BrightView at IEEE VR 2018
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1. The document presents a study on improving the perceived brightness of virtual objects in optical see-through head-mounted displays (OST-HMDs) by gradually reducing the transparency of liquid crystal (LC) visors. 2. An experiment was conducted where participants observed virtual objects through an OST-HMD equipped with LC visors while the visors' transparency gradually decreased. Participants then evaluated changes in brightness of the real and virtual scenes. 3. Analysis of results found that as the visors darkened, participants were less aware of decreases in real brightness but perceived the virtual objects to grow brighter, supporting the study's hypotheses. Longer dimming periods also reduced perceptions of real brightness changes more.
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BrightView at IEEE VR 2018
- 1. BrightView Increasing Perceived Brightness of Optical See-Through Head- Mounted Displays Through Unnoticeable Incident Light Reduction Shohei Mori1, Sei Ikeda2, Alexander Plopski3, and Christian Sandor3 1Keio University, Japan 2Ritsumeikan University, Japan 3Nara Institute of Science and Technology, Japan
- 2. Real-Virtual Brightness Inconsistency • Our visual system can perceive… • 10-2 cd/m2 on an asphalt road under moonlight • 2×105 cd/m2 on a sunlit beach • Off-the-shelf OST-HMDs’ projector • approx. 103 cd/m2 OST-HMD Eyes Real object Virtual Real Perceived image (inconsistent) Eyes Virtual Real Perceived image (consistent) OST-HMD + Dimming Visors Real object MS HoloLens Epson Moverio BT-300 2
- 3. Related Work MS HoloLens Epson Moverio BT-300 FixedVisors Sony Glasstron AdjustableVisors Seiko Transitions Photochromic Visors Products Research Fields [Lincoln et al., I3D, 2017] [Hiroi et al., AH, 2017] Our Approach Psychologically correct rendering 3
- 4. Bright Environment Under gradual real light reduction, OST-HMD users will be... 1. Less aware of the real light dimming 2. Still aware of improvement of the virtual light brightness Idea of Our Study Virtual teapot Dark Environment 4
- 5. Our Goal • Improve the perceived brightness of virtual objects for OST-HMDs • Use programable liquid crystal (LC) visors • Gradually change the LC visors' opacity in an unnoticeable rate • Demonstrate the following facts 1. Users feel increases in virtual content brightness while they are less conscious of decreases in the real scene brightness after a gradual increase in the opaqueness of the LC visors 2. Variations in durations have effects 5
- 6. Proof-of-Concept Prototype • OST-HMD: Epson BT-300 • Display: 1,280×720px ×2, Diag. 23° FoV • Camera: 2,560×1,920px • Illuminometer • LC Shutters: Root-R RV-3DGBT1 • Resolution: 1×1px ×2 • Transmittance: 9.0 - 22.7% (Measured using a linear camera) • Controller: Arduino Yun mini Illuminometer OST-HMD LC shutter OST-HMD LC shutter R αR V 6
- 7. Dimming Function in Illumination Shedding 1. Linear functions will work adequately for illumination shedding unless the dimming speed remains at a certain level [Akashi and Neches, 2004] 2. The longer changes, the less noticeable • A luminance fluctuation of about seven percent is not detectable [Shikakura et al. 2003] • As the luminance begins to change, the correct answer rate of the initial brightness decreases over time [Akashi and Neches, 2004] • If the luminance fluctuation ranges from several to ten-odd seconds, the detectability of the change does not depend on the initial luminance [Shikakura et al. 2003] ・Dimming Function Linear ・Duration Longer as possible Duration Transmittance Time 7
- 9. Setup 9
- 10. Procedures 1. The participant looks at virtual object (= 100 brightness) 2. He/she observes the scene during the real light dimming • α changes from 22.7% to 9.0% • Three durations: 5/10/20s 3. He/she answers the brightness of the real scene or the virtual object 10
- 11. Scenes Scene 1 Scene 2 Scene 3 Scene 1 (Flat real scene + Virtual dot) • 14 males + 2 females (age 20 to 24) • 256 raw magnitudes = 2 targets (real/virtual) × (1 control + 3 durations) × 2 times × 16 people Scene 2 (3D scene + Virtual dot) • 26 males + 5 females (age 21 to 25) • 248 raw magnitudes = 2 targets (real/virtual) × (1 control + 3 durations) × 31 people Scene 3 (3D scene + 3D object) • 26 males + 5 females (age 21 to 25) • 248 raw magnitudes = 2 targets (real/virtual) × (1 control + 3 durations) × 31 people 11
- 12. Analysis Based on Stevens’ Law 𝑃 = 𝐶𝑆 𝑘 Real Scene Perceived brightness Constant Luminance Exponent 𝑃𝑠 = 𝐶(𝛼 𝑠 𝑆𝑟) 𝑘 𝑟 Observation 𝑃𝑒 = 𝐶(𝛼 𝑒 𝑆𝑟) 𝑘 𝑟 Evaluation 𝜖 𝑟 = 𝑃𝑒 𝑃𝑠 𝛼 𝑒 𝛼 𝑠 −𝑘r Criteria ・𝜖 = 1: The evaluation follows Stevens' Law ・𝜖 ≠ 1: The evaluation deviates Stevens' Law 12 0.6 (complex scene) Stevens' Law 0.31 (dot)Virtual Object 𝑃𝑠 = 𝐶𝑆 𝑣 𝑘 𝑣 𝑃𝑒 = 𝐶𝑆 𝑣 𝑘 𝑣 𝜖 𝑣 = 𝑃𝑒 𝑃𝑠 100 Deviation Criteria 𝜖 100 User’s evaluation User’s evaluation
- 13. Hypotheses 1. Users feel increases in virtual content brightness while they are less conscious of decreases in the real scene brightness after a gradual increase in the opaqueness of the LC visors. H1 After a gradual increase in the opaqueness of the LC visors, participants will not notice a significant decrease of the brightness of the real scene (𝜖 𝑟 > 1) H2 After a gradual increase in the opaqueness of the LC visors, participants will perceive the virtual content to be brighter (𝜖 𝑣 > 1 and Pe/Ps > 1) 2. Variations in durations have effects. H3 If the brightness is adjusted over a longer period, the perceived deviation values will be larger 13
- 14. Results Scene 1 (Flat scene + Virtual dot) Scene 2 (3D scene + Virtual dot) Scene 3 (3D scene + 3D virtual object) 14
