From the course: SketchUp: Rendering with V-Ray Next

Image sampling explained

From the course: SketchUp: Rendering with V-Ray Next

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Image sampling explained

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- [Instructor] When working with a raytrace render engine such as V-Ray, having at least a basic understanding of how the technology is working can definitely benefit the image creation work that we do. And so, in order to collect all of the information that it needs to be able to create a final render from our 3D environment, such as the shape of geometric objects, the surface and volume properties of materials that have been applied, lighting and shadow information, et cetera, our render engine needs to somehow probe the 3D scene in order to determine just what ought to be drawn in each of the pixels that will ultimately make up our final image. The million dollar question, of course, is how will this information gathering or scene probing be accomplished? Well, this is where the basic workings of the raytrace process come into play, because in very general terms, raytracing works like this. From the rendering camera in the scene, the render engine will first of all shoot a number of rays through an internal frame before our grid that represents each of the pixels making up the final image. These primary rays, sometimes referred to as eye or camera rays, are pushed into the 3D environment in order to trace or bounce their way through the scene, usually with a pre-determined limit as to the number of times that they are allowed to bounce having already been fixed, either by the engine's defaults or by a user-specified override. As they travel through the scene, these rays sample, or gather information from objects that are found in their path, meaning as they hit or come into contact with surfaces they take note of and collect a wide range of information from them, such as diffused color values, specular and reflectivity levels, and so on. They also, with every hit, send out shadow rays, whose very specific job is to trace a line from the point of contact on a surface toward any direct light sources that are also found in the environment. These rays are used to determine whether or not a particular point on a surface should be rendered as if sitting in direct light or in shadow. The primary rays will also, on contact with a surface, make an evaluation regarding whether or not any secondary rays are going to be required. These coming into play whenever a surface material has extra properties attached to it, such as refraction, blurred reflections, subsurface scattering, and so on. Once the specified amount of sampling or information gathering has been accomplished, all of the data collected up to that point gets returned back along each ray's traveled path, fed into the render engine for evaluation and averaging, and then at the end of the process gets drawn in the frame buffer as a final pixel color value. Now, of course, this is an extremely simplified overview of what is, in reality, an incredibly complex process that can potentially involve millions, if not billions of different kinds of rays being cast and then traced throughout a scene in order to produce the image that we are after. This simplified view is enough for us to work with in this course though, and will definitely be of help in production when we have sampling or image quality decisions that need to be made.

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