ESFotoClix Blog

After making some disparaging remarks about Active D-Lighting (ADL), the data caused me to reconsider. Primarily, I now see I had the wrong expectations.

How I thought ADL worked: I thought ADL would auto-magically compensate for Matrix metering’s (MM) tendency to over-expose. Indeed, in some test cases I saw how ADL applies negative compensation, but not enough to make a difference consistently.

How ADL seems to do best: If you apply negative compensation to MM or otherwise meter to avoid clipped highlights, ADL helps avoid under-exposed shadows through adjustment of the tone curve (or however it does it), effectively pushing out shadow detail and producing a balanced shot.

To elaborate, I assumed that ADL would adjust MM’s tendency to over-expose, much in the same way I sometimes purposefully expose to the right by +0.3 to +0.7EV from what the Spot meter indicates as the centered exposure, then back-off the exposure in ViewNX and apply shadow protection to recover shadow detail. Why I thought ADL would do something similar I can’t really explain, but to move on and learn something new let’s compare some samples of my approach vs. ADL and see which does better. Along the way, we will examine the effect each approach has on noise, and to illustrate the effects of each of the approaches, we will use ISO800.

The first capture uses Matrix metering with ADL=OFF. The bright back-lighting against our dark subject produces the typical Matrix metering clipping in the highlights.

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For the next capture we set ADL to Normal. ADL tames down the highlights a bit, but not enough, and pushes out shadow detail in the vase. Start paying attention at the 100% crop on the right and look at whether noise is becoming more evident there.

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For the next two exposures, we use -0.7EV and -1.0EV respectivealy. Now the highlights are under control, but what is happening in the noise department?

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To arrive at this final image we use the first exposure, thankfully captured in RAW, and we apply -0.7EV adjustment in ViewNX and shadow protection = 30. (For another example of this technique, see When Over-exposure happens). Compare the resulting image to the previous 4 samples.

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Which adjusted exposure achieves the best noise performance should be self-evident. Which of these achieves a better balance in the overall exposure is probably largely a matter of preference. My perspective is that the last image balances highlights, middle tones and shadows best. I wish ADL or some other algorithm performed similar simple adjustments on the fly in-camera (hint, hint, Nikon).

In response to my Active D-Lighting (ADL) experiments, some have recommended I try ADL with Matrix metering (MM) while applying negative exposure compensation (EC). The suggestion was to use -1 EV, with the idea that this would avoid blown highlights and ADL would compensate through shadow recovery. This makes sense and promises to solve the problem with possible under-exposure that would occur if one were to address Matrix metering’s tendency to over-expose by applying across-the-board negative compensation.

I decided to give this a go with the following five captures using ISO 200, aperture=f/8 in Aperture priority mode.

EC=0 and ADL=off gives an exposure at 1/13sec. An examination of the histogram will show clipping in the reds.
EC=-1EV and ADL=off gives an exposure at 1/25sec. All highlights are well-contained, but the shadows are a bit on the dark side. Time to call ADL to the rescue.
EC=-1EV and ADL=Normal result in an exposure at 1/30sec. The shadows are recovered, and the highlights are well balanced as well.
EC=-1EV and ADL=High yield and exposure of 1/40sec, with subtle further boosting of the shadows while maintaining well-contained highlights.
EC=-1EV and ADL=Extra High also give a 1/40sec exposure, with subtle further boosting of the shadows while maintaining well-contained highlights.

Looks great, right? Well, pay attention to those shutter speeds. Even though there’s no clipping whatsoever with ADL=OFF and -1EV of compensation, ADL=Normal further under-exposes by an additional 0.3EV, and for ADL High & Extra High ADL under-exposes by 0.7EV. We can only imagine what that will do at higher ISO values. Noise will come on like gangbusters. The recommended mitigation would be to stick with lower ISO’s, though this may not always be practical.

Let’s not completely ignore these results, however. If the situation is one where we have plenty of lighting so that keeping the ISO low is possible (i.e., we’re not capturing fast action), and you want to use Matrix metering with negative compensation, ADL may indeed help balance the exposure to avoid under-exposure, especially in shadow areas.

~O~
Addendum: To further illustrate how ADL behaves with under/over-exposure, first we used Spot metering in Manual mode to determine a middle-tone exposure somewhere between 1/25sec and 1/30sec, and bracketed 8 images around this middle-tone value with ADL=off stepping exposure in 1/3 EV increments, from 1/10sec to 1/50sec. Then we switched to MM, turned ADL to High and repeated. Side-by-side comparisons are shown in the following table.

