Panasonic DMC-GH2 Dynamic Range (JPEG)
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.
Dynamic Range compared
The GH2's tone curve gives approximately three stops of highlight range from middle grey to clipped white. The roll-off to the highlights is relatively steep, meaning there can be quite stark transition from near-white areas to completely blown-out areas. With dynamic range enhancement functions turned off on all cameras, the GH2 manages to record roughly one stop less overall dynamic range in its JPEGs than APS-C rivals such as the Nikon D7000, Canon EOS 600D and Sony SLT A55.
All of these cameras have also dynamic range expansion features. However while those of the various SLRs have easily-demonstrable benefits, the GH2's iDynamic feature could not be triggered in our controlled test setup and we therefore cannot present any measured results. However, as we found when testing the GF2 (and confirmed with the GH2), the effect is subtle in real-world shooting, and only really becomes useful when capturing backlit subjects.
Like previous Panasonic G-series cameras the GH2 offers a range of color modes, most of which apply very similar tone curves to the JPEG output. However the Cinema and Smooth BW modes differ somewhat from the norm by applying more contrasty tone curves, resulting in darker images (i.e. technically underexposed). In contrast the Nostalgic mode applies a slightly less contrasty curve with a slightly more gentle transition to highlights, and gives brighter images (i.e. relatively overexposed).