Challenges with displaying enhanced and synthetic vision video on a head-up display

Displaying video on a head-up display from an Enhanced Vision System camera or Synthetic Vision System engine presents some unique challenges not seen on conventional head-down flight deck displays. All information displayed on the HUD has to be seen against a background that can vary from bright sunlight to a dark night sky. The video has to include enough grayshade information to support visual identification of runway features and the image shown on the HUD has to be visually aligned to the real world accurately enough to support low-visibility operations at airports. The pilot needs to clearly see the image on the HUD but also needs to see the real world through the display when it can be seen with the naked eye. In addition, the video display cannot interfere with the display of existing flight information symbology.