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).
ISO Sensitivity and Dynamic Range
At ISO 160 the DSC-R1 returns a reasonable 7.8EV (as good as eight stops) of dynamic range which is pretty much what we expected. At higher sensitivities however it suffers in our test due to high levels of noise which significantly cut the signal-to-noise ratio, at ISO 1600 we call the shadow range as -2.1 EV (from middle gray), at ISO 3200 its down to just -1.6 EV.
|Sensitivity||Shadow range||Highlight range||Usable range|
|ISO 160||-4.7 EV||3.1 EV||7.8 EV|
|ISO 400||-4.3 EV||3.1 EV||7.4 EV|
|ISO 1600||-2.1 EV||3.1 EV||5.2 EV|
|ISO 3200||-1.6 EV||2.8 EV||4.4 EV|
Obviously an ISO 1600 image would contain areas of shadow with a level below our 'shadow range' point however it would difficult to make out any detail because of noise, this can be seen more clearly in the 100% wedge crops below. Step 24 represents -2.0 EV on our graph above, each step represents +/- 0.3 EV. As you can see it's difficult to make out the difference between the steps below step 25, the amount of noise now overtakes any useful 'signal'.
Dynamic Range compared
At lower sensitivities the DSC-R1 delivers results similar to the Canon EOS 350D (Digital Rebel XT), the primary difference being a 0.2 EV highlight range advantage to the EOS 350D. At higher sensitivities however the picture is quite different, the DSC-R1's high 'shadow noise' cutting usable shadow range down to just -2.1 EV.
|Camera / sensitivity||
|Sony DSC-R1 @ ISO 160||-4.7 EV||3.1 EV||7.8 EV|
|Sony DSC-R1 @ ISO 1600||-2.1 EV||3.1 EV||5.2 EV|
|Canon EOS 350D @ ISO 100||-4.8 EV||3.3 EV||8.1 EV|
|Canon EOS 350D @ ISO 1600||-4.3 EV||3.3 EV||7.6 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 (actual range is calculated to sub-step fractions and using wedge calibration data).
The second part of the dynamic range story is of course the additional headroom available in RAW files. 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. Much experimentation lead us to eventually use Adobe Camera RAW for conversion with the settings show below to retrieve the maximum dynamic range from our test shots.
As you can see from the graph and wedges below Adobe Camera RAW in default mode actually returns a little less dynamic range because of its contrasty tone curve, this turns dark shadows to black much earlier than the camera would. The best we could achieve (with some pretty extreme ACR settings) was just over 10 stops total dynamic range, and more importantly about a stop more highlight range.
- ACR Default: Exp. 0.0 EV, Shadows 5, Bright. 50, Contrast 25, Curve Medium (Default)
- ACR Best: Exp. -1.35 EV, Shadows 0, Bright. 70, Contrast -50, Curve Linear
One thing to bear in mind is that although ACR was able to retrieve the 'luminance' (brightness) of wedge steps which were previously clipped there's no guarantee of color accuracy as individual channels may clip before others. (Note that the wedge below labeled as 'ISO 160' is of course a JPEG straight from the camera).