Manual Exposure	Spot, ADL=OFF	MM, ADL=High
ISO 200, f/8, 1/10sec
ISO 200, f/8, 1/13sec
ISO 200, f/8, 1/15sec
ISO 200, f/8, 1/20sec
ISO 200, f/8, 1/25sec
ISO 200, f/8, 1/30sec
ISO 200, f/8, 1/40sec
ISO 200, f/8, 1/50sec

Looking at this last set of samples, it appears ADL does much better when one negatively compensates MM. As previous samples show, when MM over-exposes the highlights by a fair amount (+0.7 to 1.0EV), ADL’s negative compensation may be insufficient to “rescue” the highlights. But if you apply negative compensation or spot-meter in Manual mode to set a middle-tone exposure, then switch back to MM, ADL is in a much better place to adjust the tone curve and achieve a more balanced look to the image. A workable strategy for harsh lighting situations may be:

1. Spot-meter against a middle-tone (approximating middle gray)
2. Manually set exposure to that value (or lock it in a non-Manual mode)
3. Switch to MM and set ADL on (normal or high)
4. Snap away.

As we saw yesterday, when presented with atrocious lighting situations, Active D-Lighting (ADL) isn’t quite the exposure savior we would like it to be, and to be fair, we should not hold such expectations. Today, let’s examine more standard scenes, and let’s see what Matrix metering and ADL do for us when the exposure is well contained within the 7 stops or so of dynamic range that most of today’s APS-C sensors provide.

That doesn’t mean we won’t get “tricksy,” though. We will throw color into the mix and see how our Matrix metering and ADL dynamic duo do for us. Before we do that, let’s see how well we can do on our own. With a little experience we know that for a flower image under these lighting conditions, spot metering in Manual mode on the pink (very close to a mid-tone) and stopping down by 2/3 to 1 full stop is what the doctor order to prevent red clipping. When we do that, we get a very nice exposure, and one that when compared to the actual scene before us, matches up very well in color and brightness. Next we follow up with three photos in Aperture priority mode, same aperture as was used in our first shot, with Matrix metering and ADL set as indicated below. How do these 3 images compare to our baseline Spot-metered baseline capture?

Manual, Spot-metered -1 stop ISO 200 – f/4 – 1/160	Aperture, Matrix, ADL=off ISO 200 – f/4 – 1/60
Aperture, Matrix, ADL=Auto ISO 200 – f/4 – 1/60	Aperture, Matrix, ADL=Normal ISO 200 – f/4 – 1/80

An examination of the histograms for the Matrix-metered shots will reveal a good deal of clipped reds. Well, maybe this was just too tough a scene for Matrix metering and ADL. Let’s try another. Again, we switch to Manual mode and Spot-meter the first shot. This time we spot on the green leaves, and the result is that we get a little clipping in the red channel. Now compare it against the results Matrix metering and ADL produce. Which method clipped the reds more?

Manual, Spot-metered -1 stop ISO 200 – f/4 – 1/125	Aperture, Matrix, ADL=off ISO 200 – f/4 – 1/80
Aperture, Matrix, ADL=Auto ISO 200 – f/4 – 1/80	Aperture, Matrix, ADL=Normal ISO 200 – f/4 – 1/100

Whatever your answer to that last question was, a more relevant question is whether one can do better than Matrix metering and ADL in arriving at a solid flower image that doesn’t clip the reds. The answer is found in this next sample, produced by applying -0.4EV of exposure compensation and Shadow protection to the Spot-metered capture in ViewNX.

As a last ditch effort, let’s try a less floral scene. Again, the first sample is spot-metered in Manual mode on the pink at the lower left third, and the remaining shots use Matrix metering with ADL. Curiously, while the ADL=off sample does not clip the reds, both the ADL=Auto and especially the ADL=Normal samples do.

Manual, Spot-metered ISO 200 – f/4 – 1/125	Aperture, Matrix, ADL=off ISO 200 – f/4 – 1/80
Aperture, Matrix, ADL=Auto ISO 200 – f/4 – 1/80	Aperture, Matrix, ADL=Normal ISO 200 – f/4 – 1/100

You may arrive at your own conclusions based on these results, but I won’t lay awake at night worrying much about what I’m missing because I don’t use ADL.

~O~
Correction: After further experimentation and review of results, I am revising my position on ADL. Whereas I originally thought and expected ADL would compensate for Matrix metering’s tendency to over-expose, it appears that a more realistic expectation is that ADL will work well when the photographer applies negative compensation on the order of -0.7 to -1 EV to mitigate Matrix metering’s tendency to over-expose. The next two ADL blog entries will cover this in greater detail.