Abstract
Low-order photometric parameters of light fields are important aspects determining lighting qualities but difficult to be measured. In this article, we did a systematical investigation into the performance of a cubic meter and a tetrahedron meter as well as an HDR panoramic map-based method in simultaneously recovering light density, direction, and diffuseness. Five metrics were introduced with two based on the measurement using a cubic illumination meter, two based on a tetrahedron shaped illumination meter and one based on SH decomposition of HDR panoramic maps. Furthermore, the measurement of five metrics was simulated under six HDR Panoramic maps of natural scenes in various postures which mimic the complexity of real environments. The results indicate that the measurement of low-order photometric parameters of light fields using Spherical Harmonics (i.e. latter referred to as SH) decomposition of HDR panoramic map gave the most reliable results. The tetrahedron meter based metrics gave more robust results in the measurement of light density while the cubic meter based metrics performed better when measuring light direction. This study also provides a solution for a more robust measurement of light diffuseness based on the ratio between the vector strength measured with a cubic meter and light density measured with a tetrahedron meter. With the quick development of high-speed built-in camera and mobile computing techniques, this research provides confidence in developing applications in mobile phone by capturing HDR panoramic maps or built in light meters to measure the low-order photometric parameters of light fields in 3D spaces.
Highlights
What determines lighting effects? Once the light is emitted from its source, it starts a journey, interacting with its surroundings
The results indicate that the ratio between the vector strength measured using the cubic meter and the scalar component estimated with the tetrahedron meter is less sensitive to the posture variations of the illumination meters
We have found that the Spherical Harmonics (SH) decomposition of HDR panoramic map-based method to simultaneously measure the light density, direction and diffuseness was more robust and it was independent of the postures of the meters used
Summary
What determines lighting effects? Once the light is emitted from its source, it starts a journey, interacting with its surroundings. Research shows that the human observers is able to distinguish the intensity, the primary illumination direction, and the diffuseness, which are three basic properties of light [15], [20], [26], [27] These three properties were found to be determined by the low-order frequencies of the light distribution and be called low-order photometric parameters of light field. VOLUME 8, 2020 measure the low-order photometric parameters of light field (i.e. light density, direction and diffuseness). Two of the methods were based on the use of a cubic illuminance meter, two of them were based on the use of a tetrahedron shaped meter and one based on spherical harmonics decomposition of HDR (High Dynamic Range) panoramic maps. The measurement of low-order photometry using panoramic HDR maps, cubic meter or tetrahedron meter expected to have a wide application prospect in the near future
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