Working with Black-and-White and Color Images - GIMP 2.6 for Photographers: Image Editing with Open Source Software - page 329

Using Channels to Extract Hair from the Background—the Procedure

You will basically perform the following tasks in this exercise: Use the Colors >
Components > Decompose menu item to create a mask layer from the channel
that has the best contrast values (the red channel). The mask layer (i.e., the
channel) can then be touched up with painting tools and exported into
another image. Using this layer, in turn, you can create a selection and use it
to edit the actual image, to emphasize and increase the contrast.
• Open the girl-color.png image in the SampleImages folder on the DVD.
• Open the context menu in the Layers dialog and add an alpha channel to
the image so that you can use transparency.
• Call the layer portrait .
• Save the image by a new name, such as portrait.xcf , in the XCF format in
your practice folder.
• To keep the color channels available as layers for further editing, select
the Colors > Components > Decompose menu item and click OK . A copy
named portrait-RGB.xcf with the red, green, and blue channels as image
layers will be created.

Figure 4.23
The Decompose window

Figure 4.24
The original portrait.xcf and portrait-RGB.xcf, the copy with the channels as image layers,
which were created automatically