Facsimile and static presentation processing – Facsimile – Picture signal generator
Reexamination Certificate
1997-10-09
2003-08-12
Lee, Cheukfan (Department: 2622)
Facsimile and static presentation processing
Facsimile
Picture signal generator
C358S487000
Reexamination Certificate
active
06606171
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an improved digitizing scanner, and more particularly to a scanner for reading and storing graphical and textual image data from transparent and translucent sheets such as developed X-ray film.
BACKGROUND OF THE INVENTION
Electro-optical digitizing scanners are commonly employed as peripheral devices linked with microcomputers and other data processing and storage devices. Scanners enable graphical and text data to be accurately converted into stored digital data for further processing and interpretation by, for example, a microcomputer. Scanners are adapted to read data from a variety of media and formats. Opaque and transparent sheets are two common forms of scanned media.
An image on a sheet is defined by light areas (“highlights”) and dark areas (“shadows”). To convert the light and dark areas into corresponding image data, the scanner typically illuminates the sheet with a light source. In one form of scanner, a camera assembly moves along the length of the sheet. In another, the sheet moves relative to a stationary camera. As the sheet moves relative to the camera, the camera “scans” the width of the illuminated image, converting the scanned portion of the image into a data signal. This scanned image is said to be “digitized” in that the image is converted into a data file stored in a digital format with information representative of discrete segments or “pixels.” The data in the file includes instructions on how to assemble the individual pixels into a cohesive two-dimensional image that reflects the original scanned image. The data file also includes information on the intensity value for each pixel and its color, if applicable, or grayscale shade.
A common form of camera assembly for use in a digitizing scanner is the solid-state CCD camera, which contains a linear array of photosensitive picture elements, often termed “pixels.” Each pixel element receives light in its local area. The pixel generates an intensity-based signal depending upon how much light it receives. The aggregate signal of all the pixel elements is a representation of a widthwise “line” of the image.
Generally, the CCD pixel array only scans a single line that is several thousand pixels wide in the fast scan direction but that has a height of only one pixel in the slow scan direction. The array is typically wide enough to scan the entire image width at once. Because an entire line is generally viewed at once, this is known as the “fast scan” direction; since the delay is only in downloading the signal from the CCD to the data processor. Conversely, the direction of movement of the camera/image is known as the “slow-scan” direction. In summary, images are scanned in a “line-by-line” manner in which the image moves in the slow scan direction relative the camera's fast scan field of view. As the image passes through the field of view, a succession of scanned width-lines of the image are converted into image data, and the CCD element generates a continuous signal representative of the intensity of each pixel in the line.
Scanners used for scanning opaque sheets must illuminate the image by reflecting illumination light off the surface of the sheet from the same side as the camera. Conversely, when transparent or translucent sheets are scanned, the image is illuminated from the opposite side of the sheet from the camera, allowing the light to pass through the image to the camera. In this manner, the image attenuates the light as it is transmitted through the sheet to the camera.
CCD elements are generally smaller in width than the scanner's total scan width. A focusing lens is employed to focus illumination light from the scanned image onto the narrower viewing area of the CCD. The focused image will generally exhibit a degradation in the field of view at the far edges of the width (e.g. a loss of exposure). This loss of exposure occurs because the amount of light entering a lens tends to decrease at the edges of the field of view according to the Cos
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characteristic of lenses. It is often desirable to increase the light near the edges of the camera's field of view to compensate for this effect. However, most illuminators comprise only one or two discrete light sources, such as a long fluorescent bulb. The intensity of such a bulb is not generally controllable along its length. In fact the bulb may exhibit variability in light output along its length, presenting a different level of intensity to different pixels in the array. This problem becomes exacerbated as the bulb ages. In addition, the pixels of the CCD camera may exhibit different responses to the same intensity of light. The CCD pixels can be calibrated to account for most variations, but it is desirable to have the capability of changing the profile of light presented to the various pixels. In general compensation for an uneven light profile is difficult using a single illumination bulb.
Scanners derive a large quantity of information from a single sheet containing an image. When a sizable number of images are stored for long-term use, superfluous data related to edges and margins can become a concern. Substantial computing resources in both time and storage capacity can be devoted to unneeded data. In particular, images substantially narrower than the maximum field of view of the scanner are often scanned as if the full width (in fast scan direction) of the scanner is employed. It is desirable, therefore, to accurately gauge the size of the needed data range, and only scan the image within the needed range in both the fast scan and slow scan directions. In the past this has been accomplished primarily by manually inputting the size of the sheet to be scanned. Alternatively, movable edge guides can be linked to a size sensor that inputs the relative width of the input sheets. An electromechanical/optical length sensor starts and ends the scanning process as the front and rear edges of the sheet pass through the scanner. However, these techniques still require accurate registration of input sheets and do not determine the size of the margins.
The scanning of translucent sheets is desirable in the medical field, and presents particular challenges. In particular, there is a need to digitally store and reproduce diagnostic radiological films, commonly termed “X-rays.” Most patient X-ray films, in fact, are produced in a “series” that can consist of six or more individual, interrelated X-rays. Hundreds, or even thousands, of X-ray films are produced daily by a large hospital. By electronically storing and indexing radiological images, they can be made available indefinitely without taking up valuable physical storage space. In addition, various specialized graphical processes and image enhancement techniques can be used in connection with stored X-ray images. Furthermore, scanned radiological data can be easily transmitted to practitioners at remote locations via electronic mail or facsimile. In all, the ability to accurately and reliably scan developed X-ray film images provides an important diagnostic tool for medical practitioners.
The scanning of developed X-ray film presents some particular challenges. X-rays tend to exhibit a large area of shadows with both abrupt transitions, and more subtle dark, clouded areas. Hence, the CCD element intermittently must operate at a low output level throughout the scanning process. Low light intensity causes the CCD element to transmit a corresponding low output signal. Electronic noise is accentuated at this low output level, causing inaccuracies in the scanned image data. Incandescent and fluorescent light sources often have short life spans that may render them unsuitable for a large volume radiological scanner. Alternatively solid-state illumination devices, such as light emitting diodes (LEDs) must be used in large arrays. While they are energy-efficient, long-lived, and consistent over their service life, they may have wide variability in output intensity—even LEDs in the same production batch. Thus the light intensity pattern presented
Fernald Mark R.
Lehman Richard F.
Renk Jeffrey D.
Winey Calvin M.
Cesari and McKenna LLP
Howtek, Inc.
Lee Cheukfan
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