Integrated circuit architecture of contact image sensor for...

Details Integrated circuit architecture of contact image sensor for... Integrated circuit architecture of contact image sensor for...

1999-02-05

2004-02-10

Garber, Wendy R. (Department: 2612)

Television

Camera, system and detail

Combined image signal generator and general image signal...

C348S210990, C348S298000, C382S237000, C382S275000

Reexamination Certificate

active

06690420

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to image sensing systems and more particularly relates to integrated circuit architecture of contact image sensors for generating bi-level or binary images in real time. Images from image sensing systems employing the present invention can be analyzed, archived or transmitted efficiently in applications that rely on binary images, such as check payment verification and optical character recognition.
2. Description of the Related Art
There are many applications that need an imaging system to convert a target to an electronic format that can be subsequently analyzed, printed, distributed or archived. The electronic format is generally a digital image of the target. A typical example of the imaging system is a scanner and the target is a sheet of paper from a book or an article. Through the scanner, an electronic or digital image of the paper is generated and subsequently may be analyzed, computed, or transmitted through the Internet.
An imaging system generally includes an image sensing module that converts a target optically into an image. The key element in the sensing module that converts the target optically to the image is an image sensor comprising an array of photodetectors responsive to light impinged upon the image sensor. Each of the photodetectors produces an electronic signal representing the intensity of light reflected from the target. The electronic signals from all the photodetectors are readout as a video signal that is then digitized through an analog-to-digital converter to produce a digital signal or an image of the target.
FIG. 1A
illustrates a configuration system
100
that has been used for the past tens of years. A scanning document
110
that can be a page from an article or book is scanned in by an image sensing system
111
that can be a scanner, such as SCANJET 4100CSE Color Scanner from Hewlett Packard. The output of the scanner is typically a digital image
114
of scanning document
110
. Scanner
111
includes an image sensor
112
and an analog-to-digital converter
115
. Image sensor
112
generates images
117
that are typically digitized to gray scale or color images of 8-bit precision. Binalization process
116
receives and converts Image
114
to binary Image
118
that is a preferred form for data analysis and understanding in data process
120
. Binalization process
116
Is typically implemented in a separate circuit or a software application. The separate circuit may be implemented in a post-processing circuit coupled to A/D converter
115
and the software application may be embedded in a scanner driver or provided in a commercial image editing software, such as Adobe PhotoShop, running in a host computer
119
.
FIG. 1B
depicts a contact image sensor (CIS) system that can; be used in image sensor
112
of FIG
1
A. Scanning document
110
is illuminated by an illumination source
121
. Reflected light from scanning document
110
is collected and focused by a full-width rod-lens system
122
. The CIS system allows one-to-one scanning of the document because rod lens
122
and an image sensor chip
124
are of the same width as (or greater width than) scanning document
110
.
FIG. 1C
is a functional block diagram of image sensor
112
, along with
FIG. 1D
showing some detail of the construction of image sensor array
126
. To be specific, a plurality of individual sensor chips
130
are butted end-to-end on a single substrate. Each of the individual sensor chips comprises a plurality of photodetectors
128
arranged in a row. In operation, image sensor array
126
is triggered by a start pulse to the first-in-sequence individual sensor chip
130
which serially activates the photodetectors on the first individual sensor chip
130
. After the signal from the last photodetector element of the first individual sensor chip
130
is read, an end-of-scan pulse is generated so that the next sensor chip in sequence is triggered.
The number of individual sensor chips chosen is dependent upon the desired width of scanning. Sensor array
126
also comprises necessary circuits to serially activate the individual chips and to readout signals generated from photodetectors. The strength of the signals is directly proportionate to the reflected light from the scanning document. To preserve the contents in the scanning document, most CIS systems produce signals that are subsequently digitized to 8 or 12 bit data by a following analog-to-digital (A/D) converter.
In many imaging applications, such as check verification at checkout counters in a retail store and document archival, the primary interest is to extract texture information from captured images, for example, for optical character recognition (OCR). To be applicable for such process, the images are preferably in binary format, namely the texture information in black and the background in white or vice versa. In other words, the digitized signals from the A/D converter must be binalized.
Considering the cost and processes associated with the subsequent binary images obtained, it will be desirable that a CIS generates directly binary images. Further, the cost of such CIS will be dramatically reduced if it employs no A/D converters to convert a gray-scale image to a bi-level image. A CIS with high performance, low cost and capable of generating the bi-level images will be very well received in the market.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above described problems and needs and has particular applications to image systems, such as scanners, digital cameras and computer vision systems. One of the advantages and benefits in the present inventions is the increased performance and reduced cost provided in the underlying architecture. Image sensing modules, especially those contact image sensors, employing the current invention can be effectively used in many imaging applications such as the check verification in checkout counters of retail stores or banks and document archival systems in which binary or bi-level images are preferred.
According to one aspect of the present invention, an image sensing module comprises an image sensor, an amplifier, an analyzing circuit and a comparator. In one particular embodiment, the image sensing module further comprises an electrically erasable programmable read-only memory (EEPROM). The image sensor comprising a number of sensor chips concatenated in series produces a video signal. Each of the sensor chips comprises a plurality of photodetectors; each of the photodetectors producing an electronic signal when the image sensor is activated. In other words, the video signal comprises electronic signals respectively from all the photodetectors in the image sensor.
The amplifier is coupled to the image sensor and receives the electronic signals. The amplifier further receives pairs of gain and offset from a memory or the EEPROM. The electronic signals are adjusted in the amplifier respectively and sequentially in accordance to the pairs of gain and offset;
The analyzing circuit is coupled to the amplifier and receives the adjusted electronic signals. The analyzing circuit produces threshold values from the electronic signals according to a threshold determination procedure. The comparator receives the adjusted electronic signals from the amplifier and the threshold values from the analyzing circuit to generate the bi-level signal from the electronic signals with respect to the threshold values.
The memory or EEPROM is used to store the pairs of predetermined gain and offset; each of the pairs of gain and offset corresponding respectively to one of the photodetectors. In other words, an electronic signals generated from one particular photodetector is registered to be adjusted by a gain and an offset designated to the particular photodetector.
In a preferred embodiment, the amplifier, the analyzing circuit and the comparator are integrated in a substrate that holds the photodetectors. As a result, the real-time binalization

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