The Chromatic Aberration section also features two automatic defringe controls. The first one is called Highlight Edges, which is able to correct for the color fringing that you sometimes see in extremely burned-out highlight areas. This type of color fringing can be caused by extreme light exposure hitting the camera sensor, which can overload individual photosites with too many photons. In turn, this can create problems in the demosaicing process. The Highlight Edges Defringe option, therefore, carries out a different kind of calculation in order to correct the magenta fringing that is sometimes seen around the highlight edges. I have to say that this correction is really subtle. It was not easy to find a photograph where I could show any difference between the before and after. Even then, I confess I had to cheat here and ended up showing a Lightroom 2 example. The new demosaic process in Lightroom 3 is so good that you are unlikely ever to need or benefit from using the Highlight Edges adjustment. So Figure 6.56 below is included to show you the type of photograph that might benefit from a Highlight Edges Defringe adjustment. In practice, I doubt you’ll ever need it.
Figure 6.56 The Highlight Edges Defringe command can be used to autocorrect color fringing in the extreme highlights. Here you can see a close-up view of a photograph of the sunlight reflecting off the sea. The left half shows an uncorrected preview, and the right half shows a preview with the Highlight Edges correction enabled.