One opinion about the difference is that mixed reality virtual objects are "anchored" in reality - they're placed specifically, and can interact with the real environment. For example, mixed reality objects can stand on or even hide behind a real table.
By contrast, augmented reality objects are not "anchored," but simply float in space, anchored not to physical spaces but instead to the user's field of view. That means Hololens is mixed reality, but Google Glass is augmented reality.
An alternative definition says that mixed reality is a kind of umbrella term for virtual objects placed into a view of the real world, while augmented reality content specifically enhances the understanding of, or "augments," reality. For example, if buildings are labeled or people's faces are recognized and information about them appears when they're in view, that's augmented reality in this definition.
Under this differentiation, Google Glass is neither mixed nor augmented reality, but simply a heads-up display - information in the user's field of view that neither interacts with nor refers to real-world objects.
Complicating matters is that the "mixed reality" label is falling out of favor in some circles, with "augmented reality" serving as the umbrella term for all technologies that combine the real with the virtual.
If the use of "augmented reality" bothers you, just wait. That, too, may soon become unfashionable.
Fact: New media are multimedia
And now we get to the confusing bit. Despite clear differences between some familiar applications of, say, mixed reality and virtual reality, other applications blur the boundaries.
Consider new examples on YouTube.
One video shows an app built with Apple's ARKit, where the user is looking at a real scene, with one computer-generated addition: A computer-generated doorway in the middle of the lane creates the illusion of a garden world that isn't really there. The scene is almost entirely real, with one door-size virtual object. But when the user walks through the door, they are immersed in the garden world, and can even look back to see the doorway to the real world. On one side of the door, it's mixed reality. On other side, virtual reality. This simple app is MR and VR at the same time.
A second example is even more subtle. I'm old enough to remember a pop song from the 1980s called Take On Me by a band called A-ha. In the video, a girl in a diner gets pulled into a black-and-white comic book. While inside, she encounters a kind of window with "real life" on one side and "comic book world" on the other.
Someone explicitly created an app that immerses the user in a scenario identical to the "A-ha" video, wherein a tiny window gives a view into a charcoal-sketch comic world - clearly "mixed reality" - but then the user can step into that world, entering a fully virtual environment, with the exception of a tiny window into the real world.
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