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When working with a ray-trace rendering engine such as V-Ray, there are certain core fundamentals of ray-tracing technology that we, or more specifically, our work, will benefit from understanding. The five videos in this chapter will help us understand some critical rendering concepts as they apply to the V-Ray renderer. Specifically, we will look at image sampling, subdivisions, the DMC sampler, and color mapping. In this particular video, we are going to focus for a few minutes on our first concept there; that of image sampling.
The natural question to start with, of course, would be, what is image sampling? When we talk about the image sampling process, we are really talking about the ray-trace rendering process itself; that is, the process of constructing a final rendered 2D image from the information collected out of our authored 3D environment. In order to collect all of the relevant information found in that environment -- that is geometric shapes, material types, light, and shadow values, etcetera -- our ray-trace renderer needs to sample the scene, so that it can determine what color value should be drawn in each of the pixels making up our final rendered image.
The million dollar question, of course, is, how is this sampling, or gathering of information accomplished? Well, this is where we need to dig a little bit into the basic workings of ray-trace rendering. The process, generally speaking, goes a little like this. From the rendering camera's point of view, a number of rays are cast or shot through each of the pixels making up our rendered frame window, and they are sent out into our 3D environment. These are called primary rays, sometimes referred to as eye or camera rays, as they are cast from the rendering point of view.
They are sent out to sample, or gather information from the objects that can be found, in the rendering camera's field of view. As these rays hit, or come into contact with geometric surfaces, they take note of, and collect a wide range of information, such as diffused color values, reflectivity, and so on. They also send out shadow rays, whose job it is to check whether or not a given point on the surface of an object is to be rendered in direct light or in shadow. At this point, our primary rays will also make an evaluation as to whether or not secondary, or bounced rays, are required.
These are needed when properties such as reflection and/or refraction are found in the scene. Once the user specified amount of sampling or information gathering has been accomplished, the collected data is returned back along each ray's traveled path, fed into the renderer for evaluation, and then drawn as a final pixel color value. Of course, this is an extremely simplified overview of what is, in reality, an incredibly complex process, that can potentially involve millions of different kinds of rays being cast and traced through our scenes in order to produce a final image for us.
Well, this simple overview is enough for us to work with in this course. It will really help us when we take a look, a little later on, at V-Ray's image sampling engines themselves, and indeed, it is enough for us to be able to move on to our second critical concept video, which will deal with the topic of subdivs, or subdivisions in V-Ray.
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