JPEGs at low ISO sensitivities look good from a noise-profile perspective, with relatively clean-looking images up through ISO 1600. When you compare them with their raw counterparts, however, you see how much fine detail gets lost in the processing (see slide 3).
Frankly, I expected the JPEG processing at low ISO sensitivities in this camera to be a lot better than it is. Color differences aside (although you can see how much more tonal subtlety there is in the raw), the JPEGs are so much more mushy and overprocessed-looking, with a significant loss of detail -- and this is at ISO 200 with no raw processing at all, merely opening it at the default Adobe Camera Raw settings.
(1/250 sec, f9.0, ISO 200, spot metering, Standard Picture Style, 24-70mm f2.8L lens at 70mm)
ISO 800 JPEGs look somewhat oversharpened in the default Picture Style, but there's no perceptible color noise, and the processing in the out-of-focus areas is better than average. Once again, the raws look better.
(1/80 sec, f3.2, ISO 800, spot metering, Standard Picture Style, 24mm f1.4L lens)
Unlike at low ISO sensitivities, starting at about ISO 3200 the JPEG processing compares fairly well to the raw results; the raw offers a bit more detail if you're willing to put up with some graininess. Raw also allows for bringing back blown-out highlights, which become more common in the high-contrast, high ISO sensitivity images.
(1/60 sec, f2.8, ISO 3200, spot metering, Standard Picture Style, 24-70mm f2.8L lens at 70mm)
While the photos get soft at the higher ISO sensitivities, there's still quite a bit of detail and the brighter areas look pretty good, and I like the quality of the colored lights. I think the 5DM3 would make an excellent camera for concert photographers.
(1/125 sec, f5.6, ISO 12800, spot metering, Standard Picture Style, 24-105mm f4L lens at 28mm)
As usual, Canon's default Picture Style (Standard) pushes saturation and contrast more than I'd like, and it now offers an Auto setting, which pushes it even further. However, the Neutral and Faithful settings deliver the more-accurate color one expects from a professional camera.
(1/100 sec, f11, ISO 200, spot metering, 24-105mm f4L lens at 105mm)
This is a particularly hard shot for the AF system to keep up with; the dog is difficult to differentiate from the background, and he's moving erratically. It did a pretty good job, all things considered.
(1/500 sec, f5.0, ISO 400, centerweighted metering, Neutral Picture Style with sharpness +2, 24-70mm f2.8L lens at 70mm)