Coded data generation or conversion – Analog to or from digital conversion – Analog to digital conversion
Reexamination Certificate
1998-07-24
2001-05-01
JeanPierre, Peguy (Department: 2819)
Coded data generation or conversion
Analog to or from digital conversion
Analog to digital conversion
C358S461000
Reexamination Certificate
active
06225934
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image reading apparatus for reading an original image using an image sensor.
2. Related Background Art
As conventional image reading apparatuses for reading an original image using a linear CCD (charge coupled device) image sensor, an apparatus which has an ABC (Auto Back-ground Control) circuit for automatically varying the read signal in correspondence with the brightness of an original, is known.
FIG. 17
shows an example of the arrangement of the conventional image reading apparatus with such ABC circuit (to be referred to as a first conventional apparatus hereinafter). In
FIG. 17
, a B/W (black/white) CCD image sensor
1801
converts an optical signal coming from an optical system (not shown) into an electrical signal, and outputs it as an image signal. An amplifier
1802
amplifies the output from the CCD image sensor
1801
to a predetermined level. An A (analog)/D (digital) conversion circuit
1803
converts the output from the amplifier
1802
into a digital signal. A comparator
1804
compares the digital image signal output from the A/D conversion circuit
1803
with a predetermined reference level for ABC comparison. An LPF (low-pass filter)
1805
removes (cuts) components in the high-frequency range (high-frequency components) of the output signal from the comparator
1804
. A reference voltage source
1806
generates a reference voltage VREF to be input to VB (bottom reference) of VT (top reference) and VB (bottom reference), which determine the input range of the A/D conversion circuit
1803
.
In
FIG. 17
, the output signal from the comparator
1804
, from which high-frequency components have been cut by the LPF
1805
, is input to the VT (top reference) terminal of the A/D conversion circuit
1803
. For this reason, when the signal level of the digital image signal output from the A/D conversion circuit
1803
is larger than the reference level for ABC comparison, the VT (top reference) of the A/D conversion circuit
1803
is controlled to increase, and consequently, the signal level of the digital image signal output from the A/D conversion circuit
1803
decreases. By contrast, when the signal level of the digital image signal becomes smaller than the reference level for ABC comparison, the VT (top reference) of the A/D conversion circuit
1803
is controlled to decrease, and as a result, the signal level of the digital image signal output from the A/D conversion circuit
1803
increases.
As a result of the control, the average level of the digital image signal output from the A/D conversion circuit
1803
matches the reference level for ABC comparison.
In
FIG. 17
, the comparator
1804
receives an area signal for ABC, so that the comparator
1804
outputs a comparison signal in only an image area to be subjected to ABC comparison, but stops its output in an image area (e.g., a non-image period and image edge portions) not to be subjected to ABC comparison.
Hence, in the first conventional apparatus, since the read signal level is controlled so that the average level obtained by reading an original image always matches the reference level for comparison, both dark and light original images can always be read with optimal signal levels.
FIG. 18
shows an example of the arrangement of another image reading apparatus using a linear image sensor (to be referred to as a second conventional apparatus hereinafter). In this second conventional apparatus, an original
1911
on a platen glass
1910
is illuminated using a light source
1909
for illuminating an original, and a reflection member
1908
, and an optical original image is formed on the light-receiving surface of a CCD linear image sensor
1901
via first, second, and third mirrors
1907
,
1904
, and
1905
, and a lens
1902
. A first moving unit
1906
bounded by the one-dashed chain line in
FIG. 18
moves at a speed V in the direction of an arrow A in
FIG. 18
, and a second moving unit
1903
bounded by the two-dashed chain line moves at a speed V/2 in the direction of an arrow B in
FIG. 18
(to be referred to as a subscan hereinafter) at the same time, thus reading the image on the entire original
1911
by the CCD linear image sensor
1901
.
FIG. 19
shows an example of the flow of signal processing of an image signal obtained from the CCD linear image sensor
1901
shown in FIG.
18
. In
FIG. 19
, the output signal from the CCD linear image sensor
1901
is amplified by a gain amplifier
2001
, and is input to an analog signal processing circuit
2002
to extract an image signal component. The analog image signal is converted by an A (analog)/D (digital) conversion circuit
2003
into a digital image signal. The digital image signal is subjected to shading correction for uniformly reading an original image in a shading correction circuit
2004
. After that, the digital image signal is output from an output terminal
2005
.
In still another conventional image reading apparatus (to be referred to as a third conventional apparatus hereinafter), since the reading speed of an original image is low like in facsimile apparatuses and the like, a photoelectric conversion element for one line can correspond to a single A/D converter. For this reason, the individual differences (variations in characteristics) of A/D converters upon processing one-line data of an original using different A/D converters need not be taken into consideration.
In recent years, demand has arisen for mounting an ABC circuit on the above-mentioned first conventional apparatus in a color image reading apparatus using a color CCD image sensor.
However, when the arrangement of the ABC circuit is used in the color image reading apparatus, the following problem is posed.
That is, when independent ABC circuits are added for the read signals of the respective colors read by the color image reading apparatus, the reading levels of the respective colors are independently controlled. For this reason, the color tone of the read image has a large difference from that of the original.
In the flow of the signal processing shown in
FIG. 19
in the second conventional apparatus, when the original has a color background or a background pattern, and characters are printed thereon, if such original is read by the image reading apparatus, since the level difference between the background and characters is small, the characters may become unclear when the read original image is printed, output to a TV monitor, or output as a facsimile image.
In the third conventional apparatus, when an apparatus with high work efficiency is to be constructed without impairing productivities of the individual functions in a multi-functional image forming apparatus, some of the functions that can operate even at a low reading speed of an original image are required to have a high reading speed of an original image so as to optimize productivities. In an image reading unit, since the photoelectric conversion/transfer speed of the photoelectric conversion element serving as a reading means has an upper limit, photocells which line up in the main scan direction are divided into some groups using their even- and odd-number column positions to attain parallel signal processing, thereby apparently increasing the reading speed. However, when background removal (processing for forcibly recognizing the background as a white background) for an original to be fed and read, the original cannot be read again. Hence, real-time processing is inevitably required, but is impossible to attain in practice.
SUMMARY OF THE INVENTION
It is a first object of the present invention to provide an image reading method and apparatus, which can prevent any large difference from being produced between the color tones of the read image and an original, can reduce variations in ABC control effect among apparatuses due to shading nonuniformity, and can realize ABC control in accordance with not the color tone of an original but its brightness (luminance).
It is a second object of the present invention to prov
Chizawa Noriyoshi
Kamei Masafumi
Ohashi Kazuhito
Sugiura Takashi
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Jean-Pierre Peguy
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