Nokia's camera guru on the secrets behind the N9's sensor
GLOBAL - With the Nokia N9, the design team set a sky-high ambition level with the industrial design. As a result, there were a number of significant challenges in realising this design intent. The uni-body itself (I’ve heard) is Nokia’s most complex single component ever! I’ll let others explain more of the details behind this incredibly challenging component. But I thought I’d share some of the challenges we had with the camera development as well as provide more details in a number of areas of which you won’t be aware just by looking at the N9’s beautifully clean exterior.
Our biggest challenge without doubt has been to reduce the size of the camera to such a degree that the design intent could be realised, whilst also targeting performance as close as possible to the industry-leading and highly regarded Nokia N8.
To put some context around this, to achieve the design goal we knew the camera would have to be a certain set of dimensions. Those dimensions are equivalent to a massive 70% reduction in size compared to the module used in the Nokia N8!
To me, the combination of performance and capabilities of the camera defies expectation for a product so elegant in its form. On the face of it, the camera is so elegantly integrated you’d be forgiven for thinking that from a capability perspective, it was an afterthought. And then you look at the long list of the Nokia N9’s imaging capabilities:
- Industry-first imaging sensor which is FULLY optimised for BOTH 16:9 AND 4:3 images
- Industry-leading Carl Zeiss optics
- Super wide-angle optics – the widest in the industry. Up to as much as 60% more viewing area than other broadly comparable devices
- f/2.2 aperture – largest ever in a mobile device
- Extremely responsive, especially switching from stills to video and vice-versa and shot to shot
- Touch AF for both video and stills
- Full time continuous AF in BOTH video and stills plus face detection
- HD video with stereo audio (still one of very few devices that provide high quality audio recording in video)
- Seamless workflows optimised for speed or editing & sharing
- Zoom in to images directly in the post capture view, edit and share all without leaving the camera – the most seamless mobile imaging experience
- Non-destructive editing of images – go back to the original image at any time. Undo or redo edits even months later
- New high power dual LED flash – 20% more powerful than our previous most powerful LED flash despite its compact size
- Geo tagging with place names rather than just co-ordinates
- AMBR – Automatic Motion Blur Reduction
- Not forgetting the touch to share of images between handsets using NFC technology
A number of these have already been covered in other entries on this site. However, there are a few I wanted to share some further details around.
New Generation Sensor
Since day one, mobile phones have used sensors with a 4:3 aspect ratio. With the increasing popularity of viewing images electronically and on widescreen displays (typically 16:9) we’ve for some time wanted to optimise the experience around this increasingly popular format. Since the introduction of the Nokia N900 and more recently the Symbian^3 family of products led by the Nokia N8, we’ve been using 4:3 sensors but with the default setting of 16:9 image/video capture. To achieve the 16:9 format from a 4:3 sensor has meant cropping the top and bottom of the image. This is pretty much what any product that provides the 16:9 option does, even virtually all dedicated digital cameras.
A few years back when we were debating how best to optimise the experience around 16:9, the solution that emerged first was, of course, to choose a sensor which is already sized to the 16:9 proportions. However, 4:3 still provides advantages, especially for portrait oriented images. The challenge was how could we retain the best of both worlds? That’s when we came up with the idea of using a sensor which would allow exactly that.
Take a look at this first illustration.
The image formed by the optics is circular rather than as we know it to be typically rectangular. The key behind this concept is how a 16:9 area fits differently within the optical circle to that of a 4:3 area. One provides more height to the image, the other more width. Current 16:9 crops only provide less, but formatted to the 16:9 aspect ratio.
To have a single sensor that provides this capability, however, means a sensor with more pixels than you need at any one time. In the case of the new Nokia N9, while it says 8-megapixels on the product, the sensor is actually 8.7-megapixels. You can see in the illustration the total area covered by the image sensor as well as the portions of the sensor used according to the chosen aspect ratio. The result of this is the only mobile device which genuinely gets more in the width of the picture than the industry norm 4:3, leaving you the flexibility to choose the best aspect ratio for the scene.
One of the benefits of Nokia’s scale has long been being able to work directly with component manufacturers to design and develop bespoke components. This new sensor, like in many of our products, especially the Nokia N8, is designed and developed to our own specification and exclusively supplied to Nokia, as are our optics of course: no off-the-shelf components will meet our demanding requirements.
These are actual N9 images downscaled in Photoshop for the purposes of this article. You can click through to see them a little larger.
The first allows you to see the difference it can make on the composition for the same subject by using different aspect ratios.
The second allows you to see the difference between the N9 and a very popular competitor device. The highlighted area is the area you won’t capture with other popular devices. There are many devices which don’t even come close to this. I used a competitor’s product with quite a wide angle lens as a reference device to be fair.
Using conventional comparisons to 35mm, the Carl Zeiss optics are equivalent to 28mm, currently the widest in the industry. However this assumes the 4:3 aspect ratio. However, because we’re using the image circle more effectively in 16:9, to achieve the same horizontal field of view the Nokia N9 provides, you’ll need a 26mm equivalent wide-angle lens from a 4:3 image sensor to rival it. That’s by far the widest currently and wider than many digital cameras provide. We believe this fits extremely well with the 24/7 nature of these devices. What’s also important to note is that wide-angle capability is also realised when shooting video where many broadly comparable devices use a crop to help improve performance. Despite this super wide-angle the benefit of working with Carl Zeiss means we’re able to still keep distortion under control. It’s a real feat of optical engineering.
