Image Processing Reference
In-Depth Information
(with a variety of tool pointers) to add, delete, or edit masking sections. When
you are finished working, you switch back into selection mode by clicking
Toggle Quick Mask again.
We will have a look at the second method, using an example.
Extracting an Image Object with the Help of a Painted Mask
The first steps in the process consist of preparing the selection with the
“regular” select tools as far as possible. It makes sense to first select the
background around the actual object you want to extract. For example, if the
background has similar, contiguous colors, which are easy to select with one
of the tools for selecting by color, it could be easier to select the background
of the image object first. This also reproduces the contours of the object, from
the outside. The selection can then be inverted. Then you'll have selected your
image object, exactly as you wanted it.
The Procedure
• Open the lion.png image from the SampleImages folder on the DVD.
• Perform an automatic color level adjustment ( Colors > Levels > Auto ) to
further offset the background from the lion.
• Next, make a rough selection of the area around the lion with the Fuzzy
Select tool . I suggest starting at the top of the lion. Your aim is to get a
good selection of the lion's straggly mane. You won't be able to select
individual strands of hair, but at least you will get a good grasp of the
mane's contour. Select the Add to the current selection mode in the Fuzzy
Select tool's settings. You might need to reduce the Threshold setting to
about 15 so that not too much is selected at once. You will certainly have
to click several times, and you will have holes in your selection. Some
of the selection might go over the surface of the lion. Most importantly,
take care that the lion's mane gets a good contour. Selecting hair strands
is among the most difficult tasks when selecting objects.
• Use the Free Select tool to roughly enclose the background around the
lion. Enclose the yet to be selected “islands” in the selection by drawing
around them. To be able to add these “islands” to the existing selection
created with the Fuzzy Select tool , choose the Add to the current selection
mode in the tools options.
• When the area around the lion is roughly selected, invert the selection
with the Select > Invert menu item. Previously the area around the lion
was selected; now the lion himself is selected.
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