Consider the scene above where a user, standing inside an archway, looks out on a clear day. As the user pans their gaze, the camera's AGC (Automatic Gain Control) changes, to capture subject matter of different illumination.
Lightspace/Comparametric imaging uses this change in camera gain to combine properly exposed areas of the image into a single image of extended dynamic range. Furthermore, the change in gain can be calculated, and this can be used to spatially register images of different gain. Finally, by mimicking the response of the camera, computer-generated information can be displayed in a tonally accurate manner, reflecting the current gain/exposure of the camera.