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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.


Assembly of lightdrum, step 7 to 12 from three different views. Row 1: mounting auto-collimator; Row 2: populating six microcomputers Hardkernel Odroid-XU3; Row 3: populating the microcomputer Raspberry Pi 2; Row 4: mounting the RS485 bus distribution boards; Row 5: connecting the first distribution board to LED modules; Row 6: connecting eight distribution boards to LED modules.
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sensors-17-00423-f030: Assembly of lightdrum, step 7 to 12 from three different views. Row 1: mounting auto-collimator; Row 2: populating six microcomputers Hardkernel Odroid-XU3; Row 3: populating the microcomputer Raspberry Pi 2; Row 4: mounting the RS485 bus distribution boards; Row 5: connecting the first distribution board to LED modules; Row 6: connecting eight distribution boards to LED modules.

Mentions: The assembly is shown in a series of 30 images from three different views in Appendix D, in Figure A1, Figure A2, Figure A3, Figure A4 and Figure A5. The device requires careful assembly, paying attention to the cleanliness of the assembly process as metal splinters and particles remaining from the manufacturing could damage the electronics in the long term. Also the carbon cover protecting the device from outside illumination has to be protected by a lacquer as the carbon particles are highly conductive. Cleaning is best done by a vacuum cleaner and air pressure repeatedly applied during assembly.


Lightdrum — Portable Light Stage for Accurate BTF Measurement on Site
Assembly of lightdrum, step 7 to 12 from three different views. Row 1: mounting auto-collimator; Row 2: populating six microcomputers Hardkernel Odroid-XU3; Row 3: populating the microcomputer Raspberry Pi 2; Row 4: mounting the RS485 bus distribution boards; Row 5: connecting the first distribution board to LED modules; Row 6: connecting eight distribution boards to LED modules.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

sensors-17-00423-f030: Assembly of lightdrum, step 7 to 12 from three different views. Row 1: mounting auto-collimator; Row 2: populating six microcomputers Hardkernel Odroid-XU3; Row 3: populating the microcomputer Raspberry Pi 2; Row 4: mounting the RS485 bus distribution boards; Row 5: connecting the first distribution board to LED modules; Row 6: connecting eight distribution boards to LED modules.
Mentions: The assembly is shown in a series of 30 images from three different views in Appendix D, in Figure A1, Figure A2, Figure A3, Figure A4 and Figure A5. The device requires careful assembly, paying attention to the cleanliness of the assembly process as metal splinters and particles remaining from the manufacturing could damage the electronics in the long term. Also the carbon cover protecting the device from outside illumination has to be protected by a lacquer as the carbon particles are highly conductive. Cleaning is best done by a vacuum cleaner and air pressure repeatedly applied during assembly.

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.