Unsharp mask does the biz for most pictures. It's basically a sharpening process (high pass / boost) with a threshold, below which it doesn't operate. So it enhances transitions but you can hold back for low level patterns / noise. The 'radius' button adjusts the range over which you do the enhancing. You always have to check the whole picture or a sharp edge can have a black / white border. You really have to try it. It does a lot for craters and highlights in eyes.