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Photoshop Tips
Identify Problem Image Areas With the Magic Wand in Photoshop
By Simon Tuckett
Dateline: March 21, 2006
Version: Photoshop CS
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Superficially, the Magic Wand tool has a limited faculty for selecting areas of similar color. Selections often have ragged edges and connect parts of an image you never noticed were
connected. Yet, it’s this very ability where the strength of the tool lies—it sees what we cannot.
I had always thought of the Magic Wand,
rather derisively, as a tool for newbies. It
wasn’t until much later that I came to realize
its power. As it often happens, it was
the result of a job that went to press with
a mistake included. I had used a white
airbrush to remove the background of
an image while protecting the shadow
and the product. I must have missed areas
because it showed up on the printed
piece as regions with a faint dot. Not a
glaring error, but certainly annoying
and more than a little embarrassing.
I now use the following technique with
the Magic Wand tool to identify such
regions before they become problems.
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Download the vase.zip archive (10MB), extract the vase.psd file and open it. I have already color-balanced and
created a path for the image. Your goal is to make the vase image’s
background white while protecting its
shadow. To load the vase outline path,
Command/Ctrl-click it in the Paths palette.
Press Command/Ctrl-J to copy the
selection to a layer, then add a new layer
and position it under the vase.
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Make your Foreground Color white.
Speaking of eradication of potential
mistakes, get into the habit of physically
choosing white, whether by clicking
white in the Foreground/Background
section of the toolbox, choosing it from
a swatch, or specifying it in the Color
palette. Never assume you have white
chosen just because the active color
looks white. A 4% white value looks
much the same as a 0% value unless the two are adjacent. Select a large 300-pixel
airbrush and while avoiding the shadow,
paint out the background on the new
middle layer. Leave a couple of spots untouched
for the purpose of this tutorial.
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Now choose the Magic Wand tool
(W), set Tolerance to 0 in the Options
bar, and check Use All Layers. Uncheck
Contiguous so you’ll select the target
value anywhere in the file—checking it
selects connected pixels only. Click once
in the white area close to the vase. If your
image resembles what mine did, you’ll
have ants marching everywhere. It’s not
as clean as you thought! Now Option/
Alt-click the Save selection as channel
icon in the Channels palette, and choose
Masked Areas in the dialog box. When
the alpha channel appears in the Channels
palette, turn on the channel’s visibility,
deselect your selection, and airbrush
all the regions that still need to be white.
You won’t see a change in the image as
you paint because you are looking at the
alpha channel while painting on the RGB
channels. The tinted selection region is
only a visual guide to the problem areas
and even then, it only indicates regions
that don’t match the pixel you clicked.
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Click in the white region again with
the Magic Wand tool, and you are likely
to find a tremendous improvement. The
background should now be all white. If
not, save another alpha channel selection
and target the remaining regions
with the airbrush.
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Tips:
In the interests of keeping your
file size down, once you have a clean
selection of the vase and shadow, you
can load the selection by choosing
Select > Inverse, and Select > Modify >
Expand. Set it to 20 pixels, and choose
Image > Crop. By expanding your
selection a bit, it ensures you’ll crop
outside the end of the shadow.
I will often use the Magic Wand
to test color matching. First, I fill a
rectangular marquee selection with
my target color on a new layer in my
image. I select the Magic Wand and in
the Options bar, I check Use All Layers,
uncheck Contiguous, and set Tolerance
to 10. I click in my color rectangle
to select all the pixels on either side of
my target color rectangle. Obviously,
the Tolerance varies based on how
stringent my color matching requirements
are. This technique provides
a powerful visual cue as to which
regions match the target color.
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Simon Tuckett is an illustrator and
retoucher in Toronto.
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