Studying User Perceptible Misalignment in Simulated Dynamic Facial Projection Mapping

High-speed dynamic facial projection mapping (DFPM) is an advanced technology that aims to create perceptual changes in facial appearance by overlapping images based on facial position and shape. Compared to traditional monitor-based augmented reality systems, DFPM offers a higher level of immersion because users can directly observe digital content on their faces. However, DFPM suffers from misalignment issues owing to a slight temporal delay from sensing to projection, which reduces the level of immersion. To the best of our knowledge, no previous study has established the necessary latency requirements to avoid perceptible misalignment and achieve an immersive experience. Furthermore, conventional DFPM works followed latency requirements that were not reported for the DFPM scenario. Therefore, this study measured the latency that provided a just-noticeable difference (JND) in DFPM under different facial motion conditions, using the weighted up-down two-alternative forced-choice method. The results showed that user-perceptible misalignment was influenced by facial motion types and their velocities. Additionally, it was found that an average latency of 3.87 ms was necessary to avoid perceptible misalignment in the DFPM system when the translation speed was 0.5 m/s, which contradicts the commonly held belief regarding the required latency threshold.