Motion blur has always been a key pain point in XR headsets. With the continuous development of micro-display technology, the motion blur problem has been improved to a certain extent. As user demands and product performance improve simultaneously, new and ideal solutions carry out advanced optimizations in many aspects such as removing motion blur interference and improving the eye-protection of the screen, so that micro-display products can better serve users.
About Motion Blur
Motion blur is common. For example, in a fast-moving vehicle, the camera-captured scene has it. In photography, it can simulate an object's motion trajectory for a more realistic effect; in film-making, it serves as a special visual effect.
Motion blur also exists on display screens. Moving objects in an image leave blurry traces. In VR, as the display screen moves with the head, the situation is more complex. It's not as appropriate as in film-making nor as negligible as on traditional screens, and it can cause motion sickness and disrupt the experience.
So, to ensure the experience, XR display devices need to reduce or eliminate motion blur, which is a key issue. To solve it, we first need to understand its generation principle.
As the screen moves with the head, the picture blurs.
Exploring Motion Blur Generation and Removal in Display Screens
Traditional displays simulate dynamic pictures by periodically refreshing static ones, not presenting motion continuously and smoothly. Each refresh is a frame image, which remains unchanged until the next frame.
In a VR environment, due to the human eye's persistence of vision, each frame of the picture is retained in the brain for a while according to its position, creating a residual image. When the head moves, the old residual image and the new-position image in the brain are superimposed, causing blurring. The longer the picture is held, the more obvious the blur, and users are more likely to get motion sickness and feel dizzy or nauseous.
Based on this, reducing a frame's holding time is an effective way to solve motion blur. Shorter holding time shortens the residual time in the brain. Before significant head-movement-induced position changes, the frame's residual image in the brain can be quickly replaced by the next updated picture (or a black frame in black-insertion technology), reducing the picture-superposition and motion-blur effects.
So, how much should it be reduced?
In the real environment, the human eye also has motion-blur. Excessive motion blur from the display beyond the natural environment affects our experience. Thus, the ideal VR experience should simulate the real-life natural environment and avoid unnatural motion-blur interference from the display.
Traditional Solutions for Weakening Motion Blur - Black Insertion Technology.
For different refresh rates (60Hz-16.666 ms, 90Hz-11.111 ms, 120Hz-8.333 ms...), as the rate rises, picture-holding time drops. But a very high refresh rate isn't practical due to whole-machine system limits and power/cost balance. So, conventional displays use black-insertion technology: shorten the display time within each frame's due time instead of just increasing the refresh rate. For example, 20% black-insertion means a frame is on for 20% of the time and off for 80%.
The principle is to reduce frame-picture holding time. For 60Hz with 20% black-insertion, the holding time is 16.666 ms×20% = 3.332 ms (shortened from 16.666 ms), weakening motion blur. Similar calculations for 90Hz and 120Hz.
In practice, increasing the display-off proportion can further weaken motion blur. For 60Hz with 90%:10% black-insertion, the holding time is 16.666 ms×10% = 1.666 ms, and similar for 90Hz and 120Hz.
However, continuously increasing the display-off proportion has limitations. As it rises, the screen's instantaneous brightness requirement increases, challenging device lifespan. Also, it may cause harmful stroboscopic effects and harm the eyes (IEEE "Std 1789™ - 2015": <1250 Hz likely harmful, 1250 - 3125 Hz lower risk, >3125 Hz risk - free; black-frame-insertion is 90 - 120 Hz, digital driving is >3600 Hz).
So, a better solution is needed. Fortunately, digital driving can solve this problem.
The Solution for Eliminating Motion Blur - Digital Driving Technology
Digital driving uses a similar principle to address motion blur but focuses on "sub-frames" instead of "frame pictures". It divides each frame into dozens of sub-frames and does black-insertion within each sub-frame, increasing black-insertion efficiency dozens of times. This removes motion blur without harming the eyes, and the flicker frequency after black-insertion meets stroboscopic-exemption conditions.
In micro-OLED's pixel driving circuits (analog and digital), digital driving keeps the control voltage constant and adjusts the on-off time ratio of each pixel to get different gray values and colors. Pixels with different gray levels have different display-off proportions, like dividing a frame into multiple sub-frames. Each sub-frame has different brightness due to different display-off proportions, so when refreshing a frame, it's actually refreshing multiple sub-frames. The display time of each picture becomes very short, shortening the holding time of the same picture.
For example, Lumicore Technology's digital driving with 30 sub-frames increases the display's refresh rate from 90Hz (frame holding time: 11.111 ms) to 2700Hz (sub-frame holding time: 0.278 ms), greatly reducing motion blur. After configuring 30 sub-frames, the black-insertion efficiency is 30 times that of traditional displays. Most sub-frames are low-brightness with large display-off proportions, further reducing picture-holding time and suppressing motion blur.
Finally, digital driving technology offers a real-life natural environment experience.
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