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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 camera's) 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.

All the D90's tests have been conducted with D-Lighting set to off, even though the default setting is 'Normal.' The affects of Active D-Lighting are assessed on the next page.

Picture Control presets

The graph below shows the dynamic range response from each of the D90's five Picture Style settings. Each has a slightly different response curve, with Vivid offering the most contrast and Neutral giving the least. The Standard setting treads a careful line between these two extremes, offering quite high contrast in the shadows and a more gentle curve for the highlights. Shooting in Adobe RGB (not shown), gives the same response as the Standard setting.

Contrast settings

The graph below shows how the camera's tone curve and dynamic range is affected by the (admittedly small) range of contrast settings. Whilst the standard/default setting offers the most pleasing 'out of camera' results you can eke a little more (by which we mean maybe a third of a stop) out of the shadows by opting for the flatter -3 setting.

ISO Sensitivity and Dynamic Range

The D90's sensor has a native sensitivity of ISO 200, with ISO 100 equivalent available by using the Lo 1 setting. The dynamic range of Lo 1 has almost exactly one stop less dynamic range in the highlight regions, which is what you'd expect from what is essentially an ISO 200 image overexposed by a stop.

Beyond ISO 1600 the dynamic range figures appear to extend in the shadow regions. This is because our dynamic range test measures the shadow range when the dark areas reach a luminance level near black (or when they become too noisy), in these instances, we suspect the noise reduction is creating a dark gray blur such that our analysis tool doesn't recognise it as noise or as being close enough to black to stop measuring. As such we assume the values are in the region of those recorded at lower ISO settings.

Sensitivity Shadow range Highlight range Usable range
ISO 100 (Lo 1) -4.6 EV 3.0 EV 7.6 EV
ISO 200 -4.4 EV 3.9 EV 8.3 EV
ISO 400 -4.8 EV 3.9 EV 8.6 EV
ISO 800 -4.5 EV 3.9 EV 8.4 EV
ISO 1600 -4.8 EV 3.9 EV 8.4 EV*
ISO 3200 -5.4 EV 3.9 EV 8.4 EV*
ISO 6400 (Hi 1) -7.7 EV 3.7 EV 8.2 EV*

*Usable range assuming shadow range figure remains at ISO 800 levels

Dynamic Range compared

Looking at the usable range figure might give the impression that the D90 is lagging behind its competitors but its the ability to retain highlight detail that tends to define the perception of dynamic range. Images are rarely ruined by shadow areas clipping to black a little early (though not doing so provides more to work with if you want to post-process and retrieve shadow detail), but bleached-out white skies are much more disconcerting and noticable. Because of this, the Nikon's very impressive 3.9 stops of detail above middle gray are more important. And, at default settings (With Active D-Lighting set to 'Normal'), the shadow range increases to -4.8, giving an overall figure of 8.8 EV dynamic range.

Camera
Shadow range
Highlight range
Usable range
Nikon D90 (ISO 200) -4.4 EV 3.9 EV 8.3 EV
Canon EOS 450D (ISO 100) -4.9 EV 3.7 EV 8.6 EV
Pentax K20D (ISO 100) -5.8 EV 3.2 EV 9.1 EV
Nikon D80 (ISO 100) -4.8 EV 3.2 EV 8.0 EV
Sony A700 (ISO 200) -4.9 EV 3.9 EV 8.8 EV
Sony A350 (ISO 100) -4.9 EV 3.7 EV 8.6 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 (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. As with previous reviews we settled on Adobe Camera RAW for conversion to retrieve the maximum dynamic range from our test shots.

As usual the default Adobe Camera RAW conversion delivers less dynamic range than JPEG from the camera (a more contrasty tone curve and very little noise reduction in shadows). Simply switching to 'Auto' in the ACR conversion dialog produces some benefit (we measured the result to have 9.7 stops of dynamic range), though the images risk looking a little flat. This test is not intended as a measure of the maximum dynamic range of the sensor, but a demonstration of the level of additional information that can be incorportated into an image. To show that this doesn't involve pushing an image to an unrealistic extent, we have processed a shot with the settings that ACR's Auto setting applied to our test shot (Exp. -0.95EV, Recovery 0, Contrast 0, Linear curve).

  • ACR Default: Exp. 0.0 EV, Blacks 5, Contrast +25, Curve Medium
  • ACR Auto: Exp. -0.95 EV, Recovery 8, Brightness 0, Contrast 0, Curve Linear

Jpeg output Adobe Camera RAW




The cut-off point of the D90's default tone curve appears very conservative, clipping everything to white at a point that it is still capturing color detail. This is made noticable as the camera's metering seems a bit too happy to let highlights into this area. All this means the raw files contain additional detail that can be pulled back and re-worked into your image (or brought back in using a 'highlight recovery' option in software). Moving exposure compensation down to -2EV continues to reveal additional detail, though beyond -1EV, the likelihood of color accuracy being maintained drops off.

Using your own tone curve (or the Active D-Lighting option), can help incorporate some of this additional highlight detail into your images but even if you don't want to go to that extent, you can be sure there is additional information to call on if you want to recue or get the best out of a specific image.

Adobe Camera RAW default conversion Adobe Camera RAW with -2.35 EV digital comp.

 

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