Raw Dynamic Range

Exposure Latitude

In this test we look to see how tolerant of pushing exposure the RX100 IV'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 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 stead, so this test gives you an idea of the amount of processing latitude different formats give.

*The RX100 IV hasn't been shot at the shutter speeds shown on the pull-down menu because the aperture was held wider-open, to give better sharpness. The total exposure (taking into account aperture and shutter speed), is the same though.

Sony's sensor designs contribute very low levels of noise, which means highly 'pushable' Raw files. There isn't any major difference between the I and the IV, in this respect. They both cope relatively well with a five stop push, which is impressive for a small 1"-type sensor. Compare to the Nikon 1 J5 and the Sony appears to be adding less noise.

Again, in this test (as in the real world), larger sensor cameras will show less shot noise, such that a larger-sensor camera that contributes similarly little electronic noise to its images will still look better than the RX100 IV will. This is the case with the Nikon D5500. However, the RX100 IV's result is good enough that it can out-perform a larger sensor that is adding electronic, read noise, such as the Canon Rebel T6i/750D.

The interesting thing about the RX100 IV is what happens when the camera automatically will switch on its electronic shutter (at a high shutter speed or in continuous shooting modes). Having a camera do this automatically typically would be a worry. As we can see on the Panasonic G7, the fully electronic shutter has a DR cost. The RX100 IV, however, faces no penalties for making the switch, which means there are no worries in letting the camera decide when it will use a fully electronic shutter.

ISO Invariance

A camera with a very low noise floor is able to capture a large amount of dynamic range, since it will add very little noise to the detail captured in the shadow regions of the image. This has an interesting implication: it minimises 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) and digitally correcting the brightness, later.

As you can see on the left: there's no visual difference between shooting at ISO 1600, compared with using the camera's base ISO (125) and digitally pushing. Why does this matter? Well, for a start, it shows that the sensor is contributing very low levels of downstream read noise, which is impressive in itself. But it also opens up the option to use the shutter speed and aperture value you'd usually use for ISO 1600, while staying at ISO 125 and using a much lower level of amplification, and then selectively brightening your image later. Using a lower level of amplification means that highlight detail is less likely to get over-amplified and blown-out.

On many cameras this can be an awkward way of working, because it can mean trying to operate with a very dark screen (because the camera thinks you're under-exposing by 3.7 stops - not realising you plan to brighten the image later). But on the RX100 IV you can employ the ultra-flat S-Log2 gamma curve from the Picture Profile menu. This super-flat tone curve ends up representing relatively dark captured tones as mid-tones, which allows you to see the wider dynamic range the camera and our eyes are capable of. For example, the scene below traditionally yields plugged up shadows in the foreground on the back of your LCD; hover over 'S-Log2' to get a preview of what you see when enabling this mode.

Picture Profile: Off
S-Log2 Graded

On the plus side, this way of working will also prompt your camera to use the exposures you'd expect from ISO 1600, but with low levels of amplification behind the scenes (in fact it could almost be made for this way of working). This gets you somewhere between 3 and 4 EV additional highlight detail, which you'll immediately see in retained sunset skies, for example, when you enable Picture Profile with S-Log2 gamma. Furthermore, you'll essentially get a Raw file that's exposed for the highlights, and a JPEG that has a lot of detail from shadows to highlights, which you can even 'grade' later by adding some contrast to (see 'S-Log2 Graded' above). This, of course, is what movie shooters do when shooting high contrast scenes, but we also find this way of shooting useful for capturing Raw stills exposed for the highlights, since these exposures conventionally yield previews on the back of the camera screen that are far too dark to be of use in composing and executing your shot.

One potential drawback of enabling S-Log2, however, is that applying a flat gamma curve can make autofocus less reliable, as the lower contrast output makes it harder for the camera's contrast detection AF system to obtain focus.