Olympus OM-D E-M1 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.
The E-M1 has a fairly simple DR expansion mode - Auto Gradation. This combines an adaptive shadow brightening algorithm that Olympus calls Shadow Adjustment Technology, with a change in the camera's metering that will slightly reduce exposure to capture a fraction more highlight detail. Below you can see the effect on our DR test and in a real-world example.
The representation of high and low key dynamic ranges in the chart above shows what we expected - more-or-less a simple shift of the same S-curve to higher and lower ranges. This also gives some idea of how Auto gradation works - here shifting the exposure to capture more in the highlights, and pulling up the shadows to reveal more detail.
|Normal Gradation||100% crop|
|Auto Gradation||100% crop|
|HDR Mode 1||100% crop|
|HDR Mode 2||100% crop|
Here the 'Normal Gradation' setting lets much of the tone in this scene clip to black or close to it, resulting in very blocked-up shadows. Switching to 'Auto' pulls up a lot more shadow detail, while still balancing local contrast pretty well. In comparison, the multi-shot HDR modes reveals progressively more detail, but with this scene, HDR2 in particular looks distinctly 'flat' with mushy detail in the 100% crop.
Below you'll find a comparison of the E-M1's dynamic range settings compared to the rest of the field. Its results don't look drastically different from the APS-C cameras we've set as default comparisons.
The cameras we're showing here all offer broadly similar results in the shadows, and for the most part clip the highlights similarly too, although with detail differences in the tone curves. The E-M1 adopts the middle ground between the Sony NEX-7's relatively high contrast and gentle highlight rolloff, and the Nikon D7100's lower contrast and more-abrupt clipping. The Fujifilm X-Pro1 clips earlier, but its highlight range can be expanded dramatically using its in-camera DR settings.
The E-M1's precise tonal response can be easily modified using its in-viewfinder Highlight and Shadow adjustments, but this won't affect the clipping point.
ISO 'LOW' Setting
As was common on many Olympus models since the E-30, but missing on more recent cameras like the E-M5, the E-M1 offers an ISO 100 equivalent setting with reduced highlight range. This is because the ISO Low and ISO 200 settings are derived from the same sensor amplification setting - ISO 200 images are exposed to less light, protecting highlights, compared to ISO 100. The two settings have different tone curves applied so that both give the same image brightness, despite the difference in exposure.
The upshot of this is that the ISO Low shots include less highlight detail but with 'cleaner' shadows, while the ISO 200 shots strike the opposite balance. So it's normally best to use LOW only in relatively low-contrast situations, or when you have complete control over your lighting.
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