| Color-based selections can be fast and convenient but they often invite an unwanted guest—a bit of color fringe left at the edges. With minimal preparation, you can use Levels to not only eliminate the fringe, but also control edge softness to make a selection blend with a new background.
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Many selection techniques require
you to carefully trace around edges.
When you encounter an image with
a fairly uniform color in either the
foreground or background, you can
save time with the Magic Wand tool
or the Select > Color Range command
to perform a color-based selection.
However, these approaches sometimes
leave the background color at
the edges and create a harder edge
than you’d like.
Download the mousetrap.zip archive (10 MB) and extract the mousetrap.tif and hand.tif files, shown at left. Open mousetrap.tif, double-click the Background layer to convert it to
a new layer, and name it Mousetrap. Open hand.tif, select the Move tool (V), drag the image to the mousetrap image while pressing Shift to center it, and name the layer Hand.
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Since the hand has a nearly uniform
background color, it should be easy to
isolate it. Select the Magic Wand tool (W),
set Tolerance to 10 in the Options bar,
and make sure Contiguous is unchecked.
Click in the black background to select
it. Although you’ll use a layer mask to
fine-tune the composite in a moment,
briefly check the selection’s edges by
pressing Delete/Backspace. Turn off the
visibility of the Mousetrap layer, zoom in,
and press Command/Ctrl-H to hide the
selection marquee. A bit of background
remains around the hand—enough to
be objectionable, but not more than you
can remove with this technique. Undo
(Command/Ctrl-Z) to return the background
to the Hand layer, and turn on
the visibility of the Mousetrap layer.
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To convert the background (instead
of the hand) to a mask, Option/Alt-click
the Add Layer Mask icon at the bottom
of the Layers palette. The hand’s edges
are sharp because almost all of the pixels
in the layer mask are either pure white
or pure black. To view the mask directly,
Option/Alt-click the layer mask thumbnail
in the Hand layer. Option/Alt-click
again to display the image.
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You can soften the edges by making
some of the edge pixels in the mask
gray, which is the equivalent of using
the Feather command on a marquee
selection. Click the layer mask thumbnail
on the Hand layer, choose Filter > Blur >
Gaussian Blur, set the Radius to 6 pixels,
and click OK. The blurring softens the
edges, but shows a bit more of the black
background. That’s fine because you’ll
be tightening up the edges in the next
step. As a general rule, you should blur
the mask roughly twice as much as you’d
want for the final composited image.
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With the layer mask thumbnail still selected,
press Command/Ctrl-L to access
the Levels dialog box. You’ve probably
used Levels to adjust an image’s tonality,
but now you’ll use it on the layer mask to
increase its contrast. Dragging the black
Input slider to the right makes more of
the dark-gray pixels in the mask pure
black, effectively shrinking it. Drag it
until the fringe disappears from around
the hand. To further sharpen the mask,
drag the white Input slider to the left,
which makes the light-gray mask pixels
white. If you’re unclear why this works,
try Option/Alt-clicking the layer mask
thumbnail before you access Levels.
You’ll see the mask appear to grow and
shrink as you adjust its contrast by moving
the Levels sliders. The final image is shown at left.
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Gary Young has written Photoshop
courses taught worldwide in training
centers and online. Contact him at Tectrixinc.com.
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