How Ray Tracing works Part.1

Evolution of Tomb Raider Graphics (1996 ~ 2016)

Looking back just 30 years ago, it was almost unimaginable for the modern cgi to eventually reach. We've obviously gone from artificial, plastic-looking disgust to almost realistic beautiful artwork.

How did we get here what algorithms enable such photorealistic results? Today we'll look at <Ray tracing> the dominant technique used for movies artworks and infrequently but increasingly in video games we'll also look at rester a recent innovation that substantially increases speed without sacrificing much quality.

Light Reflection in the Real World

At its core raytracing is able to replicate reality because it almost exactly replicates how light works. Light is generated by light sources bounces around a scene and eventually hits the retina or sensor of an observer. As it bounces around the light becomes tinted by the colors of surfaces it encounters. This is because the surface always absorbs a certain amount of the incoming light what's left over gets reflected.

Capturing Light Source with Camera

Ray tracing replicates this it creates many mathematical objects called rays. Emitting them from light sources and seeing where they intersect objects in the scene. When they do other rays are randomly fired from the points of intersection hitting other points where other rays are emitted repeating until the rays hit the simulated camera.

The original color of the light and the color of the surfaces the rays hit determines what color of light has arrived at the camera.

The exact spot the camera has hit determines where on the image that color goes. If multiple rays hit the same spot their colors are averaged together. The more rays we fire the brighter and less grainy the image gets. If you've taken pictures with an old film camera you may be familiar with this effect where long exposure times are required to get an image that isn't noticeably grainy.

Grainy Image Example

Let's dig a bit deeper into the details of how this all works every ray of light starts its life imbued with a particular color given by the light source it's emitted from.

In computer graphics we often represent colors using amounts of red green and blue light(RGB). We do this because it's enough to replicate most of the colors visible to the average person. Here's some examples of how to make different colors by combining different amounts of red green and blue light. What this means mathematically is that every color in computer graphics is represented by three numbers