Dynamic Range Expansion
The X100 has two dynamic range expansion settings to bolster its already-decent highlight range. The DR200 (200%) setting adds an additional stop of information in the highlights, and DR400 (400%) adds two stops. However the minimum ISO available in each mode is limited to ISO 400 at DR200, and ISO 800 at DR400. Like ISO, DR is set individually for each exposure mode, so if you switch from aperture priority to manual your settings are likely to change in an infuriating fashion.
For raw shooters, using DR200 will give the the same image data as underexposing a DR100 shot by one stop, and DR400 will be the same as underexposing DR100 by 2 stops. The raw files will however have different metadata reflecting the exposure intent, which with any luck will be recognized by your favorite raw converter (although this isn't yet the case with ACR 6.4). The embedded review image should also be closer to your intended output, and the image histogram with it.
The interaction between the ISO and DR settings is complicated. When setting the ISO manually, it takes priority over Dynamic Range: if you have DR set to 400% and drop the ISO, the X100 will successively reset DR back down to 200% at ISO 400, and 100% at ISO 200 (and highlight these changes in yellow in the viewfinder). This means that on bright, contrasty days you can set the DR to 400%, then use the ISO control as a proxy for changing the DR setting. The flip-side of this prioritization, though, is that the camera won't let you set the DR above the highest available at the currently-used ISO, so to set DR400 you have to first turn the ISO up to 800 or higher.
When using Auto ISO, the situation is a little different. In this case the camera will prioritize the DR setting over the manually-set ISO (which it normally uses as the preferred minimum). So if you have DR set to 400% and the ISO to 200, switching on Auto ISO will cause the camera to switch to ISO 800.
The X100 also has an Auto DR option that presumably attempts to analyse the contrast of the scene and set the DR automatically. This works best when used in conjunction with Auto ISO, as it (obviously) can't access the higher DR settings if the ISO is fixed at 200. Unfortunately the camera doesn't inform you of the DR setting it's planning on using before you take the shot; you can only see this in play mode afterwards.
|DR100 (ISO 200)||DR100, 100% crop, highlight region|
|DR200 (ISO 400)||DR200, 100% crop|
|DR400 (ISO 800)||DR 400, 100% crop|
This set of shots illustrates the benefits of DR expansion. The highlight regions at DR100 are clipped, but progressively more detail is recorded in the highlights as the DR setting is raised. The differences can appear pretty subtle, though - partially because Fujifilm is using a global tone curve adjustment and local contrast in the highlights is distinctly low. However the highlights obviously aren't the whole story, and the DR setting has an impact on the rest of the image too.
|DR100 (ISO 200), 100% crop, midtones||DR100, 100% crop, shadow region|
|DR200 (ISO 400), 100% crop, midtones||DR200, 100% crop, shadow region|
|DR400 (ISO 800), 100% crop, midtones||DR400, 100% crop, shadow region|
This set of crop demonstrates the flipside of the coin; increasing the DR requires the ISO to be increased too, and the image inevitably gets noisier at higher ISO settings, especially in the darker regions. The subtle tonalities and fine low-contrast detail of the orchid are also progressively lost as the ISO increases. As always, which rendition to choose is very much a matter of personal preference.
What's going on under the hood - RAW comparison
Just to give a little more insight into how DR expansion works, we've looked at the raw files to show both how much additional highlight information is being captured, and how well it's being translated into the camera's JPEGs.
As it happens Adobe Camera Raw 6.4 doesn't yet understand the X100's DR settings, and develops these extended DR raw files simply as if they were ISO 200 underexposed by 1 or 2 stops. The results are shown below - it's easy enough to see where the additional highlight detail in the JPEGs has come from, but also quite striking how little of it is genuinely used. Indeed even at base ISO ACR does a better job of rendering highlight detail than the camera's JPEG engine, and there's very much more detail in the DR200 raw file than actually makes it to the JPEG output.
|DR100 (ISO 200), RAW + ACR||DR100, 100% crop, highlight region|
|DR200 (ISO 400), RAW + ACR (-1 EV)||DR200, 100% crop|
|DR400 (ISO 800), RAW + ACR (-2 EV)||DR 400, 100% crop|
In practice, what this means for raw shooters is that using DR200 in particular can work effectively as a kind of highlight insurance policy in contrasty situations, ensuring that highlight detail is retained in the raw files without having to employ exposure compensation to bias the metering. The usefulness of DR400 in raw is less clear-cut - it's just not that often that you really need so much highlight range.
