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.
Note: this page features our new interactive dynamic range comparison widget. The wedges below the graph are created by our measurement system from the values read from the step wedge, the red lines indicate approximate shadow and highlight range (the dotted line indicating middle gray).
The RX1 uses quite a gentle tone curve if you turn DRO off - capturing and conveying more highlight tones in its JPEGs than most of its rivals. Indeed Canon 6D owners will need to engage highlight tone priority mode if they wish to capture the same amount of the very brightest tones. This highlight capability is paid for in the shadows, where the RX1 clips to black rather sooner than most of its rivals.
The result, thanks to the camera's pretty reliable metering, is JPEGs with a nice, smooth transition to white when there are overexposed regions. And, while without DRO this can mean slightly plugged-up shadows, turning DRO on means you get well-balanced shadow regions too.
At RX1 uses slightly different tone curves for most of its color modes but they're all subtle variations on a theme, usually including slight variations on the standard tone curve with a slight increase or decrease in either or both of shadow and highlight contrast.
DRO (Dynamic Range Optimization) is an adaptive algorithm that brightens the dark regions of images to give a more balanced result while retaining local contrast. Understandably it gets a bit confused by our test chart but the test shows how it can effectively pull more detail out of the shadows and into the more visible areas of the image.
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