The actual sensitivity of each indicated ISO is measured using the same shots as are used to measure ISO noise levels, we simply compare the exposure for each shot to the metered light level (using a calibrated Sekonic L-358), middle gray matched. We estimate the accuracy of these results to be +/- 1/6 EV (the margin of error given in the ISO specifications). Note that these tests are based on the sRGB JPEG output of the cameras, in accordance with ISO 12232:2006, the standard used by camera manufacturers.
By our tests, the X100's measured sensitivities are about 1/6 stop lower than indicated (i.e. images are fractionally darker than expected for any given set of exposure values), which is within the tolerance allowed by the ISO specification.
Noise and Noise Reduction (JPEG)
Note: this page features our new interactive noise comparison widget. By default, we show you the default noise reduction settings of the camera tested, and three other models of the same class. You can select from all available NR options, and from other cameras. The 'tricolor' patches beneath the familiar gray/black/portrait images are taken from the same test chart, and show how noise impacts upon blue, green and red areas of a scene.
ISO range noise comparison
The X100 does extremely well in these tests, giving remarkably detailed, low-noise images across almost all of the ISO range. Image detail only starts to visibly deteriorate at ISO 3200, and even at ISO 6400 the results are pretty impressive. At the maximum JPEG-only sensitivity of ISO 12800, detail and colour saturation are both visibly degraded.
In comparing to the other cameras in this group, it's important to bear in mind that the Nikon D7000's ISOs are underrated by about 1/3 stop, making a total half stop difference compared to the X100 (the X1 and E-PL2 are, however, within 1/6 stop of the X100). Despite this the X100 holds up extremely well against the competition, producing cleaner, more detailed results than the Leica X1 at all ISOs, and pulling visibly ahead of the Olympus E-PL2 in terms of fine, low-contrast detail at ISO 800 and above. It's at least a match for the Nikon D7000 across the range too, despite its older sensor design. Very, very impressive.
JPEG Noise reduction settings
The X100 has five JPEG noise reduction settings - here we compare the weakest and strongest to the default 'Normal' setting. There's little visible difference at ISO 100 and 200, but at ISO 400 and above the NR settings have a progressively larger impact. The settings on offer cover a useful range of tradeoffs between fine detail and visible noise: we actually think that the Normal setting is very well-judged, but if you want less noise at the expense of fine detail, or more detail but a grittier, noisier image, the option is there.
Effect of DR setting on measured noise
The X100 has two dynamic range expansion settings to increase its highlight range; DR200 (200%) adds a stop of information in the highlights, and DR400 (400%) adds two stops. However because of the way they work these expanded DR settings can't be used across the full range of ISOs; DR200 is only available at ISO 400 and above, and DR400 at ISO 800 and above. We'll dissect this in detail later, but in this section we'll first take a quick look at their effect on JPEG noise levels.
What's striking on looking at these tests, either the graphs or the crops, is that the expanded DR settings have to all intents and purposes no noise penalty at any given ISO; all the available DR settings measure identically, and more importantly the image crops are visually indistinguishable. For chroma and grey noise at least this is absolutely expected; for black noise it's a sign that Fuji has got read noise (i.e. the noise added to the image by the camera's electronics) under good control.
This isn't quite the whole story, though. Because noise inevitably increases with ISO, it's still the case that using DR100 at ISO 200 will a result in cleaner image than DR200 at ISO 400 or DR400 at ISO 800. Free lunches, as always, are in short supply.
RAW noise (ACR 6.4 - noise reduction set to zero)
Here we look at the RAW files processed through Adobe Camera Raw (in this case version 6.4). Images are brightness matched and processed with all noise reduction options set to zero.
Adobe does a degree of noise reduction even when the user-controlled NR is turned off. The amount of NR applied 'under the hood' is not high, but it does vary by camera (Adobe is attempting to normalize output across different sensors), so inevitably we are still looking at a balance of noise and noise reduction, rather than pure noise levels. However, the use of the most popular third-party RAW converter is intended to give a photographically relevant result, rather than simply comparing sensor performance in an abstract manner.
The similarity of both the figures and the appearance of these crops suggests they tell us as much about Adobe's ability to normalize the various cameras' outputs as about the cameras themselves. The X100 won't record raw files at ISO 100 and 12800, but across the available ISO range it's producing excellent results, with impressively low visible noise and high levels of detail retention. It does notably better than either the Olympus E-PL2 or Leica X1, producing results to rival the Nikon D7000. Switching to graph view simply confirms its low-noise credentials.