Path Tracing: What Is It and How Does It Work?

Diana Ipacs

December 7, 2023

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What is path tracing? Learn how it works, what it means for the gaming industry and why it's a game-changer for visual tech.


Path tracing in 3D graphics is often considered a game-changing technique among industry professionals.

With the power to deliver real-time, photorealistic rendering, it's no surprise that this technique has piqued the interest of creators and developers alike. This advancing technology is revolutionizing the way we experience visual projects, raising the bar for realism and accuracy in 3D environments.

In video games, path tracing stands out as an advanced rendering technique that significantly elevates visual realism beyond previous methods by simulating how light behaves and interacts within a virtual environment.

Unlike earlier techniques like rasterization or basic ray tracing, which approximate light behavior, path tracing meticulously calculates the paths of light rays as they bounce and scatter across surfaces. As a result, this method is capable of creating stunningly realistic visuals, effectively capturing subtle effects such as shadows, reflections, refractions, and more, resulting in a more lifelike gaming experience.

By the late 2010s and early 2020s, advancements in hardware, particularly GPUs, along with optimized algorithms, made this technique more accessible and practical for a wider range of applications, leading to its increased adoption.

This article provides a comprehensive overview of path tracing: what it is, how it works, its core principles, and the substantial influence it holds over the future direction of computer graphics.

Let's get started!

Path Tracing – Bluebird Blog

What Is Path Tracing?

Path tracing, which is a form of global illumination technique in computer graphics, has long been a cornerstone in the movie industry for creating photorealistic visual effects and animations. Characterized by its high computational demand, this technique simulates the way light interacts with objects in a scene to produce images with realistic lighting, shadows, and reflections. 

However, recent years have brought a significant advancement in its adoption, especially in the gaming industry, thanks to rapid improvements in GPU technology and algorithms. Real-time path tracing aims to bring a level of visual fidelity to games that was previously exclusive to pre-rendered content, within the constraints of running interactively.

Ray-Surface Interactions

Path tracing works by casting rays from the camera into the scene. When a ray hits a surface, it can be absorbed, reflected, refracted, or scattered, depending on the material's properties. The algorithm recursively traces these interactions to simulate complex behaviors of light, such as caustics and indirect illumination.

Physics-Based Approach

Unlike traditional rasterization-based rendering methods, which focus on converting 3D geometry into pixel values, path tracing takes a more physics-based approach. This allows it to produce a high level of realism but at the cost of increased computational complexity.

Path tracing requires detailed models of materials and lights to accurately simulate light interactions. This includes descriptions of how materials absorb, reflect, and transmit light (defined by Bidirectional Reflectance Distribution Functions, BRDFs, and Bidirectional Transmission Distribution Functions, BTDFs) and models for various light sources in a scene.

Unbiased Rendering Method

Path tracing is an unbiased rendering technique, meaning it aims to simulate the behavior of light as accurately as possible without resorting to approximations or simplification strategies often employed in other rendering methods.

Unlike biased rendering techniques, which take shortcuts to reduce computation time often at the expense of accuracy, unbiased techniques aim to produce images that are mathematically correct representations of the scene without introducing systematic errors or biases.

The main advantage of unbiased rendering is its potential for photorealistic results, as it can more accurately simulate the interactions between light and materials.

Global Illumination

One of the most significant advantages of this method is its ability to calculate global illumination. In contrast to local illumination techniques that focus solely on direct lighting, global illumination also accounts for indirect lighting, meaning light that bounces off surfaces multiple times before reaching the viewer. This results in much more photorealistic images and more immersive video game experiences. Read more about global illumination here.

Sampling and Noise

Because path tracing relies on random sampling, the resultant images can contain noise, especially with a low number of samples per pixel. High-quality, noise-free images require a large number of samples, which increases rendering time. Noise reduction techniques and denoising algorithms are crucial for making path tracing feasible for both offline and real-time rendering.