Raw highlight recovery
One of the advantages of shooting in raw is that you can often recover a bit more highlight detail beyond the point that the camera's JPEGs clip to white. As shown in the examples above, this is particularly the case when using the X100 at its higher DR settings.
There's not, however, a huge amount of highlight detail to be recovered from the X100's standard DR100 raw files at low ISOs. This is shown in the example below (compare it to the DR200 raw conversion shown above). There's a a little more detail in the petal, and certainly more than can be obtained by trying to recover highlights from the camera JPEG, but nothing like as much as you can get from reducing the exposure. The same story holds true across other overexposed regions, such as the blue sky.
|ISO 200 DR100, RAW + ACR||100% crop|
|ISO 200 DR100, RAW + ACR, -1 EV||RAW + ACR, -1 EV, 100% crop|
|ISO 200 DR100, JPEG, -1EV||JPEG, -1 EV, 100% crop|
High ISO highlight recovery
One interesting technical quirk of the X100's operation (that's completely transparent in normal use) is the way it implements its highest ISO settings. At sensitivities above 1600 it stops applying any further gain to the signal read from the sensor prior to A/D conversion and writing the raw file, and instead increases the final image brightness simply by applying a different tone curve to the raw data.
This has a couple of interesting practical consequences. For raw shooters, it means that ISO 3200 and 6400 files will retain essentially the same image data as ISO 1600 underexposed by 1 and 2 stops respectively. The advantage here is that highlight data which would otherwise be clipped is still present, and the raw files therefore have correspondingly more highlight headroom and recovery potential. This is illustrated below.
|ISO6400, RAW + ACR||RAW + ACR, 100% crop|
|ISO 6400, RAW + ACR, -1 EV||RAW + ACR, -1 EV, 100% crop|
|ISO 6400, RAW + ACR, -2 EV||RAW + ACR, -2 EV, 100% crop|
This ISO 6400 image has lots of blown highlight detail, but applying progressively more negative exposure compensation during raw conversion recovers it with full colour detail. This is visible in the 100% crop above, and holds true across all of the other highlight regions of the image too. For raw users this means there's often plenty more information to work with than is captured in jpegs.
For JPEG shooters this also helps explain why there's no noise penalty for using extended DR settings at high ISOs. At ISO 6400 all three DR settings are derived from exactly the same raw data - the lower DR settings essentially just discard highlight information during JPEG processing.
It's important to appreciate that there's nothing underhand about what Fujifilm is doing here. The 'traditional' method of producing high ISOs by increasing the gain is used purely to minimize the impact of the noise that's added to the image data by the camera's electronics. It appears the Fujifilm has reached the conclusion that beyond ISO 1600 there's no further benefit to be gained - at which point it makes perfect sense to retain highlight data instead.
Overall Image Quality / Specifics
Overall, the X100's image quality is little short of superb. Exposure and white balance are both well-judged, and noise is extremely well-controlled. If you want punchy, saturated colour you can use the Velvia mode, but we found ourselves most drawn to Astia for its well-balanced, natural colour and lovely skin tones. The X100 is particularly notable also for its ability to retain rich, attractive colours at high ISO settings where many of its potential competitors struggle (particularly the current round of compact Micro Four Thirds cameras). Even ISO 6400 returns remarkably useable results.
In fact the X100's image quality is so good that finding flaws becomes a process of nit-picking at the extremes of its capabilities. At the very highest ISOs - 6400 and 12800 - you can occasionally encounter some horizontal banding, especially under low-colour temperature artificial lighting (which requires the blue channel of the image to be highly amplified to achieve an acceptable white balance).