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July 9, 2010

Nokia N8 Camera – 2,260 days in the making Part 2/2

LONDON, England – This post is the second part of my explanation of the capabilities of the camera on the Nokia N8 (if you missed the first part, it’s here). In this post, I discuss some of the video capabilities of the device, and how the hardware works together to produce the best imagery possible, even when you push it to its limits.

We’ve seen how, when taking still photographs, the specifications on the Nokia N8 allow us to do without some of the artificial image processing tricks that have become the norm on camera phones. In the case of video, we’re again combining the benefits of the large sensor and the Carl Zeiss optics but also with this new incredibly powerful graphics processing engine where we’re able to record at up to 12mpbs using the extremely compression efficient H.264 video codec.

Using this very high bit rate, we’re not seeing any compression artefacts, even fine background detail during panning. Also of particular note is some incredible work from our audio engineers, specifically new algorithms for handling a wide range of audio levels from the subtlety of bird song to the loud and harsh environment of a live rock concert. Words really can’t do their work justice in this regard. We’ll share some video soon for you to experience this yourself. To retain as much of the captured detail and fidelity as possible we sample the stereo audio at 48kHz and encode it at 128kbps using the AAC audio format. Even the placement of the digital mics in the Nokia N8 is unique. One being positioned on the front of the device, whilst the other is positioned on the rear. The benefit of this approach is a much greater sense of the original ambience of the surroundings. It’s also of benefit if you are narrating over any action as the front mic [the one on the display side] is particularly effective at recording very clear speech. There are also new algorithms to help reduce wind noise.

So you’ve recorded some great video footage but what are you going to do with it next? For many you’ll simply play it and enjoy it in it’s uncut form. But for those feeling more creative you’ll want to go further. For this reason the N8 sees a welcome return to a comprehensive onboard editing application allowing you to trim clips, add music, text and photos as well as transitions between each of these elements. Some PC’s struggle to edit HD video but this is done on a device that fits in your pocket! It’s amazing how pocket processing power has developed over recent years.

Let’s consider the benefits of the sensor/optics combination a little further. In good light recording, we take full advantage of the high resolution sensor. Through the downscaling and binning process from the 4000×3000 pixel sensor to 1280×720 video pixels, any visual noise that may have required some degree of noise reduction is effectively filtered out, therefore allowing us to process the video with noise reduction disabled. This means in reasonable lighting you won’t see any noise in the video during play back. This has allowed us to retain incredible levels of detail rather than losing it to noise reduction. It’s also allowed us to implement digital zoom which is virtually as good as optical zoom.

Here are four frame grabs from a video clip (apologies for not choosing something more interesting for you to look at). Again, these are with development hardware and software (specifically, just in the last few days we’ve improved the colour reproduction, exposure and contrast since I captured these). The first shows the natural detail we resolve with no noise at the normal setting (1x) All the details are clearly defined. Remember this is video, which doesn’t need to be as sharp as stills since each frame is only visible for 1/25th second. Between 1x and 2x the image becomes progressively a little softer but remains highly usable. But at 2x zoom we’re at a point where we’re simply downscaling the video. This means there’s no loss of resolution which usually occurs through the binning process. I think you’ll agree the performance at 2x is really stunning. This performance is pretty much maintained up to 2.5x as you can see where it starts to tail off a little at 3x which is pretty much the limit imposed by the original resolution of the sensor. This is why we’ve capped the zoom at 3x in video to ensure you always have great video quality.

My personal recommendation is to use the touch-enabled zoom control rather than the physical keys. I find it provides a faster yet smoother control (at least with a little practice) I also recommend that you avoid zooming during filming if you can. If you watch a movie it’s relatively rare that you’ll see the camera zooming in/out of the shot. Video is all about smoothness, so think about what you’re shooting first and then avoid camera movement, especially panning unless you move the camera slowly and smoothly. The basic rule is to control the camera as smoothly as possible so the viewer is not immediately aware of camera movement.

1X Zoom

2X Zoom

2.5X Zoom

3X Zoom

Another area I wanted to cover was relating to autofocus during video. The N8 uses a system we refer to as ‘Active Hyper-focal Distance’. Hyper-focal distance is a specific lens focus position which by using depth of field allows the greatest range from near to infinity for objects to appear in focus. The Nokia N8 uses a 28mm (35mm film equivalent) focal length Carl Zeiss lens. This provides us with huge depth of field. But by using the hyper focal distance means objects placed between roughly 60cm and infinity will appear sharply focused.

The reference to ‘Active’ relates to the nature of how we maintain this hyper-focal distance lens position. Most autofocus camera modules in camera phones rely to some degree on friction. The problem with this is that the lens which moves for focus adjustment can slip after being driven to the correct intended lens position. This isn’t normally a problem in the case of still photography, but in the case of video can create problems especially when recording with HD resolution. To combat this problem, for the first time we actively monitor the lens position and then adjust it if required. The result is simply, video that’s always in focus.

The alternatives today are as follows: 1. Focus at the beginning of the exposure and then lock it or 2. continuously focus during the video. Unfortunately both have disadvantages. The first means if your subject moves or you alter the composition it will be out of focus. The second means the image in screen needs to be always be in focus. However, maintaining this without seeing focus hunting is very difficult. Add to this, when your subject moves from it’s original position, or there is insufficient contrast or illumination it simply won’t be able to focus and unless you’re lucky, your video will be out of focus. Before I continue, yes our system does have the disadvantage of only being effective for subjects which are beyond 60cm. We felt however, this was a worthwhile trade-off given the benefit you get in return, always in focus video, regardless of where your subject is, how fast it moves, how much contrast there is or how much available light there is. And you’ll never see it focusing or hunting during filming either.

Of course the ultimate solution would be to combine both of these in some way. Earlier in development we trialled a continuous autofocus system for video, but concluded for the time being that the performance didn’t warrant its inclusion in the product at sales start. Having said that, we are continuing investigations to find a way to get the best of both worlds in the future. Let’s see…

Having put all this effort into the audio and visual recording side of the N8 and provided some versatile editing tools out of the box, it would all be wasted if you couldn’t appreciate it on the biggest screen in the house, the one you spend most time sitting comfortably in front of, your HD TV. The Nokia N8’s HDMI connection provides full stereo and 720p output to your HD TV, so you don’t lose any of the original digital information in the process. A complete digital recording process coupled to pure digital playback. It’s worth noting the HDMI output also supports Dolby 5.1 surround sound (where pre-recorded digital media includes the appropriate soundtrack). It’s almost like a mini Blu-ray player in your pocket. I mustn’t forget of course about the Bluetooth capability to control your N8 wirelessly from the comfort of your sofa using a Bluetooth keyboard and/or Bluetooth mouse.

I hope that helps to answer many of your questions about the video capabilities of the device. Do feel free to leave any more that you feel need to be answered.