Patent Publication Number: US-2007097329-A1

Title: Rear projection system

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a rear projection system capable of adjusting an output image according to a sensing result of a light sensor, and more particularly, to a rear projection system capable of adjusting an output image according to a sensing result of a light sensor positioned behind a reflector.  
      2. Description of the Prior Art  
      Increasing demand for large screen televisions is giving rise to an expanding market for planar televisions. Advanced technologies overcome the obstacles of manufacturing large-scale planar displays and gradually lower the prices of the products. Therefore, large-scale planar displays, once appearing as expensive professional equipment, have found an increasing number of household applications, such as in home theaters. Various projection techniques aiming at providing better visual experience are constantly being researched and developed. Among them, rear projection displays feature high contrast, high brightness, large viewing angles, sharp picture definition and low geometrical distortion, and are therefore very competitive in the market.  
      Please refer to  FIG. 1  and  FIG. 2 .  FIG. 1  is a perspective drawing of a rear projection system  10  of the prior art, and  FIG. 2  is a diagram of internal components of the rear projection system  10 . The rear projection system  10  can be a cathode ray tube (CRT) monitor, a digital light processing (DLP) monitor, a liquid crystal on silicon (LCOS) monitor, or a liquid crystal display (LCD) monitor, depending on the kind of image source. The rear projection system  10  includes a housing  12  for covering internal components, a reflector  14  installed inside the housing  12 , an image source  16  installed inside the housing  12  and positioned on one side of the reflector  14  for projecting an image to the reflector  14 , a screen  18  installed on the housing  12  for receiving the image projected from the image source  16  to the reflector  14  and reflected from the reflector  14  so as to display the image, and a plurality of light sensors  20  installed on the housing  12  and around the screen  18  for sensing light reflected from the reflector  14 . The image source  16  can be a source with a single light source or multiple light sources. The image source  16  can project an image to the reflector  14 , and the reflector  14  can reflect the image projected from the image source  16  to the screen  18  so that the image can be presented on the screen  18 .  
      If the image source  16  includes multiple light sources, such as three cathode ray tubes, there is a need to detect or adjust the image focused on the screen  18 . The light sensors  20  positioned around the screen  18  can sense light projected around the screen  18 , and the rear projection system  10  can detect the focus status of the image according to the sensing result of the light sensors  20  so as to adjust the image. The advantage of positioning the light sensors  20  around the screen  18  is to prevent the light sensors  20  from blocking light projected to the screen  18 . However, the disadvantage of positioning the light sensors  20  around the screen  18  is that the light sensors  20  can only detect the focus status of the light surrounding the screen  18  and cannot detect the focus status of the entire image on the screen  18 . Hence the light sensors  20  are useless for detecting the focus status of the image on the screen  18  despite the number of light sensors positioned around the screen  18 .  
     SUMMARY OF THE INVENTION  
      It is therefore a primary objective of the claimed invention to provide a rear projection system capable of adjusting an output image according to a sensing result of a light sensor positioned behind a reflector for solving the above-mentioned problem.  
      According to claimed invention, a rear projection system includes a partially transmissive reflector with light-transmissivity, an image source installed on one side of the reflector for projecting an image to the reflector, a screen for receiving the image projected from the image source and reflected from the reflector so as to display the image, at least one light sensor installed on the other side of the reflector for sensing light of the image projected from the image source to the reflector and passing through the reflector, and a control module coupled to the light sensor for controlling the image source to project a next image according to the sensing result of the light sensor. 
    
    
      These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.  
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a perspective drawing of a rear projection system in the prior art.  
       FIG. 2  is a diagram of internal components of the rear projection system of  FIG. 1 .  
       FIG. 3  is a perspective drawing of a rear projection system according to the present invention.  
       FIG. 4  is a diagram of internal components of the rear projection system of  FIG. 3 .  
       FIG. 5  is a functional block diagram of the rear projection system of  FIG. 3 . 
    
