If you’re interested in the technical aspects of great gaming or graphics experience, or are looking for a GPU that can handle the most advanced graphical techniques, you’ll need to know about path tracing.

As computer graphics have become increasingly sophisticated, path tracing has been a game changer for the quality and realism of computer-generated images. But, you’ll need the right hardware to get the very best out of this graphics technology. 

Understanding what path tracing is can help you evaluate how it can enhance your graphics experience without compromising the speed and performance of your GPU.

In this article, we’ll explain what path tracing is, how it works, and how path tracing impacts GPU processing. Let’s jump in!

What is Path Tracing?

Path tracing is a computer-based method of adding realistic illumination to three-dimensional digital images. It uses a set of computer algorithms known collectively as the Monte Carlo method to determine where the luminescence should be on the image.

This mathematical computation determines the levels of luminescence across the entire image to arrive at a single point of origin of the object’s surface. The path tracing function then attributes a level of luminescence to each pixel of the processed image. 

Path Tracing is a Type of Rendering 

Rendering is image synthesis, the creation of realistic two or three-dimensional computer images using software.

Rendering forms a major part of the production of three-dimensional graphics with path tracing and other effects applied to the images to give them their final appearance. The computer-generated images or render are processed as scene files containing the data that defines the geometry, texture, lighting, and shading of the output digital images.

Path Tracing Simulates Natural Lighting

Path tracing is key to transforming computer graphics into realistic photo-quality images. This technique can be used in any media that requires sophisticated digital imaging like gaming, architecture, digital art, film and television effects, and image simulation. 

It is effective at rendering several lighting effects that would have to be individually added to a computer graphic including: 

  • Ray tracing
  • Depth of field 
  • Indirect lighting
  • Ambient occlusion

Modeling is key with path tracing, using accurate modeling data from a variety of real surfaces, light sources, and cameras to determine suitable illumination. Path tracing is detailed and unbiased with a high degree of accuracy, making it suitable for generating reference images for testing other rendering algorithms. 

Path Tracing vs. Ray Tracing

Path tracing is a type of ray tracing.

Ray tracing comprises a broad range of techniques and rendering for modeling light transport in digital images. Along with path tracing, ray tracing includes rendering techniques like ray casting, photon mapping, and recursive ray tracing.

Unlike path tracing, ray tracing can render a more expansive range of visual effects; it can even model sound waves as well as light for an immersive audiovisual experience.

Ray tracing techniques are detailed and high fidelity. Up until recently, this has made them slow as they place heavy demands on the GPU. Ray tracing and path tracing were commonly used for still images rather than film, animation, or gaming, which would have required significant real-time computation for rendering each displayed frame.

The History of Path Tracing 

The question of how to realistically render 3D images on a 2D surface is a question that has bridged the worlds of art and mathematics for centuries. Many distinguished fine artists developed techniques for replicating 3D objects, like the 16th-century painter and printmaker, Albrecht Dürer, who used string and weights to accurately map objects to canvas.

Dürer‘s string and weights technique was an early version of the ray tracing technique that path tracing is related to. Dürer’s string is identical to the paths of light that travel between objects and the eye of the viewer. 

From Ray Tracing to Path Tracing 

James Kajiya, a post-doctoral computer engineer, devised the mathematical equations that led to the development of path tracing in the 1980s. His research focused on using Monte Carlo experiments, a class of computational algorithms that use randomness to solve deterministic problems. 

His paper in 1986 proposed a light transport equation that forms the basis of path tracing. This involves the generation of numerous scattering events creating paths that start at the camera and end at individual light sources in the computer-generated scene.

The basic light transport equation that Kajiya proposed has since been developed into the path-tracing algorithms used for contemporary graphics. 

Light refraction ray tracing
Path tracing uses the principles of light refraction to send rays in a digital image.

How Does Path Tracing Work?

Path tracing works by using its underlying algorithms to send rays from the camera view in a digital image. When the ray reaches a reflective or refractive surface in the image, it continues the path until it hits a light source and recurses the process until it reaches a light source. This creates a “path” that originates at the camera and ends with the light.

