How to set up automotive studio lighting in Unreal Engine

Epic Games Technical Account Manager Dawei Ji |
2021年5月10日
The purpose of this guide is to help automotive users create high-quality studio renderings using the fundamentals of the Unreal Engine automotive template. Users will be able to follow along and improve their lighting, ray tracing, and environment rendering. Our solution offers a fully dynamic rendering scenario that allows users to work in real-time.
Studio renderings are used to create state-of-the-art visual experiences for industries such as film and interactive animation.
This guide uses a method of manual lighting to studio render a car in Unreal with no external lighting HDRI textures. 

Image based lighting usually generates complex reflections/colors from an HDRI image but doesn’t help here because we want to exercise pure CG-based lighting rather than just use IBL rendering with an HDRI map. This also presents a more adaptive way to show off the car’s original design while providing an elegant rendering atmosphere. 

This guide consists of two main parts; one is for exterior rendering, and the other is for the interior. I will walk you through this step by step by modifying the model, creating lighting and materials, and will share some tips on how to reach the target rendering results below. 
Exterior rendering
Interior rendering

Exterior rendering

Setting up the level

Most rendering theories respect the rule that less is more, which means keeping the scene as simple as possible. A complex environment that includes millions of polygons and tons of textures isn’t necessary for studio rendering. 

Here, we’re going to focus on aspects that help create an appealing real-time render, which includes elements like lighting, reflection, composition, and more.

Let's start by creating a new automotive project and then opening the cinematic level of the automotive template, as shown below. We will be cleaning up the scene a bit by removing the default car with the notes from the level before creating the lighting for the scene. It’s a good idea to create lights on a separate level so you can add and tweak the lights around cars on any of the levels more easily.
Build the studio environment
Once your car model is imported with its material assignments, a bit of modification is required to modify the template scene. In this case, the backplate is not useful here due to the distracting reflections/specularity. Hiding or deleting the backplate mesh can solve this issue.
The floor’s material should be modified by increasing the roughness and tile scale a bit to provide the ground a realistic, reflective look.

Set up the lighting

1) Ambient lighting with BP light cards

First of all, let’s change the exposure method to manual in the project settings and post volume.
There are two BP light cards that we can use to easily create a base lighting/reflection for the car. The BP light cards also define the ambient lighting for the entire scene as well.
Avoid applying a high value for the intensity of the BP lights since the BP light cards are actually connected to a skylight, which could expose the scene too much.
Insert an HDR map to the color of the BP lights to get more detailed color and reflections on the car’s paint and windshield glass.
Lower the light intensity and change the color temperature by adjusting the intensity and kelvin from the BP light panel. This sort of dimmer ambient lighting fits the mood we want the scene to set and provides a smooth reflection on the car’s paint and windows.
2) Add your lights

Place a couple of lights to fill some specific dark areas as needed. Use rect light as key lights to lighten up some of the large surfaces of the car, and use spot lights to highlight sections of the car that may be shrouded in darkness. Point lights can be used to help reveal the shape of the car. These three types of lights help offer direct lighting and reflections with BP lighting cards, serving up ambient lighting and base reflections.
Always remember that it’s important to make the lighting look as clean as possible. Ensure that all of the lights you add are changed to movable so that you can tweak the lights around the car to generate the desired lighting and reflection you’re going for before adding new lights to the scene. Doing so allows you to tweak the position, orientation, and size of each light to instantly get the lighting and reflection you desire. 
Rect lights generate more physically correct lighting in certain areas, which can create a nice reflection on the side of the car. It works well on either curvy or angular car bodies. 

Rect lights’ diffuse/specular heavily affects the final look of the car. Make sure you don’t place too many big rect lights in the scene that may flatten the lighting and ruin the reflection of the car. It’s good to just tweak the rect light’s size, position, or orientation until you get it working well. Sometimes the specular may not look good, but that may depend on your viewing angle. 

There are a couple of ways you can try to improve the reflection: 

1) While I personally didn’t use it here, you can insert a white-black ramp texture to soften the edge of the light reflected onto the surface. 

2) You can reduce the specular parameter or even set it to 0 when the specular looks too bright or is off-putting.
Point lights can help light complex structures of the model, such as the headlights. They can also be used to add specularity to certain areas. For instance, a point light was placed in front of the car as a fill light to brighten the dark side of the logo.
Spot lights help fill darker areas like the intake, wheels, or to emphasize the outline of a car. Also, spot lights can provide the car a very dramatic ground shadow with falloff on the shadow edge from a far distance. Decreasing the cone of the light with a softened cone edge can nicely blend the spot’s contribution with the existing lighting.
The final step of finishing the exterior lighting is to add two rect lights on both sides of the car as seen in the image below. This fills in the dark areas on the sides of the car and provides a nice-looking reflection across the shoulder line. 

Interior lighting

Exterior lighting leak check

Make sure the exterior lighting of the car doesn’t affect the interior as much as possible, especially the areas of the console. Seats, in particular, are better lit with interior lights.

Turn off the BP lights to see if the exterior lights affect the interior. If they do, adjust the attenuation of the exterior lights or disconnect the light links using the light channel.

Ambient lighting

Since we don’t need the skylight to contribute to the interior lighting because the space is small, we want more detailed interior lighting with higher contrast than the exterior while enabling the skylight’s raytraced shadows, which serves as a good starting point for the interior lighting.

Adding extra lights

Add some rect lights on the windshield, ceiling, and side windows to bring light inside and resize and rotate the lights as you would like. You can choose to reduce or remove the reflection cast from specific light by searching for “specular” and lowering it in the rect light’s detail panel.

You can add point lights and spot lights to emphasize certain areas like the steering wheel, console, and seats.
Interior lights off
Interior lights only
Exterior and interior lights on

Light channel 

As the interior structure is a bit narrow and more complex than the exterior, sometimes users may encounter issues where certain areas are over-lit or have unwanted light. We can easily use light channels as an effective way to add/break light links for specific objects.

Ray traced ambient occlusion is a huge benefit that casts soft shadows with depth and contrast to the interior, raising the per-pixel sample to reduce noise. You can make the raytraced AO adaptive to the interior by adjusting the ambient radius in the post volume and cine camera panels. 

Global illumination

GI was not used because it breaks the balance of lighting and shadow, which would brighten and flatten the interior lighting. In some cases, ray tracing GI within interior rendering could even generate light leak.

Post effects and final rendering

Finally, select all rect lights and search “sample” and increase the values for rendering for high quality, which you can also do within the post volume for reflection and AO. However, higher percentage or samples will seriously impact the performance, so it’s recommended to set them up carefully according to your scene size or complexity.

For the final output, you can either choose to make a quick screen snapping with the screen percentage set to 150 or higher using the High Resolution Screenshot or setting up a rendering using the Movie Render Queue for better anti-aliasing and denoising.
 

Conclusion

All of the steps above help create high-quality studio rendering in an efficient way for both car interiors and exteriors using Unreal’s real-time techniques. As you can see, by leveraging the power of ray tracing in real-time, users can tweak BP light cards as the base of ambient lighting and reflections, along with extra lights that you can add to the template scene to get an appealing studio render that feels completely intuitive. This ultimately saves you time creating an offline render. To top it off, no external resources are required in this tutorial. All users need to do is download Unreal Engine and give it a try today!

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