What Is Path Tracing?

Turn on your TV. Fire up your favorite streaming service. Grab a Coke. A demo of the most important visual technology of our time is as close as your living room couch.

Propelled by an explosion in computing power over the past decade and a half, path tracing has swept through visual media.

It brings big effects to the biggest blockbusters, casts subtle light and shadow on the most immersive melodramas and has propelled the art of animation to new levels.

More's coming.

Path tracing is going real time, unleashing interactive, photorealistic 3D environments filled with dynamic light and shadow, reflections and refractions.

So what is path tracing? The big idea behind it is seductively simple, connecting innovators in the arts and sciences over the span half a millennium.

What's the Difference Between Rasterization and Ray Tracing?

First, let's define some terms, and how they're used today to create interactive graphics - graphics that can react in real time to input from a user, such as in video games.

The first, rasterization, is a technique that produces an image as seen from a single viewpoint. It's been at the heart of GPUs from the start. Modern NVIDIA GPUs can generate over 100 billion rasterized pixels per second. That's made rasterization ideal for real-time graphics, like gaming.

Ray tracing is a more powerful technique than rasterization. Rather than being constrained to finding out what is visible from a single point, it can determine what is visible from many different points, in many different directions. Starting with the NVIDIA Turing architecture, NVIDIA GPUs have provided specialized RTX hardware to accelerate this difficult computation. Today, a single GPU can trace billions of rays per second.

Being able to trace all of those rays makes it possible to simulate how light scatters in the real world much more accurately than is possible with rasterization. However, we still must answer the questions, how will we simulate light and how will we bring that simulation to the GPU?

What's Ray Tracing? Just Follow the String To better answer that question, it helps to understand how we got here.

David Luebke, NVIDIA vice president of graphics research, likes to begin the story in the 16th century with Albrecht D rer - one of the most important figures of the Northern European Renaissance - who used string and weights to replicate a 3D image on a 2D surface.

D rer made it his life's work to bring classical and contemporary mathematics together with the arts, achieving breakthroughs in expressiveness and realism.

The string's the thing: Albrecht D rer was the first to describe what's now known as ray tracing, a technique for creating accurate representations of 3D objects on a 2D surfaces in Underweysung der Messung (Nuremberg, 1525),f15 In 1525 with Treatise on Measurement, D rer was the first to describe the idea of ray tracing. Seeing how D rer described the idea is the easiest way to get your head around the concept.

Just think about how light illuminates the world we see around us.

Now imagine tracing those rays of light backward from the eye with a piece of string like the one D rer used, to the objects that light interacts with. That's ray tracing.

Ray Tracing for Computer Graphics Turner Whitted's 1979 paper, An improved illumination model for shaded display, jump-started a ray-tracing renaissance. In 1969, more than 400 years after D rer's death, IBM's Arthur Appel showed how the idea of ray tracing could be brought to computer graphics, applying it to computing visibility and shadows.

A decade later, Turner Whitted was the first to show how this idea could capture reflection, shadows and refraction, explaining how the seemingly simple concept could make much more sophisticated computer graphics possible. Progress was rapid in the following few years.

In 1984, Lucasfilm's Robert Cook, Thomas Porter and Loren Carpenter detailed how ray tracing could incorporate many common filmmaking techniques - including motion blur, depth of field, penumbras, translucency and fuzzy reflections - that were, until then, unattainable in computer graphics.

Jim Kajiya's 1986 paper, The Rendering Equation, not only outlined an elegant, physics-based equation for describing how light moves around in a scene, it outlined an efficient way to put it to work. Two years later, CalTech professor Jim Kajiya's crisp, seven-page paper, The Rendering Equation, connected computer graphics with physics by way of ray tracing and introduced the path-tracing algorithm, which makes it possible to accurately represent the way light scatters throughout a scene.

What's Path Tracing? In developing path tracing, Kajiya turned to an unlikely inspiration: the study of radiative heat transfer, or how heat spreads throughout an environment. Ideas from that field led him to introduce the rendering equation, which describes how light passes through the air and scatters from surfaces.

The rendering equation is concise, but not easy to solve. Computer graphics scenes are complex, with billions of triangles not being unusual today. There's no way to solve the rendering equation directly, which led to Kajiya's second crucial innovation.

Kajiya showed that statistical techniques could be used to solve the rendering equation: even if it isn't solved directly, it's possible to solve it along the paths of individual rays. If it is solved along the path of enough rays to approximate the lighting in the scene accurately, photorealistic images are possible.

And how is the rendering equation solved along the path of a ray? Ray tracing.

The statistical techniques Kajiya applied are known as Monte Carlo integration and date to the earliest days of computers in the 1940s. Developing improved Monte Carlo algorithms f

LINK:	https://blogs.nvidia.com/blog/2022/03/23/what-is-path-tracing/...
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