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 GX1 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-GX1's noise performance with its 16MP stablemate, the Panasonic Lumix DMC-G3 and two of its closest competitors, the Olympus PEN-EP3 and Sony NEX-5N, with all cameras at their default noise reduction settings.
The GX1, like the G3 before it, makes use of a Panasonic 16MP sensor, but interestingly the GX1 benefits from image processing improvements that provide better noise performance at higher ISO values. Overall, both cameras strike a more pleasing balance between chroma noise suppression and detail preservation than the Olympus EP3 manages with its now aging 12MP Micro Four Thirds sensor. Up through ISO 1600, the GX1 compares favorably with its APS-C competition, showing an impressive amount of fine detail and avoiding an overly processed, 'plasticky' appearance. At ISO 3200 and above, the GX1 offers noticeably improved performance over the G3, only falling behind its APS-C competitors, with noise levels at ISO 12,800 that, while not pretty, are still marginally usable. For a look at real-world noise performance among competing cameras see our high ISO comparison page of this review.
Looking at the graph it is clear that the GX1 is applying relatively conservative noise suppression, trailing the performance of its 12MP Micro Four Thirds competition, not to mention the larger APS-C sensors, which produce less measurable noise throughout the ISO range. Crucially though, as the samples clearly indicate, the 12MP Micro Four Thirds sensors achieve their noise reduction at the expense of image detail, which is hardly ideal. And it is really only above ISO 1600 that you see visually significant differences in preservation of detail between the GX1 and its APS-C sensor rivals.
Noise and Noise Reduction (JPEG)
Between ISO 160 and 1600, the graph shows how much closer the NR 0 performance of the GX1 is to the maximum noise reduction setting (NR+2) than it is to NR -2, which is nominally the NR 'off' position. As we've seen in recent G-series models, Panasonic's attempt to strike a balance between image detail and noise suppression gives priority to pleasing image results that don't demand in-camera NR adjustments. We can't find much fault with this approach, given that Panasonic's default noise reduction setting maintains impressive distinction of fine details even up to ISO 3200.
Raw noise (ACR 6.6, 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.As you'd expect, raw files processed with no additional noise reduction show greater noise levels than their JPEG counterparts. The GX1 easily outperforms the 12MP Micro Four Thirds competition, which displays noticeably higher levels of both chroma and shadow noise beginning at ISO 1600.
In comparison to its APS-C sensor competition, the samples show that the GX1's 16MP Micro Four Thirds sensor - while susceptible to a bit more noise at the highest end of its ISO sensitivity range - maintains comparable image detail even at ISO 12,800.
A glance at the graph makes clear the virtually indistinguishable noise levels between the GX1 and its 16MP companion, the G3 at NR 0, suggesting that the differences we did see between the cameras at very high ISO sensitivity settings in JPEG mode are a result of in-camera image processing rather than sensor performance.
The graph also shows that while the G3 applies noise reduction even to its Raw files at NR +2, the GX1 opts for the more conventional approach in which noise levels at both its default and maximum NR settings remain identical.