We have previously had a couple of attempts at measuring dynamic range. One of the biggest issues is coming up with a test which can reliably give a good approximation of the available dynamic range from a single shot. Our new test 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.
UPDATE: 18 February 2006
Here at dpreview we are constantly refining our testing procedures, we now have a fully automated method for measuring Dynamic Range, this now gives us a far more accurate measurement of the 'best case' dynamic range based on the clip point and the point at which there is no more useful shadow information (either below a luminance threshold or because of noise). The following two pages have now been updated using our new DR measurement system.
How to talk about and measure Dynamic Range
Throughout the production of this part of the review we worked hard on developing a logical way to measure, represent and explain dynamic range. Because we chose to use middle gray as our starting point we were left with 'two sides' to our results, the amount of shadow range (below middle gray) and the amount of highlight range (above middle gray). Note that we only show shadow range to -6.00 EV on our graphs but we can actually measure to approximately -7.73 EV.
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).
Image Parameters and Dynamic Range
As we have already discussed the EOS 5D uses different tone curves depending on the Picture Style selected. The first is slightly more contrasty ('punchy') and appears to be used in Standard, Portrait, Landscape and Monochrome Picture Styles, the second more neutral and essentially identical to the 'all zeros' option on previous Canon digital SLR's is used by Neutral and Faithful Picture Styles.
The graph below shows the difference between these two tone curves as well as the option which should provide you the most dynamic range ('best case') in a JPEG shot (Neutral Picture Style with Contrast -4). As you can see the primary difference between the two Picture Style tone curves is in handling of highlights (anything above middle gray). The 'best case' option of the Contrast -4 setting will help to lift shadow detail and produce a flatter (less compressed) highlight response, it extends highlight range just slightly (the difference is minute).
ISO Sensitivity and Dynamic Range
As noted in previous Canon digital SLR reviews the 'ISO 50' (L) option is a special 'out of range' feature for very low noise shooting, its downside is limited highlight range as demonstrated here. ISO 50 clips highlights about 1.0 EV (one stop) earlier than ISO 100. At higher sensitivity of course noise becomes the issue, at ISO 1600 noise nudges the our measurement of shadow range down by 0.3 EV (a third of a stop), this difference would seldom be noticeable unless you 'lifted the shadows' in post-processing.
- Image format: JPEG
- Picture Style: Standard
Dynamic Range compared (JPEG)
Having now re-run our tests using our new measurement system we have a better representation of the usable DR for each camera. All four cameras here deliver around 8.2 EV of dynamic range, the primary difference between the Canon cameras and the Nikon D2X tone curve delivers less highlight range (above middle gray) but slightly more shadow range. The D2X also has a harder edge to highlights with a virtually linear 'curve' from middle gray onwards.
Note that we used the 'Auto Tone' setting on the D2X as this is the camera default. Use of the 'Normal Tone' produced exactly the same highlight range but less shadow range; see this graph.
|Camera (ISO 100)
|Canon EOS 5D
|Canon EOS-1Ds Mark II
|Canon EOS 20D
- Nikon D2X: Auto Tone
- Canon EOS 20D: Parameter 1
- Canon EOS-1Ds Mark II: Standard
- Canon EOS 5D: Standard Picture Style
The wedges below are created by our measurement system from the values read from the step wedge, the solid red lines indicate measured shadow and highlight range (dotted line is middle gray).