Core Path Tracing Algorithms

At the heart of this technique are several algorithms that work in tandem to produce accurate and photorealistic renderings. Some of these key algorithms include:

Monte Carlo Integration: This method is widely used to handle the complex integrations involved in global illumination, efficiently approximating the rendering equation in path tracing and significantly reducing noise in the final render.

Bidirectional Path Tracing (BDPT): An enhancement to the standard path tracing algorithm, BDPT traces two separate light paths - one from the light source and another from the camera. These paths are then joined, reducing the overall rendering time and improving visual quality, particularly in scenes with indirect lighting.

Metropolis Light Transport: This advanced algorithm helps optimize the sampling of light paths, reducing noise and providing a more efficient rendering process. It is particularly efficient in handling difficult light transport situations, such as caustics and complex interreflections.

Computational Processes

Path tracing relies heavily on high-performance computing systems to perform the myriad calculations essential for generating realistic visuals. Graphics processing units (GPUs) play a significant role, as they can tackle multiple operations simultaneously, dramatically speeding up rendering times.

Parallel processing, leveraging multiple processor cores to perform numerous tasks concurrently, is also crucial for the efficient execution of path tracing algorithms. Further, it often necessitates immense amounts of memory to store the vast data involved in simulating intricate light behavior and material interactions. More about 2024 advancements in this area in a sec.

How Does Path Tracing Work? Enhancing Realism

This technique is renowned for its ability to simulate realistic lighting effects in virtual environments. This is made possible through a combination of complex calculations and algorithms that ensure accurate light behavior within digital scenes.

The Role of Light Simulation in Path Tracing

One of the key factors contributing to enhanced realism with this technique is 3D light simulation. Superior rendering accuracy is achieved by simulating natural lighting conditions and the physical behavior of light, including the way it interacts with various materials. The simulation of these factors enables photorealistic light rendering and path traced lighting in digital environments.

Passes, or iterations, are employed by path tracing to calculate light paths. Each pass adds more depth to the scene, predicting different light behavior scenarios. The final image is formed by combining the light paths from multiple passes. The end result is an accurate representation of light behavior that is in line with real-world physics.

Calculating Reflections and Refractions in 3D Environments

Path tracing also excels in calculating reflections and refractions within 3D environments, a critical aspect in achieving realistic material rendering. The complex light path algorithms employed in path tracing enable digital scenes to accurately portray the interactions of light with surfaces such as glass, water, and other materials that exhibit reflective and refractive properties.

Here's how path tracing accounts for reflection and refraction calculations:

  1. 1
    Reflection: In the case of reflective surfaces, this method calculates how a light ray bounces off an object and influences the colors of other objects in the scene.
  2. 2
    Refraction: As for refractive materials, path tracing determines how light travels through these surfaces and how it is bent or refracted in the process.

When path tracing calculates convergence of both reflective and refractive properties, the outcome is a significantly improved representation of materials within the scene.

As the technical aspects continue to advance, so too do the realistic visual effects the technology is capable of producing. The combination of accurate 3D light simulation and refined reflection and refraction calculations equips creators and artists with a powerful tool for realizing their digital visions with extreme realism.

difference between ray tracing and path tracing

Although path tracing and ray tracing share some similarities, they are distinct rendering methods in computer graphics.

Ray Tracing vs Path Tracing – Bluebird Blog

Let's see an in-depth comparison of path tracing and ray tracing, shedding light on (no pun intended) when one method might be more suitable than the other.

Technical Variations

The primary difference between ray tracing and path tracing lies in the approach used to simulate light behavior within a 3D environment. Ray tracing traces individual rays of light, casting rays from the camera to each pixel in the image, and then calculating any resulting intersections with the scene's objects.

On the other hand, path tracing shoots multiple light paths from the camera caused by reflection, refraction, or scattering, and calculates a combined result for each pixel. This difference ultimately affects the realism and subtlety of the resulting images.

