Images in which areas of background and foreground intermix, possibly even with a measure of transparency thrown in are certainly challenging, but they can usually be tackled with the techniques illustrated in Hair and Lattices. However, when you add to this situation, foreground colors that are both darker and lighter than the foreground, such as you frequently find with the highlights and shadows of hair, then a couple additional tools are useful.
Patches are useful for isolating problem areas so that you can adjust the Edge Finding and Blending options to suit the problem without affecting the entire image. The Patch edge blending options also includes an additional option, Complex - Hair, for use when the foreground is both darker and lighter then the background. The Complex - Hair option is computationally expensive, so you should keep the patches as small as possible to avoid excessive cut-out rendering times.
In the first Hair example, simply painting blend mask over the area of mixed hair and background was good enough because the hair was fairly even in tone and distinct from the background. The image In this example is more complex and getting a good cut-out requires masking some of the pixels in the area with keep and delete masks to help the blending process. The masks still don't need to be painstakingly accurate and time consuming to create. The trick is to provide hints to the blending process as to which areas are foreground and which are background.
1. Load the image.
2. In this example, we will use a patch (and ignore the rest of the image.
3. Quickly mask the really obvious parts of the foreground.
4. Now, use the Color Workspace to mask the solid, easily identifiable strands of hair. We don't need to mask every pixel.
5. Still using the color workspace, select the intermediate colors - both colors that are darker and colors that are lighter than the background - and assign them to the blend mask.
6. Look for any stray strands or ends of hair that may have been missed. Draw a line of blend mask over these with the Blend Exact brush.
7. Select Clean All from the Image menu to fill in any holes.
8. Fill the rest of the patch with delete mask using the Auto-Fill with Delete from the Patch menu.
9. View the cutout by selecting Preview Cut-out in Patch from the Patch menu.
10. If patches of background are showing in the cut-out, usually a few well placed pixels of delete mask will take care of the problem.
11. If too much detail is lost, or alternately, too much noise from the background is showing up in the cut-out, Check the Complex - Hair option on the Patch Properties dialog.
12. Start with a medium level of detail setting, and experiment to find the optimum value. Move the slider toward High to increase the amount of detail. If this adds too much noise to the cut-out, move the slider back toward Low.