Below are our standardised ISO test shots, starting with the Panasonic Lumix GH3's lowest setting of ISO 125, going all the way up to 12800.
Full frame ISO 125
As we'd expect of a modern high-end camera, image quality is almost flawless up to ISO 400, with only the slightest softening of the finest details due to noise reduction.
By ISO 1600 the Panasonic Lumix GH3 is beginning to show green and red coloured flecks of image noise and a drop in detail but overall image quality is still excellent, demonstrating the advantage of the larger micro four thirds sensor over the much smaller sensors in compact cameras.
Full frame at ISO 12800
By ISO 12800, image quality is essentially unusable for all but the most casual of shots but this is of course an extreme setting that should seldom need to be used. However, compare it to a full-frame sensor equipped SLR such as the Canon 5D Mark III and you can see the downside of the smaller micro four thirds sensor in this camera - that's what you get for trading off image quality for size and weight.