title: Near-field projection as an adaptive driver assistance system - a technical and human-oriented consideration for future traffic scenarios
Creators: name: Stuckert, Alexander
Publisher: name: UNSPECIFIED
Year: 2023

description: The present work deals with the fundamental consideration of optical parameters for designing a projection system for near-field projections based on perceptual-physiological criteria to enable a user-oriented and technology-independent design of the projection system. For this purpose, different psychophysical tests on resolution and brightness perception of near-field projections investigated the parameters and dependencies in seven participant tests.

Therefore, the testing on resolution perception shows that for a near-field projection at a maximum distance of 5m from the vehicle, the resolution requirements for dynamic representations 25 pixels per degree (ppd) are almost just half as high as for static symbols or texts 40 ppd in the mesopic adaptation level, which in the studies is between 0.5 and 2 cd/m². In addition, DIN 1450 recommends compliance, as non-compliance with this standard leads to increased resolution requirements due to the influence of projection size and text type, especially for safety-relevant near-field projections. From the psychophysical tests performed and the perceived resolution requirements for near-field projections, it is finally possible to conclude the resolution of the microdisplay to evaluate the current technology in this respect. State of the art shows that the resolution requirements of the subject studies are already achieved with a DMD or LCoS system for near-field projections, and a µLED microdisplay still requires 2.5 times the resolution for dynamic projections.

The tests on brightness perception show various influences on the perception of near-field projections based on psychophysical data. A significant influence of adaptation environment on the threshold of contrast perception is present between mesopic ~0.6 cd/m² and photopic (above 210 cd/m²) adaptation luminances. In addition, the influence of projection content, whether a near-field projection is symbol-based or text-based, impacts the perception of the near-field projection since, at reaction times of 600 to 650 ms, the symbol-based near-field projection has lower detection contrast thresholds. Furthermore, compared to a static representation of the same projection content in the mesopic region, a dynamic projection shows a 38 % lower detection contrast threshold, providing better detectability in safety-critical situations in urban road traffic. Finally, the dependence of the recognition contrasts on the position of the near-field projection in the peripheral visual field was also determined.

The perception tests' results and the projections' associated illuminance levels create a model that defines the necessary illuminance level of the projected object for direct or peripheral viewing of a near-field projection as a function of the ambient lighting level. This model can determine for each environmental condition the necessary illuminance of the projection for a detection probability of 90 % and the resulting characteristics of the projector. Furthermore, this model evaluates the current state of the art and assesses the limitations of the available technologies for near-field projections using a user-oriented model, such as that an LCoS projection system is only sufficient for projections at night and in illuminated streets. In contrast, if the brightness increases thrice, a DMD projection system guarantees visibility during dusk and dawn.