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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.


The example measurement data on example material sample 009-Basketball from The MAM 2014 sample set ([35]). (top) changing the viewing direction for illumination direction close to the normal for ; (bottom) changing the illumination direction, the camera at direction , .
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sensors-17-00423-f023: The example measurement data on example material sample 009-Basketball from The MAM 2014 sample set ([35]). (top) changing the viewing direction for illumination direction close to the normal for ; (bottom) changing the illumination direction, the camera at direction , .

Mentions: We ran over 60 measurements to find the important issues and get practical experience. Some material samples were measured twice to check the measurement reproducibility. Based on our experiences we came up with the description of the measurement setup procedure as described in Section 7.3. For debugging we first measured samples in laboratory conditions with the holder frame for the floor samples. After finishing the instrument debugging in the lab, we tested the device in situ for both frame holders. We measured different data at different locations and with different instrument orientations as shown in Figure 4. The example of data illustrating the measurement procedure for 3 material samples are shown in Figure 22, Figure 23 and Figure 24.


Lightdrum — Portable Light Stage for Accurate BTF Measurement on Site
The example measurement data on example material sample 009-Basketball from The MAM 2014 sample set ([35]). (top) changing the viewing direction for illumination direction close to the normal for ; (bottom) changing the illumination direction, the camera at direction , .
© Copyright Policy - open-access
Related In: Results  -  Collection

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

sensors-17-00423-f023: The example measurement data on example material sample 009-Basketball from The MAM 2014 sample set ([35]). (top) changing the viewing direction for illumination direction close to the normal for ; (bottom) changing the illumination direction, the camera at direction , .
Mentions: We ran over 60 measurements to find the important issues and get practical experience. Some material samples were measured twice to check the measurement reproducibility. Based on our experiences we came up with the description of the measurement setup procedure as described in Section 7.3. For debugging we first measured samples in laboratory conditions with the holder frame for the floor samples. After finishing the instrument debugging in the lab, we tested the device in situ for both frame holders. We measured different data at different locations and with different instrument orientations as shown in Figure 4. The example of data illustrating the measurement procedure for 3 material samples are shown in Figure 22, Figure 23 and Figure 24.

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.