Juha Alakarhu has been at Nokia since 2004, and currently holds the position of Head of Imaging technologies. We spoke to him recently near our Seattle offices about the 808 PureView.
A few weeks ago we had the opportunity to speak to Juha Alakarhu, head of imaging technologies at Nokia and someone who has been involved in the 808 PureView from its inception. As well as letting us get our grubby hands on his baby, he also let us ask some questions about the PureView technology that makes the 808 so interesting to photographers. Read our exclusive interview below.
What is wrong with current/competitive cameras on phones in your opinion?
Some of the key issues are related to low light performance or and unnatural looking images (due to heavy processing), lack of sharpness, lack of proper zoom, lack of proper flash, lack of proper audio quality in videos, or slow speed or clumsy use.
What are the benefits of the PureView technology?
The key benefits of the 808 PureView compared to conventional mobile phone cameras are:
- Wonderful sharpness and very natural 'non-processed' look without noise filtering or sharpening artifacts.
- Excellent noise and low light performance.
- You can zoom without the maximum aperture or focus distances changing.
- Blurred backgrounds when shooting closeup subjects.
- Very fast operation - you can get straight into photo mode by pressing the camera button even if the phone is locked.
- Very nice new user interface for zooming that we call 'slide zoom'.
- A high-power xenon flash.
- Full HD video with zoom, and advanced stereo audio recording.
- Powerful photographic controls in 'Creative mode'.
All of those apply to both stills and video. The zooming interface is especially useful in video. Speaking about video, we should not forget the new audio technology that we have in the product: rich recording with very high quality stereo microphones that can handle up to 140dB sound pressure. We also have Dolby Digital Plus playback via HDMI, and Dolby headphone technology.
How long have you been developing this technology?
The idea of a super high-resolution camera squeezed to a phone was born five years ago in bar in Tokyo with my boss Eero Salmelin. In the beginning we were focussed on technology development: optics, sensor, mechanics, algorithms (and tons of other details). The actual product program was started much later.
What are the challenges of putting zooms into mobile phone cameras?
Before the 808 PureView, we had been working quite a while with optical zooms, and we actually had two products with optical zoom in the market (N93 and N93i). However, there some very big challenges with optical zoom technology in mobile phones.
To make them small enough, the sensor size tends to get small, which results in bad or average image quality. Also, the optics get complex, with very many elements and two moving groups. Even if the optics design looks good on paper, manufacturing tolerances can seriously hurt its performance in actual use.
|The Nokia N93 was released in 2006 and featured a 3MP camera and 3X optical zoom.|
Another issue is aperture - the F number at the lens' tele position would be pretty small. This would reduce the low light performance, obviously, but would also reduce the sharpness due to diffraction. Another issue is that the exposure times might get too long, causing a lot of blurry images due to handshake.
The 808 PureView camera solves all those problems: we can use a very large, high quality sensor, the optics are simple and elegant which makes images extremely sharp, and because zooming isn't optical, the lens' F number stays the same throughout the zoom range. Also, the closest focussing distance stays the same throughout the zoom range for the same reason.
What challenges did you encounter in putting such a high-resolution sensor into a phone?
There were many challenges but one of the biggest was how to process all the data fast enough. Making that happen required a lot of innovation in all technology areas: optics, sensor, mechanics, image processing, algorithms… and then we had a lot of work to do, getting all of this to integrate seamlessly. You simply cannot design optics, sensor and image processing independently from each other.
How will you send the message that the 41MP sensor is for better quality images, not bigger images?
I think the easiest way to get the message of the image quality is just to see the images!
In the default mode the camera captures 5MP images, and the quality of those 5MP images is just amazing. We need to separate two things: output resolution - what is right number of megapixels for the outputting image files - and input resolution - what is the resolution of the sensor that is used to capture the image.
When we have the huge input resolution, we have a lot of advantages: oversampling improves the signal to noise ratio, dynamic range, and the output files have very natural non-processed look without signs of interpolation, sharpening or noise filtering. In addition, we can zoom without reducing the lens' maximum aperture.
Starting with a larger number of smaller photosites but outputting at a lower resolution allows us to increase the signal to noise ratio, too, too. By combining the signals from 7 neighboring diodes, you can get the same signal to noise ratio as you would from a photodiode seven times larger (if you do it right). Of course, we could have just used fewer, larger photosites, but then you would lose all the advantages of oversampling, plus the ability to zoom.
So, its not the number of megapixels, but how they are used. Why make 41MP output an option at all?
Even if the camera is 5MP in the default mode, we don’t want to limit how people use the camera.
If you capture the full resolution image, you do record the highest possible amount of details. We can envisage situations where somebody might want to use the full resolution mode for important images or for making very big prints (like the 9 meter print I mentioned earlier).
|This shot was taken at the 808's maximum resolution of 38MP.||This is a 2MP crop of the image on the left, which gets rid of the distracting foreground - 2MP is still a perfectly useable resolution for small prints and web use.|
Another advantage is having the ability to crop. I was skiing in Northern Finland recently, and I suddenly saw some reindeers. I only had a couple of seconds to get the shot. I started the camera by pressing the camera button, pointed it in the right direction, and captured a full resolution image, then cropped it down later, on a computer.
Can you give us any detail about how the oversampling works?
I cannot tell you much. But I can tell you that it happens in various steps and obviously it depends on the zoom ratio. Also, we are using a separate chip for image processing to handle the huge amount of data.
Have you been working with Microsoft on PureView?
Ha ha! We are discussing many topics with Microsoft...
Why Symbian? And will we see Pureview on future Nokia/Microsoft phones?
Nokia only announced our collaboration with Microsoft a little over a year ago. You don’t develop something like PureView in such a short time. We have already announced that our plans are to bring Pureview technologies to our future Windows Phone portfolio.
How do you think people will use this technology in the 808?
I think people will use the 808 not only because it’s the proverbial 'camera that you have with you' but because it is a really good camera! I’m an amateur photographer myself and I have been surprised how many of my 'serious' photos have been captured with the 808 PureView in the past months (rather than my bigger cameras).
The 808 PureView might also be attractive to professionals who need a high quality and durable camera as a backup to their main equipment. There can be also applications where a big professional device just does not fit due to their size or some rougher environments where you don’t want to risk something more costly.
Because of its portability, I think the 808 PureView would be great for many hobbies, like skateboarding, digiscoping, underwater (with some protective cover of course). I have actually received lots of emails from poeople all over the world with ideas for all kinds of interesting projects. Now that the product is available, I look forward to see these ideas put into practise.
What next for Nokia? Do you want to become the serious photographers' phone manufacturer?
Nokia has long heritage of producing excellent camera phones. We made our first camera phone, the 7650 ten years ago. The N90 was our first device with autofocus and Carl Zeiss optics, the N93 featured our first optical zoom in a mobile phone camera, and the N95 introduced a 1/2.5" sensor. More recently the N82 was our first cameraphone with a xenon flash, the N86 had a variable lens iris, the N8 had a 1/1.8" image sensor, and now we're introducing the 808 PureView, which introduces an even bigger sensor, and our proprietary oversampling.
It's hard to believe that all of this has happened in just ten years. Mobile imaging technology has been progressing amazingly fast in all its technology areas… and we are not stopping here!