Ray Tracing:

  1. 1
    Sampling: Utilizes a single sample per pixel.
  2. 2
    Approach to Simulate Light: Traces individual rays of light, emphasizing their intersections with scene objects.
  3. 3
    Image Realism: Achieves a realistic appearance but may suffer from aliasing and artifacts.

Path Tracing:

  1. 1
    Sampling: Employs multiple samples per pixel.
  2. 2
    Approach to Simulate Light: Shoots multiple light paths, accounting for reflections, refractions, and scattering within the scene.
  3. 3
    Image Realism: Offers increased subtlety and improved realism, and is less prone to artifacts compared to ray tracing.

Ray Tracing vs Path Tracing: Visual Differences

As a result of these different approaches to light simulation, path tracing and ray tracing produce distinct visual outcomes. The multi-sample approach of path tracing allows it to achieve superior realism, capturing indirect lighting and subtle nuances in shadows and reflections that ray tracing may struggle to reproduce. However, ray tracing excels in generating crisp, sharp reflections and refractions, due to its focus on direct light interactions. 

This is primarily due to its focused approach on direct light interactions. Ray tracing calculates the precise behavior of light as it interacts directly with reflective and refractive surfaces, like mirrors, glass, or water. This results in highly accurate and realistic renderings of sharp reflections and clear refractions.

Path tracing excels at rendering:

  • Indirect lighting

  • Soft and subtle shadows

  • Diffuse and glossy reflections

Path tracing, while comprehensive in simulating a wide range of light behaviors including indirect lighting, may not always match the precision of ray tracing in these specific scenarios. Its strength lies more in capturing the overall lighting of a scene, particularly the subtleties of indirect light and soft shadows, rather than the exactness of direct light reflections and refractions.

Ray tracing excels at rendering:

  • Direct lighting effects

  • Sharp and precise reflections and refractions

  • Caustics

The choice between path tracing and ray tracing depends on the specific needs and priorities of a given project. If subtle realism and the accurate simulation of indirect lighting are the main goals, path tracing may be the superior choice. In contrast, ray tracing could be the preferred choice if precise reflections, refractions, and direct lighting effects are the primary focus.

From Traditional Path Tracing to Real-Time Path Tracing

Path Tracing In the Movie Industry

When it comes to movies, frames can be rendered offline over hours or even days. Traditional path tracing prioritizes quality over speed because it can afford to use a high number of samples per pixel to reduce noise, resulting in highly realistic images.

The movie industry uses path tracing to render scenes with complex lighting conditions, including global illumination, caustics, and subtle material properties. The ability to accurately simulate light behavior results in a level of realism that is hard to achieve with other techniques.

However, rendering movies often requires vast computational resources, typically utilizing render farms with thousands of CPUs or GPUs working in parallel to process frames, a feasible approach given that movie production is not real-time.

Path Tracing in Video Games: Speed over Absolute Quality

With advancements in GPU technology, particularly with dedicated ray tracing hardware, path tracing is increasingly being used in real-time applications, such as video games. This requires further optimizations and sometimes the use of hybrid techniques that combine path tracing with faster rendering methods to maintain interactive frame rates.

Real-time path tracing has to make concessions on the number of rays sampled per pixel and the complexity of scenes to maintain interactive frame rates. Despite these limitations, it still manages to significantly elevate the visual quality of games.

The emergence of GPUs with dedicated ray tracing cores (e.g., NVIDIA's RTX series) and intelligent algorithms like DLSS for upscaling allows games to run path tracing in real-time. These technologies balance the computational demands with the need for speed.

Video games often use a hybrid rendering approach, combining rasterization for most of the scene with path tracing for specific effects that benefit most from it, such as realistic lighting and shadows. This strategy allows games to leverage the strengths of path tracing without incurring prohibitive performance costs.

Real-time path tracing has to make concessions on the number of rays sampled per pixel and the complexity of scenes to maintain interactive frame rates. Despite these limitations, it still manages to significantly elevate the visual quality of games.

