Photorealism approaches
In this section, you will learn about and explore the main approaches usually deployed to generate photorealistic synthetic data. We will learn about the following:
- Physically based rendering
- Neural style transfer
Physically Based Rendering (PBR)
The Physically Based Rendering (PBR) approach is widely used in game engines such as Unity and Unreal to accurately simulate how materials in the 3D virtual world interact with light. In the real world, this is a complex process, thus it requires a significant understanding of optics and many simplifications to make these processes applicable to game engines. Physically based materials are essential to this approach. They resemble how similar materials in the real world interact with light. These materials usually have properties and parameters that are calculated based on real measurements from real-world materials. The properties may include absorption, scattering, and refraction coefficients and parameters. It should be noted that the main principle behind PBR is energy conservation, which means that light energy reflected and scattered by a material should not exceed the total incoming or received light energy by this material.
As expected, deploying a photorealistic rendering pipeline will help us to simulate and render more accurate and realistic light behaviors and materials. Thus, we can generate more photorealistic synthetic data.
Neural style transfer
Neural style transfer is a well-known technique that transfers an artistic style from one image to another while preserving the content of the latter. This method can be applied to synthetic datasets to improve their photorealism and thus mitigate the domain gap between synthetic and real data. For example, the Sim2Real-style transfer model can be deployed to bridge the gap between synthetic and real data for the task of pose estimation. For more information, please refer to Sim2Real Instance-Level Style Transfer for 6D Pose Estimation (https://arxiv.org/abs/2203.02069). Additionally, there are many interesting works that explore how to adapt the GTA5 synthetic dataset (https://www.v7labs.com/open-datasets/gta5), which was generated from the Grand Theft Auto V video game, to the real Cityscapes dataset (https://www.cityscapes-dataset.com).