Limits...
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 prototype LED module on a hexagonal printed circuit board (PCB) with an outer diameter of 46 mm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC5375714&req=5

sensors-17-00423-f010: The prototype LED module on a hexagonal printed circuit board (PCB) with an outer diameter of 46 mm.

Mentions: The LED modules are powered by 5 V and are equipped with a 4-line connector for power and communication. The set and execution commands are passed through a serial protocol over a RS485 communication line from the host microcomputer. Each LED module has a programmable ID. This way we can control one or many LEDs up to the limit of the power supply capability. The circuitry of the LED module consists of 24 parts of which 6 integrated chips are located on one side of the PCB. The second side of the PCB contains only an LED. The LED module also allows us to use an LED located outside the PCB. In this case the thermal protection cannot be used. The prototype of the PCB is shown in Figure 10.


Lightdrum — Portable Light Stage for Accurate BTF Measurement on Site
The prototype LED module on a hexagonal printed circuit board (PCB) with an outer diameter of 46 mm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

sensors-17-00423-f010: The prototype LED module on a hexagonal printed circuit board (PCB) with an outer diameter of 46 mm.
Mentions: The LED modules are powered by 5 V and are equipped with a 4-line connector for power and communication. The set and execution commands are passed through a serial protocol over a RS485 communication line from the host microcomputer. Each LED module has a programmable ID. This way we can control one or many LEDs up to the limit of the power supply capability. The circuitry of the LED module consists of 24 parts of which 6 integrated chips are located on one side of the PCB. The second side of the PCB contains only an LED. The LED module also allows us to use an LED located outside the PCB. In this case the thermal protection cannot be used. The prototype of the PCB is shown in Figure 10.

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.