Phase shifted noise masks motion judder in low frame rate rendering
Masking Judder in Foveated Rendering with Phase-Shifted Noise
Graphics
Summary
When computers create images too slowly, the motion can look jumpy or choppy, which is called judder. This is a problem in special rendering techniques like foveated rendering, where only the center of vision is detailed to save computing power. The authors found a way to use special noise patterns that shift in phase to trick the eye into perceiving smoother motion, even when the frame rate is low. By carefully choosing the noise type based on how fast things appear to move, their method hides judder without causing other motion problems. Tests with people showed that this approach lets screens look smoother without much loss in image quality.
What this means in practice
- •For virtual reality developers: Maintain smooth perceived motion in VR scenes rendered at reduced frame rates using phase-shifted noise to mask judder.
- •For game engine developers: Improve motion quality in games employing foveated rendering by integrating spatial noise patterns that reduce motion judder without costly temporal filters.
Authors
Ville Cantory, Danhua Zhang, Victoria Interrante, Piotr Didyk
Abstract
Low framerates during rendering arise when frame time exceeds the rendering budget, or can be introduced deliberately to save computation, for example in foveated rendering, where the periphery can be rendered at a reduced spatial and temporal resolution. However, low frame rates also cause non-smooth motion, or judder, degrading perceived image quality. Judder manifests as aliasing in the spatiotemporal frequency domain; temporal filtering, such as blurring, can suppress it, but at an additional computational cost and incur a larger loss of detail. Prior work has shown that inexpensive synthesized noise can compensate for the loss of spatial detail and velocity perception caused by foveation, but its potential for restoring motion cues lost to reduced temporal resolution has not yet been explored. We show that such noise can itself restore these cues: translating a Gabor kernel reduces to a phase shift, and modulating a kernel phase creates a perception of smooth motion without having to fully rerender the noise. We derive a method that, given the on-screen angular velocity and the temporal rendering rate, selects a spatial frequency noise band such that phase shifts perceptually mask judder without introducing motion aliasing of their own. User experiments show that our technique substantially expands the range of angular velocities over which motion at reduced temporal resolution remains smooth, without objectionable degradation of image quality.