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Although it seemed perfectly fine at the time, watching VHS tapes is far inferior to the DVDs that many of us enjoy today. Likewise, the Blu-Ray format is an improvement again on the DVD viewing experience.

This subtle, and yet very real, progress in home entertainment provides a neat analogy to the technological advances made by Nokia’s engineers for the PureMotion HD+ screen on the Nokia Lumia 920.

PureMotion HD+ is the fastest screen on a smartphone. In fact, it is over twice as fast as the displays on competitor smartphones currently on the market.

It’s a result of an evolutionary process that, with each new development, has enhanced the user experience one step further. With the PureMotion HD+ display you get crisper graphics and less blurring while e.g. scrolling, navigating and playing games.

If you’re interested in the technical details of what makes the screen on Lumia 920 so fast, read on!

The challenge

“There are a few things that really affect the blurriness of the display,” says Jussi Ropo, Nokia’s Senior Technology Manager.

speed blur

“First of all, all rendering should happen at a stable 60fps as only then you get rid of the jaggedness in the moving content. You can say it’s a prerequisite for all the further improvements.”

Another important aspect related to displays is LCD and how fast the liquid crystal can change its state, meaning how fast it can change from one colour to another.

“First, when you measure 60fps it means 16.7ms – you have a new image coming every 16.7ms on the display. It is intuitive to think that when your LCD response or transition time is longer than this one frame period then you will actually get quite a lot of blur. This is because your liquid crystal is still trying to get the previous value at the same time as it has to start turning again for the next frame,” says Jussi.

looking back

Transition speeds

Therefore, the trick, and the solution on the Lumia 920, is to actually have a faster response time than 16.7ms.

“On average it takes about 9ms for all of the transitions so regardless of e.g. what shade of blue you are turning into what shade of yellow, it is always below 9ms. This is the biggest step forward in the screen speed of the Lumia 920.”

This phenomenal transition speed was achieved by boosting the voltage to each LCD pixel – overdriving the panel. By comparison, other competitor phones will have a like-for-like transition speed of around 23ms.

“We have the capability of actually showing all the frames as intended rather than creating blur because the LCD could not respond fast enough,” says Jussi.

More technical details of how this was done can be found in the PureMotion HD+ White Paper.

Ultimate blur-free?

As well as the transition speeds, there are other factors that can cause blurriness on your screen. The ultimate display, says Jussi, for blur free motion is the old Cathode Ray Tube (CRT) televisions but obviously given their size (and power consumption) they are not practical at all for mobile phones.

Modern LCD and plasma TVs also use upscaling via frame interpolation (inserting extra frames) to dramatically increase the fps rate. Again though, compared to mobile phones, TVs are immensely power-hungry, so these techniques are not directly applicable to mobile phone displays.

light trailss

Of course, progress never rests. Nokia is still looking to improve their displays to reduce blur even further. It is a complex problem that requires a detailed understanding of how the human eye works and balancing other factors such as power consumption.

For now though, Nokia has already produced a world-leading display on the Lumia 920. Whether you are scrolling, navigating, playing games or watching video it offers a real feast for your eyes.

Read also about the screen brightness and sunlight readability and the super sensitive touch capability of the screen on the Lumia 920.

image credits: MSVG, Patrick Hoesly, Nathan E photography