Environmental HDR Lighting & Reflections in ARCore: Implementation in Unity 3D (Part 3)

Reflective Sphere in Google ARCore with Environmental Mapping

How to make real-time HDR lighting and reflections possible on a smartphone? Based on the unique properties of human perception and the challenges of capturing the world’s state and applying it to virtual objects. Is it still possible?

Google found an interesting approach, which is based on using Artificial Intelligence to fill the missing gaps. In this article, we’ll take a look at how ARCore handles this. The practical implementation of this research is available in the ARCore SDK for Unity. Based on this, a short hands-on guide demonstrates how to create a sphere that reflects the real world – even though the smartphone only captures a fraction of it.

Google ARCore Approach to Environmental HDR Lighting

To still make environmental HDR lighting possible in real-time on smartphones, Google uses an innovative approach, which they also published as a scientific paper . Here, I’ll give you a short, high-level overview of their approach:

First, Google captured a massive amount of training data. The video feed of the smartphone camera captured both the environment, as well as three different spheres. The setup is shown in the image below.

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Environmental HDR Lighting & Reflections in ARCore: Virtual Lighting (Part 2)

FOV of a smartphone

In part 1, we looked at how humans perceive lighting and reflections – vital basic knowledge to estimate how realistic these cues need to be. The most important goal is that the scene looks natural to human viewers. Therefore, the virtual lighting needs to be closely aligned with real lighting.

But how to measure lighting in the real world, and how to apply it to virtual objects?

Virtual Lighting

How do you need to set up virtual lighting to satisfy the criteria mentioned in part 1? Humans recognize if an object doesn’t fit in:

The left image shows a simple scene setup, where the shadow direction is wrong. The virtual object doesn't fit in.
In the ideal case on the right, the shadow and shading is correct.
Comparing a simple scene setup to environmental HDR lighting. Image adapted from the Google Developer documentation.

The image above from the Google Developer Documentation shows both extremes. Even though you might still recognize that the rocket is a virtual object in the right image, you’ll need to look a lot harder. The image on the left is clearly wrong, especially due to the misplaced shadow.

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Environmental HDR Lighting & Reflections in ARCore: Human Perception (Part 1)

Screenshot of the reflective sphere placed in the real world, based on the Environmental HDR lighting by Google ARCore.

Realistically merging virtual objects with the real world in Augmented Reality has a few challenges. The most important:

  1. Realistic positioning, scale and rotation
  2. Lighting and shadows that match the real-world illumination
  3. Occlusion with real-world objects

The first is working very well in today’s AR systems. Number 3 for occlusion is working OK on the Microsoft HoloLens; and it’s soon also coming to ARCore (a private preview is currently running through the ARCore Depth API – which is probably based on the research by Flynn et al. ).

But what about the second item? Google put a lot of effort into this recently. So, let’s look behind the scenes. How does ARCore estimate HDR (high dynamic range) lighting and reflections from the camera image?

Remember that ARCore needs to scale to a variety of smartphones; thus, a requirement is that it also works on phones that only have a single RGB camera – like the Google Pixel 2.

Continue reading “Environmental HDR Lighting & Reflections in ARCore: Human Perception (Part 1)”