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 (98 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 a6000's tone curve is very similar to the Nikon D5300's: offering a good amount of dynamic range with a nice subtle roll-off between bright tones and completely clipped regions. The Olympus offers a more relaxed tone curve than either, meaning that you get a little more at both ends of the brightness range, but the 'flatter' approach to highlights is likely to mean a lower contrast in the brighter regions of the image.

As we'll see further down this page, the DRO+ mode does give a6000 users a means of gaining a broader dynamic range capture and incorporation.

DR Modes

In common with Nikon's 'Active D-Lighting,' Sony's DRO (Dynamic Range Optimization) uses an adaptive algorithm that brightens the dark regions of images to give a more balanced result while retaining local contrast. However, the key difference is that, unlike the Nikon system, DRO+ doesn't adjust the camera's exposure to capture more highlight information, it just pulls up the shadows and mid-tones.

The upshot of this is that you get better balanced images, but no additional highlight DR.

DRO Real World Example

Off Lvl 1 Lvl 2 Lvl 3 Lvl 4 Lvl 5 Auto

While not the most exciting example, above you can see what each DRO setting does in a high contrast situation - making no attempt to recover any additional highlight information, just brightening mid-tones and shadows. The Auto setting appears to be using DRO level 3 in this instance. What we can't explain is why the camera's vignetting correction ('Shading Correction,' set to Auto, in this instance), appears to have been disengaged when the DRO level is manually selected.

In terms of use, it's worth noting that you can easily choose to apply some exposure compensation to capture more highlight information, then use DRO to balance up the image. It's sometimes a little hard to judge exactly how much DRO to add, which makes the absense of a post-shot in-camera Raw conversion option all the more furstrating.

ISO 100, F5.0, 1/2500th sec
-1EV Exposure Comp, DRO Lv 5

Just as an example, here is the above scene with -1EV exposure comp, and DRO turned up to level 5. The result is a little dark (-0.7EV would have made more sense), but suceeds in giving an image with more highlight information and better-balanced shadows than the DRO Off image did.