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December 22, 2010

Low light Imaging on the Nokia N8: Who's afraid of the dark?

Holiday season is upon us, and unfortunately so is the darkest time of the year in Finland. On the plus side it´s the perfect time to consider low light imaging, after all, whether we like it or not, it´s dark when coming to work and it´s dark when leaving the office, so we don´t really have much of a choice do we? =)

When starting the N8 project there were two main targets when it comes to imaging performance. One was to create a mobile phone camera that captures the most realistic colours, details and tones in the market and the other one was to set up a benchmark for low light imaging in mobile world. Even though I think we achieved both our targets; good photos in extreme low light are still not self-evident but the user plays a major role in the successful low light photography.

I guess it goes without saying that the real enemy in low light imaging is the noise. So in practice almost all my advice in this article is about avoiding it. Quite contradictory to common beliefs but there are several ways to avoid or hide the noise in pictures just by using the camera slightly differently compared to daylight photography.

The most significant contributors to good low light performance are of course a good and sensitive image sensor and a proper Xenon flash. With the biggest sensor ever in a mobile phone and good Xenon I believe we can tick those boxes. At least as important as good sensor and flash is the auto exposure used in N8. Uncommonly to the mobile world is the N8 spot metering which is used and this means that the exposure parameters are measured from the relatively small spot in the middle of the view finder image. This allows way more precise control to exposure compared to more common matrix metering where the whole frame is used to calculate these parameters.

My first example images are captured from New York Times Square and they both highlight the same things. The first thing to consider in these images is that since the target I’m taking pictures of is pretty far away the flash is useless, so remember to switch it off in situations like these. I would recommend using the flash only when your target is closer than 5 meters away. Switching the flash off actually allows longer exposure times to be used and if your target is still this is very much recommended.

Another point and actually a more important one is the correct usage of the auto exposure spot metering system. We all know that when the shutter button on the N8 is half pressed the AF is locked but not everybody knows that the auto exposure and auto white balance settings are locked also.

In these example images I chose the brightest part of the image to be the area where I locked the AE. For example, in the picture of the statue I pointed the camera to the bright billboard at the background, half pressed the shutter button to lock the AF, AE, and the AWB and then re-composed the image so that my main target, the statue, is nicely positioned according to the rule of thirds. This causes the darkest parts of the image to be practically pitch black creating a nice silhouette of the statue and at the same time this also hides practically all noise in the image. It’s also interesting how people generally don’t mind if parts of the image are under exposed but if even a small portion is over exposed it immediately looks somewhat wrong.

To further demonstrate this I added two pictures captured in Tokyo, the promised land of neon lights. (And I’m hoping that there’s no rude things on these signs since my Japanese is as good as my figure skating skills). In both of these images I did exactly the same things. I picked the brightest part of the image, locked the AF, AE and AWB there by half pressing the shutter button and then re-composed the image to look pleasant and dynamic.

Correct usage of spot AE being the key to success in low light imaging there’s also other tricks you can use to improve your hit rate in the dark. One good way to land impressive results is to try not to avoid the noise but to hide it. This can be done for example by choosing your target so that it’s very busy. By this I mean that if your picture has lot of details in it, the human eye tends not to see the noise as disturbing thing but it actually associates the noise with details. My next two images depict this quite nicely.

Even though these pictures were taken in very low light one can see hardly any noise because there’s so much happening in the photos that the noise is very effectively hidden by all the small details.

So to summarise my pointers for successful low light images:

1. Expose your images according to the brightest part of the image.

2.Use the flash when your subject is closer than 5 meters.

3.If the noise can’t be avoided hide it in the detail.

And maybe even more important pointers:

1.If you visit Tokyo try the Sushi at Tsukiji fish market, it’s something to die for!

2.If you visit New York pay a visit to Museum of Modern arts. There are some killer photos on display.

-Ari Partinen