The GH3's still image performance is a significant step up from the GH2's. ISO performance has definitely been improved, while the GH2 should stop at ISO 3200, the GH3 can go higher and look better. Although noise does start to appear around ISO 1600, it's fine-grained and you'll need to zoom in to notice it. It's more noticeable at ISO 3200, but you could shoot comfortably up to ISO 6400 and not be too affected by it. Shooting in raw is significantly better than shooting in JPEG, the Panasonic JPEG engine tends to create blocky or artificial-looking jaggies at ISO 6400, while noise in raw looks more organic (for a more detailed ISO report as well as comparisons against the Olympus E-M5, see the next page).
Megapixel count hasn't increased, from 16MP to 16MP, but the GH3 captures more detail at 2200 LPH on our resolution chart (horizontal and vertical) compared to 2000 LPH on the GH2. The automatic white balance seems to prefer shifting to the warm tones, but unlike the Olympus OM-D E-M5 there's no option to tell it not to.
Panasonic calls the latest version of their AF system "Light Speed AF", and while it's quite the name it certainly deserves it; auto-focus is snappy and accurate. In those rare times when it doesn't seem to lock onto exactly what you want, you can simply tap the screen and the GH3 will focus on your subject.
The GH3 comes with wireless control for external flashes, but flash sync speed is very slow, at only 1/160th of a second.
Like the G5, the GH3 comes with an option to shoot using an electronic shutter. Unlike the GH2 which could capture stills at only 4MP with its electronic shutter, the GH3 can shoot full-resolution images. The biggest advantage to using the electronic shutter is how quiet it is; except for the initial lens focusing noise the camera is completely silent when taking a photo.
While this can be quite fun, there are several limitations. For one, you cannot use flash with the electronic shutter, nor can you make exposures longer than one second or use an ISO higher than 1600. There are also visible rolling shutter effects; if you move the camera, straight lines can become skewed - that includes moving as well as still subjects. Even if you move the camera slightly, you might get skewed-looking subjects.
Video recording comes with SMPTE-compliant time codes, but the GH3 still doesn't come with focus peaking or zebra stripes (for showing overexposure). It does come with manual focus magnification. We didn't have a GH2 to compare it against, but it seems like while its still image quality has seen a significant boost, the improvements for video image quality are more subtle. However, the GH3 offers more compression and resolution options than the GH2, not to mention quality that's broadcast-compatible. Compared against HD-DSLRs, the GH3 offers superior handling, faster auto-focus and the convenience of a touch-screen.