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Lightdrum — Portable Light Stage for Accurate BTF Measurement on Site

View Article: PubMed Central - PubMed

ABSTRACT

We propose a miniaturised light stage for measuring the bidirectional reflectance distribution function (BRDF) and the bidirectional texture function (BTF) of surfaces on site in real world application scenarios. The main principle of our lightweight BTF acquisition gantry is a compact hemispherical skeleton with cameras along the meridian and with light emitting diode (LED) modules shining light onto a sample surface. The proposed device is portable and achieves a high speed of measurement while maintaining high degree of accuracy. While the positions of the LEDs are fixed on the hemisphere, the cameras allow us to cover the range of the zenith angle from 0∘ to 75∘ and by rotating the cameras along the axis of the hemisphere we can cover all possible camera directions. This allows us to take measurements with almost the same quality as existing stationary BTF gantries. Two degrees of freedom can be set arbitrarily for measurements and the other two degrees of freedom are fixed, which provides a tradeoff between accuracy of measurements and practical applicability. Assuming that a measured sample is locally flat and spatially accessible, we can set the correct perpendicular direction against the measured sample by means of an auto-collimator prior to measuring. Further, we have designed and used a marker sticker method to allow for the easy rectification and alignment of acquired images during data processing. We show the results of our approach by images rendered for 36 measured material samples.

No MeSH data available.


Instrument positioning: (a) on a desk/floor; (b) for measurement of a vertical wall near the floor; (c) for measurement of a vertical wall using a tripod; (d) for measurement of a ceiling using a tripod.
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sensors-17-00423-f004: Instrument positioning: (a) on a desk/floor; (b) for measurement of a vertical wall near the floor; (c) for measurement of a vertical wall using a tripod; (d) for measurement of a ceiling using a tripod.

Mentions: The device can be used for measurement in the lab preferably on a desk where the sample is placed. However, our design was motivated by the need for measurement outside the laboratory. We can categorise these outside laboratory situations into four different measurement positions for which we propose a solution as shown in Figure 4.


Lightdrum — Portable Light Stage for Accurate BTF Measurement on Site
Instrument positioning: (a) on a desk/floor; (b) for measurement of a vertical wall near the floor; (c) for measurement of a vertical wall using a tripod; (d) for measurement of a ceiling using a tripod.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5375714&req=5

sensors-17-00423-f004: Instrument positioning: (a) on a desk/floor; (b) for measurement of a vertical wall near the floor; (c) for measurement of a vertical wall using a tripod; (d) for measurement of a ceiling using a tripod.
Mentions: The device can be used for measurement in the lab preferably on a desk where the sample is placed. However, our design was motivated by the need for measurement outside the laboratory. We can categorise these outside laboratory situations into four different measurement positions for which we propose a solution as shown in Figure 4.

View Article: PubMed Central - PubMed

ABSTRACT

We propose a miniaturised light stage for measuring the bidirectional reflectance distribution function (BRDF) and the bidirectional texture function (BTF) of surfaces on site in real world application scenarios. The main principle of our lightweight BTF acquisition gantry is a compact hemispherical skeleton with cameras along the meridian and with light emitting diode (LED) modules shining light onto a sample surface. The proposed device is portable and achieves a high speed of measurement while maintaining high degree of accuracy. While the positions of the LEDs are fixed on the hemisphere, the cameras allow us to cover the range of the zenith angle from 0∘ to 75∘ and by rotating the cameras along the axis of the hemisphere we can cover all possible camera directions. This allows us to take measurements with almost the same quality as existing stationary BTF gantries. Two degrees of freedom can be set arbitrarily for measurements and the other two degrees of freedom are fixed, which provides a tradeoff between accuracy of measurements and practical applicability. Assuming that a measured sample is locally flat and spatially accessible, we can set the correct perpendicular direction against the measured sample by means of an auto-collimator prior to measuring. Further, we have designed and used a marker sticker method to allow for the easy rectification and alignment of acquired images during data processing. We show the results of our approach by images rendered for 36 measured material samples.

No MeSH data available.