Sometimes your client has an image in which he would like to have the object cropped out of the background but retain the shadow. If the object is on a light background, as in Figure 2-35, this is generally a simple matter of dropping out the background.
I will usually make a selection of the object or the background (whichever is easier) and invert the selection (if necessary so only the background is selected. Then I use a curve adjustment or a selective color adjustment to drop out the background, as shown in Figure 2-36.
If you have an image in which you want to retain the shadow, but have the shadow in black only, try this technique. First, make a path or selection of your background, and then make a copy of the image and change that copy to grayscale, as shown in Figure 2-37.
Use the same selection of the background method used above, only this time use your new black and white image. Then copy and paste it into the black channel of the original four-color image (Figure 2-38).
Make sure you delete any color in the shadow in the cyan, magenta, and yellow of the image you are retouching, as shown in Figure 2-39.
The final results of your new black-only shadow are shown in Figure 2-40.