Image analysis – Image sensing – Multiple scanning
Reexamination Certificate
1998-05-27
2001-09-18
Patel, Jayanti K. (Department: 2723)
Image analysis
Image sensing
Multiple scanning
C382S128000
Reexamination Certificate
active
06292596
ABSTRACT:
FIELD OF THE INVENTION
This invention relates in general to the field of digital data processing and acquisition for imaging systems using flat-bed scanners. A primary application of the invention relates to the automatic digitization of small format films, such as dental radiograph films, and to the processing of digital images.
BACKGROUND OF THE INVENTION
Film digitization can be a low-cost and practical alternative to digital radiographic approaches such as storage phosphor computed radiography (CR) or direct digital image capture (CCD). In the absence of digital image capture, hybrid imaging systems can provide an expedient and low cost solution for both dentists and insurance companies. Without the more significant capital investment required for direct digital devices, the dental practitioner can have the advantages that the digital modality can offer, such as imaging capability to practice management, larger format imagery, and electronic insurance claims. Insurance companies are also motivated to advance to the electronic domain in order to reduce the overhead associated with manual claims submission. U.S. Pat. Nos. 5,164,993 and 5,633,511 generally disclose the construction of tone-scale look-up-tables.
An important step in any hybrid imaging system is the initial image capture, in this case the scanning process. Exposure conditions should be carefully controlled in order to capture the image more optimally so that further degradation of the image in subsequent steps can be minimized. In practice this means controlling unwanted exposure or flare and maintaining proper alignment of the scanned images with the optical configuration. There is much variability among dental radiographs. Both varying x-ray exposure and processing of the radiograph contribute to this. This means that the dental x-ray can range from a very light “under-exposed” image to a very dark in appearance “over-exposed” image. Where there is too much exposure on the platen for an under-exposed radiograph, for example, the captured image will not have enough gray value content. Another important consideration during image capture is the alignment of the radiograph on the platen in the correct horizontal and vertical directions to maintain consistency with the CCD array of the digitizing scanner. If the image is not aligned properly during scanning, image rotation may be required, which can alter the aspect ratio of the original image. To minimize the effects of unwanted flare and image rotation, it is desirable that a template be used that will surround a small film with a dark mask. Alternatively, images can be in a holder typical of the dental practitioner's record keeping.
There is much in the literature that provides approaches for rendering digitally captured imagery. What has not been found is image processing that is specific to dental radiographs or addressing the problem of image capture using a flat-bed scanner and transparency adapter where the initial image capture can be degradated by excessive flare, and that incorporates specific information about the nature of the dental radiograph into an image processing algorithn.
U.S. Pat. No. 5,345,513 discloses the method for enhancement is based on histogram analysis of the digitized x-ray film image so that each pixel represents a density value. In particular, this analysis is demonstrated on chest x-rays The histogram has unique regional signatures, each corresponding to anatomical structures, such as heart or lung regions. The image is then processed dynamically by constructing a piecewise contrast curve specific to chest x-ray anatomy. This method relies on the characterization of the histogram to provide region specific information for rendering the image, but does not address the problem of digitizing film.
U.S. Pat. No. 5,283,736 addresses the need for medical diagnosis from a digitized radiographic image providing a means for signal dependent image processing by thresholding relevant image areas to determine key values for each desired image area The image data from desired regions of interest are used to determine a preferred density range, or a tone scale map.
U.S. Pat. 5,172,419 provides a system to correct exposures of x-ray film thus bypassing the need for second exposure so that an image acquisition, storage and display device can be used to improve image density. This system includes a film densitometer for digitizing film, storage, image processing and film recorder. The digitizer produces a representation of the optical densities for each pixel. Reference data (LUT) is stored consisting of optical densities and corresponding exposure for radiographic films. Using the LUT corresponding to the desired film type, the digitized data is compared to the table to determine the exposure of the image and a correction value is calculating and used to modify the pixel data so that the transformed pixels can be mapped for hard copy output (film) yielding the enhanced x-ray image European Patent Application 90200969.5, entitled “Processing and Digitizing Apparatus for Medical Radiographic Film,” provides the means for processing and digitizing exposed film, offering a way to automatically digitize conventionally produce radiographs so that patient information is associated with each image for archival purposes.
U.S. Pat. No. 5,483,325 describes an accessory frame that can be mounted on a photocopier or electronic flatbed scanner that facilitates location and removal of small opaque originals, such as business cards. This patent does not address the problem of flare in copying transparent originals.
Where the processing of radiographs is controlled, a sensitometric curve can be relied upon to adjust pixel values found in the corresponding digitized radiograph. This technique requires more precise knowledge of the exposure levels, film and sensitometry, usually found in larger medical facilities. In the dental community that this work addresses, the wide range in variability of film type used and in film processing would make this technique unfeasible for digitized dental films.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a solution to the problems of the prior art.
According to a feature of the present invention, there is provided an image dependent hybrid imaging system for small format films, such as dental radiographs. The invention has two stages. The first is the scanning of the small format films, such as dental radiographs on a flat-bed scanner. The second is the processing of the digitized images for soft copy display. The first stage consists of image dependent capture. There are two components. First is the pre-scanning of the platen area using an image template, or any such film holder. Subsequent to the pre-scan is the automatic determination of the image to be scanned by bounding only the image area(s) desired. In the dental radiograph application, a template containing apertures dimensioned for size 0, 1, 2, 3, or 4 dental films, for example, is placed on the platen and dental radiographs can be placed inside the template apertures. This is done to minimize unwanted flare during scanning. The image of the pre-scanned platen is presented to the user on a video display (e.g., CRT) and images are selected from the display to be digitized (further). If the exact dimensions and position of the template apertures are known, then the location of the closest open region from the user selection point defines the image area to be scanned. To accommodate use of dental holders where the template is not used or exact dimensions are not known, the Hough transform can be implemented along with apriori knowledge of the pre-scan image size. The scan area of interest can then be determined automatically and each dental radiograph as represented by the pre-scan can be bounded by a rectangle. Exposure levels during scan time are automatically adjusted to provide better image capture conditions on an image by image basis. The desired image area of the platen is scanned twice. A histogram analysis of a smoothed
Hasso Charles A.
Masi Louis P.
Snyder Patricia D.
Eastman Kodak Company
Noval William F.
Patel Jayanti K.
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