Accordingly:- Make sure the Source 1 and Source 2 pop-up menus are
set to Hair Assault.jpg. - This is a single-layer document, so both Layer options are
automatically Background. No need to change them. - Set the first Channel option to Red. Set the second one to
Blue, as I have in Figure 10-20.
Figure 10-20.- Change the Blending. As you can see in the figure, the results
so far are unhelpful in terms of selecting the hair. Choosing
the Blending mode is the least predictable step in the process
because the ideal settings vary radically depending on the com-
position of your image. Bear in mind, the goal is to select the
foreground subject by making her white against a deselected
black background. Of all the Blending options in the pop-up
menu, you’ll usually find that Add and Subtract are your best
bets. So start by choosing Add from the Blending pop-up menu. - Invert the blue channel. Since we want to work with the highest
degree of contrast between our two source channels, it might
help to invert one of them to increase that difference. Turn on
the Invert check box in the Source 2 section of the dialog box.
Unfortunately, the image is still way to bright. Even if you change
the Offset value to –100, as I did in Figure 10-21 on the next
page, we’re still swimming in a sea of gray on gray.
Masking with the Calculations Command 353