Without doubt, the most welcomed features of Aperture 2.0 are several new image adjustment features included in the program You can almost close your eyes and point them out because they’re so clearly evident. While I greatly welcome the new Lightroom-like features such as vignetting and vibrancy, when I tried out the little feature called Definition, all I could say was, sweeeet.
We all know that both Aperture and Lightroom basically make adjustments to the entire image when they are applied, but with Aperture 2.0, Apple has included Definition as a way of adding local contrast when adjusting an image. Basically it seems to add more contrast to a Contrast adjustment. While the latter affects the entire image, the Definition adjustment affects more local areas, helping to further get rid of haze in the photo.
You can see the changes when applied, but sometimes using the Loupe tool will help you see the changes even better.
Before Definition adjustment:
After Definition adjustment