Let’s now look at how we were able to reduce the size of the module. One of the most important considerations was low light performance. The principle contributor to the size of the module used in the Nokia N8 is the industry’s largest ever imaging sensor, this causes not just the footprint to be larger but also the height of the module. Hence why the N8 has a raised area on the rear of the device to accommodate the camera module. For the design to be successful it was essential to eliminate this protrusion.
To do so meant it was obvious the camera was going to have to be significantly slimmer. 12-megapixels in a module that size wasn’t going to be possible unless we’d been prepared to compromise the low light performance. We had a lot of internal debate around that point! On one side there are still a lot of people who believe megapixels is a measure of camera performance, while a growing number of others know it can result in compromise. We had the same challenge with the Nokia N8, should we go for 12-megapixels like others with smaller pixels and a smaller module or do what we felt was right? It’s always been our intent to provide cameras with a focus on real world performance. But on the flip side we need to consider what’s believed to be competitive in the market. We don’t believe in adding pixels just for the sake of it, if it doesn’t provide any genuine benefit.
The 8.7-megapixel sensor allowed us to reduce the footprint and height of the module. We also weren’t going to be able to incorporate xenon flash due to the size of the component, especially the capacitor. The way our engineers talk about the size of this component you’d think it was the size of a house! Relative to the other components, it is though. This meant LED flash. We’re using our most powerful LED flash to date. It’s 20% brighter than our previous brightest, yet in an even smaller package than before. Reducing the size of the pixels from those used in the N8 also allowed us to make a further reduction in sensor foot print as well as the most critical dimension, the height of the module. So we’d realised our goal in terms of physical design but the concern relating to low light performance remained.
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Two developments helped us greatly here.
1. Super large f/2.2 aperture allowing approximately 75% more light to reach the image sensor. This is the largest aperture ever incorporated in to a mobile and larger than most digital cameras.
2. Adoption of the latest generation sensors which provide increased sensitivity as well as improvements in the processing of data resulting in lower visual noise.
Combining these improvements, the low light performance between the new Nokia N9 and the N8 is broadly comparable depending on your preference of noise handling. When shooting with flash, the xenon-equipped N8 still has the edge over the N9 in terms of shooting distance and ability to freeze movement but these are two quite different devices. One is focused on creation, the other all-round capability in an extremely seductive body.
Given the extremely positive reaction to our image optimisation approach with the Nokia N8, we’ve tried to get as close to that as we can with the N9: natural detail with little/no sharpening, little/no noise reduction (in good lighting at least) with punchy but not oversaturated colour. I’ve had a lot of people in the last few days ask me about which is best, the N8’s camera or the new one in the N9. I think the N8 can still retain its crown as world’s best camera smartphone given it’s all-round performance is so good, but given the N9’s camera is 70% [!] smaller, I think the team have done a really great job in getting as close as they have. In fact, for some people, in some situations, you may prefer the Nokia N9. We’ll share some sample images with you all very soon.
Flexible autofocus options
The Nokia N9 provides a great deal of flexibility in focusing. Providing both touch and full time continuous autofocus as close as 10cm. The N9 is a full touch capture experience. Touch AF means your finger or thumb can easily move between focus point selection and the touch based capture key without changing your grip on the device. You can still perform focus lock by keeping your finger on the touch capture key like you would with a physical key although in most cases touch AF means you don’t need to do this as you simply touch where the subject is in the frame. Face detection is also provided for improved ease of use, reducing any need for changing the focus point when faces are detected.
Full-time continuous AF works in both still and video modes. In video, its benefit is to provide smooth focus from 10cm through to infinity. Touch selection of the focus point is also available to provide flexibility when you want your subject to be positioned at the edge of the frame for example or moves during recording. In stills mode continuous AF helps to eliminate in the majority of cases the lag associated with autofocus. In many cases, once you’re ready to shoot, continuous AF will already have correctly focused the scene or subject. Simply touching the capture key results in almost instant capture with virtually no delay.
A great deal of optimisation has gone into creating a highly responsive device and the freedom to capture when you want to. Pressing the capture key will immediately capture the image, whether focusing is complete or not. In most situations focus will be complete before you press the capture key. This was a conscious decision to provide fast capture at all times. If however you want to ensure the image is in perfect focus (assuming it’s not already indicated by the colour of the focus area) holding the capture key will focus and when complete lock. As you lift your finger from the screen it immediately captures the image. If, however, you slide your finger off the capture key it will cancel focus lock and no image is captured, so you have exactly the same control as a physical key but with great ergonomics.
The teams have also been working hard on creating and optimising seamless imaging workflows. The first of these is optimised for speed. From first use, you’ll find that when you capture an image/video, it will return you immediately to the viewfinder ready for the next image/video. This is the fastest way of using the Nokia N9. However, if you prefer to see the image you just captured or have the ability to immediately edit and/or share the content, change the setting for ‘show captured content’ to ‘2 seconds’, ‘5 seconds’ or ‘No time-out’ (my personal preference being ‘no time-out’). Now you’ll access the second workflow. Immediately after capture you’re able to zoom in to the image to check sharpness etc without having to access the gallery from a separate link. Popular editing options for stills are built-in and sharing for both stills and videos is also available, without ever having to leave the camera. It’s a really slick, seamless experience.
Non-destructive still editing
Jens Wilke has already touched on this but I just wanted to mention it again as it’s a really great innovation. The Nokia N9 provides the ability to edit images on the device using a set of popular editing options but whilst being able to go back even months later to the original with just one click. This is really powerful, and for many, completely removes the PC from the traditional imaging chain.
So beauty on the surface but something of a beast inside…