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Lasso Tools (l to r): Lasso, Polygonal Lasso and Magnetic
Lasso.
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Photoshop has the most powerful array of selection tools in the graphics
world. Many are not used though, and it is only when you understand what
all the selection tools can accomplish, that you are able to effectively
use this power. We still have the three lasso tools to cover and make
sure you do not miss the Quick Mask section of this tutorial. Keep your
eye out for a full tutorial on Photoshop paths very soon, since Paths
are very much selection tools. They would fit here, but I would rather
handle that subject on its own, since there are many new concepts to learn. |
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Top: The Lasso tool in action. In the lower image,
a straight line has been created when the mouse button was released
away from the starting point.
High magnification of the image shown to the right.
Note how much easier it is to see where the selection boundaries should
be.
Photo © Tom
Thomson Photography. Used with permission.
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Lasso Tool
The first place we turn when we cannot do an area selection with one
of the marquee tools, or an automatic selection with the Magic Wand,
is the basic Lasso tool. This tool offers a very simple concept: Click
and drag around the area you wish to select. Sounds easy, but the reality
is often quite different. The Lasso tool is shown at the left, tracing
out a complex set of curves. Of all the lasso tools, this one offers
the most flexibility, but also requires the highest mouse skill level.
To use the tool, click and drag in the shape your require. When you
release the mouse, the start and end points are automatically joined
in a straight line, as shown in the sample at the left.
Zooming in to a high magnification will usually return the best results
when using the Lasso tool. Selecting the small tulip in the image at
the left would be very difficult at actual size. The sample below shows
how much easier it is to see the actual outline of the flower. At times,
it can also be hard to discern where the outline of the actual object
may be, and you will find that you must select roughly at actual size
and then fine-tune at high magnification. See the next page on editing
your selection for this technique.
The Lasso tool offers two options. Double-click on the tool to open
the Lasso Tool Options Window. You can choose anti-aliasing, which is
usually desired unless you require pixel by pixel accuracy. The Feather
option is one I never use. You can feather your selection at any time,
and I would prefer to concentrate on an accurate selection than where
the feathering may affect.
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The Polygonal Tool in action. The lower image shows
a curved portion that was created with the ALT or Option key pressed
down, temporarily converting the Polygonal tool to the basic Lasso tool.
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Polygonal Lasso Tool
I call this the straight line lasso tool, although I suppose the lofty
name is technically correct, since you cannot select an open area. However,
the only thing about this tool that counts, is that it will select straight
areas with ease.
To use, you simply click, move to the next anchor point, click, move
to the next point, etc. To complete your selection, move your cursor
close to the starting point. An o shape appears beside the cursor,
signifying that the start and end point will be joined when you release
the cursor.
You can constrain your selection to horizontal or vertical lines by
holding the SHIFT key down before you select the next point. If you
press your ALT or Option key at any point in your selection process,
the Polygonal Lasso tool converts to the Lasso tool, making it easy
to do a combination selection as shown at the left. My ALT key was pressed
at the lower right corner and released at the end of the curved section,
returning my selection to straight lines. Toggle back and forth as required.
The options for the Polygonal Lasso tool are the same as for the Lasso
tool.
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The Magnetic Lasso tool snaps to the edge, even though
the cursor is quite far away.
Note the o shape on the cursor, indicating that a closed
selection will be created when the mouse is released.
Even a slight feathering on the edge is enough to make
the magnetic properties fail.
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Magnetic Lasso Tool
This is a selection tool that is more exciting in concept than in practical
use. In theory, it is like the Lasso tool, with a strong attraction
to an edge. The problem with the tool comes in the struggle between
what you consider to be the edge and what the tool considers to be the
edge. I hate to admit how often the tool wins, so I use it only under
ideal circumstances (and usually when there is nobody around to witness
my imminent defeat).
The top image at the left is an example of a perfectly behaving Magnetic
Lasso tool. Note how far the cursor is from the edge. The selection
boundary is snapping to the edge as I drag the mouse carelessly around
the area. In the second image, note how tightly the selection is against
the edge. Also note the o by the cursor indicating that the start
and end points will be joined when the mouse is released. Pretty slick
... when it works.
This was an ideal edge for the Magnetic Lasso tool to work. In fact,
it was custom designed to show how the tool works and I made sure that
there was plenty of contrast and nothing to distract the selection.
Take a look at the next image though. As soon as I added feathered
edges to the shape, the magnetic properties became confused. Unless
this tool can get a solid grasp of the edge, it is almost impossible
to control. In this case, I would have been better with a plain Lasso
tool selection. Or, better yet, if you have the background clear for
selection, the Magic Wand. Select the background and choose Select>Invert
from the main menu.
If you are determined to work with this tool, though, you can adjust
the parameters to customize the magnetic properties.
The Feather and Anti-aliased options are the same for the Magnetic
Lasso tool, as for the first two lasso tools. The remaining options,
however, are strictly to guide the magnetic snapping to the edge. The
Lasso Width refers to how close you must bring the cursor to the edge
for the snap to take place. Taking this value down too low, though,
kills the effect, since you must trace almost as carefully as you would
with the Lasso tool.
The Frequency represents the number of anchor points that will be created
as you complete the selection. A lower number will result in a less
accurate, but smoother selection. Finally, Edge Contrast is the amount
of difference you expect the magnetic properties to recognize. If you
are selecting from an image with high contrast, this number can be increased.
A low contrast image will require that you reduce this number.
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