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Sensors 2017, 17(3), 423; doi:10.3390/s17030423

Lightdrum—Portable Light Stage for Accurate BTF Measurement on Site

1
Faculty of Electrical Engineering, Czech Technical University, Karlovo nám. 13, 121 35 Praha 2, Czech Republic
2
Faculty of Mechanical Engineering, Czech Technical University, Technická 2, 166 07 Praha 6, Czech Republic
*
Author to whom correspondence should be addressed.
Academic Editor: Vittorio M. N. Passaro
Received: 2 December 2016 / Revised: 11 February 2017 / Accepted: 11 February 2017 / Published: 23 February 2017
(This article belongs to the Section Physical Sensors)

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. View Full-Text
Keywords: surface reflectance; bidirectional texture function; surface reflectance measurement surface reflectance; bidirectional texture function; surface reflectance measurement
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Havran, V.; Hošek, J.; Němcová, Š.; Čáp, J.; Bittner, J. Lightdrum—Portable Light Stage for Accurate BTF Measurement on Site. Sensors 2017, 17, 423.

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