Abstract:
The integrating cavity effect is reduced by using a polarizing filter. The polarizing filter reduces the secondary illumination onto a document being scanned. The filter is placed at the opening to the cavity of the scanner. The sum effects of using a polarizing filter reduces the integrating cavity effect by a factor of 2.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     This invention is directed towards reducing the integrating cavity effect. 
     2. Description of the Related Art 
     Scanners and other image capture devices read information from an original image to generate electronic data representing the scanned original image. A typical image capturing device includes an illumination system including a light source and an array of photosensitive elements, and may include mirrors and/or lenses. The photosensitive elements produce electrical signals in proportion to the amount of light to which each photosensitive element has been exposed. The mirrors and lenses, if included, usually are mounted in a cavity between an imaging surface on which the original image sits and a surface on which the light source and the photosensitive elements are mounted. The original image is placed on the imaging surface. The light source is aimed at the original image. The light reflects off the original image back into the cavity toward the photosensitive elements, where the intensity of the reflected light is measured. 
     SUMMARY OF THE INVENTION 
     In many scanner systems, the generated image data is affected by variable illumination intensity arising from the integrating cavity effect. The integrating cavity effect describes the secondary illumination of a pixel of the original image being measured due to multiple reflections that illuminate that pixel. That is, when scanning a document, light is projected onto the document and the light is reflected off the document into an illumination cavity, where the intensity of the light is measured for each individual pixel. A secondary illumination also occurs which alters the accuracy of the measurement. This secondary illumination is a function of the image surrounding the pixel being measured. Light reflecting off the surrounding pixels enters back into the cavity and then is reflected back onto the document and the pixel being measured. The lighter the surrounding image of a given pixel, the more light that is reflected back into the cavity and onto the document. This is referred to as the integrating cavity effect. 
     Techniques exist that can partially correct for the integrating cavity effect. These techniques determine the point reflectivity by measuring both the point intensity and a local average of the image intensity. Using both these values, the point reflectivity is calculated. However, these techniques can be costly and require large amounts of processing resources. 
     This invention provides systems and methods that optically reduce the integrating cavity effect and do not require any measuring or processing resources. 
     This invention separately provides an image capture device that includes a polarizing filter that optically reduces the integrating cavity effect. 
     In various exemplary embodiments of the systems and methods according to this invention, a polarizing filter is placed over the opening to the cavity to reduce the integrating cavity effect. This reduces the amount of light that is reflected back onto the image being captured. The light that is reflected off the document is sufficiently randomized that only a fraction of the reflected light will be able to pass through the polarizing filter. Therefore, the amount of light that re-enters the cavity is diminished. Accordingly, the light that is reflected back onto the image, causing a secondary illumination of the image, is reduced. The overall effect of the polarizing filter reduces the integrating cavity effect by at least a factor of 2. 
     These and other features and advantages of this invention are describes in or are apparent from the following detailed description of the apparatus/systems and methods according to this invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various exemplary embodiments of this invention will be described in detail, with reference to the following figures, wherein: 
     The FIGURE illustrates an image capture device according to this invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The FIGURE shows an image capture device scanner  100  that includes one or more photosensitive arrays  140  and a scanning system assembly  130 , that may move together as a single unit along the scanning path or may be stationary. The photosensitive arrays  140  may include sensors (not shown), such as CCDs or photodiodes, that are controlled to sense light reflected from an original array during an illumination period. The photosensitive sensors develop a charge indicative of the amount of light detected. The scanning system assembly  130  includes several optical components, including a light source  131 , a reflector  132 , and a baffle  133 . The light source  131  illuminates the original image  200 . The light source  131  can be any light emitting element that emits light at a sufficiently high intensity, such as a fluorescent lamp. The reflector  132  and the baffle  133  are used to help direct the light onto a small area of the platen  110 . The reflector  132  reflects the light onto a certain point through the baffle  133 . The baffle  133  has a small opening that only allows a small amount of light to pass through it and onto the original image  200 . The scanning system assembly  130  may also include a polarizing filter  136  and may include a lens  134  and one or more mirrors  135 . The lens  134  and mirrors  135  help focus the light reflected off an original image  200  onto the photosensitive array  140 . The entire scanning system assembly  130  is located in a cavity  240 , formed between the platen  110  and the photosensitive array  140 . 
     The polarizing filter  136  continues to polarize any light that is reflected back towards the original image  200 . The sum effect of the polarizing filter  136  reduces the integrating cavity effect by at least a factor of 2 each time the light passes to and from the original image  200  though the polarizing filter  136 . Depending on the smoothness of the reflector  132 , the integrating cavity effect can be reduced even more. This reduction in the integrating cavity effect allows for more accurate measurement of the individual pixels in the original image  200 . 
     Using the polarizing filter  136  provides an effective and inexpensive way to reduce the integrating cavity effect. The polarizing filter  136  is easily implemented and obviates the need for correction of the generated image data using electronic image processing, which is expensive and requires either more space, if implemented in hardware, and/or more processing resources, if implemented as software or firmware. 
     During operation of a typical image capture device, the original image  200  to be captured is placed on the platen  110 . The light source  131  is driven to emit light. The light from the light source  131  is directed by the reflector  132  through the polarizing filter  136  towards the original image  200  through the baffle  133 . The light is then reflected back from the original image  200  through the polarizing filter  136  towards the lens  134  through the mirrors  135 . The lens  134  focuses the light before it reaches the photosensitive array  140 . The image signals generated by the photosensitive array  140  are then output to an image data sink  300  over a link  310 . 
     While the FIGURE shows the image capture device  100  as a separate device from the image data sink  300 , the image capture device  100  may be an integrated device, such as a digital copier, computer with a built-in printer, or any other integrated device that is capable of producing a hard copy image output. With such a configuration, for example the image capture device  100  and the data sink  300  may be contained within a single device. Alternatively, the image capture device  100  may be a separate device attachable upstream of a stand alone image data sink  300 . For example, the image capture device  100  may be a device which interfaces with the image data sink. 
     In general, the image capture device  100  can be any one of a number of different sources, such as a scanner, a digital copier, or a facsimile device that is suitable for generating electronic image data. Thus, the image capture device  100  can be any known or later developed device that is capable of generating image data by illuminating an original image. In general, the image data sink  300  can be any device that is capable of outputting or storing the processed image data generated according to the systems and methods of this invention, such as a printer, a copier or other image forming devices, a facsimile device, a display device, a memory, or the like. The link  310  can be any known or later developed device or system for connecting the image capture device  100  to the image data sink  300 , including a direct cable connection, a connection over a wide area network or a local area network, a connection over an intranet, a connection over the Internet, or a connection over any other distributed processing network or system. In general the link  310  can be any known or later developed connection system or structure usable to connect the image capture device  100  to the image data sink  300 . 
     While this invention has been described in conjunction with the exemplary embodiments outlined above, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the exemplary embodiments of the invention may be made without departing from the spirit and scope of the invention.