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.
The E-P3 uses a JPEG tone curve that's essentially the same as the E-P1 and E-P2 before it, and is also used by the E-5. It offers approximately 3.3 stops of highlight range, with a fairly gentle roll-off at the top end (which means that highlights don't clip too abruptly to white). In this it's subtly different from the E-PL2 or Panasonic G3, both of which are a bit more contrasty at the very top end and offer fractionally less highlight range. However it lags a little behind the best of its competitors such as the Sony NEX-5, which offers a full four stops in the highlights.
The E-P3's various picture modes all use essentially the same tone curve, the difference between them being much more about colour rendition than anything else. The one exception is the portrait mode, which gives a fractionally lighter image (by perhaps 0.3 stop) for any given exposure, while maintaining the same white point.
The E-P3 features Olympus's familiar set of gradation settings - Normal, High Key, Low Key, and Auto. These adjust both the tone curve and exposure to apply different 'looks' to the image (previewed in real time on the live view display). High and Low Key do pretty well exactly what they say on the tin, giving lighter- and darker-toned images respectively.
Auto Gradation is a little more complex - it uses Olympus's Shadow Adjustment Technology, and analyses the tonal distribution of the scene to tweak exposure and local contrast in a bid to improve the balance between shadow and highlight detail. As can be seen from our graphs, auto gradation demonstrably works - in this case it's effectively extended the highlight range by perhaps a stop - but this does tend to come at the expense of increased noise in the shadows.