Facsimile and static presentation processing – Natural color facsimile – Scanning
Reexamination Certificate
1998-06-18
2001-03-13
Lee, Cheukfan (Department: 2722)
Facsimile and static presentation processing
Natural color facsimile
Scanning
C358S509000, C358S474000, C358S475000, C358S487000, C358S488000, C358S497000
Reexamination Certificate
active
06201619
ABSTRACT:
BACKGROUND OF THE INVENTION
Digital scanners are used to digitize the graphic content, be it color or black and white photographs, artwork, text, and other graphics, from reflective and/or transmissive original documents. This capability is useful in digital document storage, digital content generation, and in more industrial pre-process environments. In this latter application, chemical film-based photographs, for example, can be digitally scanned for pre-print review, followed by production printing.
One of the most common scanner configurations is the flatbed scanner. A transmissive or reflective original document is placed face down on a bed having a glass plate or in a slide tray. A carriage, under the glass plate having a slit aperture facing the document, is then scanned over the original document. A relay optical system in the carriage successively picks-off scan-lines. In the one configuration, a single fold mirror is used in a high-resolution mode, and a series of larger fold mirrors are used in a low-resolution mode. In either case, the fold mirror(s) relay the scanned lines to high/low resolution in the optical imaging system, which images the scan-lines onto a linear or two dimensional image detector, such as a trilinear charge-coupled device (CCD) array or CMOS-based image detector.
Although speed of scanning, for example, is an important capability, one of the major factors in distinguishing scanners is resolution, or the fineness of the detail that the scanner can digitize. Consumer-grade scanners are offered with optical resolutions approaching 600 dots per inch (dpi). Currently, commercial-grade scanners are offered with resolutions of greater than 1,000 dpi, in standard resolution modes. Generally, the increases in resolution are related to the size and levels of integration in the image detectors.
Optical resolution, however, is not increased simply by increasing the density of or number of elements in the image detector since a precision optical imaging system is required to form the image of a scan-line, for example, from the document on the image detector, and its focus must be correct. In the prior art, the scanner's optical imaging system was calibrated in the factory or during a hardware setup procedure associated with a particular document holding device, such as a slide tray for example. A predetermined image was sent through the optical imaging system and received by the image detector. The data from the image detector was then analyzed while adjusting the optical imaging system to obtain the best focus. This best focus position was then stored for all subsequent scanning operations.
SUMMARY OF THE INVENTION
The problem with the conventional technique is that it fails to account for two problems. First, the scanner may slowly move out of calibration with aging and environmental effects such as shock exposure. Secondly, the optimum focus position for the optical imaging system may be dependent upon the particular original document being scanned. Typically, the calibrated object plane corresponds to the top surface of the glass plate on the scanner's bed. When transparency material is being scanned and its image is removed from the glass plate's top surface, the ideal object plane differs from that used during calibration. A similar problem occurs with mounted slides, for example, where the image does not reside at a predictable position.
To confront these problems, the invention thus allows autofocussing of the document to be scanned. Problems associated with loss of calibration are avoided. Moreover, the system is able to adapt to documents where the image is not at the scanner's nominal focal plane.
In general according to one aspect, the invention features an autofocus process for imaging optics of an image acquisition device such as a scanner. The same principles of the invention apply to capturing a section of an image with an area array detector and using that information for making autofocussing decisions, rather than the information obtained from individual scan lines. The process comprises performing multiple image captures of the document to be imaged. In the preferred embodiment, these captures are of essentially the same region (e.g. area or line) of the document.
A focal position of imaging optics, which forms the image, is adjusted relative to an image detector in between the multiple captures of image data. In the preferred embodiment, the imaging optics is adjusted. Relay optics or a position of the image detector could alternatively be adjusted.
In any case, a focus setting for a subsequent imaging operation is then calculated based on the image data from the multiple captures. In the preferred embodiment, this calculation yields a lens position for the imaging optics.
In the preferred embodiment, the image scan-line or area captures are treated as a single image capture from the perspective of the hardware. The image detector electronics need to only be prepared for a single imaging operation.
Also, the image data should be analyzed to determine whether it is indicative of a focus prior to the calculation of the focus setting. The analysis can be for one or each primary color. If no data set is indicative of focus, a stored best focus setting is retrieved and the imaging optics and/or image detector is adjusted as based on the stored best focus setting. Further, corrections for magnification changes caused by adjustment in a focal position of the imaging optics should be made between separate image captures.
In the preferred embodiment, image data groups from multiple analysis regions of the image captures are used. This allows the generation of a focus setting based on more than one point in the document, but magnification changes caused by adjustment in the focal position of the imaging optics should be addressed.
In general, according to another aspect, the invention also features an image acquisition device having an autofocus capability. The device comprises an image detector that generates image data descriptive of a scan-line or region of the document (i.e. the image to be acquired). Imaging optics are used to form an image on the image detector, and relay optics picks-off the image from media being acquired. A focus actuator adjusts a focal position of imaging optics relative to the image detector under control of a control system. The system modulates the focus actuator based on the image data from multiple image captures of the same scan-line or area.
The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.
REFERENCES:
patent: 5365053 (1994-11-01), Schielke et al.
patent: 5430288 (1995-07-01), Schielke et al.
patent: 5532846 (1996-07-01), Brook et al.
patent: 5767989 (1998-06-01), Sakaguchi
Neale Timothy E.
Strazdas Richard J.
Agfa Corporation
Houston J. Grant
Lee Cheukfan
Sabourin Robert A.
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