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.
Highlight Tone Priority
In common with many contemporary DSLRs, the 1D Mark IV has a highlight boosting feature, in this case Highlight Tone Priority (HTP). HTP reduces the amplification of the sensor by one stop, so that it takes one stop more light before it clips to white (and, as a result, you cannot select ISO 100 because this unamplified state is needed to provide HTP ISO 200). A new tone curve is then applied so that images still produce the same image brightness.
This one-stop reduction in amplification results in a raw file that is effectively push-processed by the new tone curve and would be underexposed if the normal tone curve were applied.
There's a downside, of course - that additional highlight dynamic range comes at the expense of greater shadow noise. It's also worth bearing in mind that not all RAW converters will implement the correct tone curve, so you risk all your images appearing underexposed until you've worked out your own 'push-process' workflow.
As we have previously seen the various Picture Styles use either one of two tone curves, the first more contrasty curve for Standard, Portrait, Landscape and Monochrome Picture Styles and a slightly flatter curve for Neutral and Faithful Picture Styles. Neither curve delivers more dynamic range and they both clip highlights at the same point.
The graph below shows how the camera's tone curve and dynamic range is affected by the wide range of contrast settings. The lowest contrast setting (-4) is almost linear for at least two thirds of the range and offers the widest dynamic range, but only by a whisker.
ISO Sensitivity and Dynamic Range
The EOS-1D Mark IV has an indicated base sensitivity of ISO 100 and the top setting by default is ISO 12,800 (A range from ISO 50 to 102,400 is available if you engage the additional steps using C.Fn I-3). ISO 50 is essentially the opposite of Highlight Tone Priority mode - the sensor amplification isn't changed but the exposure is, effectively over-exposing an ISO 100 shot. Unsurprisingly this means we see almost exactly 1EV reduction in its ability to capture highlight data.
Within its standard ISO range the 1D Mark IV produces very consistent highlight dynamic range figures, with the shadow range increasingly being eaten into by noise in the shadows. (The 102,400 curve plotted on the graph below shows an extreme example of this).
|Sensitivity||Shadow range||Highlight range||Usable range|
|ISO 50*||-5.2 EV||2.7 EV||7.8 EV|
|ISO 100||-5.1 EV||3.5 EV||8.6 EV|
|ISO 200||-5.1 EV||3.5 EV||8.6 EV|
|ISO 400||-5.2 EV||3.4 EV||8.6 EV|
|ISO 800||-5.1 EV||3.4 EV||8.5 EV|
|ISO 1600||-4.9 EV||3.5 EV||8.4 EV|
|ISO 3200||-4.9 EV||3.5 EV||8.4 EV|
|ISO 6400||-4.3 EV||3.5 EV||7.8 EV|
|ISO 12,800||-3.4 EV||3.5 EV||6.9 EV|
|ISO 25,600*||-2.7 EV||3.5 EV||6.2 EV|
|ISO 51,200*||-1.6 EV||3.4 EV||5.0 EV|
|ISO 102,400*||-1.3 EV||3.2 EV||4.5 EV|
* Non-standard sensitivities
Dynamic Range compared
The Nikon D3S is doing a better job of capturing highlight detail though the overall figure is the same, so you could theoretically set the 1D Mark IV to underexpose if you're willing to always process RAW files using your own tone curve. 3.5 stops above middle gray isn't a bad result by any means. It's only the combination with slightly over-keen metering that might make it occasionally noticeable.
|Canon EOS 1D MkIV (ISO 100)||-5.1 EV||3.5 EV||8.6 EV|
|Nikon D3S (ISO 200)||-4.7 EV||3.8 EV||8.5 EV|
|Canon EOS 7D (ISO 100)||-4.9 EV||3.3 EV||8.2 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 files have an inherently wider dynamic range than JPEGs, because the date that they contain has a greater bit depth. What this means in practice is that careful processing of a raw file will reveal a lot more tonal information in the brightest and darkest areas of a scene than an equivalent JPEG. This allows you to rescue poor exposures more effectively, and - should you want to - you can also combine different versions of the same raw file to create composite images with a broad tonal range. Making extreme brightness adjustments to JPEGs is generally a bad idea, since it compresses the number of tones in the image (which is less than a raw file in the first place) and can lead to banding and false colors.
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.
- ACR Default: Exp. 0.0 EV, Blacks 5, Contrast +25, Curve Medium
- ACR Auto: Exp. -0.75 EV, Recovery 7, Blacks 0, Brightness 0, Contrast 0, Curve Linear
- ACR Best: Exp. -0.9 EV, Blacks 0, Brightness +100, Contrast -50, Curve Linear
|ACR Default||7.2 EV|
|ACR 'Best'||12.0 EV|
These figures don't directly tell you how much dynamic range you can capture in a conventional exposure (the results would look pretty flat, dull and risk featuring strange colors in the highlights), but give an idea for how flexible the raw files are. Below we try to give an idea for how much extra highlight detail can be recaptured.
When experimenting with some files shot in daylight conditions, we found that once the green channel had clipped in the JPEGs, then highlight recovery was impossible from a file exposed 0.33EV more (there's less that 0.33EV headroom above what's in the JPEGs in daylight). However, in the red channel we were able to recover highlights from a file exposed 1EV beyond the point where the channel had clipped in the JPEGs. This disparity means that you can expect to recover around 1EV of detail in the highlights but that color accuracy is likely to drop off after as little as 0.33EV if the green channel has clipped.
|JPEG version||Adobe Camera RAW with -2.0 EV digital comp.|
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