Assassin - The Photoshop: Professional Retouching and Compositing Tips, Tricks, and Techniques - page 547

Figure 11.54
Tip
To reposition the vignette, use the Move tool (V). With the layer mask attached to
the Levels adjustment layer active, drag in the image area.
3. Add a new blank layer to the top of the layer stack, name it darken bottom , and
with the black soft-edged brush paint across the very bottom of the image to
darken it further.