Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
1999-11-23
2001-12-25
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S235000, C250S225000
Reexamination Certificate
active
06333498
ABSTRACT:
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.
REFERENCES:
patent: 4595259 (1986-06-01), Perregaux
patent: 5847846 (1998-12-01), Wu et al.
Le Que T.
Oliff & Berridg,e PLC
Xerox Corporation
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