Path Tracing Developments In 2024: NVIDIA announcements

NVIDIA has played an important role in advancing path tracing technology, especially through its development and introduction of GPUs equipped with dedicated ray tracing cores (RT cores). These innovations have made real-time path tracing more feasible for consumer-level hardware, previously limited to high-end rendering farms used in the movie industry.

They haven't stopped, though: NVIDIA has made a series of announcements at CES (Consumer Technology Alssociation) in January 2024, and a lot of it had to do with the direct or indirect advancement of path tracing technology.

Enhanced GPU Performance: GeForce RTX 40 SUPER Series Graphics Cards

The introduction of the GeForce RTX 4080 SUPER, RTX 4070 Ti SUPER, and RTX 4070 SUPER, with their increased core counts and faster memory, directly translates to improved path tracing performance. The additional computational power and efficiency will enable more complex and detailed real-time path tracing scenarios in games and applications, making high-fidelity graphics more accessible to a wider range of users.

14 New RTX Games

The announcement of 14 new games receiving RTX upgrades, including ray traced effects and DLSS 3, indicates a growing library of titles that leverage real-time ray tracing and potentially path tracing. This expansion suggests that developers are increasingly integrating advanced lighting techniques into mainstream titles, improving the visual quality and realism achievable in real-time rendering.

AI Acceleration with DLSS 3

With DLSS (Deep Learning Super Sampling) 3, games can run at lower native resolutions and then be intelligently upscaled, maintaining high visual quality while improving performance. This is particularly beneficial for path tracing, as it allows for rendering at a fraction of the computational cost. Enhanced performance with DLSS 3 means path-traced games can achieve higher frame rates on the same hardware, making the technology more feasible for real-time applications.

Generative AI and Rendering

NVIDIA's focus on accelerating Generative AI tasks with their GPUs could also indirectly benefit path tracing by enabling more efficient material, texture, and content creation workflows. These AI-based tools can help produce high-quality assets that are optimized for path-traced environments, reducing the manual effort needed and enhancing the realism and detail in scenes.

Which Game Engines Are Embracing Path Tracing?

As of 2023, among the widely used game engines, Unity and Unreal Engine are the primary ones that have integrated and emphasized support for path tracing.

Unreal Engine

Unreal Engine, particularly with its latest versions (like Unreal Engine 5), offers advanced ray tracing and path tracing capabilities. Unreal Engine's rendering architecture is designed to leverage modern GPU technologies, making it suitable for high-fidelity graphics and realistic lighting simulations, including this method.


Unity has also made significant strides in integrating path tracing, especially with its High Definition Render Pipeline (HDRP). This pipeline is designed to provide tools for creating high-quality, realistic virtual environments, and it supports real-time path tracing, enhancing the realism of the scenes.

Other game engines, including Godot and the Open 3D Engine (O3DE), originally developed as Amazon Lumberyard, have focused on different aspects of rendering and may not offer native path tracing support as prominently as Unity and Unreal Engine. However, due to the open-source and modular nature of some of these engines, there is always potential for path tracing capabilities to be integrated by third parties or in future updates.

The integration of this technique in Unity and Unreal Engine marks a significant step in the industry, reflecting the ongoing trend towards achieving photorealistic rendering in real-time applications, especially in gaming and virtual reality.

Pros and Cons of Path Tracing

This technique has made significant strides in the world of 3D graphics, providing professionals in the visual effects industry, game development, and computer graphics with opportunities to create immersive visuals. Let's see the advantages and disadvantages of path tracing, complete with the limitations imposed by current technology:

Advantages of Using Path Tracing in Visual Projects

Path tracing offers several key advantages over other rendering techniques, dramatically impacting the quality of generated visuals.

