Apparatus and methods for capturing defect data

Details Apparatus and methods for capturing defect data Apparatus and methods for capturing defect data

1999-02-04

2002-08-20

Le, Que T. (Department: 2878)

Radiant energy

Photocells; circuits and apparatus

With circuit for evaluating a web, strand, strip, or sheet

C250S559070, C250S559110, C382S275000

Reexamination Certificate

active

06437358

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to electronic image enhancement and recovery, and more particularly, to a method and apparatus for collecting defect data from documents and films for use in removing defects from an image.
BACKGROUND OF THE INVENTION
The field of electronic imagery has long aimed at capturing and reproducing an accurate digital representation of an image as it currently exists on a physical medium, such as a document or film. Often, however, such digital representations appear distorted. One cause of such distortions is a defect in an image-capturing system component. For example, the translucent document-scanning surface or “platen” in an electronic document image scanner might contain scratches or other optical path obstructions. More frequently, however, distortions result from factors outside the image-capturing system. For example, a photograph, film or other medium in which an image is contained might itself become scratched or otherwise distressed or deformed despite even the most careful handling. In addition, foreign matter, such as a hair or dust, might become deposited on the physical medium. Thus, even where an image captures what it “sees,” distortions might yet occur.
Traditionally, the above distortions have been largely ignored in favor of increasingly accurate image capturing and reproduction.
FIG. 1
, for example, broadly depicts a conventional flatbed document image scanner or “flatbed scanner.” (For clarity, electronic data processing and storage elements have been removed.) As shown, scanner
100
includes platen
101
and, below platen
101
, light source
103
, mirror
105
, and sensor
107
. Sensor
107
further includes lens
107
a
and image sensor
107
b.
Image sensor
107
b
is typically a linear or a multi-linear sensor such as a charge-coupled device (“CCD”). However, other image-capturing devices might use other sensor types. For example, a drum scanner might utilize a point or multi-point sensor, such as a photomultiplier tube or “PMT.”
Operationally, an original document is positioned on platen
101
such that the source image faces platen
101
. Light source
103
is then illuminated, and source image
121
a
is scanned. During scanning, light source
103
directs light toward and causes reflections from a region of source image
121
a.
Mirror assembly
105
then re-directs or “folds” the reflected light to lens
107
a,
which focuses received light onto image sensor
107
b.
Next, sensor
107
b
converts the focused light to electrical signals. The electrical signals are then converted to digital image data using an analog-to-digital (A/D) converter (not shown), and the digital image data is further processed and stored. While multiple sensor arrays might be utilized, the whole of image
121
a
is typically scanned in successive regions, thereby limiting the number of sensors needed. Such region-to-region scanning is typically accomplished by sequentially moving mirror assembly
105
and sensor
107
. As mirror assembly
105
is moved, sensor
107
receives reflected light from successive regions of document
121
. The image is then reconstructed from the image data during image processing.
To assure image-capturing accuracy, flatbed scanners and other optical image-capturing systems have continually refined the nature of the light source
103
, mirror
105
's position, and sensor
107
. For example, a document, film, or other subject must be sufficiently and evenly lighted to allow capturing of image reflections from source document
121
without causing glare. Therefore, a single, typically fluorescent light source is provided. In addition, the mirror is positioned such that glare is avoided and both primarily bright and primarily dark images will be accurately captured. Therefore, each sequential mirror position is set such that light is directed from the light source to the image at a first angle and is then reflected (from the image) to a sensor at a significantly different second angle. More specifically, image clarity is assured in most devices by providing first and second angles which differ by at least 45 degrees. The resolution and optical efficiency of the sensor have also been continually improved.
Traditionally, image-capturing devices have not provided image distortion (or “defect”) detection, let alone correction. Rather, their objective was strictly directed at image-capturing accuracy. Therefore, the above arrangement was considered optimal for its intended purpose. Unfortunately however, such an arrangement also produces optical effects that not only fail to provide for defect detection, but also impose an optical environment that runs counter to such an objective.
While recent image-capturing devices attempt to detect image defects, such attempts depend on the image-data accuracy provided by the above image-scanning method. In such devices, an image is scanned in the traditional manner. Scanned image data is then reviewed in much the same way that a human observer might look for defects in a reproduced image. More specifically, after capturing image data, mathematical algorithms are used to search the image data for extraneous dark spots that might be indicative of image defects. Upon locating such dark spots, the algorithms determine whether the located spots are likely indicative of an image defect, determine the graphic features of selected defects, and attempt correction. Unfortunately, defects are difficult to separate from other image data, let alone correct, by reviewing the captured image data in this manner.
A system and method that corrects defects in an image is described in U.S. Pat. No. 5,266,805, entitled “System and Method For Image Recovery”, and is assigned to International Business Machines (“IBM”). The invention teaches sequentially transmitting through film red, green, blue and infrared light, and then performing correction by dividing out defects using the resulting image data, or alternatively, using an automated fill-in algorithm.
Further methods and apparatus that provides for detecting image defects are described in co-pending U.S. application Ser. No. 08/999,421, filed Dec. 29, 1997, entitled Defect Channel Nulling” and U.S. application Ser. No. 09/156,271, filed Sep. 16, 1998, entitled Method And Apparatus For Capturing Defect Data From Documents And Films, both commonly owned by the assignee of the present application.
The contents of U.S. Pat. No. 5,266,805, U.S. application Ser. Nos. 08/999,421 and 09/156,271 are hereby incorporated by reference as if repeated verbatim immediately hereinafter.
While the above prior patent and patent applications provide for defect handling in image-capturing systems, the new technological area of defect detection and correction remains subject to such a further advance as will become apparent in the discussion that follows.
Accordingly, there remains a need in the art for a system that enables defect data to be accurately captured for use in removing defects from an image.
SUMMARY OF THE INVENTION
According to a first aspect, the invention provides a positional relationship between system elements such that defects within an image are rendered more apparent. According to a second aspect, the invention provides for identifying defects within an image. According to still further aspects, the invention provides for rendering defects more apparent and identifying such defects within an image-capturing device. Advantageously, the present invention enables defects to be clearly captured, identified and corrected. In addition, the invention facilitates the use of various light sources and/or mechanisms within an image-capturing device for defect detection and/or correction in accordance with the constraints of a particular application.
The present invention provides a method and apparatus for image-capturing devices, such as scanners, to accurately identify defects in objects. The objects can be the physical images to be captured or elements of the image-capturing devices such as the platen and mirrors. The imag

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