A practical analytic model for daylight

www.cs.utah.edu Figure 1: Left: A rendered image of an outdoor scene with a constant colored sky and no aerial perspective. Right: The same image with a physically-based sky model and physically-based aerial perspective. Sunlight and skylight are rarely rendered correctly in computer graphics. A major reason for this is high computational expense. Another is that precise atmospheric data is rarely available. We present an inexpensive analytic model that approximates full spectrum daylight for various atmospheric conditions. These conditions are parameterized using terms that users can either measure or estimate. We also present an inexpensive analytic model that approximates the effects of atmosphere (aerial perspective). These models are fielded in a number of conditions and intermediate results verified against standard literature from atmospheric science. These models are analytic in the sense that they are simple formulas based on fits to simulated data; no explicit simulation is required to use them. Our goal is to achieve as much accuracy as possible without sacrificing usability

Realistic rainbow rendering considering light attenuation due to scattering and absorption in the atmosphere

これまで、波動光学を考慮した虹のレンダリング法が開発され、過剰虹や異なる半径の水滴による虹の表示が行われてきた。しかし、大気中の水滴分布を一様と仮定しており、大気による光の散乱・減衰も考慮されていなかった。本研究では水滴ボリュームを設定し任意の密度と半径の水滴分布を考慮できるように改良した。また、光の減衰を考慮することで太陽高度の違いによる虹の色変化を表現できるようになった。さらに、街灯のような多様なスペクトル分布を持つ点光源も扱えるように拡張した。これらを考慮することで半径に応じて変化する虹や、高度によって色が変わる虹、また、点光源によって発生する特殊な形状の虹など様々な虹をレンダリングできるようになった。A method for rendering rainbows considering the wave optics has been developed and supernumerary rainbows and rainbows generated by different radii of raindrops were rendered. However, the method assumes that the distribution of the raindrops in the atmosphere is constant, and the attenuation of light due to the scattering and absorption in the atmosphere is not taken into account. We improved the rendering method considering both density and radius of raindrops using volume representation of raindrops. Considering attenuation of light, our method can render the change of rainbow color depending on solar altitude. In addition, we extended the method to be able to use a point light source with various spectrum distributions like streetlights. Our method can render various rainbows depending on radius of raindrops, the solar altitude, and light sources

The development of local solar irradiance for outdoor computer graphics rendering

Atmospheric effects are approximated by solving the light transfer equation, LTE, of a given viewing path. The resulting accumulated spectral energy (its visible band) arriving at the observer’s eyes, defines the colour of the object currently on the line of sight. Due to the convenience of using a single rendering equation to solve the LTE for daylight sky and distant objects (aerial perspective), recent methods had opt for a similar kind of approach. Alas, the burden that the real-time calculation brings to the foil had forced these methods to make simplifications that were not in line with the actual world observation. Consequently, the results of these methods are laden with visual-errors. The two most common simplifications made were: i) assuming the atmosphere as a full-scattering medium only and ii) assuming a single density atmosphere profile. This research explored the possibility of replacing the real-time calculation involved in solving the LTE with an analytical-based approach. Hence, the two simplifications made by the previous real-time methods can be avoided. The model was implemented on top of a flight simulator prototype system since the requirements of such system match the objectives of this study. Results were verified against the actual images of the daylight skies. Comparison was also made with the previous methods’ results to showcase the proposed model strengths and advantages over its peers

Rendering of light shaft and shadow for indoor environments enhancing technique

The ray marching methods have become the most attractive method to provide realism in rendering the effects of light scattering in the participating media of numerous applications. This has attracted significant attention from the scientific community. Up-sampling of ray marching methods is suitable to evaluate light scattering effects such as volumetric shadows and light shafts for rendering realistic scenes, but suffers of cost a lot for rendering. Therefore, some encouraging outcomes have been achieved by using down-sampling of ray marching approach to accelerate rendered scenes. However, these methods are inherently prone to artifacts, aliasing and incorrect boundaries due to the reduced number of sample points along view rays. This study proposed a new enhancing technique to render light shafts and shadows taking into consideration the integration light shafts, volumetric shadows, and shadows for indoor environments. This research has three major phases that cover species of the effects addressed in this thesis. The first phase includes the soft volumetric shadows creation technique called Soft Bilateral Filtering Volumetric Shadows (SoftBiF-VS). The soft shadow was created using a new algorithm called Soft Bilateral Filtering Shadow (SBFS). This technique was started by developing an algorithm called Imperfect Multi-View Soft Shadows (IMVSSs) based on down-sampling multiple point lights (DMPLs) and multiple depth maps, which are processed by using bilateral filtering to obtain soft shadows. Then, down-sampling light scattering model was used with (SBFS) to create volumetric shadows, which was improved using cross-bilateral filter to get soft volumetric shadows. In the second phase, soft light shaft was generated using a new technique called Realistic Real-Time Soft Bilateral Filtering Light Shafts (realTiSoftLS). This technique computed the light shaft depending on down-sampling volumetric light model and depth test, and was interpolated by bilateral filtering to gain soft light shafts. Finally, an enhancing technique for integrating all of these effects that represent the third phase of this research was achieved. The performance of the new enhanced technique was evaluated quantitatively and qualitatively a measured using standard dataset. Results from the experiment showed that 63% of the participants gave strong positive responses to this technique of improving realism. From the quantitative evaluation, the results revealed that the technique has dramatically outpaced the stateof- the-art techniques with a speed of 74 fps in improving the performance for indoor environments