1. Field of the Invention
The present invention relates to a projector. More particularly, the present invention relates to a projector for image projection in a full-color manner, and capable of effectively compensating for unbalancing of colors by use of auxiliary illuminating light.
2. Description Related to the Prior Art
A liquid crystal projector is known as an image display device. The liquid crystal projector of a full-color type includes plural liquid crystal display panels (LCD panels), which optically modulate light so as to project image light to a screen for displaying an image. Two types of the liquid crystal projector are known. A first of those is a front type in which an image is projected to a front side of the screen in a direction toward the rear. The second of the methods is a rear type in which an image is projected to a rear side of the screen in a direction toward the front. Also, there are plural illuminating methods different from one another according to a transmission type or reflection type of the LCD panels to be used. In any of them, the LCD panels are driven to indicate an object image, which is illuminated with illuminating light. Image light is projected by a projecting lens to a screen in a focused state.
The LCD panels in the liquid crystal projector are three panels for blue, green and red colors. For the illuminating light from a light source in the liquid crystal projector, dichroic mirrors are used for color separation. The illuminating light from the light source is separated into components of the blue, green and red colors, which are applied to corresponding ones of the LCD panels. For the respective channels of the primary colors, the light is optically modulated by the LCD panels, and is combined by a combining optical system such as a prism, to project a full-color image to a screen.
A light source for use in the liquid crystal projector should have well-balanced color components of primary colors. However, an ultra high pressure mercury lamp generally used in the liquid crystal projector does not have a good balance between color components. See FIG. 7. Although the color of daylight or solar light is sufficient white light, the color of the light of the ultra high pressure mercury lamp has higher levels in the blue and green components. A light amount of the red component of the light of the light source is smaller to an amount of a remarkable shortage. Also, a further difference occurs. The illuminating light is separated into the components of the primary colors, before the components are combined by a combining prism to obtain the image light. In this process after the light separation, there occur deficits in the light amount of the components. However, there are differences in the deficit between the primary colors.
In the travel of the illuminating light from the light source in the liquid crystal projector, a balanced state between the color components in the image light comes to have a lower quality, to lower the image quality of the projection. It is required to correct the color balance of the components.
Techniques of laser have been used widely in various fields. A laser medium is supplied with energy to emanate laser light. A wavelength or color of the laser light is peculiar to and depends upon a characteristic of the laser medium. Also, a laser diode is very useful as laser medium because of a small size of a semiconductor. It is conceived to use laser as the illuminating light.
However, there arises a problem derived from a characteristic of laser. Illumination of laser light is influence by coherency of the laser, to create noise called speckles in an illuminating region. When laser is used as light surface in the liquid crystal projector, flickering is likely to occur in a displayed image. Furthermore, black spots may occur in the displayed image, to lower the image quality.
JP-A 2001-148345 discloses an optical instrument for illumination, in which a mirror is shaken or oscillated in a light path from a laser light source to an object, for the purpose of virtually removing unwanted influence caused by coherency of laser light. U.S. Pat. No. 6,317,169 (corresponding to JP-A 2002-543455) discloses a display in which an image itself is shaken or oscillated to a small section.
However, the structures according to the prior document have a problem in an enlarged size of the shaking device because of a great size of a vibrating element. If the image to be displayed is shaken itself, the image quality will be low.