Text enhancement for color and gray-scale documents

Details Text enhancement for color and gray-scale documents Text enhancement for color and gray-scale documents

1998-08-18

2001-05-08

Rogers, Scott (Department: 2624)

C358S001110, C358S462000, C382S176000, C382S180000, C382S200000

Reexamination Certificate

active

06227725

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention is directed to image processing and in particular to enhancing the legibility of text in document copies that photocopiers produce.
The vast majority of documents that are photocopied consist primarily of text, and the usefulness of the resultant copy depends greatly on the text's legibility. Unfortunately, many factors in the photocopying environment conspire to reduce text legibility. One of these is that the text may be embedded in a background image, and the copying process may tend to lose the contrast between text and the image and thereby impair the resultant copy's legibility. Another common difficulty arises when a document original is printed on two sides, or there is another document located behind it. It often happens in such situations that the text from the reverse side or other document “bleeds through,” making the front-side text hard to read.
Photocopier manufacturers have accordingly attempted to deal with this problem by so processing the scanned digitized image as to emphasize the delineation between text and image or background. Common among the approaches to solving this problem is the use of digital filters that so process the digital image as to emphasize differences between a pixel's value and those of pixels in its immediate neighborhood. This has a tendency to darken text characters' outlines and thus enhance legibility.
But it also has a drawback. Although it does tend to enhance legibility, it also emphasizes annoying aliasing artifacts, which result from digital processing's necessarily discrete nature.
SUMMARY OF THE INVENTION
We have found that, particularly in laser-type photocopiers, legibility enhancement yields less-annoying aliasing results when the text-edge emphasis is placed, not at the highest-gradient locations, but rather in properly selected neighbors of such locations. In one of the invention's embodiments, for instance, we mark a pixel as being a text edge if it has a certain minimum darkness—and, in color systems, sufficiently low saturation—and the magnitude of its brightness gradient is less than a predetermined threshold while that of a neighboring pixel exceeds a predetermined threshold. Each pixel labeled as a text edge is then set to a predetermined dark value, typically maximum black. Because this approach does not eliminate the high gradients adjacent to text edges, it preserves natural gradations whose removal, we have discovered, tends to lead to the annoying aliasing artifacts. It also reduces the tendency, exhibited by some approaches, of widening text-character elements.
According to another aspect of the invention, we additionally assign text-edge labels to pixels that are flanked by previously identified text-edge pixels at which the gradients are oppositely directed away from the pixel thus flanked. This tends to improve the legibility of a character element that is, say, only three or four pixels wide.
As will be described below, some embodiments will refine this initial assignment of text-edge labels by a selective re-labeling, in which text-edge labels are removed from some pixels and newly assigned to others. One of the beneficial effects of such re-labeling is to smooth text edges.


REFERENCES:
patent: 4499598 (1985-02-01), Chittineni
patent: 5381241 (1995-01-01), Kawanaka et al.
patent: 5392365 (1995-02-01), Steinkirchner
patent: 5463451 (1995-10-01), Acquaviva et al.
patent: 5583659 (1996-12-01), Lee et al.
patent: 5625719 (1997-04-01), Fast et al.
patent: 5666443 (1997-09-01), Kumashiro
patent: 5710840 (1998-01-01), Hideshima et al.
patent: 5956468 (1999-09-01), Ancin

Affiliated with

Also associated with

Rating

Text enhancement for color and gray-scale documents does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Text enhancement for color and gray-scale documents, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Text enhancement for color and gray-scale documents will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2511632