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.


(a) The conceptual scheme of our device, consisting of one rotational motion around the z-axis of the hemisphere and one linear motion that approximates to the rotational movement of the six cameras along the meridian; (b) assembled device with electronics without carbon cover and servo motor during debugging.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

sensors-17-00423-f003: (a) The conceptual scheme of our device, consisting of one rotational motion around the z-axis of the hemisphere and one linear motion that approximates to the rotational movement of the six cameras along the meridian; (b) assembled device with electronics without carbon cover and servo motor during debugging.

Mentions: To attain the desired goals, careful co-operative design involving several issues in software and hardware (mechanics, electronics and optics) had to be carried out. The conceptual scheme of our device is depicted in Figure 3a. We have achieved the goals by a new concept and by utilising recent results from the miniaturisation of camera and computer hardware. While we have used a light stage concept as the most natural solution for measuring surface reflectance, we have extended the light stage concept by adding two motions/degrees of freedom to allow for the arbitrary positioning of the camera over the measured sample. The device contains a hemispherical skeleton with custom LED modules mounted on it. The first degree of freedom is performed by a highly accurate rotational stage powered by a servo motor equipped with a gear box. This rotates the whole gantry over a measured sample. The second degree of freedom is achieved by a stepper motor over a linear rail, which moves six cameras along the meridian from the hemisphere pole () toward the equator (maximum in our case). This linear motion in a short range closely approximates the required circular motion.


Lightdrum — Portable Light Stage for Accurate BTF Measurement on Site
(a) The conceptual scheme of our device, consisting of one rotational motion around the z-axis of the hemisphere and one linear motion that approximates to the rotational movement of the six cameras along the meridian; (b) assembled device with electronics without carbon cover and servo motor during debugging.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

sensors-17-00423-f003: (a) The conceptual scheme of our device, consisting of one rotational motion around the z-axis of the hemisphere and one linear motion that approximates to the rotational movement of the six cameras along the meridian; (b) assembled device with electronics without carbon cover and servo motor during debugging.
Mentions: To attain the desired goals, careful co-operative design involving several issues in software and hardware (mechanics, electronics and optics) had to be carried out. The conceptual scheme of our device is depicted in Figure 3a. We have achieved the goals by a new concept and by utilising recent results from the miniaturisation of camera and computer hardware. While we have used a light stage concept as the most natural solution for measuring surface reflectance, we have extended the light stage concept by adding two motions/degrees of freedom to allow for the arbitrary positioning of the camera over the measured sample. The device contains a hemispherical skeleton with custom LED modules mounted on it. The first degree of freedom is performed by a highly accurate rotational stage powered by a servo motor equipped with a gear box. This rotates the whole gantry over a measured sample. The second degree of freedom is achieved by a stepper motor over a linear rail, which moves six cameras along the meridian from the hemisphere pole () toward the equator (maximum in our case). This linear motion in a short range closely approximates the required circular motion.

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.