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Active-D Lighting, Nikon, Affect on Raw

Discussion in 'Developing your Photos' started by Ferguson, Mar 19, 2017.

  1. Ferguson

    Ferguson Linwood Ferguson

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    A discussion started in another thread (here), and rather than further polluting that thread I thought I would start a new one.

    The question for me is whether ADL has any impact on the actual raw data other than reducing the auto-exposure.

    I set up a high contrast subject, and shot it twice:

    1) With ADL set to high, and auto-exposure in aperture mode with auto-iso off. It chose an exposure of 1/40th of a second.

    2) Without changing anything else, I turned ADL to off, mode to manual, and set exposure to 1/40th.

    I then imported the photos and looked at the preview of the results (the jpg preview in the file, which is what I see on the LCD). I got this:

    [​IMG]

    The image on the left is with ADL off, the one on the right is ADL on. You can see how in post-processing in camera, the ADL caused the shadow to be raised. Not really shown (since I explicitly forced the next exposure to be the same) is that it also reduced the exposure so as to protect highlights - most of the shade is not truly blown, certainly in raw. If I had turned ADL off and left auto-exposure set it would have used a longer exposure than 1/40th and blow out the shade worse.

    To be clear, this difference is in Photo Mechanic which uses the embedded preview. Imported into lightroom there is no difference in the preview lightroom shows, as it ignores the ADL.

    But all that is well understood. What I was after is to know if there was any change in the raw image. I then pulled these into photoshop with zeroed ACR settings. They looked nearly identical, so I put them in layers, let photoshop align the layers, and did a difference.

    Aside and example: For those who have not used layer arithmetic, doing a difference in two layers causes any identical pixels to zero out (it literally subtracts the pixel values of one from the other). Non-identical portions appear as various colors and patterns that represent the difference. Here's an example in two consecutive shots at a baseball game:

    [​IMG]
    See they are similar but not identical. Layer and subtract and you get this:
    [​IMG]
    Notice most is black - the background did not change. The far left and right show the field of view shifted, as you see a regular image (subtracting to negative flips the sign so you still see the regular image).

    Notice the players moved, the ump ever so slightly, the other two quite a bit. Any different jumps out at you. You can brighten it to show subtle changes.

    Anyway, back to the ADL example, here's what it looks like subtracted:

    [​IMG]
    The parts around the outside show the camera shifted a tiny bit. The black in the center says "mostly identical". But not quite, necessarily. A difference may be imperceptibly small, so I increased the exposure uniformly by 5 stops. 5 stops is 32 times the brightness of course, so any brightness difference now should jump out as 5 stops brighter:

    [​IMG]

    Still darn close to nothing. I'd argue 5 stops is way beyond anything noticable in the final result. But just to see what I can get (and in photoshop unlike lightroom you get more than 5 stops), here's 10 stops (1024 times the light):

    [​IMG]
    The difference now is visible, but in a specific place -- it's light coming in from outside, reflecting across. My guess is the partly cloudy day had a slight change in light (remember these changes are hugely amplified).

    Nothing here would seem to indicate that there's any difference in the raw bits due to ADL.
     
  2. Hal P Anderson

    Hal P Anderson Lightroom Guru Staff Member Lightroom Guru

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    Linwood,

    Thanks for doing the experiment. Your results were what I would have predicted based on what I've been led to believe about ADL.
     
  3. bob chadwick

    bob chadwick New Member

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    Linwood,

    This discussion comes up occasionally on Nikonians and while no one has done the excellent analysis you have done, my recollection of the conclusions there has been that it does impact the RAW file baking in exposure adjustments that can't be manipulated out unless you are using the Nikon software.

    I started out shooting sports with ADL on in JPG, which produced a pleasing result. I was not happy when I switched to RAW using Lightroom. I saw noticeable impact on the RAW images and after reading about the impact of ADL, turned it off.

    Bob
     
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  4. Ferguson

    Ferguson Linwood Ferguson

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    The internet is full of facts, and alternative facts. Sorting them is tough.

    I'd welcome ideas how to prove that variations are baked in in some other fashion. It's hard to prove an absence, but to me the lack of any difference in the pixels is pretty telling in the above. Takes only about 10 minutes to do the test, give it a try with your own choice of scene and body.

    Maybe ADL's post processing is more sophisticated, but to me it doesn't look much different than setting highlight at about -60 and shadow at about +80. If you leave them at zero it's pretty harsh.
     
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  5. bob chadwick

    bob chadwick New Member

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    I hear you. Everyone has an opinion and I'm certainly not qualified to do the testing you have done. Just sharing what I have been told.
     
    Last edited: Mar 20, 2017 at 2:38 PM
  6. Ferguson

    Ferguson Linwood Ferguson

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    Actually, short of someone pointing out a flaw of the technique, it's dirt simple. Photoshop does all the work. You can even go through lightroom first (use no develop preset), and then edit-in-photoshop-as-layers. Select both layers and Edit, align layers, then change it to "difference". Magic. To magnify the differences add an adjustment layer over top and increase exposure as desired.

    It's a handy way to look for any kind of artifact differences, even if it's in the subject matter, like changes in lighting between two shots, or long exposure noise reduction, etc. It doesn't quantify the difference directly, but it lets one visualize it nicely.
     
  7. Hal P Anderson

    Hal P Anderson Lightroom Guru Staff Member Lightroom Guru

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    It's also a neat way to show the difference between a lossy-compressed DNG and the raw file it was derived from.I find in my testing that the two are astoundingly close. Does this mean I'm a heretic? :)
     
  8. Ferguson

    Ferguson Linwood Ferguson

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    Galileo was a heretic. Lots of others. So you're in good company.

    I've always wondered if lossy was not a bit like JPG's. The difference in a quality 12 and quality 10 (or if using percent say 92 vs 100 percent) was always incredibly slight to me, given the 40-50% savings in space. I wonder if Nikon's is not similar. But then again on my D300 I always shot 14 bit and paid the frame rate penalty, and still shoot 14 bit (lossless compressed). Just in case.

    But yes, it would certainly highlight the differences. What's a bit more problematic is how much enhancement (added exposure) should one do to the result to know what's relevant. Using my example above, with the 10 stop enhancement showing a clear pattern -- at what point does the difference yield a visually detectable difference in the original image. My GUESS is since most images are maybe 5-8 stops total they can show (i.e. printed on paper, or viewed on a screen), that by blowing this out to 5 stops before it becomes apparent at all, means it would be undetectable in the original. But I wonder if someone with more (optics? physics? Physiology?) background could say?
     
  9. Victoria Bampton

    Victoria Bampton Lightroom Queen / Owner Staff Member Administrator Moderator Lightroom Guru

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    Yes, it is a JPEG compression that's being applied.

    I have seen examples where it's really noticeable - like people gathered round a bonfire in the dark, that was underexposed and the Exposure slider pushed to recover it. Then you see it. Most pictures won't notice though.
     

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