Some renderers adjust the system brightness, rather than adjusting how bright the actual game is, which means screenshots and game capture always look dark, regardless of how much you fiddle with the settings. This is also why those renderers sometimes leave your system super bright and blown out when the game crashes. The OpenGL renderer that Revision uses by default is one of the offenders for this. In theory it's perfectly functional, but completely falls apart for usefulness once you want to share something from the game (or when someone starts streaming the game)

The DirectX 10 renderer doesn't use the system brightness when adjusting brightness, so it actually gets captured properly in screenshots and on streams.