Lab Report - JPEG tone curves / dynamic range

By Rishi Sanyal

Our Dynamic Range measurement system involves shooting a calibrated Stouffer Step Wedge (13 stops total range) which is backlit using a daylight balanced lamp (95 CRI). A single shot of this produces a gray scale wedge from the camera's clipped white point down to black (example below). Each step of the scale is equivalent to 1/3 EV (a third of a stop), we select one step as 'middle gray' (defined as 50% luminance) and measure outwards to define the dynamic range. Hence there are 'two sides' to our results, the amount of shadow range (below middle gray) and the amount of highlight range (above middle gray).

To most people highlight range is the first thing they think about when talking about dynamic range, that is the amount of highlight detail above middle gray the camera can capture before it clips to white. Shadow range is more complicated; in our test the line on the graph stops as soon as the luminance value drops below our defined 'black point' (about 2% luminance) or the signal-to-noise ratio drops below a predefined value (where shadow detail would be swamped by noise), whichever comes first.

Note: this page features our new interactive dynamic range comparison widget. The wedges below the graph are created by our measurement system from the values read from the step wedge, the red lines indicate approximate shadow and highlight range (the dotted line indicating middle gray).

Cameras Compared

The graph below compares the Panasonic FZ1000's default JPEG tone curve to those of some of its most obvious competitors.

The graphs indicate a slightly harsher highlight rolloff than most of its competitors - notably the RX10 and Olympus Stylus 1. It does, however, have a slightly smoother rolloff and a bit more highlight range than the Canon G1X II. Shadow tones drop off rather quickly, especially in comparison to the Olympus Stylus 1 and Canon G1X II. This dropoff is not much different, and perhaps a bit smoother, compared to that of its direct competitor: the Sony RX10.

In real-world terms, this means the FZ1000 will show you similar shadow detail in JPEG compared to the RX10, but less than what you'll see with the brighter rendering of shadows by the Olympus Stylus 1 and Canon G1X II. Highlights will clip to white in a smoother fashion on the FZ1000 in comparison to the G1X II, but more harshly than what you're likely to see with the RX10 and Olympus Stylus 1.

DR modes: in the real world

The FZ1000 uses the latest version of Panasonic's 'iDynamic' dynamic range compensation feature for coping with high contrast scenes. It's an 'active' system that can reduce exposure to capture more highlight tones, while boosting the shadows and mid-tones to give the correct image brightness. There are three levels of iDynamic, plus an Auto setting that attempts to use the most appropriate setting for the scene being captured.

It's worth mentioning that Panasonic's particular implementation here is almost midway between Sony's DRO (Dynamic Range Optimizer) and Nikon's ADL (Active D-Lighting) features. While Sony's DRO modes are entirely inactive (no exposure adjustment), Nikon's ADL modes are very much active in that each mode has a pre-determined amount of negative exposure shift associated with it. Panasonic has chosen a middle way: the camera appears to make a scene-dependent decision on how much, if any, exposure shift to apply. Furthermore, it appears rather conservative in its approach. We typically noted 0 to -1/3 EV exposure shift for 'Low' and 'Standard' iDynamic settings, and typically -1/3 to -2/3 EV for the 'High' setting. What this means in the real-world is that you won't typically see drastic highlight retention with progressively higher iDynamic modes.

Below, we show you how the FZ1000's various iDynamic settings handled this fairly challenging real-world sunset scene. iDynamic 'Auto' chose a setting of 'High', which was appropriate for a scene of this dynamic range. Even set to 'Off' the camera's metering has concentrated on protecting the highlights, and iDynamic - with its rather conservative levels of exposure shift - makes only a limited effort to capture more. That said, shadow tones become much more visible at the higher iDynamic levels.

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The significant amounts of shadow boosting with iDynamic set to 'High' mean you can choose an exposure that renders highlights relatively well, and then use an appropiate iDynamic setting to boost shadows to visible or desirable levels. Of course this'll only get you so far for very high dynamic range scenes, such as the scene above, which could still benefit from a bit more shadow boosting than even 'High' provides.

DR modes: in the studio

In our studio test, the FZ1000 did not actively adjust exposure in any of its iDynamic modes - which isn't surprising given the large dark area surrounding our Stouffer transmission wedge. Therefore, the graphs below show the shadow boosting effect of the progressively more aggressive tone curves as you engage higher iDynamic modes. The tone curves essentially represent how real-world tones are represented in the final JPEG if you shoot manual (keep exposure constant) and apply the different iDynamic levels.

To correlate our studio test above to the real-world, we've shot our previous sunset scene in a manner similar to how our studio tests were done: hold exposure constant, while increasing iDynamic levels. The shadow-boosting effect of higher iDynamic modes seen in our studio test can be seen in the real-world below.
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Higher levels of iDynamic will simply make your shadows brighter when you maintain exposure (hold shutter speed, aperture, and ISO constant). We should point out that the significant amounts of shadow boosting the FZ1000 applies means that low contrast scenes that don't require such DR-enhancing modes might look flat if inappropriately high settings of iDynamic are used. On the other hand, the significant shadow boosting applied with the 'High' setting means you can often decrease your exposure to retain highlights without pushing too much of the image to black.

DR modes: with manual exposure compensation

While of its own accord the FZ1000 tends to be rather conservative in terms of shifting exposure to retain highlights, the boosts to shadows it will make are significant enough that you can manually capture more highlight tone by using negative exposure compensation yourself.

In our studio test, we determined the levels of negative exposure compensation needed to maintain midtones for each iDynamic setting. We then show how much highlight detail can be retrieved when using these iDynamic modes paired with their 'appropriate' amounts of negative exposure compensation.

What you see here is that if you choose to manually combine some negative exposure compensation with the iDynamic modes, you can get well-exposed images with additional highlight capture. iDynamic settings of 'Low', 'Standard', and 'High' can be combined with -1/3, -2/3, and -1 1/3 EV respectively, while maintaining midtones at the same brightness levels they'd have with iDynamic turned off. This, in turn, means that you can capture 1/3, 2/3, and 1 1/3 EV extra highlight detail using iDynamic with exposure compensation in this manner.

Below we demonstrate the real-world effect of manually reducing exposure in conjunction with iDynamic modes. The results are just as the graphs above lead us to expect - the shadow and midtone lift brought by applying iDynamic 'Low', 'Standard', and 'High' does enough to compensate for 1/3EV, 2/3EV, and 1 1/3EV reduction in exposure, respectively. This exposure reduction helps bring back tones in the sky and clouds, while maintaining the correct image brightness.

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Given the low noise floor of the sensor, you generally won't pay too much of a noise cost in shadows from applying these levels of exposure reduction. Save for, of course, the increase in shot noise - noise due to the random nature of light - which inevitably results from the decrease in exposure.