The present invention relates to a system that automatically adjusts a liquid-crystal projector according to environmental conditions such as lighting conditions and projection-surface conditions. 
Image projection equipment such as liquid-crystal projectors and cathode-ray-tube projectors (referred to below as LCD projectors and CRT projectors, respectively) are used in classrooms and meeting rooms, for example, to project various types of images onto a projection surface such as a screen or a wall.  To project a clearly visible image, a CRT projector generally has to be used in a dark or at least a dim environment.  LCD projectors, however, are now able to project images bright enough to be seen under a wide range of lighting conditions, including rooms illuminated by fluorescent or incandescent lights. 
The quality of the projected image is strongly affected by the brightness and color of the ambient lighting.  Image quality is also affected by the brightness (or reflectivity) and color of the surface onto which the image is projected.  To project a clear image with natural coloration, it is necessary to adjust the contrast, brightness, and color balance of the image to compensate for these environmental conditions.  The color-balance adjustment is often performed as a white-point adjustment or color temperature adjustment.  In conventional projection equipment, the adjustments are performed manually. 
Since an LCD projector is portable, it tends to be used in environments with many different lighting conditions and many different types of projection surfaces.  Each time a conventional LCD projector is brought into a new environment, the user is forced to adjust the projector manually in order to obtain a clear and natural image.  Different adjustments are necessary depending on, for example, whether the ambient lighting is fluorescent (which has a bluish cast) or incandescent (which has a reddish cast), and whether the projection surface is a white screen, a white wall surface, or a non-white wall surface. 
There is a known technology (disclosed in Japanese Unexamined Patent Publication No.  5-227497, for example) for sensing ambient brightness and adjusting the brightness of the displayed image automatically, but this technology fails to adjust the color balance, and fails to compensate for the color and reflectivity of the projection surface. 
Accordingly, even with the above technology, the user of a conventional liquid-crystal projector is faced with the need to make manual adjustments each time the liquid-crystal projector is set up in a new environment.  These adjustments are troublesome and take time. 
An object of the present invention is to provide an image-quality adjustment system that automatically adjusts an image projected by an LCD projector according to the brightness and color of ambient light and the brightness and color of the projection surface. 
The invented image-quality adjustment system includes a photosensor and a processor, forming part of an LCD projector.  The photosensor detects the brightness and color of external light.  The processor adjusts an image signal according to the detected brightness and color, preferably adjusting the brightness, contrast, and color balance of the image signal.  The LCD projector projects an image according to the adjusted image signal. 
The image-quality adjustment system may also include a control circuit that controls the intensity of the lamp in the LCD projector according to the detected brightness. 
The external light detected by the photosensor may be ambient light, or light reflected from the surface onto which the image is projected.  Alternatively, the image-quality adjustment system may have photosensors for detecting both types of external light.