Extremely relevant patent: Controlling brightness of a displayed image

This is one of the patents purchased by Microsoft from ODG.

[...] environmental light may make it difficult to view the displayed image, depending upon a relative brightness of the displayed image and the see-through view [...] brightness of the displayed image may be increased as the brightness of the background scene increases, and/or electrochromic or photochromic shield lenses may be used for automatically darkening or lightening in response to changes in brightness in the environment. [...] this disclosure relates to controlling a brightness of an image displayed on a see- through head mounted display via measuring a brightness of a see-through view via light sensor located on a same side of a see-through display as a user's eye [...] one or more lenses 110 includes a shield lens 310, which can be tinted with a constant darkness of tint or can be electrochromic or photochromic with variable darkness of tint or variable optical density.

And so on. The key part of this patent is its integration of the light sensor and the way it adapts to changes in background brightness. It takes advantage of non-linear sensitivity of eyes to illumination to maximize perceived changes in brightness and has a method for computing brightness that accounts for the amount of background light present over a time period. The patent also has user-controllable opacity of the light shield that provides darkening. It doesn't suggest that the brightness of the scene is boosted by projecting an image of the scene, but it doesn't preclude that possibility either.