JPEG Tone Curves / Dynamic Range
Our 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 clipped white point down to black (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' (defined as 50% luminance) 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 above middle gray the camera can capture before it clips to white. Shadow range is more complicated; in our test the line on the graph stops 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.
The X-Pro1's default tone is identical to the X100's, and offers a decent highlight range of about 3.7 stops, with just enough of a roll-off into the highlights to prevent harsh-looking clipping. This places it only marginally behind the likes of the Nikon D7000 and Sony NEX-7, even before you take into account its extended dynamic range settings.
The X-Pro1's colour Film Simulation modes show subtly different tone curves, which translate into visible real-world differences. Velvia/Vivid is very contrasty indeed, clipping more abruptly to both white and black, while Astia/Soft echoes Provia/Standard across the highlight range but is more contrasty below middle grey, resulting in somewhat deeper shadows. The Pro Neg Hi mode lies somewhere between Velvia and Astia in terms of its shadow contrast, while Pro Neg Std closely matches Provia/Standard. Likewise, the various Monochrome modes all match Standard exactly.
Dynamic Range Expansion Modes
The X-Pro1 has two dynamic range expansion settings to bolster its highlight range: DR200 (200%) adds an extra stop of information in the highlights, and DR400 (400%) adds two stops. Technically, the camera achieves this by applying less amplification to the sensor's output than usual prior to AD conversion to avoid clipping highlight data, then pulling-up the midtones to the correct brightness in JPEG processing. This is essentially the same process as Canon and Pentax use for their highlight-expansion modes.
An alternative way of thinking about this is that DR200 is like underexposing a stop to retain highlights then adjusting the brightness afterwards, and DR400 is like underexposing by two stops and adjusting further. Because of this, the minimum ISO available in each mode is limited: ISO 400 at DR200, and ISO 800 at DR400. The flipside to this approach is shown by ISO 100, which is effectively the opposite; i.e. ISO200 overexposed by a stop then pulled-down in processing. This results in the loss of stop of highlight range - to all intents and purposes it counts as DR50, and should therefore normally be avoided. (Note ISO 100 is only available in JPEG anyway).
In this comparison we can see the impact the DR setting has on highlight range. DR200 offers a huge 4.7 stops of highlight range, and DR800 goes another stop beyond this, disappearing off the scale of our graph. Note that this advantage isn't just for JPEG shooters - it extends to RAW files too. On paper at least this is very impressive indeed; we'll see how it translates into real-world results later in the review.
Shadow and Highlight Tone controls
Unusually, rather than having a single 'Contrast' or 'Tone' control, the X-Pro1 allows you to tweak Highlight Tone and Shadow Tone completely independently around a fixed point of middle grey. Each control offers 5 settings, and here we're comparing Normal (as used in the comparisons above) to the two extremes, Soft and Hard. Naturally the Highlight Tone control interacts with the DR setting, so first we'll look at DR100. In the graphs 'N-N' means Shadow and Highlight Tone are both set to Normal; S denotes Soft and H denotes Hard.
Here we can see that the Highlight Tone control technically has no effect on the white point of the image, and just on the contrast, although the H setting attempts to compress the brightest 0.7 stop of dynamic range into such few levels that visually it will appear to clip earlier. Meanwhile the Shadow Tone setting gives a wide range of control over the openness of the darker regions of the image.
Switch the DR setting to 400% and it's much the same story, only more pronounced. Now setting the highlight tone to Hard results in earlier clipping according to our measurement tool, effectively throwing away much of the benefit of that expanded range. The results in the shadow range are, as expected, essentially identical to those at DR100.
The adjustments offered by these controls are large compared to the differences between the film modes, and in principle this allows you to tailor the camera's JPEGs very specifically to your taste. For example, if you like the colour of Velvia but find it too contrasty and prone to highlight clipping, then you can tame it by softening the Highlight Tone.
However there's a catch - the tone adjustments are universal, and any change is applied to all of the film modes. One way around this is to save your preferred options to one of the cameras 'Custom Settings', which can then be recalled through the Shooting menu. But then there's another catch; these also include ISO and DR settings.
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