Raw Dynamic Range

Exposure Latitude

In this test we look to see how tolerant of pushing exposure the X-Pro2's Raw files are. We've done this by exposing our scene with increasingly lower exposures, then pushed them back to the correct brightness using Adobe Camera Raw. Examining what happens in the shadows allows you to assess the exposure latitude (essentially the dynamic range) of the Raw files.

Because the changes in this test noise are primarily caused by shot noise and this is mainly determined by the amount of light the camera has had access to, the results are only directly comparable between cameras of the same sensor size. However, this will also be the case in real-world shooting if you're limited by what shutter speed you can keep steady, so this test gives you an idea of the amount of processing latitude different formats give.

It's widely assumed that Fujifilm's X-Trans sensors use low-noise Sony silicon behind their unusual color filter arrays, and the performance of the X-Pro2 is certainly up to that standard. Compared here with the Nikon D5500 (using the same shutter speeds so that they are working with the same amount of light), you can see very similar amounts of noise up to a 4EV push, and possibly a fraction more after a 5 stop push, though the difference may simply be one of grain structure, caused by the different demosaicing processes.

This performance gives plenty of flexibility when it comes to pulling extra tonal information out of the shadows. It means there's more scope for processing than with the likes of the Canon EOS 70D, and very similar to the results of the Samsung NX1.

This test doesn't tell the whole story in terms of dynamic range: the lower ISO ratings of some cameras may mean that they can tolerate more light before over-exposing the highlights, and hence will produce cleaner shadows in real-world shooting. Without a saturation-based test, we're just looking at the response of shadows to the same exposure.

On further investigation of the Raw files' saturation point, we found that the X-Pro2's ISO 200 Raw files clip sooner than the Sony a6300's ISO 100 files, suggesting that the X-Pro2's base ISO is applying more analogue amplification than the Sony's is. This means it has slightly less dynamic range than the Sony at base ISO.

ISO Invariance

A camera with a very low noise floor is able to capture a large amount of dynamic range, since it add very little noise to the detail captured in the shadow regions of the image. This has an interesting implication: it minimizes the need to amplify the sensor's signal in order to keep it above that noise floor (which is what ISO amplification conventionally does). This provides an alternate way of working in situations that would traditionally demand higher ISO settings.

Here we've done something that may seem counter-intuitive: we've used the same aperture and shutter speed at different ISO settings to see how much difference there is between shooting at a particular ISO setting (and using hardware amplification) vs. digitally correcting the brightness, later. This has the advantage that all the shots should exhibit the same shot noise and any differences must have been contributed by the camera's circuitry.

As you can see, there's essentially no difference between shooting at a high ISO and using a lower ISO and pushing the file later. This not only suggests the sensor is adding very little downstream read noise, it also opens up the option to use the shutter speed and aperture value you'd usually use for a high ISO shot, while staying at a low ISO to use a much lower level of amplification. Using this lower level of amplification means that highlight detail is less likely to get over-amplified and blown-out.

It's exactly this behavior that the camera's DR modes exploit: they give you the choice of using one of three different exposure/amplification balances (one each for DR100%, 200% and 400%), that use lower levels of amplification to position captured tones further down the Raw file, meaning more highlight detail is retained.

For instance: take three shots at ISO 800 (using the same exposure settings), one at DR100%, one at DR200% and one at DR400% and you'll see the results. Despite pulling tones from further down the Raw file, they'll have the same noise level (because almost all of the noise is coming from shot noise, which is defined by exposure), but the DR400% image will have more highlight detail.

In bright situations, the same behavior looks slightly different. If you're at base ISO in bright light and switch to DR200%, the camera halves the exposure (which you'll see as a jump in the lowest available ISO setting) but leaves hardware amplification the same, brightening the image later while incorporating that extra stop of highlight information (essentially using a flatter JPEG tone curve). Shifting to DR400% does this again: another 1EV drop in exposure without a change in amplification, to protect an extra stop of highlight information.

For a more complete explanation of what's going on, read our article about in-camera DR modes.

Electronic Shutter

In the right-hand column you can see that the electronic shutter shot pushed by 4EV has a little more noise than the image shot with the mechanical shutter - suggesting it's contributing additional read noise but that a very small amount, such that it only becomes visible in heavily pushed dark tones.