1. Technical Field
The present invention relates to screens and projection systems.
2. Related Art
Various types of screens are available as projection screens used with projectors (projection-type display apparatuses) to display large images in presentations such as in exhibitions and conferences, including academic conference, or in screening of videos such as in home theaters.
However, there is a problem in these types of screens. For example, in a reflection-type screen, the ambient outside light such as illumination light and window sunlight is also reflected in reflecting the projected light from a projector to display a projection image. Accordingly, the contrast, or the luminance ratio between white (maximum luminance) and black (minimum luminance) becomes low in a bright environment, and it is difficult to display a clear image.
In an effort to develop a screen that can achieve high contrast even under bright settings, there have been attempts to reduce the minimum luminance by suppressing the adverse effect of contrast-lowering outside light such as sunlight and illumination light. This type of screen is proposed in, for example, JP-A-2002-107828 (Patent Document 1) and JP-A-2006-317832 (Patent Document 2), in which a light absorbing layer that includes a light absorbing dye or pigment is provided to absorb unnecessary outside light.
Ordinary screens are provided with a light diffusing layer that diffuses light to increase the viewing angle. Regarding such screens, Patent Document 2 points out the adverse effect caused by the reflected light of the light diffusing layer on the image quality of a projection image. Specifically, the publication points to the wavelength dependency of the intensity of the reflected light at the light diffusing layer as the cause of an incorrect white balance in the light reflected by the light diffusing layer, and thus in the projection image.
To overcome this problem, Patent Document 2 proposes providing a light absorbing layer on the back side (opposite from the viewing side) of the light diffusing layer disposed on the viewing side to make the absorbance of the light absorbing layer larger on the longer wavelength side (toward the red) and smaller on the shorter wavelength side (toward the blue) and thus cancel out the intensity distribution of the reflected light at the light diffusing layer and improve white balance.
However, the screen structures described in the foregoing publications are for solving the low contrast caused by one kind of outside light, such as illumination light in airplane (Patent Document 1), and room illumination such as a fluorescent lamp (Patent Document 2). Neither publication makes a thorough assessment regarding problems that might occur when unintended outside light falls on the screen.
A representative example of such unintended outside light sunlight. When a screen is used in a room with a window, sunlight may fall on the screen through the window with an angle different from the incident angle of the room illumination, with the result that the contrast is reduced.
Unlike the fluorescent lamp and other types of room illumination identified as a problem in the related art, sunlight contains the whole range of light in the visible light region. Thus, when the screen is adapted to suppress a contrast drop by, for example, selectively absorbing the wavelengths of room illumination, the screen also removes a part of sunlight at the wavelengths corresponding to the specific wavelengths of the room illumination upon incidence of sunlight, which contains the whole range of light in the visible light region. The remaining component of the sunlight imparts color.
The coloring that occurs on the screen in this manner disrupts the white balance of the projection image, and deteriorates image quality. The foregoing publications do not take any measure against such an anticipated problem.