For Windows 21 day free trial
Requires Windows 2000, XP, Vista or 7. As a plugin, supports Adobe Photoshop version 7, CS to CS5 and later in both 32- and 64-bit, Photoshop Elements version 5 and later, and Corel Paint Shop Pro version X2 and later. | 
For Mac 21 day free trial
Requires Mac OS X 10.6 (Snow Leopard) or later. As a plugin, supports Adobe Photoshop version 7, CS to CS5 and later in both 32- and 64-bit, and Photoshop Elements version 5 and later. |
 | You might also like to try Urban Lightscape: correct exposure, make localised brightness adjustments and introduce artificial lighting to photos. |
