edge dialog box contains the following adjustment options:
Radius improves the selection edge in areas with soft transitions or fine details.
Contrast makes soft edges crisp and removes fuzzy edges along the selection edge. It also removes artifacts that are created by increasing the Radius setting.
Smooth reduces any “hills and valleys” in the selection and creates a smoother outline.
Feather adds a soft-edged transition between the selection edge and the surrounding pixels. Larger values create softer transitions.
Contract/Expand expands or contracts the boundaries of the selection. At the bottom of the dialog, you can choose a method for previewing Refine Edge adjustments. Options include Standard, Quick Mask, On Black, On White, and Mask. In Standard mode, refer to the marching ants in order to preview your Smooth and Choke adjustments. For a better preview of Feather adjustments, choose On White or Mask mode.

Border
By applying the Border command to a selection, you can make specific color adjustments to the edge of an image selection.
To apply the Border command, select an object, such as the coffee (selected with the Magic Wand), and choose Select --> Modify --> Border. Enter a pixel width amount in the dialog that appears and click OK.

After the Border command is applied, the selection path automatically takes the shape of the border width you’ve entered in the dialog box. You can then add a new Hue/Saturation adjustment layer by choosing Layer --> New Adjustment Layer --> Hue/Saturation. Alternatively, you can choose the same option from the pop-up menu accessible by clicking the Create New Fill Or Adjustment Layer button at the bottom of the Layers palette. Use the controls in the Hue/Saturation dialog to adjust the color of the selected image’s edge.

Smooth
The Smooth command does just what its name indicates—it smooths out the edges of a selection path. This can be a great way to add rounded edges to a selection made with the Polygonal Lasso tool.
For example, let’s say the Polygonal Lasso is the selection tool you are most comfortable working with, and you’ve chosen it to select the rail car shown in Figure 2.44. The only drawback to tracing with this tool is that you cannot create any curves, which there are plenty of in this image. As a result, the final selection path contains a series of sharp-edged corners rather than smooth curves. To fix this, all you need to do is apply the Smooth command. With the Polygonal Lasso selection already made, choose Select --> Modify --> Smooth. Enter a pixel width amount in the dialog that appears and click OK.

The Smooth Dialog Box
Keep in mind that the more sharp edges there are in the selection path, the larger the sample pixel radius should be. Larger values mean smoother edges. In order to smooth the edges of the selection I applied a 10-pixel radius.