  1. 1
    Enhanced realism in visuals: This technique accurately simulates natural lighting conditions and produces realistic results, generating photorealistic images and animations.
  2. 2
    Superior shadow and light rendering: Path tracing considers the physical behavior of light in 3D environments, reproducing intricate patterns of lighting, shadow, and reflections for a more visually engaging experience.
  3. 3
    Accurate material representation: By simulating how light interacts with various materials in a scene, path tracing generates realistic depictions of glass, water, metal, and other surfaces with precise reflection and refraction calculations.
  4. 4
    Visual effects industry impact: The adoption of path tracing in movie and television productions adds depth and polish to visual effects, raising the bar for photorealism in various media formats.
  5. 5
    Greater creative freedom: With path tracing, artists and developers can focus on refining their creations in real-time while eliminating the need for manual tweaking of lighting settings, allowing for a smoother workflow and increasing overall productivity.

Limits and Considerations in Current Technology

Despite its numerous benefits, path tracing comes with its share of limitations and challenges that could hinder rendering times or widespread adoption.

  1. 1
    Computational demands: This technique relies heavily on complex algorithms and calculations, resulting in higher computational requirements and potentially slower rendering speeds compared to traditional techniques.
  2. 2
    Technological barriers: As a relatively new technology, it may face complications in terms of hardware and software optimization, such as inadequate GPU capabilities or existing pipeline incompatibilities.
  3. 3
    High-precision output: The extremely detailed output of path tracing can result in large file sizes and increased memory usage, posing a challenge for storage and distribution of the final product.
  4. 4
    Specialized knowledge required: Implementing it effectively may require developers and artists to possess a deep understanding of the technology's principles and applications, potentially posing a steep learning curve for newcomers. (Caveat for video games: game engines like Unreal Engine and Unity offer path tracing capabilities through more user-friendly interfaces and tools, reducing the need for deep technical expertise.)

This method presents an array of advantages, such as greater realism and material representation, as well as challenges like high computational demands and technological obstacles.

As the technology continues to advance and become more accessible, the positive impact of path tracing on various aspects of 3D graphics and the visual effects industry is expected to grow. However, professionals must carefully weigh the benefits and limitations to determine the best approach for their specific projects.

Path Tracing in Video Games: FAQs

Q: What is path tracing and how does it differ from traditional rendering techniques?

Path tracing is a rendering algorithm that simulates the complex behavior of light in a 3D environment, offering more realism than traditional methods. Unlike rasterization or basic ray tracing, it calculates multiple light paths, including indirect illumination, to produce lifelike lighting and shadows.

Q: Can game engines efficiently integrate this technique?

Yes, modern game engines like Unreal Engine and Unity have integrated path tracing capabilities, providing developers with tools to utilize this technology effectively without needing in-depth knowledge of its underlying mechanics.

Q: What are its advantages in game development?

Path tracing provides enhanced realism in lighting and shadows, capturing subtle effects and interactions in a scene. It produces high-quality, photorealistic imagery, elevating the visual fidelity of games.

Q: Are there any disadvantages or challenges in implementing it?

Path tracing is computationally intensive, requiring powerful hardware for optimal performance. It may also present a steeper learning curve for developers unfamiliar with its principles.

Q: How do path tracing and ray tracing compare in gaming applications?

Path tracing is an extension of ray tracing, simulating not just direct light interactions but also indirect lighting and complex reflections. While ray tracing excels in sharp, direct light effects, path tracing offers a more comprehensive simulation of lighting, including soft shadows and indirect light.

Q: Is it accessible to indie developers?

With game engines like Unreal Engine and Unity offering path tracing features, it has become more accessible to indie developers. These engines provide a user-friendly interface to leverage this technique, reducing the need for specialized knowledge.

Q: What impact does it have on game performance?

Its complex calculations can impact game performance, requiring optimization and balance between visual fidelity and frame rate, especially for real-time applications.

Q: How does it influence the future of game graphics?

Path tracing represents a significant leap in achieving photorealism in games. Its ability to simulate real-world lighting more accurately sets a new standard for visual quality in future game development.

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