Indian Prince 1926 Motorcycle - HDRI Projection

Project Overview

The use of 360 HDRI in VFX projects is one of the most used techniques to create lighting setups and generate photorealistic reflections and interactions achieving more accurate integrations between CG and live action plates.

Although this technique has many advantages over the conventional use of 3D lights such as area lights, spot lights or directional lights; it also presents some challenges to make the integration of the CG element to look correctly composed in the scene.

One of these challenges lies in the fact that the 360 HDRI is a spherical representation of the real environment. This suppresses physical principles of light such as the inverse square law, eliminating the decay light sources have depending on the distance between the light source and the illuminated object. Additionally, since the 360 HDRI is captured from a specific point in space, this eliminates a correct parallax when the camera is moved through space. Although this problem can be solved in the compositing process by using backplates, it is not possible to solve if the scene is to be rendered entirely in 3D.

Understanding this context, with this project I want to present the workflow I used to solve these two problems in a fully 3D scene. Using only a single 360 HDRI as the main light source I want to show the necessary steps to solve the parallax and light intensity problems to achieve a more accurate photorealistic result.

Look Dev

The amazing photorealistic look development work was done by Risa Suzuki. She modeled and textured a high-resolution model of the iconic Indian Prince 1926 motorcycle. The software used for the modeling was Maya and Substance Painter was used to create the textures.

HDRI

The 360 HDRI was downloaded from polyhaven.com. I chose this HDRI by the artist Sergej Majboroda because it was aligned with the final aesthetic I was looking for in the final product.

Being a stock HDRI and not being produced specifically for this project, I had to analyze the best angle where I could have vanishing points and a good lighting point. For this project I used Maya and I used Arnold as render engine.

Scene Setup & Lighting

The first step was to create a proxy geometry of the space to represent the real dimensions of the space. With no measurements in the environment, this process had to be manual and approximate. If I had created the HDRI, I would have had the opportunity to take reference measurements of the space or use photogrammetry or LIDAR capture techniques to reduce the percentage of error in the proxy geometry.

After finishing the proxy geometry, I projected the 360 HDRI over the geometry. The shader I used was maya's SurfaceShader. This generates the global illumination and general reflections. Additionally, the use of this shader allows to keep the original color of the HDRI for the environment rendering.

To achieve the correct intensity of the light sources, I cut out the brightest parts of the HDRI and created individual .exr files. I then used these files as area lights maps and placed them in the corresponding locations within the 3D space. This allowed me to have control over the highest intensity light sources in the space and then adjust them to create the speculars and brightest areas on the motorcycle.

Additionally, it is necessary to reduce the double illumination that can be generated by the SurfaceShader and the aera lights so that all the main illumination is given only by the area lights. In Nuke, I covered all the higher intensity light sources and this new HDRI is the one I used for the projection.

Having the scene complete, I created the camera movements. Having a 3D space, I was already sure that the parallax of the CG with the environment was correct. In addition, this process generated a correct Zdepth to create defocus and it gave me a correct interaction in the contact zone between the floor and the motorcycle. For example, this is one of the most complicated aspects to integrate in a pipeline where the HDRI is used in dome light and rendered as a backplate for the final composition.

When the camera is moved, it is evident the difference between an HDRI only used in a domelight, vs. the result of using the HDRI as a projection on the proxy geometry. Additionally, a better light interaction is obtained because there are lights placed in the 3D space. However, it is necessary to mention that when a single 360 HDRI is used, it is not recommended to make very extreme camera movements since a stretching effect on the textures may become evident. To solve this, it is necessary to create several 360 HDRIs of the space to merge them in the project process.

Compositing & Color Grading

For the compositing process, I generated 3 independent layers: background environment, motorcycle and matte shadow. In addition to the traditional passes, I used Zdpeth, Position and Normal passes in order to recreate a representation of the space in Nuke and have a better control of the compositing. These passes gave me the control to place the volumetric lights, smoke, and dust (3D particles) in the correct space giving me a higher level of integration of these elements.

Finally for the color grading process I used Davinci Resolve. Since I worked this pipeline entirely in ACES (Academy Color Encoding System) I had more control over the color grading and I had all the necessary information to be able to add a print film emulation (PFE) treatment creating effects such as vignetting, grain, chromatic aberration, and halation.

Special Thanks

Risa Suzuki : https://www.instagram.com/risa3dart/

Sergej Majboroda: https://polyhaven.com/a/old_bus_depot

Software: Maya, Substance Painter, Arnold, Nuke, Davinci Resolve

LinkedIn: https://www.linkedin.com/in/camilogu/

Website: https://camilogu.com

Instagram: https://www.instagram.com/camilogu/

Thank you for reading my entry!