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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.


Electronics conceptual scheme for the instrument consisting of three main parts: service power box (separated by red dashed line), lightdrum itself (separated by blue dashed line), and servo motor. The three parts are connected by appropriate cables from service power box: power lines and feedback for servo motor, Ethernet cable and power cable (GND, +5 V, +12 V) to the lightdrum. Optionally, two other devices such as service notebook or data server to operate with the device can be connected via Ethernet.
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sensors-17-00423-f015: Electronics conceptual scheme for the instrument consisting of three main parts: service power box (separated by red dashed line), lightdrum itself (separated by blue dashed line), and servo motor. The three parts are connected by appropriate cables from service power box: power lines and feedback for servo motor, Ethernet cable and power cable (GND, +5 V, +12 V) to the lightdrum. Optionally, two other devices such as service notebook or data server to operate with the device can be connected via Ethernet.

Mentions: The electronics conceptual scheme is shown in Figure 15. The lightdrum mounted on its frame is connected via three cables to the service power box that contains power supplies for 5, 12, and 24 V, the servo motor driver, and the network router to connect the device to the outer network. One cable transmits the power, the second one is the Ethernet cable for communication with the servo motor driver and outer network, and the third cable connects the servo motor to the servo driver. The separation into the lightdrum and service power box allows to decrease the weight of the gantry and to easier manipulate the lightdrum over the measured sample. The measurement is carried out in standalone mode (i.e., without using any personal computer). After the measurement it is necessary to transfer the acquired data to the external computer for further processing as all data are needed at one storage place.


Lightdrum — Portable Light Stage for Accurate BTF Measurement on Site
Electronics conceptual scheme for the instrument consisting of three main parts: service power box (separated by red dashed line), lightdrum itself (separated by blue dashed line), and servo motor. The three parts are connected by appropriate cables from service power box: power lines and feedback for servo motor, Ethernet cable and power cable (GND, +5 V, +12 V) to the lightdrum. Optionally, two other devices such as service notebook or data server to operate with the device can be connected via Ethernet.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

sensors-17-00423-f015: Electronics conceptual scheme for the instrument consisting of three main parts: service power box (separated by red dashed line), lightdrum itself (separated by blue dashed line), and servo motor. The three parts are connected by appropriate cables from service power box: power lines and feedback for servo motor, Ethernet cable and power cable (GND, +5 V, +12 V) to the lightdrum. Optionally, two other devices such as service notebook or data server to operate with the device can be connected via Ethernet.
Mentions: The electronics conceptual scheme is shown in Figure 15. The lightdrum mounted on its frame is connected via three cables to the service power box that contains power supplies for 5, 12, and 24 V, the servo motor driver, and the network router to connect the device to the outer network. One cable transmits the power, the second one is the Ethernet cable for communication with the servo motor driver and outer network, and the third cable connects the servo motor to the servo driver. The separation into the lightdrum and service power box allows to decrease the weight of the gantry and to easier manipulate the lightdrum over the measured sample. The measurement is carried out in standalone mode (i.e., without using any personal computer). After the measurement it is necessary to transfer the acquired data to the external computer for further processing as all data are needed at one storage place.

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.