I am somewhat confused about the function of the ADL (Active D-Lighting) in Nikon cameras. My question is: When shooting in RAW format and the ADL is on, does ADL affect the RAW image data stored in the camera?
In various places it has been claimed that the ADL of Nikon can increase the dynamical range of the camera. If this is true, then it implies that the ADL does affect the RAW image data otherwise I would not understand why the danuamical range of the camera can be increased unless the above statement implicitly means that "the ADL of Nikon can increase the dynamical range of the camera when shooting in jpg".
To test the ADL function I shoot the same scene twice: both in raw format, one with ADL off (image1, I call it) the other with ADL on (image2). Then I uploaded the two raw files to my computer, and used NX2 to open them. In NX2, I turned off the ADL of image2, then I got a new image image2a. I found that image2a is clearly different from image1: they look different (with different exposure), and the two exposure histograms are also distinctly different. I think this indicates that the ADL cannot be "turned off" after shooting.
I would think that my test has confirmed that the ADL affetcs the raw data. That is, the raw data have been changed by ADL before they are written to the card.
I don't know if my understanding is correct so I post it here for some comments. I cannot find an "official" interpretation about what ADL has done to the RAW image data.
Frank
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I do not think Nikon actually has disclosed in what ADL is (read: how it is achieved).
As far as I understand it, it does not "alter" RAW data as such, but it does change exposure. Depending on the metering, it underexposes a bit or a bit more, to preserve highlights. In processing (either in-camera when shooting JPEG or in-computer when using a Nikon RAW convertor) a different tonal curve is applied to lift the shadows. Apparently, also some masking and processing is applied to increase local contrast, which can result in HDR like halos around bright or dark subjects.
In RAW convertors which do not do anything with the "ADL" setting, you will then just notice a slight difference in exposure, even if the EXIF settings say the exposure time is the same.
So... the RAW data is different due to a different exposure, but the RAW data collected from the sensor is not changed before being saved to NEF.
That's correct, ADL deliberately underexposes to avoid blown highlights. RAW data is not affected, camera just adds some tags for CNX2 to use (typically ignored by other RAW converters). Personally I'm not the biggest fan of ADL - noise in shadow areas sometimes look really bad, especially on higher ISO shots.
Then I don't understand why turning off the ADL in image2 in NX2 does not lead to an exposure that is the same as image1. Or, put it another way, what does the "ADL turn off" mean in NX2?
Frank
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03-20-2011, 01:45 PM
(This post was last modified: 03-20-2011, 01:51 PM by Brightcolours.)
[quote name='Frank' timestamp='1300628148' post='6963']
Then I don't understand why turning off the ADL in image2 in NX2 does not lead to an exposure that is the same as image1. Or, put it another way, what does the "ADL turn off" mean in NX2?
Frank
[/quote]
Because a photo taken with ADL on is still underexposed. Like I said above, the exposure is lower to avoid highlight blow out with ADL-on. But that does not mean that the RAW is actually changed in this respect, just a lower exposure.
[quote name='Frank' timestamp='1300628148' post='6963']
Then I don't understand why turning off the ADL in image2 in NX2 does not lead to an exposure that is the same as image1. Or, put it another way, what does the "ADL turn off" mean in NX2?
Frank
[/quote]
Actually, to my knowledge, setting the ADL off in NX2 should not show too much difference from the other image. Though, I can't say that the "off" function in NX2 should always produce "100% same" image as the original. The light metering (especially the matrix metering) is very complex and the ADL functionality can be combined with almost every setting that would effect the metering... That said, did you check if you've set manual exposure compansation in any of your sample shots?
Anyway, personally I keep my images away from ADL... If you shoot NEF, post processing in a decent raw converter (or in NX2) has always more useful functionalities. ADL changes exposure (and AFAIK not only the highlights) and therefore it is better to be used in high contrast scenes when shootin jpeg or tiff...
Serkan
I also don't like to turn ADL on. Ineed I think that if you do not know what a function does form you then do not use it. I am curious about ADL only because I read from some places that it can increase the dynamical range of the camera---if this is true then in some specfic situation I may consider to turn it on since it would allow me to get more tone range than I do without it---even when shooting with raw. If it just modifies the exposure then it is not necessary since this can always be achived by adjust exposure manually.
By the way, in my original post by "affect the raw data" I mean the raw data with ADL on are different from the raw data without ADL for the same scene with the same exposure setting.
Frank
So, probably the most important question is: can ADL really boost the dynamic range of the camera?
Frank
[quote name='Frank' timestamp='1300632885' post='6968']
So, probably the most important question is: can ADL really boost the dynamic range of the camera?
Frank
[/quote]
ADL does not boost DR... It is suggested to be used for high DR cases (or high contrast cases), which the camera cannot handle with it's normal metering functionalities.
[quote name='PuxaVida' timestamp='1300633503' post='6969']
ADL does not boost DR... It is suggested to be used for high DR cases (or high contrast cases), which the camera cannot handle with it's normal metering functionalities.
[/quote]
Probbaly I should clarify my question: can ADL really boost the *effective* dynamic range of the camera? I.e., can ADL allow the camera to capture a dynamic range larger than it would without ADL (in raw shooting)?
Frank
