Facsimile and static presentation processing – Natural color facsimile – Scanning
Reexamination Certificate
1998-07-14
2001-02-27
Lee, Cheukfan (Department: 2722)
Facsimile and static presentation processing
Natural color facsimile
Scanning
C358S512000, C358S513000
Reexamination Certificate
active
06195183
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image reading apparatus. More particularly, the present invention relates to a contact-type line image scanner for optically reading a document paper sheet in full color. The present invention also relates to an image sensor chip which may be advantageously incorporated in such an image scanner.
2. Description of the Related Art
In general, a full-color line image scanner comprises a light source for irradiating a document paper sheet with white light, apluralityof red light receiving elements for detecting a red light component of the white light reflected on the document sheet, a plurality of green light receiving elements for detecting a green light component of the reflected white light, and a plurality of blue light receiving elements for detecting a blue light component of the reflected white light. Each of the light receiving elements converts the detected amount of light into a corresponding electric signal.
FIG. 20
of the accompanying drawings illustrates a typical arrangement of light receiving elements in a full-color line image scanner. As shown, a plurality of red light receiving elements
80
R, a plurality of green light receiving elements
80
G, and a plurality of blue light receiving elements
80
B are regularly arranged in a common single row. Specifically, groups of light receiving elements are arranged in a common row in such a manner that each group includes a red light receiving element
80
R, a green light receiving element
80
G and a blue light receiving element
80
B. Each group of three different light receiving elements
80
R,
80
G,
80
B, which corresponds to a single pixel or picture element, has a primary scanning direction dimension S
2
and a secondary scanning direction dimension S
3
, whereas each light receiving element has a primary scanning direction dimension S
1
. Further, each of the light receiving elements
80
R,
80
G,
80
B is covered by a correspondingly colored filter which allows selective passage of a relevant color component of the white light.
Since the three kinds of light receiving elements detect three different color components of the white light at the same time, the image scanner described above is capable of full-color image reading at high speed. However, the prior art image scanner has been found disadvantageous in the following points.
First, since each group of three different light receiving elements
80
R,
80
G,
80
B corresponds to a single picture element, the primary scanning direction dimension S
2
needs to be set equal to or less than the primary scanning direction dimension of the single picture element. Therefore, the primary scanning direction dimension S
1
of each light receiving element must be set less than ⅓ of the primary scanning direction dimension of the single picture element. As a result, the light receiving area of each light receiving element inevitably becomes small, thus leading to a poor reading quality (i.e., a low electrical output). Such a problem is particularly remarkable when the pitch between the respective light receiving elements
80
R,
80
G,
80
B is set small to increase the reading resolution.
Secondly, since the three different light receiving elements
80
R,
80
G,
80
B in each group (corresponding to a single picture element) deviates positionally in the primary scanning direction, there may be a color deviation when the three light receiving elements in the same group read the same picture element of the document sheet.
In the third place, since the three light receiving elements
80
R,
80
G,
80
B in each group are dedicated to different colors, they need to be separately covered by different filters. Therefore, there is a need for separately attaching as many filters as the light receiving elements, consequently resulting in a cost increase.
The above-described problems may be eliminated by providing three different light sources for emitting red light, green light and blue light toward a document sheet with a time lag. In this case, a single kind of light receiving elements in a single row is caused to successively detect the reflected different color light components.
However, the latter solution is also disadvantageous in that the image reading speed becomes low due to the need for actuating the different light sources with a time lag. Further, since each light receiving element (which is normally provided by a phototransistor) is successively caused to detect different colors, unexpected mixture of two or more colors may occur due to incomplete discharge of a charge of the phototransistor. More specifically, as shown in
FIG. 21
, a phototransistor constituting each light receiving element retains a certain amount of previous charge (represented as “charge remainder ratio”) even after discharging for another light detection, so that two successive detection for two different colors may result in unexpected color mixture.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an image reading apparatus wherein the light receiving area of each light receiving element may be maximized, thereby enhancing the quality of the read image.
Another object of the present invention is to provide an image reading apparatus which is capable of reading a document sheet at a high speed without inviting a reading quality deterioration.
A further object of the present invention is to provide an image sensor chip which may be advantageously incorporated in an image reading apparatus.
Still another object of the present invention is to provide an image sensor chip which may be manufactured at a low cost.
According to a first aspect of the present invention, there is provided an image reading apparatus comprising: a light source for irradiating a document sheet with light; a row of red light receiving elements arranged in a primary scanning direction for detecting a red component of the light reflected on the document sheet; a row of green light receiving elements arranged in the primary scanning direction for detecting a green component of the reflected light; and a row of blue light receiving elements arranged in the primary scanning direction for detecting a blue component of the reflected light; wherein the row of red light receiving elements, the row of green light receiving elements and the row of blue light receiving elements are displaced from each other in a secondary scanning direction which is perpendicular to the primary scanning direction.
According to the arrangement described above, since each row of light receiving elements, extending in the primary scanning direction is dedicated only to a single color, the width of each light receiving element can be rendered substantially equal to that of each pixel (picture element). Thus, the light receiving area of each light receiving element may be maximized to provide a good image reading quality. Such an advantage is particularly significant when the pitch between the light receiving elements in the primary scanning direction is made small to increase the reading resolution.
Further, the three rows of light receiving elements may be caused to read the document sheet along three different primary scanning lines at the same time without any deviation in the primary scanning direction, and each same primary scanning line is successively read by the three rows of light receiving elements. Therefore, the image reading apparatus is capable of reading the document sheet at a high speed to provide a full-color image.
Moreover, compared with the prior art image reading apparatus wherein each light receiving element is caused to read three different colors, the image reading apparatus of the present invention does not suffer an image deterioration due to a remainder charge of a phototransistor when shifting from one color to another.
According to a preferred embodiment, the light receiving elements in each row are arranged at a first pitch in the primary scanning direction, whereas the row of red light rece
Fujimoto Hisayoshi
Imamura Norihiro
Onishi Hiroaki
Takakura Toshihiko
Lee Cheukfan
Merchant & Gould P.C.
Rohm & Co., Ltd.
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