JPEG tone curves / dynamic range

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 RX100 III's JPEG tone curve to its predecessor, and some of its most obvious competitors.

Our comparison chart shows the RX100 III's default tone curve has a fairly typical S-curve that essentially matches the RX100 II's (A slight difference in JPEG noise reduction accounts for where our test has cut-off the shadow regions). As you can see, it's fairly similar to the results from its immediate rivals, though it has a slightly more gentle roll-off between near-white and completely white regions, which should give a more natural look to the highlights.

DR modes

The RX100 III has Sony's standard 'Dynamic Range Optimization' mode, which attempts to selectively brighten shadow regions to produce a more-balanced overall image. It offers five levels which give a progressively increasing effect, along with 'Auto' which selects the level that the camera considers most appropriate, based on the scene it's looking at.

Glancing at the chart you'll notice that all of the RX100 III's dynamic range modes clip highlights at about the same place - which isn't a surprise, since the camera doesn't make any change to the exposure. That matches up with our real-world findings, demonstrated at the bottom of the page. The DRO modes mainly affect the shadow regions of the image and pull more shadow information into the image, while highlights at the very top of the range are left untouched. Again our test is cutting the bottom of the curve off, as it is interpreting those regions as too noisy.

The real-world example below shows DRO in action. As shown in the graph above, DRO leaves the clipped highlights in the scene untouched. DRO level 5 applies a dramatic brightening to shadow tone, revealing detail in shadows regions that aren't visible in the images shot with the lower settings. Auto takes a little more conservative approach, indeed for this particular scene it appears to have left the effect off.

DRO+ Off
DRO+ Level 1
DRO+ Level 2
DRO+ Level 3
DRO+ Level 4
DRO+ Level 5
DRO+ Auto

If you choose to manually combine some negative exposure compensation with the DRO modes, you'll see that it's possible to get what should be well-exposed images with a tiny bit of additional highlight capture. Sadly, the rather subtle nature of the DRO corrections means you can only do this for around 2/3EV to 1EV of extra highlight range.

Here we demonstrate the real-world effect of manually combining exposure compensation with DRO. The results are just as the graphs above lead us to expect - the shadow lift brought by applying DRO Level 5 does enough to compensate for around a 2/3EV reduction in exposure. This means you get an extra 2/3EV of highlight information, while still getting the correct image brightness - and done in such a way that it doesn't end up flattening contrast too much.

DRO Off
–0.3EV, DRO Level 2
–0.7EV, DRO Level 5
–1EV, DRO Level 5
–1.7EV, ACR conversion

However, as our Raw conversion shows, we think Sony could be more ambitious in its use of DRO+, especially if it combined it with an automatic exposure shift, as Nikon and Olympus do with their dynamic range management functions. This example, with -1.7EV of exposure comp, is enough to capture the highlights and there's plenty of scope for pulling the shadows back up to the correct brightness.