D-Range Optimizer (DRO, Dynamic-Range Optimizer) is one of the methods to adjust brightness. Although it is rather supplementary compared to brightness and contrast adjustments, sometimes it may help you reproduce the image faithfully.
Human eyes are good enough to see both contrasty bright and dark areas such as indoor/outdoor or sunshine/shade.
Meanwhile, photographs cannot reproduce that wide brightness range; if the bright area is shown clearly, dark area becomes just black. If you want to reproduce the dark area, white part is washed out. And if you weaken the contrast to show both bright and dark area, the entire picture will be weak and dull.
In this case, D-Range Optimizer extracts only dark area and makes it bright. It can also extract bright area only to make it dark. In this way, both bright and dark areas are shown clearly in the image, as the human eyes see.
of D-Range Optimizer usually provides you good-balanced photos. You can also adjust them manually if you are not satisfied with the automatic results.
To do so, adjust the image a little darker with the slider in [Brightness] palette. And in [D-Range Optimizer] palette, move the [Amount] higher to make dark area visible until you reach to your satisfied result. If you still cannot get effective result in bright area, move [Highlight] slider to minus.
Strong D-Range Optimizer may results in weak shadow; to avoid this, [Shadow] can be set higher if necessary.
The strongest D-Range Optimizer setting can show both bright and dark areas more than human eyes can see, however, it may look unnatural. It is important to find a good-balanced point of bright and dark areas.