Because of the randomness of the algorithmic calculations involved, the output images can become noisy, but the accumulation of many individual paths removes this noise. The density of generated paths can then compute effects that include:

  • Indirect illumination
  • Hard and soft shadows
  • Glossy surfaces
  • Reflections and refractions
  • Mirroring
  • Area point and directional lighting

The most advanced implementations of path tracing can accumulate up to 4 paths for each pixel in imaging in a single unified rendering process known as the High Definition Render Pipeline (HDRP). 

Designers and programmers can set up path tracing and other effects for applications like video games and animations. They can use a variety of technology to apply programmable lighting techniques to their scenes that achieve a high graphical standard. The parameters that they can work with include:

  • The number of frames that accumulate in a final image
  • The minimum and maximum number of light bounces in each path (which determines depth)
  • The intensity of each light value — capping intensity prevents the emergence of ultra-bright pixels but can make the overall image dimmer

Graphics Pipelines Are Used to Add Path Tracing to Scenes

Designers and programmers use various render pipelines to add path tracing to their scenes. Computer graphics pipelines program the steps a graphics processing unit (GPU) takes to render 3D computer-generated images on a 2D screen. 

Graphics pipelines depend on the software and hardware used to process and display the images. There is no universal standard for graphics pipelines, but developers have created several graphics application programming interfaces to unify and standardize graphics processing for GPUs.

Path Tracing and Other Rendering Effects Require Powerful Graphics Processing

Rendering a 3D digital image on a 2D screen requires complex graphics processing. In modern computing, a GPU handles this process, which is purpose-built to perform complex rendering calculations, including path tracing. 

A separate GPU with dedicated memory and graphics pipeline takes the pressure off of the CPU for completing the rendering computations necessary for creating realistic images and scenes. The path tracing function then becomes a general lighting model for all images that the GPU generates. 

GPUs can process pre-rendered 3D graphics or may be powerful enough to generate the path-tracing and other effects in real time. For the processor, path tracing is a resource-intensive process, especially in gaming because of its dynamic and randomly changing scenes.

Graphics Accelerators Can Improve Real-Time Rendering Performance

Path tracing and ray tracing are usually slow and computing-intensive processes, but since 2018, GPUs have included hardware acceleration that can support real-time ray and path tracing.

Upgrades in graphics APIs have matched this uplift in processing speed, allowing developers to include real-time path tracing in dynamic projects like video games without slowing them down.

GPUs and graphics accelerators are the same hardware component. This powerful computing unit has a dedicated processor, VRAM, I/O, and buses for high-speed graphics processing that can keep up with the most advanced graphics applications. Modern and advanced graphics processors from leading manufacturers like NVIDIA are now essential for any graphics-intensive application. 

Wrapping Up

Path tracing is one of the final steps of bringing 3D computer-generated images to life on a 2D screen.

The simulation of light makes digital images much more real. The enhanced algorithms and accelerated graphics processing hardware enable the consistent application of path tracing for high-speed animation and hyper-responsive gaming. The newest generation of GPUs, now known as graphics accelerators, is well-positioned to further integrate path tracing with fast-moving images.

Path Tracing: What is it and How Does it Work? FAQs (Frequently Asked Questions) 

What is a GPU?

A graphics processing unit (GPUs) is a processor that is dedicated to graphics processing. GPUs have their own RAM (VRAM) and accelerate the rendering of 3D graphics.

GPUs, or graphics accelerators, are mini-computers that are powerful and highly programmable. GPU technology has advanced what can be achieved with computer-generated images with the high-speed rendering of diverse visual effects and realistic scenes in animations, demos, films, and games.

What is rasterization?

Rasterization is the rendering of a 3D computer model as a 2D image. The triangles that make up a computerized 3D model are rendered as individual pixels on a screen, with further processing to create a realistic representation.

What is a graphics application programming interface (API)?

A graphics API provides a library of commands that graphics applications can use to communicate with specific hardware drivers to render 2D and 3D images appropriately.

What is the Universal Render Pipeline (URP)?

The Universal Render Pipeline (URP) by Unity is another scalable and scriptable rendering pipeline that developers can use to optimize path tracing and other graphic effects on their projects. URP is compatible with a wide range of hardware spanning smartphones to PCs.

What is the High Definition Render Pipeline (HDRP)?

HDRP is a type of rendering pipeline that adds image effects like path tracing to digital images.

HDRP is high-fidelity and scriptable, meaning developers can define and program the specific parameters for path-tracing and other rendering processes executed as a 3D image is processed by a GPU. 

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