- 15. Discussions • Summary of the experiments • H1 is supported for every condition H1: After a gradual increase in the opaqueness of the LC visors, participants will not notice a significant decrease of the brightness of the real scene. • H2 is supported for Scene 1 and 2 but in Scene 3 H2: After a gradual increase in the opaqueness of the LC visors, participants will perceive the virtual content to be brighter • H3 is supported for real scene in Scene 1 H3: If the brightness is adjusted over a longer period, the perceived deviation values will be larger • Limitations • 22.7% to 9.0% transparency of LC visors • The effects of virtual content’s size are not clear • etc. 15
- 16. Summary & Future Work • OST-HMD with LC visors control • to preserve real-virtual brightness consistency • Psychophysical study • We formulated the deviation rate ε based on Stevens’ Law • The deviation rates for real and virtual showed that the participants were • Less noticeable to real light dimming • Aware of brightness increases in virtual object • Future work • Formulation of real-virtual brightness relationship • Comprehensive study on the effects of dynamic backgrounds and other virtual contents 16
Editor's Notes
- For augmented reality, optical see-through head-mounted displays is considered rather reliable than video see-throughs, since it does not occlude the real environment.
- But due to the nature of optical combiners, it suffers from real-virtual brightness inconsistency because the projector is not powerful enough compared to the real environment luminance. For example, office environment like this room has around 300 to 500 lux but outdoor environment is much brighter. The latest off the shelf OST-HMDs like Epson BT-300 has only 2,000 Lux and as a result, the virtual object looks rather dim. So the current OST-HMDs like MS HoloLens and BT-300 has visors to reduce the amount of lights from the real scene to “relatively” increase the amount of the virtual light.
- While these two products have fixed visors, we have some alternatives such as adjustable and photochromic visors that can change the opacity manually using liquid crystal visors or automatically using chemical reactions. In research fields, we have a lot of attempts to solve the real-virtual brightness inconsistency. For example, Lincoln et al. achieved a physically high dynamic range augmentations by combining sensor arrays and a DMD projector. Hiroi et al. selectively mask or enhance the pixels based on image space intensity analysis using a scene observing camera. Our approach is, on the other hand, more focused on psychological aspect.
- So our key idea is to reduce real lights in less noticeable amount over time and, at the same time, to present perceptually bright enough virtual object. This means that the user feels bright enough virtual object without violating the brightness of the perceived real environment. To simulate the illusion, we took this picture using an auto-gain control camera to mimic the human brightness adaptation. The virtual teapot is visible in the weakly illuminated environment, although it turns into less visible in the bright environment as I explained before. So that we reduce the amount of real lights under unconscious rates and then achieve the consistent augmentation.
- This is the detail of our proof-of-concept prototype HMD. Here, we simply attached 3D glasses to BT-300 and controlled the opacity using Arduino. So that, the users receive virtual light directly from the HMD but the real lights are filtered by the transmittance alpha.
- We have several choices for how to control the real light dimming such as non linear curve, step function, but we simply chose a linear function based on the knowledge of the research area called illumination shedding. Illumination shedding is a research are aiming at efficient reduction of the amount of the office lights for energy saving. Literatures say first: linear functions will work... Second: The longer changes will be more acceptable for the users. So we chose linear dimming function with acceptable durations for AR.
- We created two environments. In scene 1, we used a flat display as real backgrounds and placed a virtual dot in front of the participant. In scene 2 and 3, we arranged 3D objects as real backgrounds and placed a dot or Utah teapot on the desk. In this experiment, the user wear a mask to avoid the real lights and given a ten key for their feedback.
- First they are asked to look at the virtual object in observation phase after the adaptation. And observe the real light dimming in randomly selected durations. Then, answer the brightness of the real or virtual stimuli.
- Consequently, we collected around 250 raw magnitudes from 16 to 31 participants.
- In this experiment, we collected data named “deviation criteria” formulated in this slide. First we use stevens’ law to describe the relationships between the luminance and the perceived brightness. Before the real light dimming, users will perceive Ps brightness regarding the real lights, and after the dimming, they will feel Pe. So the ratio of these two equations gives us deviation criteria epsilon, which means if epsilon is 1 then the evaluation follows Steven’s law, but if epsilon is not 1, then the evaluation does not follow Stevens’ law.
- So we can translate the first hypothesis into two. For the second one,
- These are the results in each scene. Here, the horizontal axis shows durations of the real light dimming. Control means we did not change the transmittance of the LC visors. The vertical axis shows the deviation criteria epsilon. In all scene, the real light dimming becomes less noticeable if we increase the duration, and we confirmed that the participants partially felt the increases in virtual lights. The duration definitely have effects for the real light dimming although we partially confirm this effect regarding the virtual lights.
- Regarding these results we have a lot of discussions.