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-308), middle gray matched. We estimate the accuracy of these results to be +/- 1/6 EV (the margin of error given in the ISO specifications). We found that measured ISO from the GF3 matches the camera-stated of ISO 160 (base ISO). We found this to hold true throughout the entire ISO range.
Here, we're comparing the Panasonic Lumix DMC-GF3's noise performance with its predecessor, the Panasonic Lumix DMC-GF2 and two of its closest competitors, the Sony NEX-C3 and Canon EOS 1100D, with all cameras at their default noise reduction settings.
Even at ISO 200 we can see relatively aggressive noise reduction at the GF3's NR 0 setting when compared to its APS-C competitors. When considering the degree of 'smoothing' applied to its images, the GF3 does a very good job of preserving fine detail up until ISO 800. At that point the APS-C cameras show their advantage in maintaining fine-detail edge contrast, which only increases at higher ISOs.
In comparing the GF3 with the GF2, the graph shows that performance is virtually identical through ISO 400. The slight 'increase' in noise that the graph indicates the GF3 displays at ISO 1600, however, can be misleading. This reflects the GF3's slightly altered handling of chroma noise. As you can see from the samples, the GF3 is slightly smoother with less blotchiness in the color patches. One would expect this to translate into more visible detail and indeed, as shown on the features page of this review, increased detail at high ISOs is the primary difference we find between the GF3 and its predecessor.
In a similar vein, although the graph would seem to indicate the GF3 'catches up' to its APS-C competitors at ISO 3200, the samples emphasize the point that at this stage, much higher degrees of noise suppression are being applied to the Micro Four Thirds output, which of course, blurs detail.
Noise and Noise Reduction (JPEG)
Between ISO 200 and 1600, the graph shows how much closer the NR 0 performance of the GF3 is to the maximum noise reduction setting (NR+2) than it is to NR -2, which is nominally the NR 'off' position. In attempting to strike a balance between image detail and noise suppression, Panasonic seems to be aiming for pleasing image results for users who have no intention of adjusting NR settings or tweaking results in raw conversion software. And to be honest, we don't find much fault with this approach, given that Panasonic's default noise reduction setting maintains perfectly acceptable distinction of fine details even at ISO 1600.
Raw noise (ACR 6.5 beta, noise reduction set to zero)
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.
All the cameras show signs of noise even at the lowest sensitivity settings (remember these samples have noise reduction turned down to zero in ACR). Yet this comparison makes clear the advantages to be gained with the larger APS-C sensors at higher ISOs. The GF3 renders fine detail in a fairly accurate manner up to ISO 800, beyond which it lags behind APS-C sensors which show significantly less color noise.
Beginning at ISO 400 it also becomes clear by comparison, just how much noise reduction is being applied by the G3's JPEG engine at its default setting.
A glance at the graph makes clear the relative similarities in noise levels between the GF3 and its predecessor, the GF2. In real-world images, the differences implied by the graph are rather negligible in terms of actual image detail that is being resolved. In this regard the GF3 is nearly indistinguishable from the GF2.