The actual sensitivity of each indicated ISO is measured using the same shots as are used to measure ISO noise levels, we simply compare the exposure for each shot to the metered light level (using a calibrated Sekonic L-358), middle gray matched. We estimate the accuracy of these results to be +/- 1/6 EV (the margin of error given in the ISO specifications). In our tests we found that measured ISOs from the Sony DSC-RX100 II were undersensitive by 1/3 stop, meaning ISO 160 indicated = ISO 125 measured.
Noise and Noise Reduction (JPEG)
The RX100 II's JPEGs are rendered with very little noise at low ISOs, with incremental increases until ISO 3200. The new BSI sensor appears to be doing its job, as an ISO 3200 shot from the RX100 II looks about the same as an ISO 800 shot from the RX100 in terms of noise, though rendering of detail in the test shot shows that the ISO 3200 shot looks more smoothed out. The Canon G1X, with a slightly larger sensor, shows its size with noticeably better detail rendering than either Sony camera at ISO 800 and above.
ACR RAW noise (ACR, noise reduction set to zero)
Detail rendered from the RX100 II in our ACR Raw noise comparison looks about as expected. At ISO 200 there's a good deal more fine detail in the RX100 II's image than the X20's, but the RX100 II doesn't fare as well as the Olympus E-M5 O-MD. The chart shows about a half stop advantage to the RX100 II over the RX100, though it's difficult to spot the difference visually in the images of the color chart.