Signal to noise ratio is a measure of the amount of random noise in the photo relative to real image data. The higher the signal to noise ratio the better – it means less noise will be visible.
JPEG signal to noise ratio: Interestingly, the Leica SL is one of the worst performers for noise in JPEG images, though studying real-world photos suggests this is a deliberate decision to limit any noise reduction and preserve fine detail.
Raw signal to noise ratio: The Leica SL's raw files are still slightly noisier than those of the Sony A7 II and Nikon D4S, but the gap is much closer. The Sony A7R II comes in last, paying the price for its high resolution and hence smaller photosites.