    
     DETAILED DESCRIPTION  
      Please refer to  FIG. 3 ,  FIG. 4 , and  FIG. 5 .  FIG. 3  is a perspective drawing of a rear projection system  50  according to the present invention,  FIG. 4  is a diagram of internal components of the rear projection system  50  according to the present invention, and  FIG. 5  is a functional block diagram of the rear projection system  50  according to the present invention. The rear projection system  50  can be a cathode ray tube (CRT) monitor, a digital light processing (DLP) monitor, a liquid crystal on silicon (LCOS) monitor, or a liquid crystal display (LCD) monitor, depending on the kind of image source. The rear projection system  50  includes a housing  52  for covering internal components, a partially transmissive reflector  54  installed inside the housing  52 , an image source  56  installed inside the housing  52  and positioned on one side of the reflector  54  for projecting an image to the reflector  54 , and a screen  58  installed on the housing  52  for receiving the image projected from the image source  56  to the reflector  54  and reflected from the reflector  54  so as to display the image. The screen  58  can be a rectangular screen. The rear projection system  50  further includes at least one light sensor  60  installed on the other side of the reflector  54  for sensing the light of the image projected from the image source  56  to the reflector  54  and passing through the reflector  54 . The light sensor  60  can be a photoelectric sensor. As shown in  FIG. 5 , the rear projection system  50  includes a control module  62  for controlling the image source  56  to project a next image (i.e. the next frame in a TV show or movie) according to the sensing result of the light sensors  60 , an analog multiplexer  64  for receiving data of light detection generated by the light sensors  60 , an analog-to-digital converter  66  for converting the data from the analog multiplexer  64  into digital data and transferring the digital data to the control module  62 .  
      Additionally, the image source  56  is positioned between the reflector  54  and the screen  58 . The image source  56  can have a single light source or multiple light sources. The image source  56  includes an image generator  68  for transforming an image signal from the control module  62  into a corresponding image, and a lens group  70  for receiving and adjusting the image generated by the image generator  68  and projecting the adjusted image to the reflector  54 . The image source  56  can project an image to the reflector  54 , and the reflector  54  can reflect the image projected from the image source  56  to the screen  58  so that the image can be presented on the screen  58 .  
      The detailed operation is described as follows. First, the control module  62  outputs an image signal to the image generator  68  so the image generator  68  can transform the image signal into a corresponding image. Afterward, the lens group  70  receives the image generated by the image generator  68 , then to adjust the image and projects the adjusted image to the reflector  54 . The reflector  54  can reflect the image projected from the image source  56  to the screen  58  so that the image can be presented on the screen  58 . When the image is projected to the reflector  54 , the light sensors  60  can sense the light of the image projected from the image source  56  and passing through the reflector  54  due to the partial light-transmissivity of the reflector  54  and the position of the light sensors  60  on the other side of the reflector  54 . When the light sensors  60  sense different amounts of light passing through the reflector  54 , the light sensors  60  can output different voltages to the analog multiplexer  64 , depending on the color of the light, the brightness of the light, the illuminated area on the light sensor  60 , and so on. The analog multiplexer  64  transfers the data from the light sensors  60  to the analog-to-digital converter  66 . The analog-to-digital converter  66  converts the data from the analog multiplexer  64  into digital data and transfers the digital data to the control module  62 . After the control module  62  receives the digital data transmitted from the analog-to-digital converter  66 , the control module  62  examines the focus status of the image projected by the image source  56 , such as by determining whether the brightness of the light is low or whether the white balance of the light is biased, and adjusts the next image appropriately so as to control the image source  56  to project the next image according to the sensing result of the light sensors  60 . The control module  62  can adjust the lens group  70  so as to adjust the size and the position of the image according to the sensing result of the light sensors  60  or to adjust the brightness of the image generated by the image generator  68  according to the sensing result of the light sensors  60 .  
      Furthermore, since the incident angle of the light emitted from the image source  56  to the reflector  54  is equal to the reflected angle of the light reflected from the reflector  54 , the position on the reflector  54  to which the image source  56  projects the image corresponds to the position on the screen  58  to which the reflector  54  reflects the image. That is, the position of the image that a viewer sees on the screen  58  corresponds to the position on the reflector  54  corresponding with the locations of the light sensors  60  installed on the other side of the reflector  54 . Therefore the sensing result at the position of each light sensor  60  can represent the detection result at the corresponding position of the image on the screen  58 .  
      The quantity and the location of the light sensors  60  according to the present invention depends on the design demand. For example, more light sensors positioned at different locations on the other side of the reflector  54  corresponding to locations on the screen  58  can increase the precision of focus detection in the rear projection system  50 . However, there is a trade-off between precision and increased cost of installing extra light sensors.  
      In conclusion, because the light sensors  60  are installed behind the reflector  54 , the light sensors  60  can detect the focus status of the entire image, such as whether the brightness of the image source  56  is low or whether the white balance of the light is biased, without blocking or obstructing the light projected to the screen  58 . Furthermore, since the reflector  54  is positioned in front of the light sensors  60  the reflector  54  can filter most stray light so that the detection quality of the light sensors  60  is improved.  
      In contrast to the rear projection system of the prior art, the rear projection system according to the present invention can detect the focus status of the entire image without affecting the light projected onto the screen. The present invention can overcome the disadvantages of positioning the light sensors around the screen.  
      Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.