How does Nikon's Active D-Lighting (ADL) work?

Someone said, in a post on another forum, that Nikon's ADL works by adjusting exposure. He mentioned as an example that if the scene has bright spots, it will underexpose the shot to prevent highlight clipping.
Given a proper exposure, it is possible to retrieve some detail both in highlights and shadows from a RAW file in PP by applying +ve and -ve EC. I thought ADL actually generates an "HDR" image from these adjustments. I was told I was wrong.
If ADL underexposed the shot to preserve highlights, how does it preserve details in the shadows? Does anybody know how ADL works?

Hi noreast,
I don't know much about Nikon's ADL, but I can tell you from what you are describing that it is not infact HDR. True HDR requires multiple exposures. Given a proper exposure and the RAW origional, you will have lots of freedom to boost shadows without any (or much) noise. If you are pushing the dynamic range of your camera where that is not possible - look into making true HDR shots.

Hi noreast,
(did I ask for a first name?
did you tell me?
have I forgotten?)

From my experience one effect I have seen of Nikon ADL on my D5000 was a dark halo around a white swan shot against a mid-grey water, so I suspect that maybe why people confuse it with the Over The Top processing that people often erroneously associate as being HDR.

So, it seems to be a locally applied variation of contrast range; possibly by effectively altering the ISO pixel by pixel. I still have it set on Auto, as 99% of the time it doesn't have that detrimental effect and probably helps.

Not a full answer, but a start :)

Thank you Dave, Kent for your replies.

For sure true HDR requires multiple exposures. I just thought that ADL borrows from the HDR techniques using a single exposure, and hence the limited range possible with ADL. I was told I was wrong but the explanation given to me (i.e ADL underexposes the shot) was not convincing, so I asked the question in this forum :)

I too keep ADL at Auto on my D5000 for almost all my shots, but in one experiment I did with various ADL values, I noticed that the difference was more visible in the highlights (more detail was visible there). Admittedly, my scene did not have deep shadows, but I did not notice any shadows being pushed down as underexposing the image would have done.

Quote:

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(did I ask for a first name?
did you tell me?
have I forgotten?)

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Aladin

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Originally Posted by noreast

Aladin

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Really! - great name, but I can see how it might set people's expectations rather high for what you can do :D

Cheers,

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Originally Posted by noreast

I noticed that the difference was more visible in the highlights (more detail was visible there).

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Yes, handy for shots of swans, although if they are too small in frame they still over expose and I have to dial in EC of -0.5 or -1 to retain the feather details.

Quote:

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Originally Posted by noreast

Admittedly, my scene did not have deep shadows, but I did not notice any shadows being pushed down as underexposing the image would have done.

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No, it is definitely something different from just under exposing, which is what negative Exposure Compensation (EC) is.

Cheers,

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Originally Posted by Dave Humphries

Really! - great name, but I can see how it might set people's expectations rather high for what you can do :D

Cheers,

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Now you udnerstand why I prefer to use only an online handle :o.
Thanks, or blame, goes to my grandmother (God rest her soul) for choosing my name.

Besides, Dave, I never claimed I could do much :D.

Of course, you could have said "Al" and we'd have assumed Alan or similar, or made one up :):D