Originally Posted by
Inkanyezi
It does not boost locally, but it lifts shadows in exactly the same way as when you lift the curve by setting a handle a bit from the far left and lift. Hence it actually decreases contrast, just as the curve tool would do. So in essence, D-Lighting - without Active - is the curve alteration. As anyone can understand, it is only a way of processing the RAW file. Active D-Lighting is something different.
Early Nikon models only had D-Lighting, not Active D-lighting. The "Active" part of it is coupled to the light meter and pulls down exposure to save highlights that are identified by the matrix metering. Hence, when there are highlights to save, "Active" reduces exposure, just as you would do with compensation, in order to save the highlights from clipping. The image then evidently becomes darker, which is what "D-Lighting" later will fix. So there are two different approaches in one setting: Avoid clipping by pulling back exposure, and in processing the jpeg, to lift shadows. Evidently only the "Active" component will influence the raw file.
So we should try not to confuse D-Lighting with Active D-Lighting. The former is part of the latter. Active D-Lighting automagically sets exposure compensation. When there are no bright highlights in the scene, exposure compensation will not be applied.
When D-Lighting has been used, metadata informs Nikon's raw converters, and they default to apply the D-Lighting values that are set in the camera. This can be overridden by the user.