Real-world Image Quality (JPEG)
The X100S is a lovely little camera which turns out very pleasing images. Like its predecessor, exposure and white balance are generally spot on, colors are lovely (and of course you the film simulation modes are on hand if you want to achieve a specific look) and dynamic range expansion is very effective when it comes to balancing contrasty scenes, thanks in part to the X-Trans sensor's low noise.
This sensor isn't new - we've seen it before in the X-Pro1 and X-E1 and it impressed us in both cameras. Like its interchangeable-lens brethren the X100S delivers very good resolution, low noise and excellent dynamic range. The addition of phase-detection AF pixels has no discernible impact on image quality, and we're just as happy with the pictures produced by the X100S as we are the results we've seen from earlier X-series cameras.
Good Light, Low/Medium ISO
Between ISO 200 and 800 the X100S delivers images which contain effectively no visible noise. This, coupled with the inclusion of a 3-stop ND filter means that it is entirely possible to shoot at ISO 800 outdoors in bright daylight for the sake of better dynamic range (see DR expansion modes section on the next page). In our everyday shooting we alternate between DR200% and 400% in especially tricky conditions, and we've learned not to worry about the consequent increase in 'base' ISO.
As you can see from the examples on this page and in our studio comparison, the X100S is capable of superb image quality which compares very well against its more conventional 16MP peers. With a bit of practise, and with judicial use of film modes and dynamic range expansion settings (both of which can - within some limits - be applied to raw files post-capture using in-camera Raw conversion) it is possible to get results from the X100S which are nothing short of stunning.
Low Light, High ISO
It's hard to say definitively that the X100S gives 'better' image quality than the X100 at low ISO sensitivities (the improved AF speed and operational refinements are without doubt the main reasons to buy the newer camera over its predecessor) but at high ISO settings, the X-Trans sensor is definitely superior to the X100's 12MP CMOS, both in terms of detail capture (there's more) and noise (there's less).
As you can hopefully see from the examples above, the X100S produces very clean results at high ISO sensitivity settings, which contain plenty of detail. You'll find more examples on the image quality comparison and Raw pages of this review (and of course in our sample galleries at the end).