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Dynamic Range

Our new 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 cameras) black to clipped white (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' 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 the camera can capture before it clips to white. Shadow range is more complicated, in our test we stop measuring values below middle gray 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.

ISO Sensitivity and Dynamic Range

The DP2's dynamic range pretty consistent in offering the ability to represent 3.8 stops of information above middle gray. The exception is ISO 50 which has been added in order to offer slower shutter speeds and is essentially an over-exposed ISO 100.

Sensitivity Shadow range Highlight range Usable range
ISO 50 -5.0 EV 3.1 EV 8.1 EV
ISO 100 -4.6 EV 3.8 EV 8.4 EV
ISO 200 -4.9 EV 3.8 EV 8.8 EV
ISO 400 -4.0 EV 3.8 EV 7.8 EV
ISO 800 -2.1 EV 3.7 EV 5.8 EV

Dynamic Range compared

The DP2's dynamic range certain does a good job of keeping up with its peers, though it loses shadow range to noise at much lower ISOs than would be expected of contemporary cameras. Its handling of highlights leaves little to complain about. However, the occasionally unpredictable metering on the camera means that you have to expose your images carefully to make the most of this capability.

Camera (ISO 100)
Shadow range
Highlight range
Usable range
Sigma DP2 -4.6 EV 3.8 EV 8.4 EV
Olympus E-P1 -5.7 EV 3.3 EV 9.0 EV
Sony DSLR A330 -5.2 EV 3.5 EV 8.7 EV
Ricoh GR Digital III -4.9 EV 3.0 EV 7.9 EV

The wedges below 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).





RAW headroom

Experience has told us that there is typically around 1 EV (one stop) of extra information available at the highlight end in RAW files and that a negative digital exposure compensation when converting such files can recover detail lost to over-exposure. For the purpose of this comparison we converted the DP2's RAW files at Adobe Camera Raw's default setting and with a set of parameters that would help give a maximum dynamic range (though not neccesarily a very useful image).

  • ACR Default
  • ACR 'Best': Exposure: -1.35EV, Contrast -50, Brightness +85, Blacks 0


Settings
Shadow range
Highlight range
Usable range
JPEG -4.6 EV 3.8 EV 8.4 EV
ACR Default -3.6 EV 3.5 EV 7.1 EV
ACR 'Best' -6.0 EV 4.5 EV 10.5 EV

WARNING: Although Adobe Camera Raw is able to retrieve some 'luminance' (brightness) of wedge steps which were previously clipped there's no guarantee of color accuracy as individual channels may clip before others.

To demonstrate the effect, we shot the same shot at +1.33 EV and at 0.33EV intevals above that. Trying to recover detail from the +2.0EV over-exposed image didn't yield any more detial once we passed -0.9EV digital exposure compensation. However, on the 1.33EV image, we were able to match the image brightness with -0.5EV exposure compensation and this yielded considerably more detal (shown below).

This suggests that there were highlights that should have been within the reach of the brighter image but that they were lost to clipping. It's reasonable to assume there's nearer 0.7 EV of recoverable highlight information than the 1.0EV we'd usually expect to see. That said, Sigma Photo Pro's highlight recovery option is good at making the most of that recoverable range.

2.0 EV over-exposed image -0.9 EV digital exposure compensation
1.33 EV over-exposed image -0.05 EV digital exposure compensation
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