Facsimile and static presentation processing – Facsimile – Picture signal generator
Utility Patent
1997-12-24
2001-01-02
Lee, Cheukfan (Department: 2722)
Facsimile and static presentation processing
Facsimile
Picture signal generator
C358S497000, C358S474000
Utility Patent
active
06169611
ABSTRACT:
BACKGROUND
The field of the present invention is optical scanning of high-resolution color images, and in particular, the use of a flat-bed scanner system for the scanning of reflective and transmissive original documents at high resolution in a high volume production environment typical in the graphic arts electronic prepress industry. The original documents scanned by such systems included color or monochrome photographs, artwork, and they are composed of both text and graphics. The actual text and graphic image content of the scanned original document is referred to as an “original”.
In use of a flat-bed scanner for reflective scanning, an original is placed with the surface containing the original document facing down on a flat transparent reference surface, typically glass. The original document is fixed on the surface such that a single scan line of the original document (hereinafter referred to as a “scan line”) is illuminated by an illumination system from below, and the light reflected from the scan line is directed through an optical system to form an image of the scan line on a sensor such as a CCD array, which converts the optical signal to an electronic representation of the scan line, comprising a line of digital picture elements, or “pixels”. The desired portion of the original document is scanned, one scan line at a time, by moving the original relative to the illumination system, optical system, and sensor along a direction hereinafter referred to as the “scanning axis”. In systems typical of the prior art, such as that disclosed in U.S. Pat. No. 5,341,225, the illumination system, optical system and sensor are configured to move together as a unit in a moveable scan carriage. In other systems, such as those of U.S. Pat. No. 5,140,443 and U.S. Pat. No. 5,227,846 the original is moved while the illumination system, optical system and sensor remain fixed. In a production environment, original documents are scanned in sequence, with each requiring a preparation step in which the original to be scanned is located and fixed on the surface in proper alignment and registration, followed by the actual scanning operation.
A transparent original document, typically a photographic transparency, is an original on one side of a thin transparent substrate. In this case, the original is illuminated from the side opposite from that containing the optical system and sensor. Use of a single flat-bed scanner for both types of scanning involves a modal configuration change. Typically, a flipcover used in reflective scanning mode to hold the original document flat on the transparent surface is replaced by a transmissive illumination module which illuminates from above the portion of the original to be scanned. As in reflective-mode scanning, prior art systems are configured so that either the original or one or more scanner illumination, optics or sensor components move to carry out the scanning process.
In addition to reconfiguration of the illumination system, the magnification of the optical system is typically changed so that the same number of pixels imaged on the CCD array, and captured by the digitizing electronics, corresponds to a larger or smaller area of the original. In high
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resolution scanning systems typically in use in graphic arts electronic prepress processing, transparencies are oftentimes scanned at resolutions of 4,000 pixels per inch (ppi) or greater, while reflective originals are usually scanned at much lower resolutions, for example 1,200 ppi. Accordingly, it is a general problem in transmissive scanning which requires a higher resolution than reflective scanning that the relative motion between the moveable scan carriage and the transmissive original document can introduce focus errors if the distance between the sensor and the transmissive original document varies over the travel of the scan carriage. Such errors may occur when the scan carriage travel axis is not parallel with a transmissive document holder supporting the transmissive original document or when the scan carriage may rotate about the scanning axis causing the ends of the scan line to become out of focus. Such focus errors can be seen in the digitized image as artifacts which generally degrade the image quality.
Prior art configurations which mount the transmissive document holder in the scanner independently of the scan carriage inevitably introduce focus errors or artifacts into the resulting scan. That is to say because the transmissive document holder is mounted in the scanner independently of the moveable scan carriage, relative positional errors between the transmissive document holder and the sensor (i.e., the transmissive document holder and the sensor are not separated by a constant distance during travel of the scan carriage) are likely due to tolerance buildups of the mounting assemblies of the transmissive document holder and the scan carriage. The relative positional errors will then introduce the focus errors or artifacts into the resulting scan because the transmissive original document is not projected onto the sensor with uniform magnification during scanning.
One solution to reducing focus errors and/or artifacts in a scanning system is disclosed in U.S. Pat. No. 5,227,846. Therein is described a mounting system in which an original document to be scanned is supported by a glass plate at an object plane during scanning. In the '846 patent, the glass plate is supported at four points, two rollers near the outer edges of the scan line and two helical compression springs one at each end of the glass plate. This mounting system allows limited tilting aid bending of the glass plate relative to the housing which is undesirable, especially at higher resolutions, because such tilting and bending can introduce a variety of scan errors in the final digitized image, including focus and color registration errors.
OBJECTIVES OF THE INVENTION
Accordingly, it is a general object of the present invention to provide a scanning apparatus which enhances the quality of digital images obtained by scanning transmissive original documents at high resolution.
It is another object of the present invention to provide a scanning apparatus which dynamically maintains the portion of the transmissive original document being scanned and the image sensor at a substantially uniform predetermined separation during scanning.
It is a further object of the present invention to minimize detrimental effects of bending a transmissive media support element by providing a three point mounting arrangement.
It is a still further object of the present invention to eliminate the need for precise alignment of a media support element over the entire travel length of the scan.
Additional objects, advantages, and novel features of the present invention will become apparent to those skilled in the art from this disclosure, including the following detailed description, as well as by practice of the invention. While the invention is described below with reference to preferred embodiment(s), it should be understood that the invention is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional implementations, modifications, and embodiments, as well as other fields of use, which are within the scope of the invention as disclosed and claimed herein and with respect to which the invention could be of significant utility.
SUMMARY DISCLOSURE OF THE INVENTION
The present invention provides a mounting system, comprising a media holder pivotally attached to a housing at a first end and movably supported by a carriage movably supported within the housing. In particular, the media holder is movably supported by first and second mounting devices affixed to and movable with the carriage. The first and second mounting devices may each further include a respective biasing device attached to the carriage to resiliently bias the media holder against the first and second mounting devices during movement of the carriage.
The carriage in the present invention is a scan carr
Brook, III Mark G.
MacNeill John A.
Mirmelshteyn Aron M.
Tellam Mark E.
Agfa Corporation
Lee Cheukfan
Sabourin Robert A.
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