Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
1998-01-15
2001-01-16
Lee, Thomas D. (Department: 2724)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C382S173000, C382S176000
Reexamination Certificate
active
06175425
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to an apparatus and method for obtaining a binary representation of a document containing text and images. In particular, the invention relates to an apparatus for autodiscrimination between document areas containing text or line art and areas containing continuous-tone images.
BACKGROUND OF THE INVENTION
Document imaging systems (e.g., copiers and facsimiles) often represent documents as digital data which is used for reproduction or transmission of an original document. Comparing the intensity level of an element of the image (e.g., a pixel) to a threshold level yields binary data. If the intensity level exceeds the threshold, the element is represented by a binary value indicating white. If the intensity level does not exceed the threshold, the element is represented by a binary value indicating black. Problems occur when the document contains both text and images (e.g., photographs). Images typically contain a range of intensity values (i.e., gray scale) which cannot be preserved by the threshold process. Lines and line art can also present a problem for the threshold process. Lines can yield intensity levels which exceed the threshold in some image locations and do not exceed the threshold in other locations, depending on the width and orientation of the lines with respect to image elements. As a result, portions of the line in the processed image can be lost.
FIG. 1
illustrates the use of a conventional image processor for reproduction of documents. An original document
10
containing areas of text (i.e., characters)
12
, images
14
and line features
16
is scanned by a document scanner
18
. The scanner
18
generates a multi-level signal which is processed by an image processor
20
. The image processor
20
processes the multi-level signal and provides a processed multi-level signal to a laser printer
22
or other output device which generates a reproduction
24
of the original document
10
.
It is advantageous to process document areas containing characters and lines differently from document areas with embedded images. For example, character and line areas can be processed to enhance contrast and image areas can be processed to enhance image quality.
FIG. 2
illustrates a document imaging system
30
described in Japanese Patent Publication No. 58-3374 utilizing two distinct image processing means. A multi-level signal representative of the document is received by a multi-level signal processing means
32
and a dither processing means
34
. The output of the multi-level signal processing means
32
is provided to a separation means
36
and a selection means
38
. The output of the dither processing means
34
is provided to the selection means
38
. The separation means
36
autodiscriminates between portions of the multi-level signal corresponding to text and portions corresponding to image information based on characteristics of the output of the multi-level processing means
32
. The separation means
36
generates a selection signal based on the autodiscrimination and provides it to the selection means
38
. The selection means
38
generates an output signal by combining portions of the outputs from the processing means
32
and
34
according to the selection signal.
FIG. 3
shows another document imaging system
40
described in U.S. Pat. No. 4,996,603. A multi-level signal representative of the document is received by a character/photo separation circuit
42
, a fixed slice processing circuit
44
and a halftone processing circuit
46
. The outputs of the fixed slice processing circuit
44
and halftone processing circuit
46
are received by a selection circuit
48
. The character/photo separation (autodiscrimination) circuit
42
generates a selection signal based on characteristics of the unprocessed multi-level signal. The selection circuit
48
generates an output signal by combining portions of the outputs from the fixed slice processing circuit
44
or the halftone processing circuit
46
.
The prior art document imaging systems illustrated in
FIGS. 2 and 3
have several disadvantages. The systems require circuitry to implement the separation and selection processes. The output signals from the processing means
32
and
34
or processing circuits
44
and
46
must be synchronized. Therefore, the memory used in the processing means
32
and
34
or processing circuits
44
and
46
must be matched to insure equal delay. Also, prior art document imaging systems are typically optimized for a particular orientation. As a result, text printed on a page in a vertical orientation might not be recognized as text and, therefore, the text might be processed as an image. The processed document would then contain inferior quality vertically oriented text. A preferred text orientation can also create other difficulties. For example, it can be more efficient (i.e., higher document throughput) to scan a standard document so that the scan line (e.g., CCD linear array line) is parallel to the longer document dimension, especially where the document processing rate is limited by the paper translation rate or scanner translation rate. The horizontal document text then appears vertically oriented to the scanner and results in inferior quality text.
SUMMARY OF THE INVENTION
The present invention relates to a document image processing apparatus and method that separate character and image data. The apparatus and method are applied to a multi-level signal containing character and image data in the document and can also contain color data.
The apparatus includes an input module for receiving the multi-level signal. In one embodiment, an optical scanner generates the multi-level signal. A content module is coupled to the input module to process the multi-level signal. Portions of the multi-level signal containing text or lines are processed to enhance contrast. Portions of the multi-level signal containing image data are processed to enhance image quality. The content module can include a digital signal processor (DSP) which can be programmable. In one embodiment, the content processor also includes a random access memory (RAM) in communication with the DSP. A halftone processor receives the content-processed multi-level signal from the content module and processes the signal according to a halftone processing technique. The halftone processor module can include a DSP. In one embodiment, the halftone processor module implements a dither processing technique. In another embodiment, the halftone processor module implements a diffusion dither technique. The apparatus also includes an output module coupled to the halftone processor module. The output module provides the output signal from the halftone processor to an output port.
The programmability of the DSP allows the methods used to process the document data to adapt to different types of documents. One program can potentially accommodate all likely document formats. The prior art document imaging systems employ separation and selection modules which can only be optimized for a particular type of document. In addition, the programmability of the DSP permits a wide range of processing sophistication which extends beyond a level reasonably implemented in fixed (i.e., hardwired) circuitry. Furthermore, orientation of the image is not critical to processing in the present invention since the memory is randomly accessible. This allows the DSP algorithms to access any part of the stored image in any order.
The invention also features a method for processing a document image. The method includes receiving a multi-level signal representative of a document. At least one filter is applied to the multi-level signal to generate templates identifying high contrast document areas (i.e., areas having text or line features). The one or more filters can be two-dimensional high pass image filters. Portions of the multi-level signal corresponding to the high contrast areas are processed to enhance the edges and text features. In one embodiment, processing includes setting the h
Brinich Stephen
Lee Thomas D.
Oak Technology, Inc.
Testa Hurwitz & Thibeault LLP
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