Panasonic Lumix G cameras already sit a notch above other compact system cameras (CSCs) and SLRs for video picture quality. The GH4 is the latest addition to the range, and from the outside it’s hard to distinguish from the GH3. However, for keen videographers, this camera marks the beginning of a new chapter.
The headline new feature is the ability to shoot 4K video. 4K refers to the horizontal resolution of each frame, which is about 4,000 pixels wide. There are actually two commonly used 4K specifications. UHD is 3,840×2,160, which is equivalent to four 1080p screens arranged in a two-by-two grid. If and when UK TV channels adopt 4K, they’ll probably use UHD. Then there’s Cinema 4K, which has a 4,096×2,160 resolution and is widely used in cinemas. The GH4 supports both, with Cinema 4K at 24fps and UHD at 24, 25 or 30fps.
FEEL THE BENEFIT
TV manufacturers would love for everyone to upgrade to 4K, but it remains to be seen whether there’s much appetite for it. However, from a videographer’s point of view, the GH4’s 4K capture delivers significant benefits even if the final delivery medium is 1080p.
This is partly because of a process called colour subsampling. Video compression algorithms use various tricks to reduce the amount of data, and one of these is to record the colour information (chroma) at a lower resolution than the brightness (luma). For example, the 4:2:2 subsampling format often used for AVC video means the colour data is recorded at half the resolution of the brightness data. If you’ve looked at a video and noticed that a bright red detail looks strangely pixelated, now you know why. By shooting at 4K, you can downsize the video to 1080p and still have each pixel captured in full colour. You may have to apply chroma subsampling again for the final 1080p distribution format, but at least you won’t be applying it twice, quite possibly in different subsampling formats.
Shooting 4K for 1080p distribution also gives some detail headroom when editing. Chroma keying and other compositing tricks often take a slight toll on detail levels, so having more than enough detail to start with ensures sharp, clean edges when exporting at 1080p. If you have a 1080p export in mind, 4K can also be cropped and enlarged without compromising quality, giving some flexibility when composing shots and getting more from your lens collection. It’s also particularly useful for digital stabilisation, where the picture is cropped and panned to compensate for motion in the source footage.
Lumix G cameras’ video modes have always excelled for details, as the algorithms they use to resize the sensor’s high-resolution output to generate a 1080p picture are superior to the competition. This requires considerable processing power, but the benefit is significant when you compare the output from Lumix G cameras that of models with simpler resizing algorithms, that result in blocky details and moiré interference. This is certainly true of the GH4, but comparing its 1080p output with that of the consumer-oriented (but still excellent) G6, there was very little discernible difference between their detail levels.
These freeze-frames from the GH4 and G6’s video output reveal there’s not much improvement to detail levels in the GH4’s 1080p output – click to enlarge