Panasonic Lumix DMC-GM1 Review
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.
This chart shows the Panasonic GM1's default dynamic range performance against a range of competitors - the APS-C Fujifilm X-M1, compact Sony RX100 II and a MFT peer, the Olympus E-P5.
With all dynamic range settings off, the GM1 shows a tone curve with a more gentle rolloff in shadow detail than at the highlight end, with a slightly steep incline before it clips to white. This is curious since we saw a new, more S-shaped tone curve from the GX7. The Fujifilm X-M1 and Sony Cyber-shot RX100 II both clip at roughly the same point, but show a slightly gentler rolloff in highlights. The Olympus E-P5 stands out from the group, retaining almost a stop more of highlight tone before clipping to white.
ISO 'Low' Setting
The GM1 offers a base ISO of 200 with the option of an extension ISO 125 setting. As the chart below shows, the extension setting sacrifices a little in the way of highlight tone.
Below you can see the effects of the GM1's various i.Dynamic settings. Higher settings use a lower-contrast tone curve to pull in more tone from shadow and highlight areas, bringing more of a gentle curve to the highlight end.
In the real-world example below, the GM1 takes on a very challenging high contrast scene. At Standard, High and Auto settings it chooses a faster shutter speed, recovering a little more of the highlight tone in the building facade. Shadows are lightened progressively from Low to High, and the washed out sky gains more blue tone. It's an effective feature, and the results don't look overly 'HDR-ish.'
As the charts above show, it has a greater effect on shadow tone than highlights, noticeably boosting tone in the leafy areas in the foreground and bringing back just a bit of highlight tone in the building facade. In the real world and in the studio test, the GM1's 'Auto' and 'High' results are almost identical.