75. Select an Object by Tracing Its Edge
Before You Begin
70 About Making Selections
72 Select a Rectangular or Circular
73 Draw a Selection Freehand
74 Select a Straight-Edged Area
76 Select Areas of Similar Color
If you want to select an object that is irregularly shapedsuch as a person sitting on a chair or an animalby outlining its edges, you accomplish this goal using the Magnetic Lasso tool. With this tool, you mark points along the edge of the object, and PhotoShop Elements connects those points with lines that follow the closest edge.
When you use the Magnetic Lasso tool, you must specify settings that help PhotoShop Elements locate the edges of your object. For example, you can indicate a pixel Width value to define the width of the area near where you drag; Photoshop Elements looks in this area to locate the object edge. Photoshop Elements places the selection line along the edge it finds in that search area. To make an object easier to select, increase the contrast along its edge. See 71 Make an Area of an Image Easier to Select for suggestions on how to do this.
Select Lasso Tool
Open an image in the Editor in Standard Edit mode and save it in Photoshop (*.psd) format. In the Layers palette, select the layer that contains the data you want to select.
Select the Lasso tool on the Toolbox. The icon for the last Lasso tool you used is the icon displayed in the Toolbox.
Select Magnetic Lasso Tool
If it's not already selected, select the Magnetic Lasso tool from the Options bar.
On the Options bar, specify a number between 1 and 256 for the Width option to indicate the number of pixels around the point you drag in which Photoshop Elements will look to locate the edge of the object. The higher the value, the more likely Photoshop Elements will locate the actual edge of your object.
You can select the exact tool you want in one step: Click the Lasso tool on the Toolbox, hold the mouse button down and, when the pop-up menu appears, choose the Magnetic Lasso tool from the list.
Set Edge Contrast
For the Edge Contrast option, specify a value between 1% and 100% to indicate the amount of contrast in the pixels that make up the edge of the object. If your object has low-contrast edges, use a higher value.
If you have images with edges that are clearly defined, set both the Width and Edge Contrast values high. In images with high-contrast edges, you can roughly trace the border of the object, and Photoshop Elements will locate the actual border.
If the edge of the object is less defined, lower the Width and Edge Contrast values so that Photoshop Elements doesn't look too far afield from where you drag for the object's edge. With objects that have less-defined edges, you must typically be more precise when you trace the edges.
For the Frequency option, specify a value between 0 and 100 that indicates the rate at which you want the lasso to set the anchor points along the object's edge as you drag. Use a higher value to set the border more quickly.
Set Other Options
Set any other options such as Anti-aliased or the amount of Feather. Click the New Selection, Add to Selection, Subtract from Selection, or Intersect with Selection button as desired, to create a new selection or add to an existing one.
Trace Object Edges
Click the location where you want to start the selection. Drag along the edge of the object you want to select. As you move the mouse pointer, a springy selection line extends between the mouse pointer and the last selection point to help you see where the selection line will land along the area you want to select. Fastening points are dropped along the edge as you drag, at the rate indicated by the Frequency value. Along edges that aren't so well defined, you might want to add your own points by clicking instead of dragging. If the edges of the object are straight, you need selection points only at the beginning and end of each edge. Edges that are more complex, such as a jagged or rounded edge, require more selection points to identify the edge.
Indicate that you have completed the selection by clicking again on the original selection point (the mouse pointer changes to a lasso with a small o under it when you reach the beginning point), pressing the Enter key, or double-clicking the left mouse button. You can also hold down the Alt key and double-click to create a straight segment between the last selection point and the starting point.
If you are using a pen and drawing tablet, select the Pen Pressure option. When this option is enabled, if you increase the pen pressure, the Width value increases for the selection.
Make changes to the area within the selection, copy or cut it to another image or layer, or delete the data. After you're satisfied with the result, make any other changes you want and save the PSD file. Resave the result in JPEG or TIFF format, leaving your PSD image with its layers (if any) intact so that you can return at a later time and make different adjustments if you want.
You can delete points from the selection as you're dragging or clicking by pressing the Delete key. Press the Delete key until you have removed all the desired points. When you press the Delete key, the points are removed in reverse order. In other words, the last point you created is the first point deleted.
In this example, I wanted to select just the Taj Mahal model from its rather plain background. Using the Magnetic Lasso tool, I set the Feather option to 0 because I wanted the outline of this selection to be crisp. I set the Width to 10 pixels and the Edge Contrast to 10% because the edges of the building were fairly easy to pick out against the background, and I didn't want Photoshop Elements to look for the edges of the building too far from where I clicked. I set the Frequency to 57 so that the tool would pick up some of the little jagged edges around the tip of the main spire and some of the other domes instead of rounding these points off. When I clicked to place anchor points, I didn't have to click all that often. Because the lines between the anchor points I clicked were not straight, the Magnetic Lasso tool followed the outline of the building (rather than drawing straight lines between the points I clicked, as the Polygonal Lasso tool would have done).
Although they both can be used to make most selections, there is a big difference between the Magnetic Lasso tool and the Polygonal Lasso tool. The Magnetic Lasso tool uses the Contrast and Width settings you specify to locate the actual edge to outline. The Polygonal Lasso tool just creates straight selection lines between the points you select.