The RAW files were processed in Adobe Camera RAW using identical settings: Sharpening at 70 / 0.5 / 36 / 10, Luminance and Colour Noise Reduction both set to zero, the White Balance set to 4300K, and the Process to 2012 with the Adobe Standard profile. These settings were chosen to reveal the differences in sensor quality and isolate them from in-camera processing. The high degree of sharpening with a small radius enhances the finest details without causing undesirable artefacts, while the zero noise reduction unveils what’s really going on behind the scenes - as such the visible noise levels will be much higher than you’re used to seeing in many of my comparisons, but again it’s an approach that’s designed to show the actual detail that’s being recorded before you start work on cleaning it up if desired.

The image above was taken with the Olympus OM-D E-M5 with the Leica 25mm f1.4 lens at f4 in Aperture Priority mode. At its base sensitivity of 200 ISO, the E-M5 metered an exposure of 0.6 seconds for this composition. The Panasonic GX1 was adjusted to deliver identical exposures, so what you see below is a like-for-like comparison: same lens, same ISO, same exposure and same RAW processing. Both cameras also share the same 16 Megapixel resolution (albeit with different sensors), so represent the pinnacle of the Micro Four Thirds system at the time of writing. Note the sensor in the Lumix GX1 is the same as that in the Lumix G3, so the results below are reflective of what you'd see from that model.

Before discussing the actual image quality though, a quick observation. Both cameras took turns mounted on the same tripod using the same lens, so since both employ the Micro Four Thirds standard, both should have captured exactly the same field of view. But when framing and later analysing images from both cameras, it became obvious the E-M5 was capturing a fractionally smaller field of view to the GX1, suggesting a fractionally smaller sensor. This in turn is why the crops below show a fractionally different area - just look around the edges. The actual difference in field of view is sufficiently small not to have any significant impact on quality or coverage, but it does reinforce Olympus' claim that the E-M5 uses a new sensor. Or at least uses it in a different way to preceding models from Panasonic. Now onto the actual quality.

The Panasonic GX1 kicks-off the sequence at 160 ISO, while the E-M5 joins-in at 200 ISO. At these lowest sensitivities, both cameras are capturing a large amount of fine detail, which the RAW processing has really brought out. There’s nothing to choose between them in terms of resolution - as you’d expect with the same number of pixels and same lens in front of them - but looking closely in the background, you may notice fractional evidence of chroma noise on the GX1 sample. It’s nothing to worry about, and easily ironed-out with minimal noise reduction, but it’s revealing to find it here and not on the E-M5 sample.

At 400 ISO both cameras are still recording lots of fine detail, but noise levels have increased a little in the background areas. There’s visible chroma noise from both, but it’s a little splotchier on the GX1 and the Panasonic also has more visible luminance noise on the pot. Again remember this is with no noise reduction applied at all.

The same story continues at 800 ISO: slightly more chroma noise in the dark background of the GX1 and slightly higher luminance noise on the pot too, but to be fair, both cameras are still holding onto a decent degree of real-life fine details.

Once again, the same trend at 1600 ISO, although some of the finest details are now covered by noise, so smoothing out these speckles would see the classic splotchy effect.

At 3200 ISO the noise levels take another turn for the worse, although again the E-M5 remains a small step ahead. Likewise to the end of the scale.

From this approach to RAW processing, I’d say the Olympus E-M5 enjoys a clear lead over the Panasonic GX1 / G3 sensor, with an advantage of at least half a stop, getting on for almost a whole stop at a push. This is a great result for the E-M5, and the Micro Four Thirds system as a whole, as it shows the standard delivering better image quality than ever before. Indeed I’d confidently say the E-M5 is delivering the best looking output from the format to date.

Having reached the high ISOs, it’s also nice to return to the top of the table to again revel in the detail captured at the lower sensitivities - by both cameras. There’s sufficient detail captured here to satisfy the most demanding owners and proves the combination of a good lens with careful sharpening really can see Micro Four Thirds compete with larger formats.

Now, head over to Ken's Olympus E-M5 sample images to see some more real-life shots in a variety of conditions.

PS - Many thanks to @BobAndersson for the brief loan of his E-M5 for this test and meeting for a lovely lunch!

Olympus OM-D E-M5 (RAW processed with ACR) Using Leica 25mm f1.4 at f4		Panasonic Lumix GX1 (RAW processed with ACR) Using Leica 25mm f1.4 at f4
160 ISO not available		160 ISO
200 ISO		200 ISO
400 ISO		400 ISO
800 ISO		800 ISO
1600 ISO		1600 ISO
3200 ISO		3200 ISO
6400 ISO		6400 ISO
12800 ISO		12800 ISO
25600 ISO		25600 ISO not available