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). Note that these tests are based on the sRGB JPEG output of the cameras, in accordance with ISO 12232:2006, the standard used by camera manufacturers. In our tests we found that measured ISOs from the GX7 match the marked ISOs within 1/6 stop accuracy, meaning ISO 200 indicated = ISO 200 measured.
Noise and Noise Reduction (JPEG)
ISO range noise comparison
The DMC-GX7 keeps noise levels low through ISO 3200, at which point it takes off rapidly. Above that sensitivity, the GX7 is the second noisiest camera in the group, though this may be due to Panasonic's light application of noise reduction. You can see this in the samples: the images from the other cameras appear blotchy, while the GX7's are grainy.
Noise Reduction OptionsThe GX7 offers 11 levels of control over noise reduction and their effects are fairly progressive. All settings appear to suppress chroma noise quite aggressively, varying mainly in terms of how heavily luminance noise (and detail) are smothered. As such they're all pretty similar until ISO 800, at which point the lower NR settings begin to show luminance noise more prominently. The higher settings keep luminance noise under control all the way through the ISO range - with the upshot that the higher sensitivities are just mush.
ACR Raw noise (ACR 8.2 noise reduction set to zero)
Adobe tries to calibrate the noise reduction on Camera Raw to normalize the baseline between cameras - so the graphs show essentially the same noise levels but the amount of detail retained in the images differs. As you can see, there's not a major difference between the GX7 and cameras such as the Sony NEX-6, up until the very highest ISO settings.