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 Panasonic Lumic DMC GH3 match the marked ISOs within 1/6 stop accuracy, meaning ISO 200 indicated = ISO 200 measured.
Noise and Noise Reduction (JPEG)
The GH3's noise levels start off fairly competitively but then start to rise noticeably above ISO 1600. Heavy noise reduction kicks-in at ISO 6400, removing a lot of detail, but noise climbs dramatically beyond this point anyway. Most fine detail is lost above ISO 6400, regardless of NR setting.
Noise Reduction optionsThe GH3 offers 11 noise reduction options, ranging from -5 to +5. There's not a huge amount of difference between them in terms of detail retention, but fine detail is lost at NR+5 compared to 0 and +2. Reducing the noise reduction setting from default (0) might not deliver that much extra, in terms of detail, but it does avoid the big NR hike at ISO 6400 if you'd prefer.
ACR noise (ACR 7.4, noise reduction set to zero)
Here we look at the RAW files processed through Adobe Camera Raw (in this case version 7.4). Images are brightness matched and processed with all noise reduction options set to zero. Adobe does a degree of noise reduction even when the user-controlled NR is turned off.
The amount of NR applied 'under the hood' is not high, but it does vary by camera (Adobe is attempting to normalize output across different sensors), so inevitably we are still looking at a balance of noise and noise reduction, rather than pure noise levels. However, the use of the most popular third-party RAW converter is intended to give a photographically relevant result, rather than simply comparing sensor performance in an abstract manner.The RAW noise data shows that the GH3 offers a clear step ahead of the GH2, providing results that essentially match the Olympus OM-D E-M5. Low ISO images are very clean, as we'd expect, and in this particular test (with all NR turned off) noise starts to creep visibly into the image at ISO800. At ISO 3200 it has a visible impact on fine detail, and by ISO 12800 it's very destructive indeed. However, the GH3 clearly does visibly better than its predecessor at high ISOs.
RAW Noise Reduction
The Panasonic GH3 applies noise reduction to its Raw files if you shoot with noise reduction set to +4 or +5. The noise reduction applied is pretty subtle - giving a slight blur to chroma noise and reducing black noise slightly. This risks limiting your processing options, so we'd recommend not engaging so much NR if you're going to shoot Raw.