Artificial Blur Effect for Optical See-through Near-Eye Displays

TL;DR

This work targets saliency modulation for optical see-through near-eye displays by optically blurring selected scene regions. It combines a digitally masked light path via a DMD with an electro-tunable lens to apply blur selectively, synchronized at 60 Hz to exceed the human flicker threshold and fused into a single percept. A border-compensation algorithm mitigates magnification-induced artifacts at sharp/blur boundaries, and a prototype OST-NED validates the approach with MTF analysis and real-world targets. The results suggest a portable, projector-free route to attention-guided augmentation, though challenges remain in brightness, alignment, and DOF limits for practical deployment.

Abstract

Saliency modulation has significant potential for various applications. In our pursuit of implementing saliency modulation for optical see-through near-eye displays, we decided to introduce a blur effect to reduce the sharpness of specific areas while preserving the sharpness of others. In this study, we used a digital micromirror device (DMD) to separate the incoming light from a scene into sharp and blurred areas. To achieve this, we integrated an electrically tunable lens (ETL), which operates in its zero optical power mode when the reflected light from the DMD represents the sharp area (i.e., the blur area is masked). Conversely, when the reflected light indicates the blur area, the ETL adjusts to non-zero optical powers. Importantly, these modulations occur at a speed that surpasses the critical flicker frequency threshold of the human eye. Furthermore, we proposed an algorithm to mitigate the artifacts around the border area between the sharp and blur areas that are caused by the magnification of the ETL. We have also developed a prototype system to demonstrate the feasibility of our method.

Figures (9)

• Figure 1: Concept of the system: Some rays are obstructed according to the DMD pattern. Unobstructed rays pass through the ETL. The upper part of the figure illustrates the passage of rays through the ETL when the optical power is nearly zero (sharp image), while the lower part depicts the passage when it exceeds zero diopter (blur image). This cycle of ray traversal through the ETL occurs continuously at a frequency of 60Hz. Note that the two lenses sandwiching the DMD are used to focus the incoming light rays from the scene onto the DMD for spatial blocking, ensuring that the FOV of the blocked scene matches that of the original scene.
• Figure 2: 2f relay system
• Figure 3: Border artifact due to magnification. (a) Artifacts in case of center in focus, (b) Artifacts in case of center out of focus.
• Figure 4: ETL-eye two-lens: Image of one point in infinity (a) when the optical power of the ETL is zero diopter; the magnification caused by the ETL is one, (b) when optical power is greater than zero; the magnification ranges between zero and one. The dotted arrow in (b) shows that when optical power is greater than zero, the image of point on human retina is blurry. Red dashed line is the principle plane for ETL-eye lens.
• Figure 5: An example of masks used on DMD for the case of center region in focus, with $d_{H0}$ to $d_{H1}$ divided into two optical power levels P1 and P2 . (a) simple blur and non-blur mask, (b) border-compensating blur mask for optical power level 1, the $s_w (P_t)$ by $s_h (P_t)$ pixels in the blur area adjacent to the non-blur area(center) are blackened and border-compensating non-blur mask, the complementary of (c) with added random pattern in border area for optical power P1, (c) border compensating blur and non-blur mask for optical power level P2.