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This leads to the heart of rendering: picking the best approach that will get the results looking as good as possible, in the time you have, and more precisely picking which attributes of an image – be it complex shading, complex motion blur, sub-surface scattering or some other light effects should be your priority – which ones will play in your shot, and which attributes need to be more heavily compromised. Modo render by Pascal Beekmans Stats: Res: 1500 500, Indirect Illumination Monte Carlo, – 24.8B Vertices – 8.27B Poly. Please just click to enlarge. There are many choices and factors that influence the decision of a studio to pick one renderer or another, from price to their pipeline experiences, but for this article we focus on a comparison based on the needs of global illumination (GI) in an entertainment industry production environment. We have chosen to focus on major studios with the expectation that many smaller facilities are interested in the choices made by those larger companies with dedicated production and R&D personnel. This is not to lessen the importance of smaller facilities but rather to acknowledge the filter down nature of renderer choices. The goal of realistic rendering is to compute the amount of light reflected from visible scene surfaces that arrives to the virtual camera through image pixels. This light determines the color of image pixels. Key to that are the models of reflection/scattering and shading that are used to describe the appearance of a surface. Shading addresses how different types of scattering are distributed across the surface (i.e. which scattering function applies where). Descriptions of this kind are typically expressed with a program called a shader. A simple example of shading is texture mapping, which uses an image to specify the diffuse color at each point on a surface, giving it more apparent detail. The modern chase for realism revolves around more accurate simulation of light and the approaches renderers have taken to provide the best lighting solution. Key to current lighting solutions is global illumination. The defining aspect of the last few years of renderers has been global illumination (GI). Jeremy Birn (lighting TD at Pixar and author of Digital Lighting and Rendering , 2006) succinctly defines GI as “any rendering algorithm that simulates the inter-reflection of light between two surfaces. When rendering with global illumination, you don’t need to add bounce lights to simulate indirect light, because the software calculates indirect light for you based on the direct illumination hitting surfaces in your scene”. We want to get all the contribution from all the other surfaces so that it takes into account BRDF and radiance from each direction. GI makes CG lighting much more like real world lighting and accounts for radiosity or the color bleeding that happens when no reflective surfaces still provide bounce, and bounce tinted to their diffuse color. In a simple ray tracer, the ray’s directions are determined regularly and normally in a simple grid. But there is a key alternative, Monte Carlo ray tracing, also known as stochastic ray tracing. In Monte Carlo ray tracing the ray’s origins, directions, and/or times are set by using random numbers. See below. The key with a ray tracer is not its complexity but the complexity of its optimizations and implementation. The key concepts are simple enough, but the demands on a production ray tracer to deliver inside a computational budget on exceedingly complex projects is no small demand. Until recently, full ray tracers were not used for animation. They were popular for still shots, or very small special cases, but most ray tracing commercially happened as part of a larger solution, as part of a hybrid solution. Now that that is changing there is great demand for the amazing accuracy and subtlety of a ray tracing solution. But the key is to stay focused on producing good results not necessarily accurate results