Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
1998-07-07
2001-10-30
Lee, Thomas D. (Department: 2724)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C382S254000, C382S274000
Reexamination Certificate
active
06310697
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The invention relates to the enhancement of text in a computer environment. More particularly, the invention relates to the enhancement of the text of a digitally scanned document in a computer environment.
2. Description of the Prior Art
Text or pictorial images are often replicated or transmitted by a variety of techniques, such as photocopying, facsimile transmission, and scanning images into a memory device. The process of replication or transmission often tends to degrade the resulting image due to a variety of factors. Degraded images are characterized by indistinct or shifted edges, blended or otherwise connected characters and distorted shapes.
A reproduced or transmitted image that is degraded in quality may be unusable in certain applications. For example, if the reproduced or transmitted image is to be used in conjunction with a character recognition apparatus, the indistinct edges, connected characters, etc. may preclude accurate or successful recognition of characters in the image. Also, if the degraded image is printed or otherwise rendered visible, the image may be more difficult to read and less visually distinct.
There are several approaches to improve image quality. A classical resolution enhancement algorithm is template matching. Template matching attempts to match a line, curve pattern, or linear pattern and then tries to find the best way to reconstruct it with the printing resolution.
Other methods for text enhancement come from the area of Optical Character Recognition (OCR). The main purpose is to isolate the characters from one another. The concern is not for enhancement. The methods apply more to morphological filters which repetitively perform thickening and thinning and opening and closing to get the desired character shape.
U.S. Pat. No. 5,351,314 issued to Vaezi on Sep. 27, 1994, is a method for image enhancement involving the smoothing and thinning of input image data by applying a filter to each pixel of input image data. Characters are segmented and identified based on a comparison of the segmented character to a dictionary of characters.
U.S. Pat. No. 5,542,006 issued to Shustorovich et al. on Jul. 30, 1996, is a method for use in an OCR system for locating center positions of all desired characters within a field of characters such that the desired characters can be subsequently recognized using an appropriate classification process. This method is used for character recognition and not for text enhancement.
There are also standard sharpening filters that convolve the image with a mask and a low-pass filtering kernel and then perform unsharp masking by a linear combination of the original and the blurred image. Another is just to convolve the image with a sharpening kernel. More sophisticated algorithms apply adaptive methods.
U.S. Pat. No. 5,644,648 issued to Bose et al. on Jul. 1, 1997, is a method for recognizing connected and degraded text that filters a scanned image to determine whether a binary image of an image pixel should be complemented. The pixel is complemented only if doing so does not reduce the sharpness of the wedge-like figures in the image.
Other simplistic approaches would be to threshold the text. A grayscale or color scanning of the text is performed. Some portion of the page is identified that is text and it is then thresholded and white placed where it is light and black where it is gray. This however, does not work.
It would be advantageous to provide a text enhancement system that improves the sharpness of the text of a scanned document by increasing the high contrast boundaries which are perceived as sharpness. It would further be advantageous to provide a text enhancement system that takes advantage of the ink centralization property of text and is independent of the type of scanner used.
SUMMARY OF THE INVENTION
The invention provides a text enhancement system. The invention comprises an easy to use page processing system that enhances the text on a digitally scanned page, thereby improving the crispness, clarity, and readability of the text. In addition, the invention is independent of the type of scanner used and utilizes an ink redistribution system that increases the contrast of digitally scanned text or facsimiles.
A preferred embodiment of the invention provides a general purpose method for text enhancement that is independent of the type of scanner that is used to scan a document or the device printing the document. It is tolerant of the artifacts and defects that the scanning process introduces on the text, mainly blurring. The invention is ideal for image reconstruction systems for scanned or digitized images that are not synthetic, i.e., the image is not a result of any PostScript or Page Description Language (PDL) processing.
Typically, a page is scanned and a digitized image is obtained that is usually in an RGB format. If no specific enhancement procedures are applied to the text in the document, then the result is text that is not crisp, clear, or sharp and is therefore harder to read and less pleasant to the eyes.
The invention preserves the amount of ink on the textual part of the page using a consistent method. The text is reconstructed through the reallocation of ink. There is a correspondence between the original amount of ink on the document and the intensity of the ink that the scanner read. The correspondence is either the same or there is some scaling factor involved. The factor is obtained by the fact that there is some overlap between two scanned pixels. The factor is also independent of the location of the pixels.
The new textual image is reconstructed where the same amount or a factor of the ink is preserved. Text has a centralization property. The ink is centralized, that is, there are rarely holes in groups of dark pixels. For example, there is a large white area surrounded by a black area in the letter “O” but it is not at the pixel level, it is at a multi-pixel level. If there are eight pixels that are black surrounding one pixel that is white, then it is likely that the white area is a misread by the scanner and there are actually nine pixels that are black.
The ink on the page is arranged so that it is more centralized, more connected to other pixels that are dark.
A window of size W×W is constructed on a scanned page with the target pixel at the center of the window. The amount of ink in the window is calculated and the number of pixels that are darker than the center pixel is counted. The window is moved along the page and each pixel on the page has a chance to be the center of a window and be allocated ink.
The invention reallocates the amount of ink in full quantities of the darkest value. Only the center pixel will actually have its ink reallocated.
This reallocation is a key feature of the invention. First, attempt to allocate the ink pixel by pixel in the window. The darkest pixel gets ink, the second darkest gets ink, and so on, until there is no more ink remaining in the bank, where the initial amount of ink in the bank is equal to the total amount of ink in the window. If the center pixel is later in darkness and there is no ink left in the bank, then it will become white. If the center pixel is reached before the ink runs out, then it will become black. Only the reallocation to the center pixel becomes effective. The attempt to allocate ink to the other pixels in the window is only done to determine the center pixel's allocation. Those pixels are reallocated ink when they become the center of a current window. The invention is not limited to black text on a white background, it also applies to grayscale, color, and white text on a black background.
For example, the amount of ink in a window is ten and the center pixel is the third darkest in the window. This means that only two other pixels in the window are darker than the center pixel. The invention reallocates the ink to the pixels. Given this example, it is desirable to have the center pixel black. If the amount of ink in the window were only three and the c
Electronics For Imaging, Inc.
Glenn Michael A.
Lee Thomas D.
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