One of the advantages of Aperture's Curves tool over those in other software is that it takes advantage of Aperture's 32-bit architecture and lets you work with values above 100 percent white. This means that if you have values that are clipped, you can use a Curves adjustment to bring the clipped areas back into the visible range. You can also use Curves as an alternative with the recover tool.
To access the extended range Curves tool, add a Curves adjustment from the Add Adjustment pop-up menu, and from the Range pop-up menu choose Extended.
Now you can see the normal range of the curve, which is the visual portion of the image, and also the Curves histogram will show any image data that is above 100 percent.
If you want to bring this clipped image data back into the visible range, then the process is pretty simple. With a Curves adjustment applied to your image and the Extended range mode selected, drag the right-most point until the range of the curve completely encompasses...