My article in Digital Life on 26 May 2010 (Choice selections) illustrated the use of the Lasso Tool, the Polygonal Lasso Tool and the Magic Wand Tool for making selections of objects or areas of the image with an irregular outline.
Red telephone booth to be selected and preserved
Surroundings toned down to Black and White
Where there is a fair amount of contrast in colour between the object to be selected – such as the red telephone booth – and the surrounding pixels, you can also use the Magnetic Lasso Tool.
Just click anywhere on the edge of the object move the mouse along the edge of the object, in this case the booth. As the mouse moves along the edge, Photoshop will detect where the edge is by examining the contrast between the pixels on either side of the mouse cursor.
Photoshop will place anchor points along the edge as you go along. You don’t have to click the mouse button.
If Photoshop places the anchor point wrongly ie. off the edge, just press Backspace or Delete to remove the previous anchor point. Move the mouse back and retrace – hopefully Photoshop will place the anchor point correctly.
You can press Backspace/Delete more than once to delete more than one previous anchor points.
To help Photoshop along, click on the mouse button on the edge of the object where Photoshop doesn’t seem to be detecting it correctly. You can also hold down the Alt (Option) key and drag the mouse to specify exactly where you want the selection edge to be.
While the Alt (Option) key is held down, the tool behaves like the basic Lasso Tool. Release the Alt (Option) key and the tool reverts to the Magnetic Lasso Tool.
To finish up, either click the starting anchor point, or double-click or Ctrl-click to let Photoshop join up the last anchor point with the starting anchor point.
Check out the Options Bar just below the main menu. There are some options you can tweak to control how sensitive Photoshop is in detecting edges.
I don’t frequently use the Magnetic Lasso Tool because I find it too much of a hassle adjusting the anchor points along the way. Usually, I have to modify the resulting selection by using other selection tools or using the Quick Mask mode.
I use it when the contrast is large enough such that Photoshop gets it mostly right on its own.
Tags: CS5, image editor, photo editor, Photoshop, tips