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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.


We propose a compact portable lightdrum for bidirectional texture function (BTF) and bidirectional reflectance distribution function (BRDF) measurements on site that uses the principle of a rotating light stage. It is suitable for real life application scenarios, including predictive rendering in cinema, design industry, etc. The project pipeline is shown, starting with our device concept to its design, construction, assembly, through measurement of a sample and finishing with a rendered 3D object covered by the measured material sample.
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sensors-17-00423-f001: We propose a compact portable lightdrum for bidirectional texture function (BTF) and bidirectional reflectance distribution function (BRDF) measurements on site that uses the principle of a rotating light stage. It is suitable for real life application scenarios, including predictive rendering in cinema, design industry, etc. The project pipeline is shown, starting with our device concept to its design, construction, assembly, through measurement of a sample and finishing with a rendered 3D object covered by the measured material sample.

Mentions: There are several challenges to obtaining a good technique to produce a realistic and accurate visual appearance of the rendered image using BTF that corresponds to the physical reality. We present such a technique starting from the conceptual idea through the design, construction, assembly and measurement to rendering images as outlined in Figure 1. The first challenge for any technique is the dimensionality of the measured and processed data. There are in total six dimensions needed for monochromatic BTF measurements (i.e., spatial position x and y, viewing direction , and illumination direction ). The measured quantity represents the visual appearance of a material sample for a surface point with coordinates for the illumination direction over the whole measured sample and view direction . The directions and are usually referred to in spherical coordinates, i.e., the incoming light direction is represented by a unit vector parameterized by and using formulae and by and .


Lightdrum — Portable Light Stage for Accurate BTF Measurement on Site
We propose a compact portable lightdrum for bidirectional texture function (BTF) and bidirectional reflectance distribution function (BRDF) measurements on site that uses the principle of a rotating light stage. It is suitable for real life application scenarios, including predictive rendering in cinema, design industry, etc. The project pipeline is shown, starting with our device concept to its design, construction, assembly, through measurement of a sample and finishing with a rendered 3D object covered by the measured material sample.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

sensors-17-00423-f001: We propose a compact portable lightdrum for bidirectional texture function (BTF) and bidirectional reflectance distribution function (BRDF) measurements on site that uses the principle of a rotating light stage. It is suitable for real life application scenarios, including predictive rendering in cinema, design industry, etc. The project pipeline is shown, starting with our device concept to its design, construction, assembly, through measurement of a sample and finishing with a rendered 3D object covered by the measured material sample.
Mentions: There are several challenges to obtaining a good technique to produce a realistic and accurate visual appearance of the rendered image using BTF that corresponds to the physical reality. We present such a technique starting from the conceptual idea through the design, construction, assembly and measurement to rendering images as outlined in Figure 1. The first challenge for any technique is the dimensionality of the measured and processed data. There are in total six dimensions needed for monochromatic BTF measurements (i.e., spatial position x and y, viewing direction , and illumination direction ). The measured quantity represents the visual appearance of a material sample for a surface point with coordinates for the illumination direction over the whole measured sample and view direction . The directions and are usually referred to in spherical coordinates, i.e., the incoming light direction is represented by a unit vector parameterized by and using formulae and by and .

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.