How it works...

Throughout the current recipe, we've had the opportunity to work with HDRi lighting. The lights that make use of this technique are usually of the Skylight type in Unreal Engine 4, a particular kind that allows for the input of the necessary textures that contain the photon information.

As we've said before, HDRi images capture the lighting state of a particular scene in order to be able to use that information in a 3D environment. The way they do this is by sampling the same environment multiple times under different exposure settings. Taking multiple pictures this way allows for their combination at a post process stage, where the differences in lighting can be interpolated to better understand how the scene is being lit.

What's important to us it that we need to be on the lookout for the right type of textures. HDRi images need to be in a 32-bit format, such as .EXR or .HDRi, as each pixel contains multiple layers of information condensed into itself. You might find HDRi images in a non-32-bit format, but these don't contain as much lighting information as the real ones because of the format they use.

Another parameter to take into consideration is the number of f-stops that a given HDRi image is composed of. This number indicates the amount of different pictures that were taken under different exposures to be able to compose the HDRi. A value of five means that the HDRi was created out of five interpolated images, and a value of seven indicates that said number was instead used. More pictures mean a wider range of values and the consequent increase of information. It is a case of the more, the better, as seen in the next screenshot:

These photographs are a sequence of different images that make up an HDRi. HDRi by HDRi labs.

In this recipe, we've taken a look at several key concepts in the PBR workflow—image-based lighting, reflections, and the different mobility types a light can belong to. These elements, while not a part of the material pipeline themselves, are an essential part of the whole physically based approach at rendering that Unreal has at its core. They work hand-in-hand with the materials we create, expanding their capabilities and complementing the base properties we define them to have. Think about it—there's not much use having a highly reflective material if we don't tell the engine how to treat those reflections. Hope you found this useful!