Assassin - The Photoshop: Professional Retouching and Compositing Tips, Tricks, and Techniques - page 540

Figure 11.47
9. With a black foreground color, choose the Gradient tool with Foreground set to
Transparent and a Linear gradient ( Figure 11.48 ) . Click the layer mask attached to
the London layer, and then drag a gradient to blend the clouds and London layers
together ( Figure 11.49 ). (Note: You may need to apply several strokes with the
Gradient tool.)
Figure 11.48