Facsimile and static presentation processing – Facsimile – Picture signal generator
Reexamination Certificate
1997-06-13
2001-05-08
Lee, Thomas D. (Department: 2624)
Facsimile and static presentation processing
Facsimile
Picture signal generator
C358S474000, C358S487000
Reexamination Certificate
active
06229628
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an image reading apparatus for applying light to an original document and reading a document image. More particularly, the invention relates to an image reading apparatus which is capable of sharply reading a transparent document.
2. Related Background Art
FIG. 6A
is a schematic diagram illustrating a conventional image reading apparatus. In the drawing, there is shown an image sensor
106
serving as photoelectric conversion means, such as a charge coupled device (CCD) for converting information concerning a scanned image into an electric signal, the sensor
106
being disposed within the main unit (apparatus unit)
100
of an image reading apparatus.
An original-document-mounting glass
101
, used as a transparent original-document-mounting table, is disposed on the top surface of the apparatus unit
100
. A document P placed on the surface of the document-mounting glass
101
is scanned by a scanning optical system
102
serving as scanning means so as to expose image information onto the image sensor
106
.
Disposed within the image sensor
106
are three rows of sensors provided with filters of three colors, such as red (R), green (G) and blue (B), respectively, thereby performing color separation when reading a document image. The image scanning means
102
is constructed of a lamp unit
103
and a mirror unit
104
, both of which are moved parallel to the glass
101
to perform scanning, and a stationary lens
105
fixed in the apparatus unit
100
.
The lamp unit
103
is formed of a white-color light source L
1
for illuminating the document P, and a first mirror M
1
for reflecting the reflected light from the image formed on the document P toward the mirror unit
104
. The mirror unit
104
is comprised of second and third mirrors M
2
and M
3
, respectively, for returning the image light reflected by the first mirror M
1
toward the image sensor
106
.
The lamp unit
103
moves at a velocity twice as fast as the mirror unit
104
to perform scanning in order to ensure a constant optical path in the overall image reading region. Accordingly, the scanning optical system
102
of the above type is referred to as a “2:1 scanning optical system”. These units
103
and
104
perform scanning (sub-scanning) using a driving source (not shown), such as a pulse motor, as a power source, in synchronization with the reading cycle of the image sensor
106
.
In
FIG. 6A
, there is also shown a transparent-document-reading light source unit
200
serving as illumination means for reading transparent documents. Disposed within the light source unit
200
are a light source L
2
located parallel to the light source L
1
within the apparatus unit
100
, and a light-diffusing translucent plate
201
placed to opposedly face the document-mounting table
101
. The transparent-document-reading light source unit
200
is attached to the rear end of the image reading apparatus and pivots about a hinge
202
.
For reading a transparent document, the light source L
2
is driven by a driving source (not shown) to scan the area covered by the document-mounting glass
101
in a direction parallel to the translucent plate
201
while synchronizing with the image scanning means
102
of the apparatus unit
100
. During this scanning operation, the light source L
1
within the apparatus unit
100
is switched off. Light emitted from the light source L
2
is diffused in the translucent plate
201
, bringing about a light distribution illustrated in
FIG. 6B
(enlarged from the region D
1
shown in
FIG. 6A
) on the document surface. From the light distributed as indicated in
FIG. 6B
, the light located on the light path in an area from the reading position of the image reading apparatus unit
100
to the image sensor
106
penetrates the document placed at a position P shown in FIG.
6
A and is directed to the image sensor
106
.
For reading a transparent document, the document is not allowed to be placed in the area A (hereinafter referred to as “the document-placing prohibited area A”) at the upper edge of the document-mounting table
101
. Prior to document reading, in this area A the image sensor
106
reads the light quantity and the light distribution directly obtained from the transparent-document light source L
2
and uses these as data concerning, for example, shading correction.
FIG. 7
schematically illustrates a document image being formed on photodetectors of the image sensor
106
. Photodetectors of three colors
106
R,
106
G and
106
B are spaced apart from each other because a portion for accumulating charges photoelectrically converted by the photodetectors and a portion for transferring signals to an output stage are adjacently disposed around the photodetectors
106
R,
106
G and
106
B of the image sensor
106
.
Since the image sensor
106
is shifted relative to the document to allow the photodetectors
106
R,
106
G and
106
B to read the same position of the document, the intervals between the photodetectors
106
R,
106
G and
106
B are determined to be integral multiples of the width of the photodetectors
106
R,
106
G and
106
B. If there is an m-line interval between the photodetectors
106
R and
106
G and an n-line interval between the photodetectors
106
G and
106
B, an image signal G representing one line of a document image is read m lines later relative to an image signal R, and an image signal B is read (m+n) lines later relative to the image signal R.
FIG. 8
is a block diagram illustrating the processing of image data read by the color image sensor
106
. After the image data items of the respective colors read by the image sensor
106
are sent to and amplified in amplifiers
121
R,
121
G and
121
B, respectively, they are converted into digital image signals by analog-to-digital (A/D) converters
122
R,
122
G and
122
B, respectively. The A/D converters
122
R,
122
G and
122
B each divide the dynamic range (a difference in the reading output between a pure white region and a pure black region of the document) of the image sensor
106
according to a bit number, thereby assigning levels of gradation according to the brightness of the document image.
For example, 8-bit-resolution A/D converters are capable of distinguishing a white to black gradation into 256 levels, while 10-bit-resolution A/D converters can differentiate the same gradation into 1024 levels. Thus, an image reading apparatus using A/D converters with RGB colors each having 8 bits can identify 24 bits, i.e., approximately 16.7 million colors, while an image reading apparatus using A/D converters with RGB colors each having 10 bits can distinguish 30 bits, i.e., about 1074 million colors.
The photodetectors
106
R,
106
G and
106
B of the respective colors of the image sensor
106
are spaced apart from each other as noted above. Accordingly, in order to perform phase matching of the respective image signals before the signals are input into an image processing circuit
124
, a (m+n)-line buffer memory
123
R and an n-line buffer memory
123
G are respectively provided at the rear stage of the A/D converters
122
R and
122
G, and the image signals R and G can be output simultaneously with the last-read B signal. In the image processing circuit
124
, the image signals are subjected to processing, such as binary processing, for color correction. The resulting image signals are output to a machine
300
, such as a personal computer, via an interface circuit
125
.
There are several types of output states of the image signals from the image reading apparatus, and a suitable type can be selected according to the use of the read image. For example, when text is read by an optical character reader (OCR), or when a monochrome diagram is read, a monochrome binary image is appropriate. More specifically, a G signal, for example, among the RGB image signals is used and binarized with a threshold in the image processing circuit
124
, and the binarized image data is selected. Further, when a p
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Lee Thomas D.
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