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Does it seem like the Magnetic Lasso tool loses its way around the simplest selection? Surprisingly,
just setting an anchor point or varying the tool size can get this tool on track again. Once you
understand the value of the tool’s options and use a few keyboard shortcuts, the Magnetic Lasso will
actually become a real time-saver.
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Have you ever started making a selection
with the Magnetic Lasso and then tried
to click on the Options bar to refine the
settings? The lasso doesn’t let go, does
it? Once you’ve begun creating a selection
with the Magnetic Lasso, the active
path will continue to track your mouse
until you complete the selection. But
you can work around that limitation by
using keyboard shortcuts to zoom, scroll,
and change the tool settings during the
selection process.
Download the parrot.zip archive, open parrot.jpg and set the View
to Fit on Screen (Command/Ctrl-0). To
access the Magnetic Lasso tool, continue
pressing Shift-L until it appears in the
toolbox. Prepare the tool in the Options
bar by setting Width to 18 pixels (based
on the resolution of the parrot image),
Edge Contrast to 10%, and Frequency
to 57. Make sure Anti-aliased is checked,
but uncheck the Pen Pressure box. At
this point, leave Feather set to 0, and
add a feather if necessary once you’ve
completed your selection. (A good tip to
remember before feathering is to clean
up your selection by choosing Select >
Modify > Contract and entering 1 pixel.)
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Set the Magnetic Lasso’s starting point
by clicking where the left edge of the
parrot’s wing meets the arm. The Width
setting tells the tool to look for edges
within an 18-pixel circle centered on
your click. The 10% Edge Contrast determines
how sharp an edge the Magnetic
Lasso will detect. If you feel the edge is
exceptionally sharp, you can adjust Edge
Contrast by pressing the Greater Than
key (>) and you’ll increase the value instantly.
To decrease the value, just press
the Less Than key (<).
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After establishing the starting point,
just move the mouse up the edge of
the parrot’s wing without clicking. The
Magnetic Lasso automatically builds a
working path by periodically placing
anchor points at a rate based on the
Frequency value, as shown at left (click to enlarge). To reduce the Frequency
value, press the semicolon (;).
To increase it, press the apostrophe (’).
When the direction of an edge changes
abruptly, like at the corner of the parrot’s
beak and neck, click once to set an anchor
point to avoid rounded corners.
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If the Magnetic Lasso loses the edge
and misplaces an anchor point, mouse
over the previous point and press Delete/
Backspace to remove it. If the working
path runs astray before setting an point,
back up and move the mouse a little
slower over the edge. If this doesn’t
help, zoom in by pressing the Plus key
(+), and press the Left Bracket key ([)
until you lower Width to 1. Press the
Spacebar and the lasso converts to a
hand to move the image. After passing
the difficult area, return Width to its original
value by pressing the right bracket
(]) and zoom out with the Hyphen key (-).
Note: This does not work with CS.
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To create a straight section of your
working path, Option/Alt-click to set
the first point, and the tool temporarily
changes to the Polygonal Lasso. Click
again to complete the straight section,
and the tool automatically returns to
the Magnetic Lasso. You can, however,
continue Option/Alt-clicking to create
multiple straight edges.
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Magnetic Lasso Tips
You can remove negative space
from a closed path by Option/Alt-clicking
the tool to set an initial
point inside a selection, then proceed
as before to define the edge
of the area to be removed.
When your working path comes
back around to the starting point,
the Magnetic Lasso will show a small
circle next to it, and you can click once
to complete the selection. If you want
to end a selection before your working
path comes full circle, double-click
the mouse.
If the working path comes across a
particularly soft border and doesn’t
handle it well, reduce Width to 1 pixel
as suggested in Step 4, but also reduce
Edge Contrast to 1 and increase Frequency
to 100. Just remember to push
values back to their original settings
after passing the ill-defined area.
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Roger Hunsicker is Advertising Coordinator
for Caterpillar, Inc., in Peoria,
Illinois, and president of Proof Positive
Design Group, a Web hosting and
Web design firm.
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