Patent ID: 8593373

Claim:
A headup display device configured to control a brightness of an image according to a present illumination in an environment of a vehicle and project the image to a front windshield of the vehicle to indicate the image as a virtual image in an interior of the vehicle, the headup display device comprising: an interior illuminance sensor detecting an interior illumination, wherein the interior illumination is an illumination of a first detection area within the vehicle; an exterior illuminance sensor detecting an exterior illumination, wherein the exterior illumination is an illumination of a second detection area external of the vehicle; an illumination determination unit configured to: determine an illumination state based on the interior illumination detected by the interior illuminance sensor and the exterior illumination detected by the exterior illuminance sensor, wherein the illumination state is in a light-adapted state when the interior illumination is greater than the exterior illumination and the illumination state is in a dark-adapted state when the exterior illumination is greater than or equal to the interior illumination, determine the present illumination of the vehicle by multiplying an increasing rate by the interior illumination, in the light-adapted state, determine the present illumination of the vehicle by multiplying a decreasing rate by the exterior illumination, in the dark-adapted state; and a brightness control unit configured to control the brightness at a brightness corresponding to the present illumination determined by the illumination determination unit.