When we hear about eye whitening our thoughts immediately turn to disturbing cases of retouching gone bad where subjects look more like dolls than humans. While YouTube is littered with videos on the subject, a good chunk of them take a brute force approach to the problem. They either crank up the luminosity or reduce the saturation; both of which will produce unnatural and sometimes frightening results. The key to restoring the whiteness of the Sclera is to treat the problem as a local color cast and work to offset just that cast and nothing else. In these two videos I'll show you how to quickly do just that using either Photoshop or Phase One's Capture One Pro 8. Keep in mind that my primary focus in these videos is on color as you generally shouldn't adjust the luminosity of the Sclera, at least not on a local level. The danger of brightening the white of the eye is that they will feel unnaturally bright relatively to the rest of the image - it is after all dark because of the direction or intensity of the original light source. What I occasionally do but haven't demonstrated here is to locally dodge and burn the sclera to remove any light or dark patches if they exist. Once again, be careful with this so that you retain the natural shadow and highlight structure of the Sclera and try to avoid globally brightening the eye in the process.
With just a little bit of masking and a few slider adjustments, the problem can easily be dealt with in Photoshop using the Select Color adjustment layer along with the help of the info panel.
Using Capture One Pro 8
If you prefer to deal with issues such as these at the raw level, the below video will show you a similar approach to what I demonstrated above, but done entirely through Capture One's local adjustment layers.
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