Fairytale Scene - The Photoshop: Professional Retouching and Compositing Tips, Tricks, and Techniques - page 441

Figure 9.39
8. With a hard-edged white brush, paint the right side of the wardrobe (to reveal the
darkening effect from the Levels adjustment layer) in the shape of a shadow com-
ing from a window on the left. (You can use the guide to create a straight line from
top to bottom by clicking at the top, holding down the Shift key, and then clicking
at the bottom near the skirting board.) When you've finished with the guide, go to
View > Clear Guides.