Dynamic Range (JPEG tone curves)
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.
The D3100 behaves in a very similar fashion to the D3000 before it, with a range of Picture Styles that vary somewhat in contrast. In Standard mode it offers a decent highlight range of about 3 2/3 stops, although it clips to white a little bit more abruptly than higher-end cameras such as the the D7000. The Neutral mode has slightly lower contrast and more 'open' shadows, while the Vivid setting is higher in contrast and therefore blocks up the shadows in comparison.
It's worth noting that, just like the D3000, the D3100's default tone curve is fairly typical for this class of camera, offering very similar results to the likes of the various Canon Rebels and entry-level Sonys.
Active D-Lighting is Nikon's dynamic range expansion option, designed for use when faced with high contrast scenes to maintain shadow detail without blowing the highlights. It's a feature shared by all of Nikon's current DSLRs, but unlike models higher up the product line, the D3100 only has two settings - on or off. The effect of Active D-Lighting differs depending on the scene, so this test, performed using our 13-stop wedge, isn't necessarily an accurate indication of 'typical' performance. It does clearly show, however, the way in which ADL is designed to work, extending the visible dynamic range by lifting shadow areas and darkening highlights, to get the most detail out of these areas in a single exposure.