After five years at the heart of Sony’s Bravia TV department, Takao Yagi moved to focus on mobile technology in 2004. Since then he has been a core part of the team that has delivered some of the world’s leading mobile displays. Here he talks to us about the new display on Xperia Z3, the technologies behind it, and how they come together to create our best display ever.
Mobile displays are always a balancing act. We strike the balance between vivid and natural colours, between brightness and battery life, between software and hardware – and when new technologies come along they allow us as engineers more flexibility in how we achieve this balance.
In Xperia Z2 we brought in a new kind of LED and, when matched with new software, it allowed us to strike a much better balance between vivid and natural colours, (you can read more about how we managed that here). The new technologies in Xperia Z2 had given us a great flexible palette to work with and software that would allow us to control the palette in any way we wanted. Our next challenge then revolved around brightness, and in Xperia Z3 we’ve introduced a number of new technologies to help meet it.
We know from our research that brightness is linked with memory in the human mind. The more vivid the memory, the brighter we remember it, and as designers we always try to create on-screen experiences that mirror the way we experience the real world, so it was really important that we found a way of creating brighter displays, but we also knew that they couldn’t compromise on battery life. We approached this challenge from three separate directions.
First, we introduced a new algorithm called “local adaptive contrast” that analyzes each pixel and optimizes every pixel contrast, having much larger dynamic range of contrast per pixel without increasing backlight intensity. That allows us to control how much light each cell lets through, and in doing so get the most brightness possible without using more battery.
The second step was that we took an approach that focussed on the way people perceive colours, and whites in particular. I know it sounds odd but there are lots of different kinds of whites. Warm whites can have some barely perceptible red and yellow tones in them whereas “cool” whites are more towards the blue end of the spectrum. Over the last few years, these cool whites have become the accepted colours for a lot of film and television, mostly because they are perceived as brighter than the warm whites. In smartphones manufacturers tend to stay away from the cool whites because they use more battery to produce but, live colour LEDs enable us to tune white colour by shifting phosphor material instead of cutting light by colour filters. That gives us huge benefit of achievement of colour tuning without any battery impact.
Finally, we adapted higher light-efficiency LEDs so that we could increase brightness as well without increasing backlight power.
Here, I introduced how we’ve achieved highly bright-perceived screen without any battery impact. Additionally, I would like to mention that we actually achieved better battery life by “memory on display.” We use some dedicated memory on the display which “remembers” what’s on the screen at any one time. This means that where you are displaying a static image, the display doesn’t need to use the phone’s processor to constantly refresh the image. This means the screen uses far less processor power, and in turn saves a lot of battery.
In each case these three approaches have been combined to create a screen that is brighter without compromising on battery performance. In fact, they have been so successful that we’ve managed to increase the brightness of the screen by approximately 20% and still set it in a smartphone that can handle up to two days’ usage. It is a testament to Sony’s heritage in this area and it’s a screen that we can genuinely say represents the best of Sony’s expertise and technology.