By Norbert Hildebrand
High resolution displays in mobile applications are a definite trend among new devices, even though this trend may be more driven by marketing thinking than actual necessity. Most people will not be able to see a difference between a 5″ HD (294ppi) and full HD (440ppi) display, but it makes for a great headline in the marketing brochure.
Making high resolution display has become the way to increase revenue for many display makers. NVIDIA is showing a high resolution display it calls a “cascaded display.” The design shows two displays combined to create a super resolution display.
They do not exactly describe the method in detail, however the following video shows the underlying set up.
The two LCD panels are mounted on top of each other with a quarter wave retarding film mounted between the two LCD screens. The technology blog InAVate notes that the two LCD screens are offset in X and Y direction by half the pixel size resulting in a quadruple resolution display. NVIDIA does not say this specifically, as they do not mention any effective resolution of the cascaded display. However they do say that the two displays have a sub-pixel lateral displacement.
They also call this approach a ‘spatiotemporal’ display solution, where additional resolution gain is made by dividing a single frame into two sub frames on top of the spatial division between the two displays.
They stress the fact that similar solutions have so far used additive superposition, while they are using multiplicative superposition. However they do not explain in detail what they mean by that. Each panel shows an altered image and they are then combined to form a better image, similar to a higher resolution display. On the negative side, the resulting display is dimmer than a single display solution due to transmission losses in the second display panel. I would also expect that there is a loss in viewing angle with this solution.
The images in the video are very convincing indeed. The solution could be used not only for tablets and smartphones, but may also be useful for other applications like virtual reality devices. The video shows a VR device similar to the Oculus Rift and a video of the resulting images both with and without the use of the cascaded display technology. The differences are very noticeable, indeed.
The shown results are quite impressive as can be seen in the screen capture below.
The resulting image is actually very close to the captured image, while the conventional LCD shows a much softer image with plenty of artifacts and lost detail.
NVIDIA also shows that when the two display panels are being refreshed at different times, the resulting video behaves as though it is higher frame rate content. They show a motorcycle moving in front of the camera, with a frame rate of 10Hz and 5 Hz. While the 5Hz display shows significant motion artifacts, the 10 Hz video is much smoother. When they run the 5Hz video on the two displays with a staggered refresh cycle, the resulting video looks a lot like the 10 Hz video. The frame rates seem to add up to a higher perceived refresh rate. It is not clear if the sub-frames for the cascaded displays were derived from the 10Hz or the 5Hz video.
NVIDIA also shows the same idea being used with LCOS projectors creating a higher resolution projected image.
For the display industry, the question is which will be a better approach? Is it better to push the pixel density or come up with super resolution displays as suggested by NVIDIA. If implemented you do, of course, need two displays instead of one. So the success of the approach may boil down to the question of whether it is more cost effective to combine two standard displays or to use a higher resolution display. Of course, combining two high resolution displays may result in a super resolution display that could drive innovations such as autostereoscopic and wavefront displays. A very interesting technology.
We contacted NVIDIA for more detailed information but have not received any response yet.